Hello All,
Several month ago, after I finished my KPA100, I found that when transmitting SSB on the higher bands (20, 17 & 15), the computer speakers across the room, when turned on, would screech - adjusting the speaker volume had no effect (but turning off the speakers quieted them). During a QSO a few weeks ago, it was commented that it sounded like I was getting RF into my audio. To make a short story long, I don't have a very good ground system, so there's a high level of RF in the shack - the shack is on the 2nd floor, about 18 ft above the ground rod. My primary antenna is a 100 ft multiband horizontal dipole feed with ladder line into a 9:1 balun, which is connected to my KAT100 via 6' of RG8. While the antenna works great on all bands (the KAT100 has no trouble tuning it), there's a fairly high SWR on the feedline on the higher bands. I have two different length wires connected the ground rod to the KAT100, and adding counterpoises for 20, 17 & 15 meters hasn't change the high level of RF in the shack on these bands. A week or two ago, I put up a second antenna, a vertical parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has very low SWR on these bands. When using this antenna, I have no problems with the computer speakers screeching, so there's apparently not much RF in the shack. This weekend, during the NA QSO party, when using the ladder line fed dipole on the higher bands, several times, I was told that my audio was distorted, and switching to the vertical coax fed dipole immediately cured the problem. So, the question is, what can be done to fix the distorted audio when there a high level of RF in the shack (besides getting a better ground system - I plan to put in one or two more ground rods, but I won't be able to do that until after the ground defrosts in the spring). The mic I'm using is a RadioShack Electret replacement element in an old mobile mic case - the case is plastic and not shielded, but the cable is shielded, and I have grounded the mike jack in my K2. All suggestions about how I can eliminate the distortion will be greatly welcomed, as well as suggestions about how I can reduce the high level of RF in the shack besides adding more ground rods. Thanks Bob W1SRB _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
> So, the question is, what can be done to fix the distorted audio
> when there a high level of RF in the shack (besides getting a better > ground system - I plan to put in one or two more ground rods, but I > won't be able to do that until after the ground defrosts in the spring). > The mic I'm using is a RadioShack Electret replacement element in an old > mobile mic case - the case is plastic and not shielded, but the cable is > shielded, and I have grounded the mike jack in my K2. > > All suggestions about how I can eliminate the distortion will be > greatly welcomed, as well as suggestions about how I can reduce the > high level of RF in the shack besides adding more ground rods. > I had similar problems, and they were cured by adding an RF choke to the SSB module: http://www.ac6rm.net/mailarchive/html/elecraft-list/2004-07/msg00453.html Tor N4OGW _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
In reply to this post by Solosko, Robert B (Bob)
Robert:
This problem is easily fixed. Add a counterpoise for each band on which you operate. The counterpoise is simply a 1/4 wave length of wire for the particular band. Attach one end of the wire to your K2's ground, run the wire as inconspicuously as possible, keeping it out of reach of animals, children, etc. Be sure the far end, which can have quite high rf voltages, is well insulated -- and the more isolated from other electronic items the better. If you operate multibands, you may run your separate counterpoises together over part of their stretch, but separate the last several feet of each from the others, and insulate well. best wishes, david belsley, w1euy On Jan 22, 2007, at 12:56 PM, Solosko, Robert B (Bob) wrote: > Hello All, > > Several month ago, after I finished my KPA100, I found that when > transmitting SSB on the higher bands (20, 17 & 15), the computer > speakers across the room, when turned on, would screech - adjusting > the > speaker volume had no effect (but turning off the speakers quieted > them). During a QSO a few weeks ago, it was commented that it sounded > like I was getting RF into my audio. > > To make a short story long, I don't have a very good ground > system, so there's a high level of RF in the shack - the shack is > on the > 2nd floor, about 18 ft above the ground rod. My primary antenna is > a 100 > ft multiband horizontal dipole feed with ladder line into a 9:1 balun, > which is connected to my KAT100 via 6' of RG8. While the antenna works > great on all bands (the KAT100 has no trouble tuning it), there's a > fairly high SWR on the feedline on the higher bands. I have two > different length wires connected the ground rod to the KAT100, and > adding counterpoises for 20, 17 & 15 meters hasn't change the high > level > of RF in the shack on these bands. > > A week or two ago, I put up a second antenna, a vertical > parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna > has > very low SWR on these bands. When using this antenna, I have no > problems > with the computer speakers screeching, so there's apparently not > much RF > in the shack. This weekend, during the NA QSO party, when using the > ladder line fed dipole on the higher bands, several times, I was told > that my audio was distorted, and switching to the vertical coax fed > dipole immediately cured the problem. > > So, the question is, what can be done to fix the distorted audio > when there a high level of RF in the shack (besides getting a better > ground system - I plan to put in one or two more ground rods, but I > won't be able to do that until after the ground defrosts in the > spring). > The mic I'm using is a RadioShack Electret replacement element in > an old > mobile mic case - the case is plastic and not shielded, but the > cable is > shielded, and I have grounded the mike jack in my K2. > > All suggestions about how I can eliminate the distortion will be > greatly welcomed, as well as suggestions about how I can reduce the > high level of RF in the shack besides adding more ground rods. > > Thanks > > Bob W1SRB > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com -------------------------------------------- david a belsley professor of economics boston college _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
In reply to this post by Solosko, Robert B (Bob)
>To make a short story long, I don't have a very good ground
>system, so there's a high level of RF in the shack Hi Bob, I've been working on a tutorial on RFI that is currently at the advanced draft stage. It is posted on my website as a pdf. The lack of, or quality of, a connection to mother earth is NOT the cause of your problems. The REAL cause of most "RF in the shack" problems is a "pin 1 problem" in one or more pieces of equipment. Most ham gear (including the K2), and most consumer products, are built with designed-in pin 1 problems. See the tutorial for details. http://audiosystemsgroup.com/RFI-Ham.pdf 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
In reply to this post by Solosko, Robert B (Bob)
Bob,
You counterpoises - are they 1/4 wave long at each of those bands? Are the far ends isolated? Are the far ends seaprated for the various bands? The answer to each of these questions should be yes. It is difficult to achieve a good RF Ground with a long run to a ground rod. At frequencies where the length of wire to the ground rod is 1/4 wavelength, there will be a high impedance to RF at those frequencies - a 16 foot run to the ground rod would actually create a high impedance at 14 MHz in your shack. In that case, the counterpoise wires are a better solution. You may want to try connecting the counterpoise wires to the coax side of your balun. You could try inductors in series with the AF line in the K2 to get rid of the distorted audio, but the real solution is to get the RF out of the shack. I wonder why you are using a 9:1 balun? You may be better off using a 1:1 balun instead. Yes, I know that 50 times 9 is 450, but that is only the characteristic impedance of your feedline - the feedpoint impedance will be quite different than 450 ohms, and may vary from very low to very high depending on the frequency. It just may be that your 9:1 balun is creating more RF in the shack. If you have no 1:1 balun available, try removing the balun and connect the feeders to the center conductor and shield of your coax - and connect your counterpoises to the shield at that point too - you may find your RF in the shack will drop dramatically. 73, Don W3FPR > -----Original Message----- > > To make a short story long, I don't have a very good ground > system, so there's a high level of RF in the shack - the shack is on the > 2nd floor, about 18 ft above the ground rod. My primary antenna is a 100 > ft multiband horizontal dipole feed with ladder line into a 9:1 balun, > which is connected to my KAT100 via 6' of RG8. While the antenna works > great on all bands (the KAT100 has no trouble tuning it), there's a > fairly high SWR on the feedline on the higher bands. I have two > different length wires connected the ground rod to the KAT100, and > adding counterpoises for 20, 17 & 15 meters hasn't change the high level > of RF in the shack on these bands. > > A week or two ago, I put up a second antenna, a vertical > parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has > very low SWR on these bands. When using this antenna, I have no problems > with the computer speakers screeching, so there's apparently not much RF > in the shack. This weekend, during the NA QSO party, when using the > ladder line fed dipole on the higher bands, several times, I was told > that my audio was distorted, and switching to the vertical coax fed > dipole immediately cured the problem. > > So, the question is, what can be done to fix the distorted audio > when there a high level of RF in the shack (besides getting a better > ground system - I plan to put in one or two more ground rods, but I > won't be able to do that until after the ground defrosts in the spring). > The mic I'm using is a RadioShack Electret replacement element in an old > mobile mic case - the case is plastic and not shielded, but the cable is > shielded, and I have grounded the mike jack in my K2. > > All suggestions about how I can eliminate the distortion will be > greatly welcomed, as well as suggestions about how I can reduce the > high level of RF in the shack besides adding more ground rods. > > Thanks > > Bob W1SRB > No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.17.4/644 - Release Date: 1/22/2007 7:30 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
In reply to this post by Solosko, Robert B (Bob)
Bob, you need quarter wave insulated radials in the shack right at the rig
ground post to eliminate the hot rf problem on each high band. Connected at the ground rod, they do no good, since that is 18 feet ? away from the RF source, (Rig). Also, how close is your antenna to the rig? Making that maximum distance separation helps. Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
In reply to this post by Don Wilhelm-3
Don, W3FPR wrote:
I wonder why you are using a 9:1 balun? You may be better off using a 1:1 balun instead. Yes, I know that 50 times 9 is 450, but that is only the characteristic impedance of your feedline - the feedpoint impedance will be quite different than 450 ohms, and may vary from very low to very high depending on the frequency. It just may be that your 9:1 balun is creating more RF in the shack. If you have no 1:1 balun available, try removing the balun and connect the feeders to the center conductor and shield of your coax - and connect your counterpoises to the shield at that point too - you may find your RF in the shack will drop dramatically. ------------------------------------ To follow up Don's comments, I've fed open wire line from a so-called "unbalanced" output with *no* balun and RF ammeters in each leg of the feeders showed that the currents were still balanced. The currents *inside* a coax line are balanced. The current flowing inside the shield is equal and opposite the current on the outer surface of the center conductor. Where things go awry is where the coax shield ends and RF can flow around the end onto the outside. Now there's two loads on those currents: one is the antenna and the other is whatever is connected to the outside of the coax shield, including the rig. If that sounds confusing, remember that RF does not flow *in* a conductor, but only along the surface. So the RF currents flowing along the inside of the coax (or inside your rig near the antenna connector) are totally independent of any RF currents flowing on the outside of the coax (or on the outside surface of the rig). It's those outside currents that tend to cause most of the problems. It's those outside currents you upset when you touch the rig and so detune the system or give yourself an RF "bite" (Ouch!). It's those outside currents that get inductively coupled into things like speaker wires, telephones, microphones, etc., and cause mischief. A balun is just a length of transmission line, sufficiently long that any unbalance at one end is "smoothed out" by the interaction between the RF fields around the wires before RF currents get to the other end. Years ago, we made a balun by winding up transmission line in a big coil. Sometimes we wound each leg into its own coil and sometimes both legs were wound next to each other in one huge 'bifilar' coil. For HF an open wire balun might be 4 to 6 inches in diameter and a foot or two long. (It was common to mount them on standoff insulators on a large board and screw it to the wall!) Nowadays we use ferrite cores that give us the inductance needed in a much smaller space, but the operation is the same. If you look at a 1:1 balun schematic, it's easy to see how it's a coiled-up two-wire transmission line. Other baluns, offering various impedance conversions, are also simply coiled-up transmission lines; usually two or three interconnected to provide the impedance conversion wanted. You could achieve the same impedance conversions with sections of open wire stretched out and interconnected. It would work exactly the same way, but take up a fair bit of space! So all you're doing when you add a balun to the end of a piece of coax (or at the "unbalanced" output of a rig) is you're isolating one end from the other by imposing a long section of transmission line between them. The simple fact is that, if it's long enough, the open wire transmission line itself will do the same thing *if* the antenna is balanced. If it's an off center fed doublet or other inherently unbalanced antenna, the feeder currents won't be balanced no matter what you do. That doesn't make the feeder inherently lossy. The worst is that the feeders will tend to radiate a bit, depending upon the degree of unbalance. The solution to unwanted RF on the outside of the rig is to stop the currents from flowing on the outside of the coax shield and the rig. Usually they get there by flowing out of the open end of the coax at the transition to the open wire line and around the edge right onto the outer surface. Sometimes a balun will provide enough isolation that the surface currents don't cause trouble, but sometimes not. Another way to reduce those currents is to put some ferrite beads over the coax. A number of companies sell ferrite beads for just that purpose. Some even provide a complete cable assembly with the beads installed. Those beads show a very high impedance to any RF currents on the outside of the shield, stopping or reducing them drastically. Your rig still is not "grounded" for RF, but you don't care. There's no RF to cause trouble on the rig anyway. Another approach many installations use is to have a long section of coax coiled up to act as an effective balun because the currents on the outside experience the coil as an inductor with reactance that stops them while the currents on the inside of the coax only "see" the transmission line and are unaffected by the fact it's wound up in a coil. (It's important the coil be solenoidal and single-layer so the input end is well isolated from the output end. A jumble of coax is not very effective). That's *not* a good idea for you because you're operating the coax at a high SWR, so you have significant losses for every foot of coax you have in the system. Keep the coax as short as possible! Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. 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In reply to this post by Solosko, Robert B (Bob)
Thanks for all of the very good information and suggestions. My
counterpoise had been several wires running together - I wasn't aware of the need to separate the ends. So, I removed the counterpoise that I had and made 3 new separate ones, 1/4 wave for 15, 17 & 20 meters, cut for the middle of the phone band on each. These are attached to the grounding screw on my KAT100 and run in 3 different directions... and guess what? The problem is still there. Measuring with my field strength meter, there appears to be no appreciable difference in the level of RF in the shack on these bands. On to the next things to try, which will have to wait until the weekend when I can hang out of my window during daylight. The next things I'll try are 1) attach the counterpoises directly to the coax ground on the balun, 2) replace the 9:1 voltage balun with a 4:1/1:1 current balun, 3) running more, and different lengths of wire from the KAT100 to the ground rod (although if the counterpoises have little affect, would this have any different affect?) 4) changing the length of ladder line to the balun and the length of coax from the balun to the KAT100 (I don't have a lot of room for flexibility here). I'll let you know the results. Thanks again for all of the information and suggestion. Bob W1SRB -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Solosko, Robert B (Bob) Sent: Monday, January 22, 2007 12:57 PM To: [hidden email] Subject: [Elecraft] Rf in the shack distorting audio Hello All, Several month ago, after I finished my KPA100, I found that when transmitting SSB on the higher bands (20, 17 & 15), the computer speakers across the room, when turned on, would screech - adjusting the speaker volume had no effect (but turning off the speakers quieted them). During a QSO a few weeks ago, it was commented that it sounded like I was getting RF into my audio. To make a short story long, I don't have a very good ground system, so there's a high level of RF in the shack - the shack is on the 2nd floor, about 18 ft above the ground rod. My primary antenna is a 100 ft multiband horizontal dipole feed with ladder line into a 9:1 balun, which is connected to my KAT100 via 6' of RG8. While the antenna works great on all bands (the KAT100 has no trouble tuning it), there's a fairly high SWR on the feedline on the higher bands. I have two different length wires connected the ground rod to the KAT100, and adding counterpoises for 20, 17 & 15 meters hasn't change the high level of RF in the shack on these bands. A week or two ago, I put up a second antenna, a vertical parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has very low SWR on these bands. When using this antenna, I have no problems with the computer speakers screeching, so there's apparently not much RF in the shack. This weekend, during the NA QSO party, when using the ladder line fed dipole on the higher bands, several times, I was told that my audio was distorted, and switching to the vertical coax fed dipole immediately cured the problem. So, the question is, what can be done to fix the distorted audio when there a high level of RF in the shack (besides getting a better ground system - I plan to put in one or two more ground rods, but I won't be able to do that until after the ground defrosts in the spring). The mic I'm using is a RadioShack Electret replacement element in an old mobile mic case - the case is plastic and not shielded, but the cable is shielded, and I have grounded the mike jack in my K2. All suggestions about how I can eliminate the distortion will be greatly welcomed, as well as suggestions about how I can reduce the high level of RF in the shack besides adding more ground rods. Thanks Bob W1SRB _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Bob,
The length of conductor from the rig chassis to the eventual ground rod, including the length of the rod to the physical dirt, all makes a resonant system. If such a "ground" lead is 1/4 wave or a substantial length at a given band, you will have a poor RF ground. As someone said, you need to find out if your antenna is causing the RF to appear in your shack. First is the antenna a dipole, and therefore balanced? Next, is the antenna remote from the shack, not just over the roof just over the shack? Are both legs of the dipole, if it is, equally spaced from nearby metal and conductors, including foliage, trees, buildings, etc.? What are you feeding the antenna with? Are you feeding with coax to a balanced antenna? These are all thought questions to get you thinking in terms of what is resonating to cause this RF to appear? How is it getting from the antenna, feeder, or rig to the undesired places? The fact that adding quarter wave elements did not change it, says the point at which you added quarter waves was not the point where the RF was strongest. Don't forget the effect of your AC wiring, it can function as an antenna if its legs make quarter wave resonant lengths on ham bands. Simplify your set up to just the rig, tuner and antenna, and work backwards to add in any computer, jumper cables, other cabling, like phone, or lighting, and see if there are complex paths the RF is taking. The ARRL publishes a book on tracking RFI problems and eliminating them. Make sure any grounding screws holding chassis boxes and cases onto the radio are really conductors by loosening them slightly, then retightening them, to break any buildup of oxides. Make sure you have proper connections of low impedance on the mike cable and its plug. Is the mike cable shielded? Sometimes there is a press to talk pair in a mike, and separately, the audio line shield and those should not be bonded together in some cases. Have you tried another mike and its cable? Well, that is a start at some diagnostics. GL and 73, Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
In reply to this post by Solosko, Robert B (Bob)
Hello All,
Several weeks ago, I posted the attached e-mail describing my problems with RF in the shack distorting the audio when transmitting. I received many responses with good suggestions about how the cure the problem -- thank you to all of you who responded, and especially thank you to Don, the "Friendly, Patient Radioman", with whom I subsequently had an e-mail dialog about the design of by balun and the materials used. The results: problem cured! The first thing I did was move the counterpoises from the ground on the KAT100 to the ground side of the coax where it connects to the balun. That had the most effect, significantly reducing the level of RF in the shack, as measured by my field strength meter, and mostly eliminated the RF getting into the computer speakers. The next thing was to use the 4:1 taps on my voltage balun instead of the 9:1 taps - that reduced the RF level a little more, at the expense of the KAT100 not being able to get down to a 1:1 SWR on 15m; the lowest SWR achieved was about 2:1 (I was using the 9:1 taps because the KAT100 could get down to essentially 1:1 on all bands). Next, AA1SB gave me a few toroid cores of unknown type that were just large enough to fit over a PN-259 connector- I slipped them over the coax where it connects to the balun. That made a slight difference in the RF level on 10m, but had no other affect on any other bands. The final step was to replace my 9:1/4:1 voltage balun, made using a T300A-1 core, with a 4:1/1:1 current balun made using a pair of FT-240-43 baluns. Don, W3FPR, had suggested that the FT material in a current balun would be much more effective at eliminating the RF problem. I finally got this current balun made and installed this weekend, and just as Don predicted, the RF in the shack is essentially completely eliminated. Also, the KAT100 now can achieve a 1:1 SWR on 15m. However, you don't get something for nothing - with this balun, I lost the upper 40 kHz of 160m... The KAT100 doesn't get the SWR down below 9:1 and just gives up. But, below that, there is about a 10kHz range over which the minimum SWR that the KAT100 can achieve goes from 1:1 to 9:1. This is not quite surprising since my antenna is a 100' shortened multi-band dipole which by design has a very narrow bandwidth on 160M. Furthermore, the inductance of the 4:1 current balun made with the FT material is about 50 times greater than the 9:1 voltage balun I made. On 160m the balun impedance was likely less that the impedance at the balun end or the ladder line (the rule of thumb is that the balun impedance should be at least 4 times the impedance at the balun input)... So, it's likely that the KAT100 was really tuning to the balun impedance and not the antenna impedance. However, with the new 4:1 current balun, the balun impedance shouldn't be much of a factor and the KAT100 is probably seeing more of the actual characteristics of the antenna... And, now that I think of it, all of the few QSOs that I've had on 160m have been below the upper 50kHz or so. So, thank you all again - I'm very satisfied with the results. Bob W1SRB -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Solosko, Robert B (Bob) Sent: Monday, January 22, 2007 12:57 PM To: [hidden email] Subject: [Elecraft] Rf in the shack distorting audio Hello All, Several month ago, after I finished my KPA100, I found that when transmitting SSB on the higher bands (20, 17 & 15), the computer speakers across the room, when turned on, would screech - adjusting the speaker volume had no effect (but turning off the speakers quieted them). During a QSO a few weeks ago, it was commented that it sounded like I was getting RF into my audio. To make a short story long, I don't have a very good ground system, so there's a high level of RF in the shack - the shack is on the 2nd floor, about 18 ft above the ground rod. My primary antenna is a 100 ft multiband horizontal dipole feed with ladder line into a 9:1 balun, which is connected to my KAT100 via 6' of RG8. While the antenna works great on all bands (the KAT100 has no trouble tuning it), there's a fairly high SWR on the feedline on the higher bands. I have two different length wires connected the ground rod to the KAT100, and adding counterpoises for 20, 17 & 15 meters hasn't change the high level of RF in the shack on these bands. A week or two ago, I put up a second antenna, a vertical parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has very low SWR on these bands. When using this antenna, I have no problems with the computer speakers screeching, so there's apparently not much RF in the shack. This weekend, during the NA QSO party, when using the ladder line fed dipole on the higher bands, several times, I was told that my audio was distorted, and switching to the vertical coax fed dipole immediately cured the problem. So, the question is, what can be done to fix the distorted audio when there a high level of RF in the shack (besides getting a better ground system - I plan to put in one or two more ground rods, but I won't be able to do that until after the ground defrosts in the spring). The mic I'm using is a RadioShack Electret replacement element in an old mobile mic case - the case is plastic and not shielded, but the cable is shielded, and I have grounded the mike jack in my K2. All suggestions about how I can eliminate the distortion will be greatly welcomed, as well as suggestions about how I can reduce the high level of RF in the shack besides adding more ground rods. Thanks Bob W1SRB _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
I found your solutions to curing RF in the shack very interesting. I have a
similiar problem to yours and would appreciate info on the 4:1/1:1 Current balun. Thanks Lowell, W5FH ----- Original Message ----- From: "Solosko, Robert B (Bob)" <[hidden email]> To: "Solosko, Robert B (Bob)" <[hidden email]>; <[hidden email]> Sent: Wednesday, February 21, 2007 11:57 AM Subject: RE: [Elecraft] Rf in the shack distorting audio - the results Hello All, Several weeks ago, I posted the attached e-mail describing my problems with RF in the shack distorting the audio when transmitting. I received many responses with good suggestions about how the cure the problem -- thank you to all of you who responded, and especially thank you to Don, the "Friendly, Patient Radioman", with whom I subsequently had an e-mail dialog about the design of by balun and the materials used. The results: problem cured! The first thing I did was move the counterpoises from the ground on the KAT100 to the ground side of the coax where it connects to the balun. That had the most effect, significantly reducing the level of RF in the shack, as measured by my field strength meter, and mostly eliminated the RF getting into the computer speakers. The next thing was to use the 4:1 taps on my voltage balun instead of the 9:1 taps - that reduced the RF level a little more, at the expense of the KAT100 not being able to get down to a 1:1 SWR on 15m; the lowest SWR achieved was about 2:1 (I was using the 9:1 taps because the KAT100 could get down to essentially 1:1 on all bands). Next, AA1SB gave me a few toroid cores of unknown type that were just large enough to fit over a PN-259 connector- I slipped them over the coax where it connects to the balun. That made a slight difference in the RF level on 10m, but had no other affect on any other bands. The final step was to replace my 9:1/4:1 voltage balun, made using a T300A-1 core, with a 4:1/1:1 current balun made using a pair of FT-240-43 baluns. Don, W3FPR, had suggested that the FT material in a current balun would be much more effective at eliminating the RF problem. I finally got this current balun made and installed this weekend, and just as Don predicted, the RF in the shack is essentially completely eliminated. Also, the KAT100 now can achieve a 1:1 SWR on 15m. However, you don't get something for nothing - with this balun, I lost the upper 40 kHz of 160m... The KAT100 doesn't get the SWR down below 9:1 and just gives up. But, below that, there is about a 10kHz range over which the minimum SWR that the KAT100 can achieve goes from 1:1 to 9:1. This is not quite surprising since my antenna is a 100' shortened multi-band dipole which by design has a very narrow bandwidth on 160M. Furthermore, the inductance of the 4:1 current balun made with the FT material is about 50 times greater than the 9:1 voltage balun I made. On 160m the balun impedance was likely less that the impedance at the balun end or the ladder line (the rule of thumb is that the balun impedance should be at least 4 times the impedance at the balun input)... So, it's likely that the KAT100 was really tuning to the balun impedance and not the antenna impedance. However, with the new 4:1 current balun, the balun impedance shouldn't be much of a factor and the KAT100 is probably seeing more of the actual characteristics of the antenna... And, now that I think of it, all of the few QSOs that I've had on 160m have been below the upper 50kHz or so. So, thank you all again - I'm very satisfied with the results. Bob W1SRB -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Solosko, Robert B (Bob) Sent: Monday, January 22, 2007 12:57 PM To: [hidden email] Subject: [Elecraft] Rf in the shack distorting audio Hello All, Several month ago, after I finished my KPA100, I found that when transmitting SSB on the higher bands (20, 17 & 15), the computer speakers across the room, when turned on, would screech - adjusting the speaker volume had no effect (but turning off the speakers quieted them). During a QSO a few weeks ago, it was commented that it sounded like I was getting RF into my audio. To make a short story long, I don't have a very good ground system, so there's a high level of RF in the shack - the shack is on the 2nd floor, about 18 ft above the ground rod. My primary antenna is a 100 ft multiband horizontal dipole feed with ladder line into a 9:1 balun, which is connected to my KAT100 via 6' of RG8. While the antenna works great on all bands (the KAT100 has no trouble tuning it), there's a fairly high SWR on the feedline on the higher bands. I have two different length wires connected the ground rod to the KAT100, and adding counterpoises for 20, 17 & 15 meters hasn't change the high level of RF in the shack on these bands. A week or two ago, I put up a second antenna, a vertical parallel dipole for 20, 17 & 15 meters, fed with RG8 - this antenna has very low SWR on these bands. When using this antenna, I have no problems with the computer speakers screeching, so there's apparently not much RF in the shack. This weekend, during the NA QSO party, when using the ladder line fed dipole on the higher bands, several times, I was told that my audio was distorted, and switching to the vertical coax fed dipole immediately cured the problem. So, the question is, what can be done to fix the distorted audio when there a high level of RF in the shack (besides getting a better ground system - I plan to put in one or two more ground rods, but I won't be able to do that until after the ground defrosts in the spring). The mic I'm using is a RadioShack Electret replacement element in an old mobile mic case - the case is plastic and not shielded, but the cable is shielded, and I have grounded the mike jack in my K2. All suggestions about how I can eliminate the distortion will be greatly welcomed, as well as suggestions about how I can reduce the high level of RF in the shack besides adding more ground rods. Thanks Bob W1SRB _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.441 / Virus Database: 268.18.3/694 - Release Date: 2/20/2007 1:44 PM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Lowell,
Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will handle up to 250 watts. If you do not need the switchable arrangement, the BL1 can be constructed for either a 1:1 or a 4:1 configuration and its power rating is 150 watts. A convenient ground lug is located on the balun output side. Look on the Elecraft website - click Our Products, and from there click on Mini-module kits. 73, Don W3FPR > -----Original Message----- > > I found your solutions to curing RF in the shack very > interesting. I have a > similiar problem to yours and would appreciate info on the > 4:1/1:1 Current > balun. Thanks > Lowell, W5FH > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.441 / Virus Database: 268.18.3/697 - Release Date: 2/22/2007 11:55 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Lowell,
Don is giving some good advice here, as usual. The circuit of balun that I built is essentially identical to the BL2. I made mine using two FT-240-43 toroid cores - I needed a balun in a watertight box since it located outside in the rain and snow. I also wanted a balun that can handle more power than the BL2, since I aspire to higher power when I grow up. The one I made uses 12 bifilar turns of #12 wire, and should easily handle a kW. A diagram of this two core balun is found on page 26-24 of the ARRL antenna book (the same diagram is also in the transmission line section of my 1999 edition of the ARRL handbook). I mounted the two toroids in a plastic box from Radio Shack, with a coax connector on one side and screw terminals for the ladder line on the another side, plus a screw terminal for the ground connection for the counterpoises. If you look at the schematic on the BL2, several of the toroid leads go the switch. In place of the switch, I brought those leads out to screw terminals and use one external jumper between screw terminal for the 4:1 configuration, and two external jumpers between from the other screw terminals for the 1:1 configuration. With wing nuts on these jumper screw terminals, I can quickly switch between the 1:1 and 4:1 configurations (for my home setup, I just keep the balun in the 4:1 configuration - the quick change ability I use when I take the K2 on the road with antennas that the characteristics will change depending on the trees they're attached to) - of course, you can put the BL2 in a watertight box, but then you don't have easy access to the 1:1/4:1 switch, which in a fix setup you probable don't need to change often anyway. 73 Bob W1SRB -----Original Message----- From: Don Wilhelm [mailto:[hidden email]] Sent: Thursday, February 22, 2007 12:44 PM To: Lowell; Solosko, Robert B (Bob); [hidden email] Subject: RE: [Elecraft] Rf in the shack distorting audio - the results Lowell, Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will handle up to 250 watts. If you do not need the switchable arrangement, the BL1 can be constructed for either a 1:1 or a 4:1 configuration and its power rating is 150 watts. A convenient ground lug is located on the balun output side. Look on the Elecraft website - click Our Products, and from there click on Mini-module kits. 73, Don W3FPR > -----Original Message----- > > I found your solutions to curing RF in the shack very interesting. I > have a similiar problem to yours and would appreciate info on the > 4:1/1:1 Current > balun. Thanks > Lowell, W5FH > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.441 / Virus Database: 268.18.3/697 - Release Date: 2/22/2007 11:55 AM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
In reply to this post by Don Wilhelm-3
On February 22, 2007 09:44 am, Don Wilhelm wrote:
> Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will handle up > to 250 watts. If you do not need the switchable arrangement, the BL1 can > be constructed for either a 1:1 or a 4:1 configuration and its power rating > is 150 watts. A convenient ground lug is located on the balun output side. How can a balun be switchable from 1:1 or 4:1? Surely the characteristic impedance of the windings will be missmatched at one of the settings. -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
On Feb 23, 2007, at 9:29 AM, Darrell Bellerive wrote: > On February 22, 2007 09:44 am, Don Wilhelm wrote: >> Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will >> handle up >> to 250 watts. If you do not need the switchable arrangement, the >> BL1 can >> be constructed for either a 1:1 or a 4:1 configuration and its >> power rating >> is 150 watts. A convenient ground lug is located on the balun >> output side. > > How can a balun be switchable from 1:1 or 4:1? Surely the > characteristic > impedance of the windings will be missmatched at one of the settings. Actually the characteristic impedance of the windings will ideally be 2*Z0. For a 1:1 balun they will appear in parallel, while for 4:1 they will appear to be in parallel at one port and in series at the other. Bob, N7XY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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