Balanced solution for KAT500 tuner?
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Re: Balanced solution for KAT500 tuner?
 
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I have a Comtek 4:1 and a Comtek 1:1 BALUN (from DXEngineering) that I
have where I can easily hook up my 450-ohm ladder line to either one. I have tested both across all the bands that I use on that particular antenna which is 80, 40, and 30. In every case, the Comtek 4:1 gives the better solution as measured by my MFJ 459 antenna analyzer. I do agree that it is not always true that a given 4:1 is better then a 1:1 because on a previous antenna (a delta loop), the 1:1 just so happened to be a little bit better then the 4:1. In all cases though, I measured impedance right from the shack where about 30 feet of coax ran up to the baluns which were mounted outside. On the current antenna, I have close to (but not exactly) 100 feet of 450 ohm ladder line to the antenna feed point. My current antenna is center-fed dipole of about 130 feet in total length. 73, phil, K7PEH On Sep 29, 2012, at 6:40 PM, Don Wilhelm <[hidden email]> wrote: > Many hams *asssume* that because the feedline character8istic impedance > is 450 ohms, that it will work better with a 4:1 balun. > > Nothing could be further from the truth, the impedance seen at the shack > end of the feedline can vary from quite high to quite low - the feedline > works as a transmission line tuner (and the ATU does too). > > For powers up to 100 watts, I suggest the Elecraft BL2 which provides a > switch to change from 1:1 to 4:1. Use the setting that provides the > best results. > > 73, > Don W3FPR > > On 9/29/2012 7:41 PM, Adrian wrote: >> Here: >> >> http://www.karinya.net/g3txq/tuner_balun/ >> >> "Amateur Radio (G3TXQ) - Tuner Balun: 4:1 or 1:1 ? >> >> Follow the discussions on any Internet Ham Radio forum and it wont be long >> before someone recommends the use of a 4:1 balun at the output of a tuner >> feeding a multiband doublet through ladderline. Often the recommendation is >> accompanied by an explanation such as: "It helps the tuner to tune" or: "It >> reduces the impedance of the 450 ohm ladderline towards 50Ω". This article >> examines whether the ubiquitous advice to use a 4:1 balun in this scenario >> is valid. >> >> The arguments put forward for a 4:1 impedance transformation often assume >> that the tuner works best when operating with a load impedance close to 50Ω. >> That simply isn't true! The chart on the right shows the losses vs load >> resistance of a typical T-network tuner on 80m for several values of load >> reactance; 80m was chosen because losses tend to be more evident on the >> lower-frequency bands. As we can see the lowest tuner losses occur when the >> load resistance is in the medium/high range 250Ω-2500Ω; the highest losses >> occur at low load resistances, particularly where they are accompanied by a >> large capacitive reactance. >> >> Let's now take the example of a commonly proposed multiband doublet - a >> half-wave 80m dipole fed with 450Ω ladderline. At modest heights above >> average ground the dipole has a feedpoint impedance close to 50Ω. That means >> that the impedance seen at the tuner end of the ladderline could have a >> resistive component anywhere from 50Ω to 4050Ω depending on ladderline >> length; that range of impedances is indicated by the lower shaded bar in the >> chart, labelled 1:1. If we now introduce a 4:1 impedance transformation, the >> range of impedances will be lower by a factor of 4 as indicated by the upper >> shaded bar labelled 4:1. It's clear that the 1:1 range of impedances will >> result in the lower overall losses. >> >> In fact, no matter what the antenna impedance, the range of impedances seen >> at the tuner end of the ladderline would have a "geometric mean" of 450Ω - >> that is they would swing equally below and above 450Ω, but once we introduce >> a 4:1 balun the geometric mean will reduce to 112.5Ω. One look at the loss >> chart tells you that centering the impedances at the higher value is the >> preferable option. >> >> >> Let's now take a look at the specific losses that would occur with our >> example 132 doublet fed with 450Ω ladderline. >> >> The chart on the right was produced by varying the feedline length from 0° >> to 180° in 10° steps. At each step the impedance seen by the tuner was >> calculated both with a 1:1 balun and then with a 4:1 balun, and the tuner >> losses determined using W9CF's T-network tuner simulator. Of course, beyond >> 180° the chart simply repeats itself. Ladderline losses were ignored. >> >> Apart from a small range of line lengths between 80° and 115°, where the >> line has transformed the 50Ω feedpoint impedance to a very high value around >> 4000Ω, the 1:1 balun is the better option; not only that, the worst case >> loss never exceeds 14% with the 1:1 balun whereas it reaches 21% with the >> 4:1 balun. >> >> But what about other bands - the doublet wont be used on just 80m! >> >> >> This chart shows the tuner loss plotted against line length for our example >> doublet on 40m. Here the doublet feedpoint impedance is around 4000Ω, so for >> short ladderline lengths the 4:1 balun shows an advantage. However, as the >> ladderline length increases and the impedance is transformed to lower >> values, the 1:1 balun soon shows the lower losses again. Across the whole >> range of ladderline lengths the 1:1 balun is twice as likely as the 4:1 to >> produce lower losses. >> >> The conclusion seems clear: if you have to choose just one balun, unless you >> know that your combination of doublet/ladderline length falls into the >> minority of cases where a 4:1 balun has the advantage, a 1:1 balun is the >> preferred choice. Add into the mix the fact that most 4:1 baluns are Voltage >> Baluns, whereas to prevent feedline radiation we want balanced currents; >> then consider that all baluns other than a 1:1 Current Balun have the full >> transmit voltage applied common-mode across one or more windings, and the >> case is compelling for a 1:1 Current Balun in this situation. >> >> In this application any small impedance transformation caused by the Current >> Balun is immaterial because the tuner will compensate, so the windings do >> not need to be of any specific characteristic impedance. Typically, bifilar >> windings using Thermaleze wire inserted in Teflon tubes are employed to cope >> with the high differential-mode voltages present at current minima. Balun >> specialists "Balun Designs" offer a nice example in their Model 1171. >> " >> >> -----Original Message----- >> From: Adrian [mailto:[hidden email]] >> Sent: Sunday, 30 September 2012 9:34 AM >> To: [hidden email] >> Subject: RE: [Elecraft] Balanced solution for KAT500 tuner? >> >> A UK G call did a graphed efficiency comparison test with the 1:1 coming out >> on top. I will post it when re-found. >> >> Also from >> http://www.theladderline.com/doublets-ladder-line-and-automatic-remote-tuner >> s ; (spell-checked) >> >> "There is also some debate about whether the balun should be a 1:1 or 4:1. I >> think 4:1 has been quite popular in the past. This perhaps comes from the >> thought that the ladder line is higher impedance than coax so we need to >> step down to get it closer to the coax impedance. On the forums, people who >> have modelled the antenna with software like EZNEC seem to make a fairly >> compelling argument that a 1:1 balun is more likely to present an impedance >> within the range of the tuner over a wide range of frequencies. The >> impedance will depend on the length of the ladder line so it's a bit of a >> gamble but I'm getting good results from a 1:1 current balun. >> >> After doing some reading and playing with a home brew balun, I finally took >> the lazy way out and splashed out on a serious balun. It's a DX Engineering >> BAL050-H10-AT. It's not cheap but I think it was a good investment. I don't >> have any hard evidence to show how good it is compared to a cheaper balun >> but I have a feeling that it contributes to the good performance I get with >> this antenna. I've had absolutely no "RF in the shack" or similar problems >> even at the old QTH when I had the ladder line coming into the shack. >> >> An interesting fact that I learned from the forums is the reason ladder line >> works more successfully than coax in a multiband situation like this. The >> common belief is that ladder line "doesn't care" about high SWR. It's true >> that ladder line usually has lower loss than coax at a given SWR but that's >> not the whole story. Another rather simple factor is that the characteristic >> impedance of ladder line is higher than coax so therefore, for a typical >> wire antenna over a wide range of frequency, the average SWR on ladder line >> tends to be lower than it would be with coax and that helps keep the loss >> low." >> >> -----Original Message----- >> From: [hidden email] >> [mailto:[hidden email]] On Behalf Of David Gilbert >> Sent: Sunday, 30 September 2012 8:37 AM >> To: [hidden email] >> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >> >> >> I don't believe that is necessarily true. Can you cite a reference to back >> up that statement? Or at least describe in physical terms (Q, currents, >> voltages, component loss, etc) why that would be so? I'm honestly curious >> what the difference would be. >> >> 73, >> Dave AB7E >> >> >> >> On 9/29/2012 2:13 PM, Adrian wrote: >>> 1:1 current balun has proven more efficient in conjunction with the >>> appropriate balanced (matchbox style)tuner. >>> >>> -----Original Message----- >>> From: [hidden email] >>> [mailto:[hidden email]] On Behalf Of Robert G. >>> Strickland >>> Sent: Sunday, 30 September 2012 4:26 AM >>> To: [hidden email] >>> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >>> >>> Jim... >>> >>> Is there anything to be gained in putting a 1:1 "balanced isolator" at >>> the feed point of an antenna that is fed by a "parallel wire" feed >>> line? Does such an arrangement achieve feed line isolation while >>> preserving the ability of such an antenna to be driven on various >>> bands other than its resonant frequency? Thanks for your input. >>> >>> ...robert >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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Phil,
That depends on the exact length of your feedline and the lengthy of your radiator. As I indicated, the impedance in the shack will depend on the feedline length, a well as your radiator length. Would you kindly share both lengths with us so we can duplicate your results. If you are like most hams, the feedline is cut to a length that reaches "from here to there", which is fine for an individual situation, but cannot be extended to a general case. In other words, your setup works for you, but it may not work with different feedline lengths. 73, Don W3FPR On 9/29/2012 10:07 PM, Phil Hystad wrote: > I have a Comtek 4:1 and a Comtek 1:1 BALUN (from DXEngineering) that I > have where I can easily hook up my 450-ohm ladder line to either one. > > I have tested both across all the bands that I use on that particular antenna > which is 80, 40, and 30. > > In every case, the Comtek 4:1 gives the better solution as measured by my > MFJ 459 antenna analyzer. I do agree that it is not always true that a given > 4:1 is better then a 1:1 because on a previous antenna (a delta loop), the 1:1 > just so happened to be a little bit better then the 4:1. > > In all cases though, I measured impedance right from the shack where about > 30 feet of coax ran up to the baluns which were mounted outside. On the > current antenna, I have close to (but not exactly) 100 feet of 450 ohm ladder > line to the antenna feed point. My current antenna is center-fed dipole of about > 130 feet in total length. > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by vk4tux
A 50 ohm non inductive purely resistive DL looks good to a MFJ 459 antenna
analyser too. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Jim Brown-10
Jim...
Thanks for your reply. I think I've been unclear in my question. I'm not concerned as to what "it" is called, how to build "it" or what "it" costs. These things can all be agreed upon and implemented. What I'm curious about is whether some such device, at the feed point of a doublet, in turn fed by window line is of any use [assuming an appropriate tuner at the radio end of the line]. You have said, accurately so, that a current choke at the feed point of a dipole [let's leave off-center fed antennas out of it at this point], in turn fed by coax, keeps RF from flowing on the outside of the coax and subsequently becoming "part of the antenna" and in turn picking up noise/etc. Another way of phrasing my question is, does the coax situation apply to open feeders, also? For example, let's say we have a Johnson Match Box with balanced output, connected to open feeders, running up to a doublet antenna; is there any point in putting some sort of coupling device at the feed point between the line and the antenna? Still another way of asking this is: assuming a real antenna will be unbalanced due to all the usual factors, is there any way, and is there any RF benefit, in forcing a current balance into the open wire feeder? Thanks for your patience and input. ...robert On 9/29/2012 21:43, Jim Brown wrote: > On 9/29/2012 11:26 AM, Robert G. Strickland wrote: >> Is there anything to be gained in putting a 1:1 "balanced isolator" at the feed point >> of an antenna that is fed by a "parallel wire" feed line? Does such an arrangement >> achieve feed line isolation while preserving the ability of such an antenna to be >> driven on various bands other than its resonant frequency? Thanks for your input. > > Phrases and words like "balanced isolator" and "balun" are not only > confusing, they are used to separate people from their money. The > chokes described in my RFI tutorial can be built for the price of a > single #31 core, a few yards of THHN wire, and a couple of connectors. > You can put it in a box if you like, but it's only cosmetic. These > chokes will handle legal power IF the antennas are not badly > unbalanced. Off-center feed creates massive imbalance, and will fry > even the best of chokes. The relatively small imbalances created by > surrounding objects will not -- they simply couple noise. > > #31 cores cost about $4.50 in 1,000 lots, about $7 if you buy 100, and > $15 from the rip-off vendors who advertise in QST. It's become fairly > common for ham clubs to get together and make a group purchase. Over a > period of about 8 years, I've been part of several at the 1,000-piece > level. There are guidelines in Appendix One of the tutorial about how > and where to buy. It's worth buying in quantity, because these 2.4-in > diameter cores are almost universally useful for RFI suppression. > > 73, Jim K9YC > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > -- Robert G. Strickland, PhD, ABPH - KE2WY [hidden email] Syracuse, New York, USA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by Don Wilhelm-4
Don,
Actually, my antenna works quite well and so far is the best performing wire antenna I have raised up for 80/40/30. My previous delta loop was pretty good for 80/30 but it was a bit too narrow due to limited space and the and 40 just did not perform as well as I had hoped. My 450 ohm ladder line is 96 feet long. It does not have to be that long but I chose a feed point further from the shack. The closest possible feed point was too short and only about 30 feet. My coax is roughly 30 feet. I have not actually measured it but the length that is outside the shack is 25 feet and I have a four foot piece on the inside of the shack to my current tuner which is a Palstar AT1KM. I have a pass-thru box that feeds through the wall from the outside to the inside. This adds a few extra inches. The dipole radiator length is 130 feet center fed. Regarding your comment: > In other words, your setup works for you, but it may not work with different feedline lengths. Well, of course! I was not selling that idea that people who use a 4:1 balun will get my same results. Indeed, I was actually agreeing with your original comments that there were no hard and fast rules you can apply for which type of balun to use. peh On Sep 29, 2012, at 7:20 PM, Don Wilhelm <[hidden email]> wrote: > Phil, > > That depends on the exact length of your feedline and the lengthy of your radiator. > > As I indicated, the impedance in the shack will depend on the feedline length, a well as your radiator length. Would you kindly share both lengths with us so we can duplicate your results. > If you are like most hams, the feedline is cut to a length that reaches "from here to there", which is fine for an individual situation, but cannot be extended to a general case. > > In other words, your setup works for you, but it may not work with different feedline lengths. > > 73, > Don W3FPR > > On 9/29/2012 10:07 PM, Phil Hystad wrote: >> I have a Comtek 4:1 and a Comtek 1:1 BALUN (from DXEngineering) that I >> have where I can easily hook up my 450-ohm ladder line to either one. >> >> I have tested both across all the bands that I use on that particular antenna >> which is 80, 40, and 30. >> >> In every case, the Comtek 4:1 gives the better solution as measured by my >> MFJ 459 antenna analyzer. I do agree that it is not always true that a given >> 4:1 is better then a 1:1 because on a previous antenna (a delta loop), the 1:1 >> just so happened to be a little bit better then the 4:1. >> >> In all cases though, I measured impedance right from the shack where about >> 30 feet of coax ran up to the baluns which were mounted outside. On the >> current antenna, I have close to (but not exactly) 100 feet of 450 ohm ladder >> line to the antenna feed point. My current antenna is center-fed dipole of about >> 130 feet in total length. >> >> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by RobertG
On 9/29/2012 9:12 PM, Robert G. Strickland wrote:
> What I'm curious about is whether some such device, at the feed point of a doublet, > in turn fed by window line is of any use [assuming an appropriate tuner at the radio > end of the line]. You have said, accurately so, that a current choke at the feed > point of a dipole [let's leave off-center fed antennas out of it at this point], in > turn fed by coax, In all of this discussion, I have not used the word "coax." You have read that somewhere else. > keeps RF from flowing on the outside of the coax and subsequently > becoming "part of the antenna" and in turn picking up noise/etc. Another way of > phrasing my question is, does the coax situation apply to open feeders, also? YES! That is EXACTLY what I have repeated, over and over again. It has NOTHING to do with coax. Coax, if it is not decoupled by a common mode choke, simply ADDS to the imbalance that is already present. EVERY transmission line needs a common mode choe at the feedpoint to decouple the line. Off-center fed antennas, like the so-called "Windom" in all of its variations, are WILDLY unbalanced. As a result, they are notorious for being NOISY, for putting RF in the shack, and for toasting common mode chokes. It is a complete fiction to feed with with parallel wire line and CALL it balanced, and decide that it needs a balanced tuner! The antenna is unbalanced, so the feedline is unbalanced, and a balanced tuner does nothing except transfer dollars between the purchaser and the seller. In the old days, when RFI did not exist (few of us are old enough not to remember TVI in the 50s), the Windom MIGHT have been a good idea. Today, with RF noise sources everywhere and home stereo rigs full of Pin One Problems ready to bring RF into equipment and detect it, Windom antennas are a really bad idea. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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On 9/30/2012 12:02 AM, Jim Brown wrote:
> YES! That is EXACTLY what I have repeated, over and over again. It has > NOTHING to do with coax. Coax, if it is not decoupled by a common mode > choke, simply ADDS to the imbalance that is already present. EVERY > transmission line needs a common mode choe at the feedpoint to decouple > the line. I think about this as an engineer, and parts of the logic are so engrained my brain that I leave them out when explaining how things work. So, let me add this. In a perfectly balanced antenna fed by parallel wire line, and terminated in a balanced circuit at the transmitter, the current on the left wire is exactly equal to the current on the right wire at every point on the line (but varies along the line, because it's a transmission line), and at every point, the current are out of polarity, so they cancel. That line does not radiate, and it does not receive. But if ANY part of the system is out of balance -- the antenna, the line, the TX end -- the two currents are NOT equal. -- the DIFFERENCE between the two currents is the COMMON MODE CURRENT, and that line DOES radiate, and it DOES receive. That common mode current goes from the antenna to wherever the line is connected. A COMMON MODE CHOKE adds some impedance in series with that common mode circuit. If it is a GOOD choke, it is a LARGE RESISTIVE impedance. It is "brute force" solution -- by adding a high resistance in series with the common mode path, we reduce the common mode current to a very small value, which causes (almost) all of the antenna current to flow from the left side of the antenna to the left side. Please don't force me to burden the entire list with an extended discussion of all of this that I have carefully prepared and posted as part of my RFI tutorial, and as part of a Power Point on coax chokes. Go study that. THEN ask questions if you have any. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by Phil Hystad-3
Phil,
It is great that you actually know the length of your feedline - most do not. I am not questioning how well your antenna/feedline combination works. All I am trying to get across is that for any claims about how easy a particular antenna is to tune (with a tuner in the shack), the length of feedline is a critical parameter. Yes, I know that most hams do not measure their feedline - it is long enough to reach from the shack to the antenna. That means the experience you have with that antenna/feedline combination may not be the same as the results obtained by anyone else. Bottom line, measure your feedline, particularly if the antenna is not matched to the feedline characteristic impedance. 73, Don W3FPR On 9/30/2012 12:46 AM, Phil Hystad wrote: > Don, > > Actually, my antenna works quite well and so far is the best performing wire antenna I have raised > up for 80/40/30. My previous delta loop was pretty good for 80/30 but it was a bit too narrow due to limited > space and the and 40 just did not perform as well as I had hoped. > > My 450 ohm ladder line is 96 feet long. It does not have to be that long but I chose a feed point > further from the shack. The closest possible feed point was too short and only about 30 feet. > My coax is roughly 30 feet. I have not actually measured it but the length that is outside the > shack is 25 feet and I have a four foot piece on the inside of the shack to my current tuner > which is a Palstar AT1KM. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Barry, Stephen
As I am not sure of this stuff I need to ask the following question.
The example below is based on a doublet antenn which has a feed point of close to 50 ohms. So the ladder line is not what you want to transform so I understand that a 1:1 is correct. However if you have an antenna such as a loop which has a feedpoint impedance of closer to 200 ohms then a 4:1 would make sense to me. The reason is I need to reduce the feedpoint resistance of the antenna as I do not change the resistance based on the feedline. The rational for the balun is to transform the feedline from balanced line to unbalanced line which is the 50 ohm coax. Thus you want the currents matched in the coax thus the balun. Conclusion balun to transform balance to unbalanced and ratio for feedpoint impedance matching if required by antenna type. Anyway I might have my terms for impedance and resistance slightly off but please verify if I am correct in thinking that you need a balun ratio based on the antenna not the type of feedline. So am I correct in my understanding or just totally out in the weeds. ~73 Don KD8NNU FH#4107 On Sat, Sep 29, 2012 at 7:41 PM, Adrian wrote: > Here: > > http://www.karinya.net/g3txq/tuner_balun/ > > "Amateur Radio (G3TXQ) - Tuner Balun: 4:1 or 1:1 ? > > Follow the discussions on any Internet Ham Radio forum and it wont be > long > before someone recommends the use of a 4:1 balun at the output of a > tuner > feeding a multiband doublet through ladderline. Often the > recommendation is > accompanied by an explanation such as: "It helps the tuner to tune" > or: "It > reduces the impedance of the 450 ohm ladderline towards 50Ω". This > article > examines whether the ubiquitous advice to use a 4:1 balun in this > scenario > is valid. > > The arguments put forward for a 4:1 impedance transformation often > assume > that the tuner works best when operating with a load impedance close > to 50Ω. > That simply isn't true! The chart on the right shows the losses vs > load > resistance of a typical T-network tuner on 80m for several values of > load > reactance; 80m was chosen because losses tend to be more evident on > the > lower-frequency bands. As we can see the lowest tuner losses occur > when the > load resistance is in the medium/high range 250Ω-2500Ω; the highest > losses > occur at low load resistances, particularly where they are accompanied > by a > large capacitive reactance. > > Let's now take the example of a commonly proposed multiband doublet - > a > half-wave 80m dipole fed with 450Ω ladderline. At modest heights above > average ground the dipole has a feedpoint impedance close to 50Ω. That > means > that the impedance seen at the tuner end of the ladderline could have > a > resistive component anywhere from 50Ω to 4050Ω depending on ladderline > length; that range of impedances is indicated by the lower shaded bar > in the > chart, labelled 1:1. If we now introduce a 4:1 impedance > transformation, the > range of impedances will be lower by a factor of 4 as indicated by the > upper > shaded bar labelled 4:1. It's clear that the 1:1 range of impedances > will > result in the lower overall losses. > > In fact, no matter what the antenna impedance, the range of impedances > seen > at the tuner end of the ladderline would have a "geometric mean" of > 450Ω - > that is they would swing equally below and above 450Ω, but once we > introduce > a 4:1 balun the geometric mean will reduce to 112.5Ω. One look at the > loss > chart tells you that centering the impedances at the higher value is > the > preferable option. > > > Let's now take a look at the specific losses that would occur with our > example 132 doublet fed with 450Ω ladderline. > > The chart on the right was produced by varying the feedline length > from 0° > to 180° in 10° steps. At each step the impedance seen by the tuner was > calculated both with a 1:1 balun and then with a 4:1 balun, and the > tuner > losses determined using W9CF's T-network tuner simulator. Of course, > beyond > 180° the chart simply repeats itself. Ladderline losses were ignored. > > Apart from a small range of line lengths between 80° and 115°, where > the > line has transformed the 50Ω feedpoint impedance to a very high value > around > 4000Ω, the 1:1 balun is the better option; not only that, the worst > case > loss never exceeds 14% with the 1:1 balun whereas it reaches 21% with > the > 4:1 balun. > > But what about other bands - the doublet wont be used on just 80m! > > > This chart shows the tuner loss plotted against line length for our > example > doublet on 40m. Here the doublet feedpoint impedance is around 4000Ω, > so for > short ladderline lengths the 4:1 balun shows an advantage. However, as > the > ladderline length increases and the impedance is transformed to lower > values, the 1:1 balun soon shows the lower losses again. Across the > whole > range of ladderline lengths the 1:1 balun is twice as likely as the > 4:1 to > produce lower losses. > > The conclusion seems clear: if you have to choose just one balun, > unless you > know that your combination of doublet/ladderline length falls into the > minority of cases where a 4:1 balun has the advantage, a 1:1 balun is > the > preferred choice. Add into the mix the fact that most 4:1 baluns are > Voltage > Baluns, whereas to prevent feedline radiation we want balanced > currents; > then consider that all baluns other than a 1:1 Current Balun have the > full > transmit voltage applied common-mode across one or more windings, and > the > case is compelling for a 1:1 Current Balun in this situation. > > In this application any small impedance transformation caused by the > Current > Balun is immaterial because the tuner will compensate, so the windings > do > not need to be of any specific characteristic impedance. Typically, > bifilar > windings using Thermaleze wire inserted in Teflon tubes are employed > to cope > with the high differential-mode voltages present at current minima. > Balun > specialists "Balun Designs" offer a nice example in their Model 1171. > " > > -----Original Message----- > From: Adrian [mailto:[hidden email]] Sent: Sunday, 30 September > 2012 9:34 AM > To: [hidden email] > Subject: RE: [Elecraft] Balanced solution for KAT500 tuner? > > A UK G call did a graphed efficiency comparison test with the 1:1 > coming out > on top. I will post it when re-found. > > Also from > > http://www.theladderline.com/doublets-ladder-line-and-automatic-remote-tuner > s ; (spell-checked) > > "There is also some debate about whether the balun should be a 1:1 or > 4:1. I > think 4:1 has been quite popular in the past. This perhaps comes from > the > thought that the ladder line is higher impedance than coax so we need > to > step down to get it closer to the coax impedance. On the forums, > people who > have modelled the antenna with software like EZNEC seem to make a > fairly > compelling argument that a 1:1 balun is more likely to present an > impedance > within the range of the tuner over a wide range of frequencies. The > impedance will depend on the length of the ladder line so it's a bit > of a > gamble but I'm getting good results from a 1:1 current balun. > After doing some reading and playing with a home brew balun, I > finally took > the lazy way out and splashed out on a serious balun. It's a DX > Engineering > BAL050-H10-AT. It's not cheap but I think it was a good investment. I > don't > have any hard evidence to show how good it is compared to a cheaper > balun > but I have a feeling that it contributes to the good performance I get > with > this antenna. I've had absolutely no "RF in the shack" or similar > problems > even at the old QTH when I had the ladder line coming into the shack. > An interesting fact that I learned from the forums is the reason > ladder line > works more successfully than coax in a multiband situation like this. > The > common belief is that ladder line "doesn't care" about high SWR. It's > true > that ladder line usually has lower loss than coax at a given SWR but > that's > not the whole story. Another rather simple factor is that the > characteristic > impedance of ladder line is higher than coax so therefore, for a > typical > wire antenna over a wide range of frequency, the average SWR on ladder > line > tends to be lower than it would be with coax and that helps keep the > loss > low." > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of David Gilbert > Sent: Sunday, 30 September 2012 8:37 AM > To: [hidden email] > Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? > > > I don't believe that is necessarily true. Can you cite a reference to > back > up that statement? Or at least describe in physical terms (Q, > currents, > voltages, component loss, etc) why that would be so? I'm honestly > curious > what the difference would be. > > 73, > Dave AB7E > > > > On 9/29/2012 2:13 PM, Adrian wrote: >> 1:1 current balun has proven more efficient in conjunction with the >> appropriate balanced (matchbox style)tuner. >> >> -----Original Message----- >> From: [hidden email] >> [mailto:[hidden email]] On Behalf Of Robert G. >> Strickland >> Sent: Sunday, 30 September 2012 4:26 AM >> To: [hidden email] >> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >> >> Jim... >> >> Is there anything to be gained in putting a 1:1 "balanced isolator" >> at the feed point of an antenna that is fed by a "parallel wire" feed >> line? Does such an arrangement achieve feed line isolation while >> preserving the ability of such an antenna to be driven on various >> bands other than its resonant frequency? Thanks for your input. >> >> ...robert >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by Jim Brown-10
> In the old days, when RFI did not exist (few of us are old enough not > to remember TVI in the 50s), the Windom MIGHT have been a good idea. > Today, with RF noise sources everywhere and home stereo rigs full of > Pin One Problems ready to bring RF into equipment and detect it, > Windom antennas are a really bad idea. Unbalanced antennas or uncorrected common mode RF were never a good idea. Even before RF noise sources on receive and other RF sensitive electronics, one could easily encounter issues with lip burns from a "hot" microphone. That is just one more symptom of common mode issues. The only advantage we had in the "old days" was that the equipment operated at much higher input levels and were thus less sensitive to the RF voltage but the problems were still there as witnessed by the RF burns from touching a hot chassis or hot mic. 73, ... Joe, W4TV On 9/30/2012 3:02 AM, Jim Brown wrote: > On 9/29/2012 9:12 PM, Robert G. Strickland wrote: >> What I'm curious about is whether some such device, at the feed point of a doublet, >> in turn fed by window line is of any use [assuming an appropriate tuner at the radio >> end of the line]. You have said, accurately so, that a current choke at the feed >> point of a dipole [let's leave off-center fed antennas out of it at this point], in >> turn fed by coax, > > In all of this discussion, I have not used the word "coax." You have > read that somewhere else. > >> keeps RF from flowing on the outside of the coax and subsequently >> becoming "part of the antenna" and in turn picking up noise/etc. Another way of >> phrasing my question is, does the coax situation apply to open feeders, also? > > YES! That is EXACTLY what I have repeated, over and over again. It has > NOTHING to do with coax. Coax, if it is not decoupled by a common mode > choke, simply ADDS to the imbalance that is already present. EVERY > transmission line needs a common mode choe at the feedpoint to decouple > the line. > > Off-center fed antennas, like the so-called "Windom" in all of its > variations, are WILDLY unbalanced. As a result, they are notorious for > being NOISY, for putting RF in the shack, and for toasting common mode > chokes. It is a complete fiction to feed with with parallel wire line > and CALL it balanced, and decide that it needs a balanced tuner! The > antenna is unbalanced, so the feedline is unbalanced, and a balanced > tuner does nothing except transfer dollars between the purchaser and the > seller. > > In the old days, when RFI did not exist (few of us are old enough not to > remember TVI in the 50s), the Windom MIGHT have been a good idea. > Today, with RF noise sources everywhere and home stereo rigs full of Pin > One Problems ready to bring RF into equipment and detect it, Windom > antennas are a really bad idea. > > 73, Jim Brown K9YC > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by KD8NNU
Don,
You must think "system" rather than individual components. Also with antennas and feedlines, the "where is it connected" is a required parameter. A halfwave dipole in infinite space has a feedpoint impedance of 70 ohms, but brought down to practical heights, the feedpoint impedance is closer to 50 ohms, which is a good match for 50 ohm coax. Put a common mode choke at the antenna feedpoint and connect the coax to it - job done. Now for the consideration of the loop - actually, a full wavelength loop oriented vertically has an impedance of about 120 ohms, so that needs to be transformed before connecting to 50 ohm coax. Typically a 1/4 wavelength of 75 ohm coax is used for that impedance transformation. Yes, put a common mode choke at the antenna feedpoint in all cases. I encourage you to NOT make assumptions, but measure your antenna feedpoint impedance. An electrical halfwave of feedline (any characteristic impedance) can be used to do that. Connect the halfwave feedline to the antenna, hoist the antenna to the operating position and measure the impedance at the end of the half wave feedline. For higher frequencies, the feedline may be multiples of 1/2 wavelength. OK, so how do you find that 1/2 wavelength (or multiple) when the feedline velocity factor is a consideration? You cut the feedline initially a little long considering the frequency and the published velocity factors for the feedline, then short the far end of the feedline while measuring the near end with your antenna analyzer. Move the shorting position closer to the near end until the antenna analyzer tells you the impedance is 0 +/-j0. The reactance term is more critical than the resistive term. Equipped with that halfwave transmission line, you can stand at a convenient distance from the antenna and measure its actual feedpoint impedance - no guessing. On 9/30/2012 8:37 AM, [hidden email] wrote: > As I am not sure of this stuff I need to ask the following question. > > The example below is based on a doublet antenn which has a feed point of > close to 50 ohms. So the ladder line is not what you want to transform > so I understand that a 1:1 is correct. > > However if you have an antenna such as a loop which has a feedpoint > impedance of closer to 200 ohms then a 4:1 would make sense to me. The > reason is I need to reduce the feedpoint resistance of the antenna as I > do not change the resistance based on the feedline. > > The rational for the balun is to transform the feedline from balanced > line to unbalanced line which is the 50 ohm coax. Thus you want the > currents matched in the coax thus the balun. Conclusion balun to > transform balance to unbalanced and ratio for feedpoint impedance > matching if required by antenna type. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by KD8NNU
> However if you have an antenna such as a loop which has a feedpoint > impedance of closer to 200 ohms then a 4:1 would make sense to me. > The reason is I need to reduce the feedpoint resistance of the > antenna as I do not change the resistance based on the feedline. The "problem" with this logic is that parallel wire line is generally not the same impedance as the antenna it is feeding - e.g., "450 Ohm" line feeding a full wave loop (ca. 100 Ohms). As such, the impedance the tuner sees can be *anything* due to the transformation effect of the unmatched feedline. This is particularly apparent if one feeds a full wave dipole (e.g. 130' on 40 meters) at the center with an odd number of 1/4 open wire feedline (e.g. 100'). The feedline will transform the high feedpoint impedance to a very low value (<10 Ohms) ... when that is further transformed down by the 4:1 balun, the tuner will have a lot of trouble (and loss) with the 2 Ohm or so load. Within limits, most tuners are better able to handle high impedance mismatches than low impedance mismatches because losses tend to be resistive in nature and the lower impedance results in lower currents and thus lower (I^2*R) losses. The lower current is also why parallel wire feedlines tend to have lower losses (particularly with high SWR) - again there is much less resistive loss due to the lower current. 73, ... Joe, W4TV On 9/30/2012 8:37 AM, [hidden email] wrote: > As I am not sure of this stuff I need to ask the following question. > > The example below is based on a doublet antenn which has a feed point of > close to 50 ohms. So the ladder line is not what you want to transform > so I understand that a 1:1 is correct. > > However if you have an antenna such as a loop which has a feedpoint > impedance of closer to 200 ohms then a 4:1 would make sense to me. The > reason is I need to reduce the feedpoint resistance of the antenna as I > do not change the resistance based on the feedline. > > The rational for the balun is to transform the feedline from balanced > line to unbalanced line which is the 50 ohm coax. Thus you want the > currents matched in the coax thus the balun. Conclusion balun to > transform balance to unbalanced and ratio for feedpoint impedance > matching if required by antenna type. > > Anyway I might have my terms for impedance and resistance slightly off > but please verify if I am correct in thinking that you need a balun > ratio based on the antenna not the type of feedline. > > So am I correct in my understanding or just totally out in the weeds. > > ~73 > Don > KD8NNU > FH#4107 > > > On Sat, Sep 29, 2012 at 7:41 PM, Adrian wrote: > >> Here: >> >> http://www.karinya.net/g3txq/tuner_balun/ >> >> "Amateur Radio (G3TXQ) - Tuner Balun: 4:1 or 1:1 ? >> >> Follow the discussions on any Internet Ham Radio forum and it wont be >> long >> before someone recommends the use of a 4:1 balun at the output of a >> tuner >> feeding a multiband doublet through ladderline. Often the >> recommendation is >> accompanied by an explanation such as: "It helps the tuner to tune" >> or: "It >> reduces the impedance of the 450 ohm ladderline towards 50Ω". This >> article >> examines whether the ubiquitous advice to use a 4:1 balun in this >> scenario >> is valid. >> >> The arguments put forward for a 4:1 impedance transformation often >> assume >> that the tuner works best when operating with a load impedance close >> to 50Ω. >> That simply isn't true! The chart on the right shows the losses vs >> load >> resistance of a typical T-network tuner on 80m for several values of >> load >> reactance; 80m was chosen because losses tend to be more evident on >> the >> lower-frequency bands. As we can see the lowest tuner losses occur >> when the >> load resistance is in the medium/high range 250Ω-2500Ω; the highest >> losses >> occur at low load resistances, particularly where they are accompanied >> by a >> large capacitive reactance. >> >> Let's now take the example of a commonly proposed multiband doublet - >> a >> half-wave 80m dipole fed with 450Ω ladderline. At modest heights above >> average ground the dipole has a feedpoint impedance close to 50Ω. That >> means >> that the impedance seen at the tuner end of the ladderline could have >> a >> resistive component anywhere from 50Ω to 4050Ω depending on ladderline >> length; that range of impedances is indicated by the lower shaded bar >> in the >> chart, labelled 1:1. If we now introduce a 4:1 impedance >> transformation, the >> range of impedances will be lower by a factor of 4 as indicated by the >> upper >> shaded bar labelled 4:1. It's clear that the 1:1 range of impedances >> will >> result in the lower overall losses. >> >> In fact, no matter what the antenna impedance, the range of impedances >> seen >> at the tuner end of the ladderline would have a "geometric mean" of >> 450Ω - >> that is they would swing equally below and above 450Ω, but once we >> introduce >> a 4:1 balun the geometric mean will reduce to 112.5Ω. One look at the >> loss >> chart tells you that centering the impedances at the higher value is >> the >> preferable option. >> >> >> Let's now take a look at the specific losses that would occur with our >> example 132 doublet fed with 450Ω ladderline. >> >> The chart on the right was produced by varying the feedline length >> from 0° >> to 180° in 10° steps. At each step the impedance seen by the tuner was >> calculated both with a 1:1 balun and then with a 4:1 balun, and the >> tuner >> losses determined using W9CF's T-network tuner simulator. Of course, >> beyond >> 180° the chart simply repeats itself. Ladderline losses were ignored. >> >> Apart from a small range of line lengths between 80° and 115°, where >> the >> line has transformed the 50Ω feedpoint impedance to a very high value >> around >> 4000Ω, the 1:1 balun is the better option; not only that, the worst >> case >> loss never exceeds 14% with the 1:1 balun whereas it reaches 21% with >> the >> 4:1 balun. >> >> But what about other bands - the doublet wont be used on just 80m! >> >> >> This chart shows the tuner loss plotted against line length for our >> example >> doublet on 40m. Here the doublet feedpoint impedance is around 4000Ω, >> so for >> short ladderline lengths the 4:1 balun shows an advantage. However, as >> the >> ladderline length increases and the impedance is transformed to lower >> values, the 1:1 balun soon shows the lower losses again. Across the >> whole >> range of ladderline lengths the 1:1 balun is twice as likely as the >> 4:1 to >> produce lower losses. >> >> The conclusion seems clear: if you have to choose just one balun, >> unless you >> know that your combination of doublet/ladderline length falls into the >> minority of cases where a 4:1 balun has the advantage, a 1:1 balun is >> the >> preferred choice. Add into the mix the fact that most 4:1 baluns are >> Voltage >> Baluns, whereas to prevent feedline radiation we want balanced >> currents; >> then consider that all baluns other than a 1:1 Current Balun have the >> full >> transmit voltage applied common-mode across one or more windings, and >> the >> case is compelling for a 1:1 Current Balun in this situation. >> >> In this application any small impedance transformation caused by the >> Current >> Balun is immaterial because the tuner will compensate, so the windings >> do >> not need to be of any specific characteristic impedance. Typically, >> bifilar >> windings using Thermaleze wire inserted in Teflon tubes are employed >> to cope >> with the high differential-mode voltages present at current minima. >> Balun >> specialists "Balun Designs" offer a nice example in their Model 1171. >> " >> >> -----Original Message----- >> From: Adrian [mailto:[hidden email]] Sent: Sunday, 30 September >> 2012 9:34 AM >> To: [hidden email] >> Subject: RE: [Elecraft] Balanced solution for KAT500 tuner? >> >> A UK G call did a graphed efficiency comparison test with the 1:1 >> coming out >> on top. I will post it when re-found. >> >> Also from >> >> http://www.theladderline.com/doublets-ladder-line-and-automatic-remote-tuner >> s ; (spell-checked) >> >> "There is also some debate about whether the balun should be a 1:1 or >> 4:1. I >> think 4:1 has been quite popular in the past. This perhaps comes from >> the >> thought that the ladder line is higher impedance than coax so we need >> to >> step down to get it closer to the coax impedance. On the forums, >> people who >> have modelled the antenna with software like EZNEC seem to make a >> fairly >> compelling argument that a 1:1 balun is more likely to present an >> impedance >> within the range of the tuner over a wide range of frequencies. The >> impedance will depend on the length of the ladder line so it's a bit >> of a >> gamble but I'm getting good results from a 1:1 current balun. >> After doing some reading and playing with a home brew balun, I >> finally took >> the lazy way out and splashed out on a serious balun. It's a DX >> Engineering >> BAL050-H10-AT. It's not cheap but I think it was a good investment. I >> don't >> have any hard evidence to show how good it is compared to a cheaper >> balun >> but I have a feeling that it contributes to the good performance I get >> with >> this antenna. I've had absolutely no "RF in the shack" or similar >> problems >> even at the old QTH when I had the ladder line coming into the shack. >> An interesting fact that I learned from the forums is the reason >> ladder line >> works more successfully than coax in a multiband situation like this. >> The >> common belief is that ladder line "doesn't care" about high SWR. It's >> true >> that ladder line usually has lower loss than coax at a given SWR but >> that's >> not the whole story. Another rather simple factor is that the >> characteristic >> impedance of ladder line is higher than coax so therefore, for a >> typical >> wire antenna over a wide range of frequency, the average SWR on ladder >> line >> tends to be lower than it would be with coax and that helps keep the >> loss >> low." >> >> -----Original Message----- >> From: [hidden email] >> [mailto:[hidden email]] On Behalf Of David Gilbert >> Sent: Sunday, 30 September 2012 8:37 AM >> To: [hidden email] >> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >> >> >> I don't believe that is necessarily true. Can you cite a reference to >> back >> up that statement? Or at least describe in physical terms (Q, >> currents, >> voltages, component loss, etc) why that would be so? I'm honestly >> curious >> what the difference would be. >> >> 73, >> Dave AB7E >> >> >> >> On 9/29/2012 2:13 PM, Adrian wrote: >>> 1:1 current balun has proven more efficient in conjunction with the >>> appropriate balanced (matchbox style)tuner. >>> >>> -----Original Message----- >>> From: [hidden email] >>> [mailto:[hidden email]] On Behalf Of Robert G. >>> Strickland >>> Sent: Sunday, 30 September 2012 4:26 AM >>> To: [hidden email] >>> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >>> >>> Jim... >>> >>> Is there anything to be gained in putting a 1:1 "balanced isolator" >>> at the feed point of an antenna that is fed by a "parallel wire" feed >>> line? Does such an arrangement achieve feed line isolation while >>> preserving the ability of such an antenna to be driven on various >>> bands other than its resonant frequency? Thanks for your input. >>> >>> ...robert >>> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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Let me rephrase what Joe is stating - in an unmatched feedline
situation, the feedline characteristic impedance is not to be considered. It does not matter whether it is 50 ohms, 300 or 450 ohms - that characteristic impedance is NOT what is being matched. The feedline acts as an impedance transformer. As a result, a 4:1 balun may do more harm than good. A simple common mode choke (usually a 1:1 current balun) will do the job of reducing the feedline radiation (and noise pickup on receive). A 4:1 balun may actually make the antenna/feedline combination difficult to match - most tuners do not match well into extremely low or high impedance loads. 73, Don W3FPR On 9/30/2012 9:28 AM, Joe Subich, W4TV wrote: >> However if you have an antenna such as a loop which has a feedpoint >> impedance of closer to 200 ohms then a 4:1 would make sense to me. >> The reason is I need to reduce the feedpoint resistance of the >> antenna as I do not change the resistance based on the feedline. > The "problem" with this logic is that parallel wire line is generally > not the same impedance as the antenna it is feeding - e.g., "450 Ohm" > line feeding a full wave loop (ca. 100 Ohms). As such, the impedance > the tuner sees can be *anything* due to the transformation effect of > the unmatched feedline. > > This is particularly apparent if one feeds a full wave dipole (e.g. > 130' on 40 meters) at the center with an odd number of 1/4 open > wire feedline (e.g. 100'). The feedline will transform the high > feedpoint impedance to a very low value (<10 Ohms) ... when that is > further transformed down by the 4:1 balun, the tuner will have a lot > of trouble (and loss) with the 2 Ohm or so load. > > Within limits, most tuners are better able to handle high impedance > mismatches than low impedance mismatches because losses tend to be > resistive in nature and the lower impedance results in lower currents > and thus lower (I^2*R) losses. The lower current is also why parallel > wire feedlines tend to have lower losses (particularly with high SWR) > - again there is much less resistive loss due to the lower current. > > > 73, > > ... Joe, W4TV > > > On 9/30/2012 8:37 AM, [hidden email] wrote: >> As I am not sure of this stuff I need to ask the following question. >> >> The example below is based on a doublet antenn which has a feed point of >> close to 50 ohms. So the ladder line is not what you want to transform >> so I understand that a 1:1 is correct. >> >> However if you have an antenna such as a loop which has a feedpoint >> impedance of closer to 200 ohms then a 4:1 would make sense to me. The >> reason is I need to reduce the feedpoint resistance of the antenna as I >> do not change the resistance based on the feedline. >> >> The rational for the balun is to transform the feedline from balanced >> line to unbalanced line which is the 50 ohm coax. Thus you want the >> currents matched in the coax thus the balun. Conclusion balun to >> transform balance to unbalanced and ratio for feedpoint impedance >> matching if required by antenna type. >> >> Anyway I might have my terms for impedance and resistance slightly off >> but please verify if I am correct in thinking that you need a balun >> ratio based on the antenna not the type of feedline. >> >> So am I correct in my understanding or just totally out in the weeds. >> >> ~73 >> Don >> KD8NNU >> FH#4107 >> >> >> On Sat, Sep 29, 2012 at 7:41 PM, Adrian wrote: >> >>> Here: >>> >>> http://www.karinya.net/g3txq/tuner_balun/ >>> >>> "Amateur Radio (G3TXQ) - Tuner Balun: 4:1 or 1:1 ? >>> >>> Follow the discussions on any Internet Ham Radio forum and it wont be >>> long >>> before someone recommends the use of a 4:1 balun at the output of a >>> tuner >>> feeding a multiband doublet through ladderline. Often the >>> recommendation is >>> accompanied by an explanation such as: "It helps the tuner to tune" >>> or: "It >>> reduces the impedance of the 450 ohm ladderline towards 50Ω". This >>> article >>> examines whether the ubiquitous advice to use a 4:1 balun in this >>> scenario >>> is valid. >>> >>> The arguments put forward for a 4:1 impedance transformation often >>> assume >>> that the tuner works best when operating with a load impedance close >>> to 50Ω. >>> That simply isn't true! The chart on the right shows the losses vs >>> load >>> resistance of a typical T-network tuner on 80m for several values of >>> load >>> reactance; 80m was chosen because losses tend to be more evident on >>> the >>> lower-frequency bands. As we can see the lowest tuner losses occur >>> when the >>> load resistance is in the medium/high range 250Ω-2500Ω; the highest >>> losses >>> occur at low load resistances, particularly where they are accompanied >>> by a >>> large capacitive reactance. >>> >>> Let's now take the example of a commonly proposed multiband doublet - >>> a >>> half-wave 80m dipole fed with 450Ω ladderline. At modest heights above >>> average ground the dipole has a feedpoint impedance close to 50Ω. That >>> means >>> that the impedance seen at the tuner end of the ladderline could have >>> a >>> resistive component anywhere from 50Ω to 4050Ω depending on ladderline >>> length; that range of impedances is indicated by the lower shaded bar >>> in the >>> chart, labelled 1:1. If we now introduce a 4:1 impedance >>> transformation, the >>> range of impedances will be lower by a factor of 4 as indicated by the >>> upper >>> shaded bar labelled 4:1. It's clear that the 1:1 range of impedances >>> will >>> result in the lower overall losses. >>> >>> In fact, no matter what the antenna impedance, the range of impedances >>> seen >>> at the tuner end of the ladderline would have a "geometric mean" of >>> 450Ω - >>> that is they would swing equally below and above 450Ω, but once we >>> introduce >>> a 4:1 balun the geometric mean will reduce to 112.5Ω. One look at the >>> loss >>> chart tells you that centering the impedances at the higher value is >>> the >>> preferable option. >>> >>> >>> Let's now take a look at the specific losses that would occur with our >>> example 132 doublet fed with 450Ω ladderline. >>> >>> The chart on the right was produced by varying the feedline length >>> from 0° >>> to 180° in 10° steps. At each step the impedance seen by the tuner was >>> calculated both with a 1:1 balun and then with a 4:1 balun, and the >>> tuner >>> losses determined using W9CF's T-network tuner simulator. Of course, >>> beyond >>> 180° the chart simply repeats itself. Ladderline losses were ignored. >>> >>> Apart from a small range of line lengths between 80° and 115°, where >>> the >>> line has transformed the 50Ω feedpoint impedance to a very high value >>> around >>> 4000Ω, the 1:1 balun is the better option; not only that, the worst >>> case >>> loss never exceeds 14% with the 1:1 balun whereas it reaches 21% with >>> the >>> 4:1 balun. >>> >>> But what about other bands - the doublet wont be used on just 80m! >>> >>> >>> This chart shows the tuner loss plotted against line length for our >>> example >>> doublet on 40m. Here the doublet feedpoint impedance is around 4000Ω, >>> so for >>> short ladderline lengths the 4:1 balun shows an advantage. However, as >>> the >>> ladderline length increases and the impedance is transformed to lower >>> values, the 1:1 balun soon shows the lower losses again. Across the >>> whole >>> range of ladderline lengths the 1:1 balun is twice as likely as the >>> 4:1 to >>> produce lower losses. >>> >>> The conclusion seems clear: if you have to choose just one balun, >>> unless you >>> know that your combination of doublet/ladderline length falls into the >>> minority of cases where a 4:1 balun has the advantage, a 1:1 balun is >>> the >>> preferred choice. Add into the mix the fact that most 4:1 baluns are >>> Voltage >>> Baluns, whereas to prevent feedline radiation we want balanced >>> currents; >>> then consider that all baluns other than a 1:1 Current Balun have the >>> full >>> transmit voltage applied common-mode across one or more windings, and >>> the >>> case is compelling for a 1:1 Current Balun in this situation. >>> >>> In this application any small impedance transformation caused by the >>> Current >>> Balun is immaterial because the tuner will compensate, so the windings >>> do >>> not need to be of any specific characteristic impedance. Typically, >>> bifilar >>> windings using Thermaleze wire inserted in Teflon tubes are employed >>> to cope >>> with the high differential-mode voltages present at current minima. >>> Balun >>> specialists "Balun Designs" offer a nice example in their Model 1171. >>> " >>> >>> -----Original Message----- >>> From: Adrian [mailto:[hidden email]] Sent: Sunday, 30 September >>> 2012 9:34 AM >>> To: [hidden email] >>> Subject: RE: [Elecraft] Balanced solution for KAT500 tuner? >>> >>> A UK G call did a graphed efficiency comparison test with the 1:1 >>> coming out >>> on top. I will post it when re-found. >>> >>> Also from >>> >>> http://www.theladderline.com/doublets-ladder-line-and-automatic-remote-tuner >>> s ; (spell-checked) >>> >>> "There is also some debate about whether the balun should be a 1:1 or >>> 4:1. I >>> think 4:1 has been quite popular in the past. This perhaps comes from >>> the >>> thought that the ladder line is higher impedance than coax so we need >>> to >>> step down to get it closer to the coax impedance. On the forums, >>> people who >>> have modelled the antenna with software like EZNEC seem to make a >>> fairly >>> compelling argument that a 1:1 balun is more likely to present an >>> impedance >>> within the range of the tuner over a wide range of frequencies. The >>> impedance will depend on the length of the ladder line so it's a bit >>> of a >>> gamble but I'm getting good results from a 1:1 current balun. >>> After doing some reading and playing with a home brew balun, I >>> finally took >>> the lazy way out and splashed out on a serious balun. It's a DX >>> Engineering >>> BAL050-H10-AT. It's not cheap but I think it was a good investment. I >>> don't >>> have any hard evidence to show how good it is compared to a cheaper >>> balun >>> but I have a feeling that it contributes to the good performance I get >>> with >>> this antenna. I've had absolutely no "RF in the shack" or similar >>> problems >>> even at the old QTH when I had the ladder line coming into the shack. >>> An interesting fact that I learned from the forums is the reason >>> ladder line >>> works more successfully than coax in a multiband situation like this. >>> The >>> common belief is that ladder line "doesn't care" about high SWR. It's >>> true >>> that ladder line usually has lower loss than coax at a given SWR but >>> that's >>> not the whole story. Another rather simple factor is that the >>> characteristic >>> impedance of ladder line is higher than coax so therefore, for a >>> typical >>> wire antenna over a wide range of frequency, the average SWR on ladder >>> line >>> tends to be lower than it would be with coax and that helps keep the >>> loss >>> low." >>> >>> -----Original Message----- >>> From: [hidden email] >>> [mailto:[hidden email]] On Behalf Of David Gilbert >>> Sent: Sunday, 30 September 2012 8:37 AM >>> To: [hidden email] >>> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >>> >>> >>> I don't believe that is necessarily true. Can you cite a reference to >>> back >>> up that statement? Or at least describe in physical terms (Q, >>> currents, >>> voltages, component loss, etc) why that would be so? I'm honestly >>> curious >>> what the difference would be. >>> >>> 73, >>> Dave AB7E >>> >>> >>> >>> On 9/29/2012 2:13 PM, Adrian wrote: >>>> 1:1 current balun has proven more efficient in conjunction with the >>>> appropriate balanced (matchbox style)tuner. >>>> >>>> -----Original Message----- >>>> From: [hidden email] >>>> [mailto:[hidden email]] On Behalf Of Robert G. >>>> Strickland >>>> Sent: Sunday, 30 September 2012 4:26 AM >>>> To: [hidden email] >>>> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >>>> >>>> Jim... >>>> >>>> Is there anything to be gained in putting a 1:1 "balanced isolator" >>>> at the feed point of an antenna that is fed by a "parallel wire" feed >>>> line? Does such an arrangement achieve feed line isolation while >>>> preserving the ability of such an antenna to be driven on various >>>> bands other than its resonant frequency? Thanks for your input. >>>> >>>> ...robert >>>> >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[hidden email] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >>> >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[hidden email] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by KD8NNU
On 9/30/2012 5:37 AM, [hidden email] wrote:
> So am I correct in my understanding or just totally out in the weeds. There may be more to it than that. First, no matter what feedline or matching system you use, there should be a serious common mode choke at the feedpoint. Second, is this a single band loop, or a multi-band antenna? The feedpoint impedance is likely to be very different on each band. A section of transmission line is often a better matching technique for single band antennas. For a multi-band antenna, it would help to know the feedpoint Z on all bands and choose a feedline on that basis. The length of the line can also be an issue. This is the sort of question that is best answered by constructing a simple model of the antenna using EZNEC. A stripped down version comes free with the ARRL Antenna Book, and is sufficient to model a simple loop at the level you need, and you can buy a more capable version for about $50. One of the major reasons for choosing some feedline other than coax is that higher impedance lines have lower loss. This matters a lot more for long runs than for short ones. Decent 4:1 impedance transforming "baluns" are not cheap, and many hams would be better off spending that money on better coax. 400 ohm line may have much lower loss than coax if the feedpoint Z is 500 ohms, but coax may have much lower loss if the feedpoint Z is 10 ohms. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Balanced solution for KAT500 tuner?
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In reply to this post by Don Wilhelm-4
> in an unmatched feedline situation, the feedline characteristic > impedance is not to be considered. It does not matter whether it is > 50 ohms, 300 or 450 ohms - that characteristic impedance is NOT what > is being matched. That's incorrect. The feedline characteristic impedance *must* be considered because it effects the *transformation* that occurs. The tuner is not matching the feedline impedance or the antenna impedance - rather it is matching the *transformed* antenna impedance at tuner end of the feedline. Because of the transformation when trying for multi-band operation, it is generally best to use completely non-resonant antenna lengths, feed line lengths that avoid even quarter wave lengths on *all* bands, and the highest possible feedline impedance. 73, ... Joe, W4TV On 9/30/2012 9:47 AM, Don Wilhelm wrote: > Let me rephrase what Joe is stating - in an unmatched feedline > situation, the feedline characteristic impedance is not to be > considered. It does not matter whether it is 50 ohms, 300 or 450 ohms - > that characteristic impedance is NOT what is being matched. The feedline > acts as an impedance transformer. > > As a result, a 4:1 balun may do more harm than good. A simple common > mode choke (usually a 1:1 current balun) will do the job of reducing the > feedline radiation (and noise pickup on receive). > A 4:1 balun may actually make the antenna/feedline combination difficult > to match - most tuners do not match well into extremely low or high > impedance loads. > > 73, > Don W3FPR > > > On 9/30/2012 9:28 AM, Joe Subich, W4TV wrote: >>> However if you have an antenna such as a loop which has a feedpoint >>> impedance of closer to 200 ohms then a 4:1 would make sense to me. >>> The reason is I need to reduce the feedpoint resistance of the >>> antenna as I do not change the resistance based on the feedline. >> The "problem" with this logic is that parallel wire line is generally >> not the same impedance as the antenna it is feeding - e.g., "450 Ohm" >> line feeding a full wave loop (ca. 100 Ohms). As such, the impedance >> the tuner sees can be *anything* due to the transformation effect of >> the unmatched feedline. >> >> This is particularly apparent if one feeds a full wave dipole (e.g. >> 130' on 40 meters) at the center with an odd number of 1/4 open >> wire feedline (e.g. 100'). The feedline will transform the high >> feedpoint impedance to a very low value (<10 Ohms) ... when that is >> further transformed down by the 4:1 balun, the tuner will have a lot >> of trouble (and loss) with the 2 Ohm or so load. >> >> Within limits, most tuners are better able to handle high impedance >> mismatches than low impedance mismatches because losses tend to be >> resistive in nature and the lower impedance results in lower currents >> and thus lower (I^2*R) losses. The lower current is also why parallel >> wire feedlines tend to have lower losses (particularly with high SWR) >> - again there is much less resistive loss due to the lower current. >> >> >> 73, >> >> ... Joe, W4TV >> >> >> On 9/30/2012 8:37 AM, [hidden email] wrote: >>> As I am not sure of this stuff I need to ask the following question. >>> >>> The example below is based on a doublet antenn which has a feed point of >>> close to 50 ohms. So the ladder line is not what you want to transform >>> so I understand that a 1:1 is correct. >>> >>> However if you have an antenna such as a loop which has a feedpoint >>> impedance of closer to 200 ohms then a 4:1 would make sense to me. The >>> reason is I need to reduce the feedpoint resistance of the antenna as I >>> do not change the resistance based on the feedline. >>> >>> The rational for the balun is to transform the feedline from balanced >>> line to unbalanced line which is the 50 ohm coax. Thus you want the >>> currents matched in the coax thus the balun. Conclusion balun to >>> transform balance to unbalanced and ratio for feedpoint impedance >>> matching if required by antenna type. >>> >>> Anyway I might have my terms for impedance and resistance slightly off >>> but please verify if I am correct in thinking that you need a balun >>> ratio based on the antenna not the type of feedline. >>> >>> So am I correct in my understanding or just totally out in the weeds. >>> >>> ~73 >>> Don >>> KD8NNU >>> FH#4107 >>> >>> >>> On Sat, Sep 29, 2012 at 7:41 PM, Adrian wrote: >>> >>>> Here: >>>> >>>> http://www.karinya.net/g3txq/tuner_balun/ >>>> >>>> "Amateur Radio (G3TXQ) - Tuner Balun: 4:1 or 1:1 ? >>>> >>>> Follow the discussions on any Internet Ham Radio forum and it wont be >>>> long >>>> before someone recommends the use of a 4:1 balun at the output of a >>>> tuner >>>> feeding a multiband doublet through ladderline. Often the >>>> recommendation is >>>> accompanied by an explanation such as: "It helps the tuner to tune" >>>> or: "It >>>> reduces the impedance of the 450 ohm ladderline towards 50Ω". This >>>> article >>>> examines whether the ubiquitous advice to use a 4:1 balun in this >>>> scenario >>>> is valid. >>>> >>>> The arguments put forward for a 4:1 impedance transformation often >>>> assume >>>> that the tuner works best when operating with a load impedance close >>>> to 50Ω. >>>> That simply isn't true! The chart on the right shows the losses vs >>>> load >>>> resistance of a typical T-network tuner on 80m for several values of >>>> load >>>> reactance; 80m was chosen because losses tend to be more evident on >>>> the >>>> lower-frequency bands. As we can see the lowest tuner losses occur >>>> when the >>>> load resistance is in the medium/high range 250Ω-2500Ω; the highest >>>> losses >>>> occur at low load resistances, particularly where they are accompanied >>>> by a >>>> large capacitive reactance. >>>> >>>> Let's now take the example of a commonly proposed multiband doublet - >>>> a >>>> half-wave 80m dipole fed with 450Ω ladderline. At modest heights above >>>> average ground the dipole has a feedpoint impedance close to 50Ω. That >>>> means >>>> that the impedance seen at the tuner end of the ladderline could have >>>> a >>>> resistive component anywhere from 50Ω to 4050Ω depending on ladderline >>>> length; that range of impedances is indicated by the lower shaded bar >>>> in the >>>> chart, labelled 1:1. If we now introduce a 4:1 impedance >>>> transformation, the >>>> range of impedances will be lower by a factor of 4 as indicated by the >>>> upper >>>> shaded bar labelled 4:1. It's clear that the 1:1 range of impedances >>>> will >>>> result in the lower overall losses. >>>> >>>> In fact, no matter what the antenna impedance, the range of impedances >>>> seen >>>> at the tuner end of the ladderline would have a "geometric mean" of >>>> 450Ω - >>>> that is they would swing equally below and above 450Ω, but once we >>>> introduce >>>> a 4:1 balun the geometric mean will reduce to 112.5Ω. One look at the >>>> loss >>>> chart tells you that centering the impedances at the higher value is >>>> the >>>> preferable option. >>>> >>>> >>>> Let's now take a look at the specific losses that would occur with our >>>> example 132 doublet fed with 450Ω ladderline. >>>> >>>> The chart on the right was produced by varying the feedline length >>>> from 0° >>>> to 180° in 10° steps. At each step the impedance seen by the tuner was >>>> calculated both with a 1:1 balun and then with a 4:1 balun, and the >>>> tuner >>>> losses determined using W9CF's T-network tuner simulator. Of course, >>>> beyond >>>> 180° the chart simply repeats itself. Ladderline losses were ignored. >>>> >>>> Apart from a small range of line lengths between 80° and 115°, where >>>> the >>>> line has transformed the 50Ω feedpoint impedance to a very high value >>>> around >>>> 4000Ω, the 1:1 balun is the better option; not only that, the worst >>>> case >>>> loss never exceeds 14% with the 1:1 balun whereas it reaches 21% with >>>> the >>>> 4:1 balun. >>>> >>>> But what about other bands - the doublet wont be used on just 80m! >>>> >>>> >>>> This chart shows the tuner loss plotted against line length for our >>>> example >>>> doublet on 40m. Here the doublet feedpoint impedance is around 4000Ω, >>>> so for >>>> short ladderline lengths the 4:1 balun shows an advantage. However, as >>>> the >>>> ladderline length increases and the impedance is transformed to lower >>>> values, the 1:1 balun soon shows the lower losses again. Across the >>>> whole >>>> range of ladderline lengths the 1:1 balun is twice as likely as the >>>> 4:1 to >>>> produce lower losses. >>>> >>>> The conclusion seems clear: if you have to choose just one balun, >>>> unless you >>>> know that your combination of doublet/ladderline length falls into the >>>> minority of cases where a 4:1 balun has the advantage, a 1:1 balun is >>>> the >>>> preferred choice. Add into the mix the fact that most 4:1 baluns are >>>> Voltage >>>> Baluns, whereas to prevent feedline radiation we want balanced >>>> currents; >>>> then consider that all baluns other than a 1:1 Current Balun have the >>>> full >>>> transmit voltage applied common-mode across one or more windings, and >>>> the >>>> case is compelling for a 1:1 Current Balun in this situation. >>>> >>>> In this application any small impedance transformation caused by the >>>> Current >>>> Balun is immaterial because the tuner will compensate, so the windings >>>> do >>>> not need to be of any specific characteristic impedance. Typically, >>>> bifilar >>>> windings using Thermaleze wire inserted in Teflon tubes are employed >>>> to cope >>>> with the high differential-mode voltages present at current minima. >>>> Balun >>>> specialists "Balun Designs" offer a nice example in their Model 1171. >>>> " >>>> >>>> -----Original Message----- >>>> From: Adrian [mailto:[hidden email]] Sent: Sunday, 30 September >>>> 2012 9:34 AM >>>> To: [hidden email] >>>> Subject: RE: [Elecraft] Balanced solution for KAT500 tuner? >>>> >>>> A UK G call did a graphed efficiency comparison test with the 1:1 >>>> coming out >>>> on top. I will post it when re-found. >>>> >>>> Also from >>>> >>>> http://www.theladderline.com/doublets-ladder-line-and-automatic-remote-tuner >>>> s ; (spell-checked) >>>> >>>> "There is also some debate about whether the balun should be a 1:1 or >>>> 4:1. I >>>> think 4:1 has been quite popular in the past. This perhaps comes from >>>> the >>>> thought that the ladder line is higher impedance than coax so we need >>>> to >>>> step down to get it closer to the coax impedance. On the forums, >>>> people who >>>> have modelled the antenna with software like EZNEC seem to make a >>>> fairly >>>> compelling argument that a 1:1 balun is more likely to present an >>>> impedance >>>> within the range of the tuner over a wide range of frequencies. The >>>> impedance will depend on the length of the ladder line so it's a bit >>>> of a >>>> gamble but I'm getting good results from a 1:1 current balun. >>>> After doing some reading and playing with a home brew balun, I >>>> finally took >>>> the lazy way out and splashed out on a serious balun. It's a DX >>>> Engineering >>>> BAL050-H10-AT. It's not cheap but I think it was a good investment. I >>>> don't >>>> have any hard evidence to show how good it is compared to a cheaper >>>> balun >>>> but I have a feeling that it contributes to the good performance I get >>>> with >>>> this antenna. I've had absolutely no "RF in the shack" or similar >>>> problems >>>> even at the old QTH when I had the ladder line coming into the shack. >>>> An interesting fact that I learned from the forums is the reason >>>> ladder line >>>> works more successfully than coax in a multiband situation like this. >>>> The >>>> common belief is that ladder line "doesn't care" about high SWR. It's >>>> true >>>> that ladder line usually has lower loss than coax at a given SWR but >>>> that's >>>> not the whole story. Another rather simple factor is that the >>>> characteristic >>>> impedance of ladder line is higher than coax so therefore, for a >>>> typical >>>> wire antenna over a wide range of frequency, the average SWR on ladder >>>> line >>>> tends to be lower than it would be with coax and that helps keep the >>>> loss >>>> low." >>>> >>>> -----Original Message----- >>>> From: [hidden email] >>>> [mailto:[hidden email]] On Behalf Of David Gilbert >>>> Sent: Sunday, 30 September 2012 8:37 AM >>>> To: [hidden email] >>>> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >>>> >>>> >>>> I don't believe that is necessarily true. Can you cite a reference to >>>> back >>>> up that statement? Or at least describe in physical terms (Q, >>>> currents, >>>> voltages, component loss, etc) why that would be so? I'm honestly >>>> curious >>>> what the difference would be. >>>> >>>> 73, >>>> Dave AB7E >>>> >>>> >>>> >>>> On 9/29/2012 2:13 PM, Adrian wrote: >>>>> 1:1 current balun has proven more efficient in conjunction with the >>>>> appropriate balanced (matchbox style)tuner. >>>>> >>>>> -----Original Message----- >>>>> From: [hidden email] >>>>> [mailto:[hidden email]] On Behalf Of Robert G. >>>>> Strickland >>>>> Sent: Sunday, 30 September 2012 4:26 AM >>>>> To: [hidden email] >>>>> Subject: Re: [Elecraft] Balanced solution for KAT500 tuner? >>>>> >>>>> Jim... >>>>> >>>>> Is there anything to be gained in putting a 1:1 "balanced isolator" >>>>> at the feed point of an antenna that is fed by a "parallel wire" feed >>>>> line? Does such an arrangement achieve feed line isolation while >>>>> preserving the ability of such an antenna to be driven on various >>>>> bands other than its resonant frequency? Thanks for your input. >>>>> >>>>> ...robert >>>>> >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:[hidden email] >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: http://www.qsl.net/donate.html >>>> >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:[hidden email] >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: http://www.qsl.net/donate.html >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[hidden email] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Joe Subich, W4TV-4
I believe Joe meant to say "...higher impedance results in lower currents..."
--[snip] Within limits, most tuners are better able to handle high impedance mismatches than low impedance mismatches because losses tend to be resistive in nature and the lower impedance results in lower currents and thus lower (I^2*R) losses. The lower current is also why parallel wire feedlines tend to have lower losses (particularly with high SWR) - again there is much less resistive loss due to the lower current. [snip] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Joe Subich, W4TV-4
Am running my fairly new kpa-500 in the rtty contest. It is situated out
in the open. it from 220v and during the run it's current runs at 10a and 64-74v. The temp starts at 35c and as I run it slowly creeps up to 55-57c and kicks out with the error message of "Pwr In High". I'm only driving this with a K-3 set at about 13w to drive the amp to 350 watts. I wanted to take it easy on the amp and seems from the specs that it should handle that. The amp. seems to be real sensitive to the driving power of just a watt difference from the K-3. The power varies at the amp from 250-350 watts when running and not fiddling with the K-3 power knob. I have the fan set on 1 and didn't make any difference if I set it to 6, it still would kick out in due time, just slightly longer. Must mention it does it whether it's into a resonant antenna or a dummy load. The temps just slowly climb. Anyone have a similar problem, makes it useless for rtty contesting and running. No problems in CW contests at full bore! 73 Dwight NS9I. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Dwight.
Something is wrong. Mine at 400-500 watts gets to about 65C during bunches of RTTY CQ's. It probably can go higher. Fan kicks in at expected values. 240v line. 73 de Brian/K3KO On 9/30/2012 14:53, DGB wrote: > Am running my fairly new kpa-500 in the rtty contest. It is situated out > in the open. > > it from 220v and during the run it's current runs at 10a and 64-74v. The > temp starts at 35c and as I run it slowly creeps up to 55-57c and kicks > out with the error message of "Pwr In High". > > I'm only driving this with a K-3 set at about 13w to drive the amp to > 350 watts. I wanted to take it easy on the amp and seems from the specs > that it should handle that. The amp. seems to be real sensitive to the > driving power of just a watt difference from the K-3. The power varies > at the amp from 250-350 watts when running and not fiddling with the K-3 > power knob. I have the fan set on 1 and didn't make any difference if I > set it to 6, it still would kick out in due time, just slightly longer. > Must mention it does it whether it's into a resonant antenna or a dummy > load. The temps just slowly climb. > > Anyone have a similar problem, makes it useless for rtty contesting and > running. No problems in CW contests at full bore! > > 73 Dwight NS9I. > ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2221 / Virus Database: 2441/5300 - Release Date: 09/30/12 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: KPA-500 and RTTY
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In reply to this post by 'DGB'
My specs:
250 watts out 10 watts drive 64 volts 8.5 amps 240 V line Temp has got up to 52c @ 300 watts. Haven't seen any warnings, but the fan kicks in more often as expected. I'm uneasy running it at 500 watts during a contest. Joe Hutchens ( AJ8MH ) http://webpages.charter.net/aj8mh-radio/ On Sun, Sep 30, 2012 at 11:15 AM, Brian Alsop wrote: > Dwight. > > Something is wrong. Mine at 400-500 watts gets to about 65C during > bunches of RTTY CQ's. It probably can go higher. Fan kicks in at > expected values. 240v line. > > 73 de Brian/K3KO > > On 9/30/2012 14:53, DGB wrote: >> Am running my fairly new kpa-500 in the rtty contest. It is situated >> out >> in the open. >> >> it from 220v and during the run it's current runs at 10a and 64-74v. >> The >> temp starts at 35c and as I run it slowly creeps up to 55-57c and >> kicks >> out with the error message of "Pwr In High". >> >> I'm only driving this with a K-3 set at about 13w to drive the amp to >> 350 watts. I wanted to take it easy on the amp and seems from the >> specs >> that it should handle that. The amp. seems to be real sensitive to >> the >> driving power of just a watt difference from the K-3. The power >> varies >> at the amp from 250-350 watts when running and not fiddling with the >> K-3 >> power knob. I have the fan set on 1 and didn't make any difference if >> I >> set it to 6, it still would kick out in due time, just slightly >> longer. >> Must mention it does it whether it's into a resonant antenna or a >> dummy >> load. The temps just slowly climb. >> >> Anyone have a similar problem, makes it useless for rtty contesting >> and >> running. No problems in CW contests at full bore! >> >> 73 Dwight NS9I. >> > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2012.0.2221 / Virus Database: 2441/5300 - Release Date: > 09/30/12 > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: KPA-500 and RTTY
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In reply to this post by 'DGB'
I thought about this for a couple seconds... I have seen some rigs have
a rather large difference in power out between mark and space tones. With a small difference in drive I would expect to see a large difference in power out of the amp with these radios. I've also heard some radios with a click between mark and space that makes the signal much wider. Check the output from the K3 and make sure the power out is constant between mark and space (don't use a peak-reading watt meter), and make sure you don't have any clicks that may be driving the amp harder. I noticed that your PS voltage has a huge swing. I'm assuming that this is the difference between transmitting and not transmitting. It should be nearly constant while transmitting. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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