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Tom W8JI wrote:
> The only time moving the balun helps is if the network is a balanced > network. Even your example shows with the 4:1 balun you still had to use Agreed. I had overlooked feed point tuner needs to balanced in that case. > a balanced tuner. With an unbalanced tuner the feedline could have > serious radiation problems (depending on feeder length). -- David Woolley "The Elecraft list is a forum for the discussion of topics related to Elecraft products and more general topics related ham radio" List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm> _______________________________________________ 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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In reply to this post by W8JI
The question is, what is good enough? To minimize radiation from an open wire tuned feeder requires, I believe, that the currents in the two wires to be equal in magnitude and have a phase difference of 180 degrees at the feedpoint of the feedline. Feeding a slanted dipole, which is certainly an unbalanced antenna, is it practical to build a 1:1 balun on a ferrite core (core type choice?) that, when placed on the output of an unbalanced tuner, is good enough to force the desired currents from 40m thru 10m without excesive losses? Using an LC inductively coupled balanced tuner on such an unbalanced antenna will not produce the desired results--deliberately unbalancing the LC tuner by offsetting the taps on the coil will sometimes get close for me.
73 Paul W5DM
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A very interesting read, I have a couple of questions about practical
considerations. The number one rule I look at all antennas with, is that all antennas are a compromise. Let me know if I am getting off on the wrong foot here. I like ladder line fed to various antennas (Horiz. Loops, Vert. Loops, Doublets and such) but if I have more than one antenna, then I have multiple sets of 450 ohm twin lead coming to the house. As I understand things, I need to keep the ladder line away from metal as much as I can. I have not found a way to safety ground ladder line and run it into the house. After taking a lightning strike last year, I have no wish to have ladder line and / or balun's inside the house. *Is there a way to properly ground that ladder line, and then run it into the house? *If there is a practical way, I assume one uses a plastic box or no box at all? Based on all of these practical considerations, I am left with the following current configuration. K3/KAT3 -> Balun (4:1) === Ladder Line === Doublet (In this case a http://www.k1jek.com/ 200' antenna) The coax is about 50' long (to get to the shack in the house, I would love to get this shorter, working on that) and the 450 ohm ladder line is about 50' long. Configuration I am working towards; K3/KAT3 -> RF Switch -> Coax (trying to get this down to about 10') to box mounted on side of house (metal) -> Lightning arrestors tied to good ground rods -> short coax to balun mounted beside house -> 450 ohm ladder line to antenna. Would like to have a vertical loop and dipole or horizontal loop, fed with ladder line. The antenna I have now, gets out very well, and tunes pretty well from 160m -> 6m. Some bands like 40m, it does not tune as well, but has performed well. I have heard very little on 6m, but did work Portugal. The 40m issue is supposed to be helped by reducing the length of coax, and lengthening the ladder line. That makes sense, to reduce the resistive losses in the coax. Understanding that this is a low dipole (about 40 - 50 feet) I'm wondering if changes to the configuration would help the antenna's ability to hear. I'm not sure it hears as well as it could. Options to improve antenna, and possibly receive ================================================ *Get current antenna higher. With the trees that I have to use, this could only be about 10'. *Drop ends of antenna to 10', and raise center higher using a different tree. This has possibilities of getting the center higher than 60'. I am not sure this would help receive, but it is an option. *Go to a different balun setup 1:1 versus 4:1. *Not sure of a practical way to get multiple ladder lines safety grounded and into the house. So I do not know how to get away from having a balun. Are there other practical options I am missing here? Yes, I would like to have a short tower and a multi-band cubical quad. Maybe at some point in the future, but not anytime soon. David Wilburn K4DGW Ron D'Eau Claire wrote: > Also, the load has a huge effect on balance. Few wire antennas for HF offer > decently balanced loads. Unless the wires are literally wavelengths (usually > hundreds of feet) from the earth and other objects, those objects will have > a strong effect on the currents on each side of the antenna. The effect is > greatest near the ends of the wires, where they typically come close to > supports, trees, houses, etc. Unless both ends have identical surroundings, > the antenna, and so the currents in the feedline, are unbalanced. > > Ron AC7AC > > > -----Original Message----- > The question is, what is good enough? To minimize radiation from an open > wire tuned feeder requires, I believe, that the currents in the two wires to > be equal in magnitude and have a phase difference of 180 degrees at the > feedpoint of the feedline. Feeding a slanted dipole, which is certainly an > unbalanced antenna, is it practical to build a 1:1 balun on a ferrite core > (core type choice?) that, when placed on the output of an unbalanced tuner, > is good enough to force the desired currents from 40m thru 10m without > excesive losses? Using an LC inductively coupled balanced tuner on such an > unbalanced antenna will not produce the desired results--deliberately > unbalancing the LC tuner by offsetting the taps on the coil will sometimes > get close for me. > > 73 Paul W5DM > > > _______________________________________________ > 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 |
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David,
The Wireman has a lightning arrestor for use with ladder line - it looks very much like a pair of spark plugs mounted on a piece of copper. It does not ground the ladder line, but it does provide suppression for lightning surge voltages. You may have better luck with a 1:1 balun rather than the 4:1 - it all depends on the electrical length of your ladder line and the antenna. To check that, measure the input impedance of the antenna and feedline with an antenna analyzer at the point where you are placing the balun. If you read a relatively low impedance with the 4:1 balun, change it to a 1:1. The L network tuners have more trouble matching a low impedance load than a higher impedance, so if you can get the impedance in the 40 to 150 ohm range at the point where the coax connects to the balun, you will have succeeded. A 3:1 SWR will not add a whole lot of extra loss up through 30 MHz. I assume you are using a low loss coax for that 50 ft run - if not, you should be. RG213 as a minimum, but LMR400 would be better. If you can find a length of the 1/2 inch data type (75 ohm) that the cable folks use, that is a good low loss cable too. There was an article in QST a month or two ago about using RG6 for transmitting, I was particularly interested in the fact that the RG6 loss is about the same as that of RG213 - the 75 ohm 1/2 inch data cable should be much lower loss than RG6. 73, Don W3FPR David Wilburn wrote: > A very interesting read, I have a couple of questions about practical > considerations. > > The number one rule I look at all antennas with, is that all antennas > are a compromise. Let me know if I am getting off on the wrong foot here. > > I like ladder line fed to various antennas (Horiz. Loops, Vert. Loops, > Doublets and such) but if I have more than one antenna, then I have > multiple sets of 450 ohm twin lead coming to the house. As I understand > things, I need to keep the ladder line away from metal as much as I can. > > I have not found a way to safety ground ladder line and run it into the > house. After taking a lightning strike last year, I have no wish to > have ladder line and / or balun's inside the house. > > *Is there a way to properly ground that ladder line, and then run it > into the house? > *If there is a practical way, I assume one uses a plastic box or no box > at all? > > Based on all of these practical considerations, I am left with the > following current configuration. > > K3/KAT3 -> Balun (4:1) === Ladder Line === Doublet > (In this case a http://www.k1jek.com/ 200' antenna) > > The coax is about 50' long (to get to the shack in the house, I would > love to get this shorter, working on that) and the 450 ohm ladder line > is about 50' long. > > Configuration I am working towards; > K3/KAT3 -> RF Switch -> Coax (trying to get this down to about 10') to > box mounted on side of house (metal) -> Lightning arrestors tied to good > ground rods -> short coax to balun mounted beside house -> 450 ohm > ladder line to antenna. > > Would like to have a vertical loop and dipole or horizontal loop, fed > with ladder line. > > The antenna I have now, gets out very well, and tunes pretty well from > 160m -> 6m. Some bands like 40m, it does not tune as well, but has > performed well. I have heard very little on 6m, but did work Portugal. > The 40m issue is supposed to be helped by reducing the length of coax, > and lengthening the ladder line. That makes sense, to reduce the > resistive losses in the coax. Understanding that this is a low dipole > (about 40 - 50 feet) I'm wondering if changes to the configuration would > help the antenna's ability to hear. I'm not sure it hears as well as it > could. > > Options to improve antenna, and possibly receive > ================================================ > *Get current antenna higher. With the trees that I have to use, this > could only be about 10'. > > *Drop ends of antenna to 10', and raise center higher using a different > tree. This has possibilities of getting the center higher than 60'. I > am not sure this would help receive, but it is an option. > > *Go to a different balun setup 1:1 versus 4:1. > > *Not sure of a practical way to get multiple ladder lines safety > grounded and into the house. So I do not know how to get away from > having a balun. > > Are there other practical options I am missing here? Yes, I would like > to have a short tower and a multi-band cubical quad. Maybe at some > point in the future, but not anytime soon. > > David Wilburn > K4DGW > > > > Ron D'Eau Claire wrote: >> Also, the load has a huge effect on balance. Few wire antennas for HF >> offer >> decently balanced loads. Unless the wires are literally wavelengths >> (usually >> hundreds of feet) from the earth and other objects, those objects will >> have >> a strong effect on the currents on each side of the antenna. The >> effect is >> greatest near the ends of the wires, where they typically come close to >> supports, trees, houses, etc. Unless both ends have identical >> surroundings, >> the antenna, and so the currents in the feedline, are unbalanced. >> Ron AC7AC >> >> >> -----Original Message----- >> The question is, what is good enough? To minimize radiation from an open >> wire tuned feeder requires, I believe, that the currents in the two >> wires to >> be equal in magnitude and have a phase difference of 180 degrees at the >> feedpoint of the feedline. Feeding a slanted dipole, which is >> certainly an >> unbalanced antenna, is it practical to build a 1:1 balun on a ferrite >> core >> (core type choice?) that, when placed on the output of an unbalanced >> tuner, >> is good enough to force the desired currents from 40m thru 10m without >> excesive losses? Using an LC inductively coupled balanced tuner on >> such an >> unbalanced antenna will not produce the desired results--deliberately >> unbalancing the LC tuner by offsetting the taps on the coil will >> sometimes >> get close for me. >> >> 73 Paul W5DM >> >> >> _______________________________________________ >> 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 - http://www.avg.com Version: 8.0.138 / Virus Database: > 270.6.5/1618 - Release Date: 8/18/2008 6:51 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 |
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In reply to this post by dave.wilburn
Hi David and all,
I have done a lot of EZNEC dipole simulations and have come to the conclusion that the loss in 100 feet of coax off of resonance is about 12 dB per 100'. Whether you use RG-8x or LMR400 doesn't make too much dfference concerning losses off of resonance where your SWR with 50 ohm transmission line can be greater than 200:1. <http://www.pituch.net/Steve%27s%20Page/Radio/Antenna4/Antenna4.htm> Because of this if I use 450 Ohm ladder line to a 1:1 baun, I try to keep the length of coax going into the house less than 15 feet. For your 50 feet of coax run you should never have a loss greater than about 1 S unit (6 dB). When I went to 100 percent ladder line including inside the residence, when I built my balanced tuner, I used two 1/4-20 stainless steel bolts to feed the signal through the exterior wood wall. I have "U" solder lugs on the two wires at the end of the 450 Ohm line, and I use two wing nuts to connect the ladder line to the house connection. When I am finished operating I go outside at spend 5 seconds loosening the wing nuts and the ladder line is no longer connected to the residence. If I wanted further protction, I guess I could drive a ground rod 15 feet away from the residence and wing nut the end of the ladder line to it when I am not operating. I don't believe you can keep your antenna connected to your equipment and ever be completely protected from lightning strikes (and that includes coax). The air gaps don't work. For coax the gas surge traps may work to a degree, but I would much rather disconnect the transmission line than depend on one of these devices. If you want so-called protection for 450 Ohm line why not use 2 Alpha Delta coax surge traps - one for each wire of the 450 Ohm line? The thing about keeping the 450 Ohm line away from metal is overdone a bit. I find keeping it away from metal about 2 or 3 inches is fine. Regards, Steve, W2MY _______________________________________________ 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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Steve,
With all due respect, the problem isn't with the coax, it is with the antenna which is designed poorly for the frequencies of operation. Even traps in a decent multiband antenna design, fed with coax, wouldn't have a 6db loss of the ladder line you're claiming is OK.. 73 de Brian/K3KO list1 wrote: >Hi David and all, > >I have done a lot of EZNEC dipole simulations and have come to the >conclusion that the loss in 100 feet of coax off of resonance is about 12 dB >per 100'. Whether you use RG-8x or LMR400 doesn't make too much dfference >concerning losses off of resonance where your SWR with 50 ohm transmission >line can be greater than 200:1. ><http://www.pituch.net/Steve%27s%20Page/Radio/Antenna4/Antenna4.htm> >Because of this if I use 450 Ohm ladder line to a 1:1 baun, I try to keep >the length of coax going into the house less than 15 feet. For your 50 feet >of coax run you should never have a loss greater than about 1 S unit (6 dB). > >When I went to 100 percent ladder line including inside the residence, when >I built my balanced tuner, I used two 1/4-20 stainless steel bolts to feed >the signal through the exterior wood wall. I have "U" solder lugs on the two >wires at the end of the 450 Ohm line, and I use two wing nuts to connect the >ladder line to the house connection. When I am finished operating I go >outside at spend 5 seconds loosening the wing nuts and the ladder line is no >longer connected to the residence. If I wanted further protction, I guess I >could drive a ground rod 15 feet away from the residence and wing nut the >end of the ladder line to it when I am not operating. > >I don't believe you can keep your antenna connected to your equipment and >ever be completely protected from lightning strikes (and that includes >coax). The air gaps don't work. For coax the gas surge traps may work to a >degree, but I would much rather disconnect the transmission line than depend >on one of these devices. > >If you want so-called protection for 450 Ohm line why not use 2 Alpha Delta >coax surge traps - one for each wire of the 450 Ohm line? > >The thing about keeping the 450 Ohm line away from metal is overdone a bit. >I find keeping it away from metal about 2 or 3 inches is fine. > >Regards, >Steve, W2MY > >_______________________________________________ >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 |
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In reply to this post by dave.wilburn
David, Industrial Communications Engineers (I.C.E.) makes a couple of open wire arrestors that I think are well designed. On both legs of the open wire they feature a DC short to ground (inductor) on the antenna side that helps drain static ( and resulting noise) from the antenna, a gas tube to ground for fast rise-time impulses, a high-voltage capacitor in series between antenna and Xceiver, and a high resistance to ground on the input. In my opinion this is about as good as you can get short of disconnecting and grounding the antenna well away from the shack.
http://www.iceradioproducts.com/impulse1.html#2 Chuck, AE4CW quote author="David Wilburn" A very interesting read, I have a couple of questions about practical considerations. I have not found a way to safety ground ladder line and run it into the house. After taking a lightning strike last year, I have no wish to have ladder line and / or balun's inside the house. *Is there a way to properly ground that ladder line, and then run it into the house? *If there is a practical way, I assume one uses a plastic box or no box at all?
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Chuck, AE4CW |
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In reply to this post by list1
For long horizontal lines near to the ground (<3ft, 1m, say) I've read that
some folks rotate the line between supports, supposedly to maintain balance; what do you think about that? David G3UNA ----- Original Message ----- From: "list1" <[hidden email]> To: "Elecraft Discussion List" <[hidden email]> Sent: Monday, August 18, 2008 4:29 PM Subject: [Elecraft] RE:balanced tuner > Hi David and all, > > I have done a lot of EZNEC dipole simulations and have come to the > conclusion that the loss in 100 feet of coax off of resonance is about 12 > dB > per 100'. Whether you use RG-8x or LMR400 doesn't make too much dfference > concerning losses off of resonance where your SWR with 50 ohm transmission > line can be greater than 200:1. > <http://www.pituch.net/Steve%27s%20Page/Radio/Antenna4/Antenna4.htm> > Because of this if I use 450 Ohm ladder line to a 1:1 baun, I try to keep > the length of coax going into the house less than 15 feet. For your 50 > feet > of coax run you should never have a loss greater than about 1 S unit (6 > dB). > > When I went to 100 percent ladder line including inside the residence, > when > I built my balanced tuner, I used two 1/4-20 stainless steel bolts to feed > the signal through the exterior wood wall. I have "U" solder lugs on the > two > wires at the end of the 450 Ohm line, and I use two wing nuts to connect > the > ladder line to the house connection. When I am finished operating I go > outside at spend 5 seconds loosening the wing nuts and the ladder line is > no > longer connected to the residence. If I wanted further protction, I guess > I > could drive a ground rod 15 feet away from the residence and wing nut the > end of the ladder line to it when I am not operating. > > I don't believe you can keep your antenna connected to your equipment and > ever be completely protected from lightning strikes (and that includes > coax). The air gaps don't work. For coax the gas surge traps may work to > a > degree, but I would much rather disconnect the transmission line than > depend > on one of these devices. > > If you want so-called protection for 450 Ohm line why not use 2 Alpha > Delta > coax surge traps - one for each wire of the 450 Ohm line? > > The thing about keeping the 450 Ohm line away from metal is overdone a > bit. > I find keeping it away from metal about 2 or 3 inches is fine. > > Regards, > Steve, W2MY > > _______________________________________________ > 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 |
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In reply to this post by alsopb
Hello Brian, I meant to write that 50 feet of coax would have _NO_ more than 6 db of loss with a dipole off of resonance. A multiband (ie. trapped) antenna design will work fine (with coax) if designed and built properly. But a dipole with ladderline is a lot simpler and matched and mismatched loss totals about .6 dB on any band (for 100 feet of ladder line), which is a lot simpler. I do not consider a non-resonant wire dipole poorly designed (or a loop like Dave has also suggested). There is very little loss with it. The antenna portion works very well. Its the feedline (transmission line) that can be the problem and usually causes almost all the loss. Conversely I have had my share of problems with the adjustment of expensive commercial "multi-band" antennas designed for 50 Ohm coax. Steve, W2MY ------------------------------------------------------- Steve, With all due respect, the problem isn't with the coax, it is with the antenna which is designed poorly for the frequencies of operation. Even traps in a decent multiband antenna design, fed with coax, wouldn't have a 6db loss of the ladder line you're claiming is OK.. 73 de Brian/K3KO _______________________________________________ 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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In reply to this post by list1
On Mon, 18 Aug 2008 10:29:21 -0500, list1 wrote:
>I have done a lot of EZNEC dipole simulations and have come to the >conclusion that the loss in 100 feet of coax off of resonance is about >12 dB per 100'. "Off resonance" is a very broad description. Loss in coax only begins to increase drastically when the SWR is VERY high. There are equations (and graphs of those equations) in both the ARRL Handbook and the ARRL Antenna Book showing that for MODERATE mismatches, the additional loss due to mismatch is rather small. There is also a computer program that comes with the Antenna Book that allows you to compute that loss for most common coaxial lines and any termination impedances. I have done that, and plotted the results. Your statement is true only if you're trying to use a single antenna to cover all frequencies. It is NOT true if you are using an antenna that is close to resonance on the bands you want to cover. I have two 80/40 FAN dipoles at right angles to each other, fed with about 120 ft of RG11. The loss in that line is less than 1.5 dB over all of 80 and 40M. By some form of luck, both of these antennas also come close enough to 75 ohms on 30M, 17M, 15M, 12M, and 6M that the SWR at the transmitter end is less than 3:1. Now, the loss in any line reduces the SWR over its length, so a measured 3:1 may be more like 5:1 at the antenna. But that still doesn't translate into anything like 12dB of loss! While I have half-wave dipoles for 30M and 6M, the 80/40 dipoles are my only antennas for 17M and 12M, and work well on all of those bands, and much better than the resonant dipoles for 30M and 6M. What do I mean be "work well?" If there's a DXpedition and I pileup, I can work them, often on the first call. My primary objection to balanced line is that it cannot be choked to kill receive noise coupled to the antenna by common mode current. This current is caused by imbalance in the ANTENNA, which in turn is caused by coupling to objects NEAR the antenna (trees, towers, buildings, the earth). The world's best balanced tuner and the world's best balanced line will not make a dent in this common mode current! It must be killed by a choke, you need choking Z on the order of 5K ohms, and it must be at the feedpoint (that is, up in the air). To do that and handle serious power, it's EASY with coax. It's hard any other way. 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 |
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In reply to this post by David Cutter
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In reply to this post by Chuck - AE4CW
Chuck - AE4CW wrote:
> David, Industrial Communications Engineers (I.C.E.) makes a couple of open > wire arrestors that I think are well designed. On both legs of the open > wire they feature a DC short to ground (inductor) on the antenna side that > helps drain static ( and resulting noise) from the antenna, a gas tube to > ground for fast rise-time impulses, a high-voltage capacitor in series > between antenna and Xceiver, and a high resistance to ground on the input. > In my opinion this is about as good as you can get short of disconnecting > and grounding the antenna well away from the shack. > http://www.iceradioproducts.com/impulse1.html#2 > http://www.iceradioproducts.com/impulse1.html#2 I've thought about these. One problem is that open-wire lines are often operated at very high SWRs, so the voltage can be enormous if you pick the wrong place along the line to install it. Open lines are often used for multiband antennas, and so the 'right' (low impedance) spot to pick will vary from band to band! ICE says that they will work with impedances of 300-600 ohms. Although the characteristic impedance of a line may be within this range, the impedance *seen* at a particular point could be very high or low. Before installing a device like this I would query the manufacturer, explaining (if this is the case) that you are planning to operate the line at 10:1 (or whatever) SWR and verifying that it will work properly in this case. You might need the high-power version for 100 watts. The other thing to keep in mind is that the effectiveness of any lightning arrestor depends on the quality of the ground system and the layout -- that is, you need a single entry point for all antennas, power lines, phone lines, etc., everything has to be bonded together, etc. There's a lot to keep in mind and it all needs to be done correctly. This is why a lot of guys choose to disconnect everything. Vic _______________________________________________ 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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In reply to this post by AC7AC
Another reason to twist flat "TV twinlead" and the currently popular
window "ladder line" is to prevent "flapping' in the wind. This it the same reason flatbed truckers twist their hold-down straps. 73! Ken Kopp - K0PP [hidden email] _______________________________________________ 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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In reply to this post by Vic K2VCO
That's important!
> ICE says that they will work with impedances of 300-600 > ohms. Although the characteristic impedance of a line may > be within this range, the impedance *seen* at a particular > point could be very high or low. Multiply line SWR by line impedance. Most ladder line is around 400 ohms, so with a 20:1 SWR you could have 8000 ohms down to 20 ohms on the line depending in where you are at along the line and what the antenna impedance is. sqrt of (8000*100) = 894 volts RMS or 1265 V peak. on the other hand 1500 watts with a 600 ohm impedance is sqrt of (600*1500) = 949 v RMS or 1341v peak. So you can easily have higher peak voltage with 100W into a high SWR (20:1) than you can with 1500W into a low SWR. This is why lightning gaps or lightning arrestors on open wire line systems are a waste of time unless SWR is low. > The other thing to keep in mind is that the effectiveness > of any lightning arrestor depends on the quality of the > ground system and the layout -- that is, you need a single > entry point for all antennas, power lines, phone lines, > etc., everything has to be bonded together, etc. There's a > lot to keep in mind and it all needs to be done correctly. 99% of it is in the bonding of entrance cables. Despite dozens of direct hits a year I get away without any lightning suppression in my system and I always keep things connected. As a matter of fact WW4LL operated right through a lighting storm this weekend in the NAQP contest. He never even knew it was storming except for the QRN. But the common points are all good and everything enters through a single entrance common ground point. **I'm not trying to encourage others to not use lightning suppression devices, I'm just pointing out I don't have problems without them.** I would never bring ladder line inside that way, however. My ladder line tuners are all outside! If I had to bring ladder line inside, I would disconnect it outside when not in use. My barn entrance is at: http://www.w8ji.com/contest_station_w8ji.htm My workshop and house entrances at: http://www.w8ji.com/station_ground.htm 73, Tom _______________________________________________ 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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In reply to this post by AC7AC
Ron,
Very pretty job! Do you recall the (approx) capacitance range of the split-stator and link capacitors? Also, your pdf file says 3" acrylic tubing for main coil. Is it 3" or 2" ? How many turns on your 10 meter and 160 meter coil and link? (I assume the pictures show the 80-10 version.) I'm becoming more and more convinced that a current balun either at input or output of even a true BALANCED-L tuner will NOT insure a balanced system, even if the ladder line and antenna are balanced (which they seldom are). The brute fact is that, with or without a balun, you're connecting one side of the line to ground at the rig, making it unbalanced by construction. Current baluns will impede common-mode current, true. That will keep RF off of the rig. But they will not give the other benefit of a balanced system, that the ladder line to the antenna won't radiate, or pick up noise on receive. So your kind of tuner is very appealing. Old ideas sometimes work. Now all you need is an electrostatic shield between the link and the main windings, hi hi. 73, Oliver W6ODJ On 16 Aug 2008, at 8:21 PM, Ron D'Eau Claire wrote: > Very nice, Steve! > > You can see my homebrew balanced tuner in the picture with my > listing on > www.QRZ.com/ac7ac. > > The alligator clips attached to the wires above the coil are for the > antenna > feeder connections. There are two alligator clips nearer the bottom > that > short out turns as needed. The knob on the end operates a split stator > capacitor directly under the coil. The knob on the front operates the > variable in series with the link to control the coupling. That coil > actually > plugs in. It works FB from 80 through 10. I have a larger coil for 160 > meters. The coil form is a 2" acrylic tube with four 1/4" tubes > glued to it > to space the turns away for easy tapping with the alligator clips. > > The "case" is 1/8" hardened masonite (a pressed wood product) with a > 1/2" > wood base and uses aluminum angle for the corner fittings. The top is > acrylic sheet to handle whatever RF voltages might appear between the > fittings. The variable has 1/4" plate spacing for high voltages. It > works > very well. > > A PDF file with close-up photos and more details is available at > www.cobi.biz/ac7ac.pdf > > Ron AC7AC > > -----Original Message----- > From: [hidden email] > [mailto:[hidden email]] On Behalf Of list1 > Sent: Saturday, August 16, 2008 3:43 PM > To: [hidden email] > Subject: [Elecraft] RE: balanced tuner > > > Hi All, > Just finished mine. > Works Well so far. > I have some pictures here: > http://www.pituch.net/Steve%27s%20Page/Radio/Link%20Coupled%20Tuner/tuner1.h > tml > or just drill down from: > http://www.pituch.net/ > No documentation yet......later. > > Elecraft should make it a kit... hi hi. > > Steve, W2MY > > _______________________________________________ > 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 > _______________________________________________ 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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In reply to this post by David Cutter
Hi David
I use the window line on a number of my antennas. I twist the lines as a matter of course, the idea being to somewhat equalize any unbalancing effects of things in the nearby fields as the line passes by. No scientific evidence that this is of real benefit, but it makes me feel that I have at least tried to maintain what balance there may be in the total antenna system. 73, Bob N6WG ----- Original Message ----- From: "David Cutter" <[hidden email]> To: "Elecraft Discussion List" <[hidden email]> Sent: Monday, August 18, 2008 10:08 AM Subject: Re: [Elecraft] RE:balanced tuner > For long horizontal lines near to the ground (<3ft, 1m, say) I've read that > some folks rotate the line between supports, supposedly to maintain balance; > what do you think about that? > > David > G3UNA > > > ----- Original Message ----- > From: "list1" <[hidden email]> > To: "Elecraft Discussion List" <[hidden email]> > Sent: Monday, August 18, 2008 4:29 PM > Subject: [Elecraft] RE:balanced tuner > > > > Hi David and all, > > > > I have done a lot of EZNEC dipole simulations and have come to the > > conclusion that the loss in 100 feet of coax off of resonance is > > dB > > per 100'. Whether you use RG-8x or LMR400 doesn't make too much dfference > > concerning losses off of resonance where your SWR with 50 ohm transmission > > line can be greater than 200:1. > > <http://www.pituch.net/Steve%27s%20Page/Radio/Antenna4/Antenna4.htm> > > Because of this if I use 450 Ohm ladder line to a 1:1 baun, I try to keep > > the length of coax going into the house less than 15 feet. For your 50 > > feet > > of coax run you should never have a loss greater than about 1 S unit (6 > > dB). > > > > When I went to 100 percent ladder line including inside the residence, > > when > > I built my balanced tuner, I used two 1/4-20 stainless steel bolts to feed > > the signal through the exterior wood wall. I have "U" solder lugs on the > > two > > wires at the end of the 450 Ohm line, and I use two wing nuts to connect > > the > > ladder line to the house connection. When I am finished operating I go > > outside at spend 5 seconds loosening the wing nuts and the ladder line is > > no > > longer connected to the residence. If I wanted further protction, I guess > > I > > could drive a ground rod 15 feet away from the residence and wing nut the > > end of the ladder line to it when I am not operating. > > > > I don't believe you can keep your antenna connected to your equipment and > > ever be completely protected from lightning strikes (and that includes > > coax). The air gaps don't work. For coax the gas surge traps may work to > > a > > degree, but I would much rather disconnect the transmission line than > > depend > > on one of these devices. > > > > If you want so-called protection for 450 Ohm line why not use 2 Alpha > > Delta > > coax surge traps - one for each wire of the 450 Ohm line? > > > > The thing about keeping the 450 Ohm line away from metal is overdone a > > bit. > > I find keeping it away from metal about 2 or 3 inches is fine. > > > > Regards, > > Steve, W2MY > > > > _______________________________________________ > > 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 _______________________________________________ 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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In reply to this post by bruce bennett
David,
I have enjoyed the dialog on this subject immensly as it reminds me of the jouney I travelled to opitmize my wire antenna. The two major sources I have studied include www.dxengineering (their articles on baluns and coax losses in multiband antenna installations are excellent) and www.cebik.com. Without going through the entire story (it is LONG) I have determined that: 1) All antennas need to be grounded via lightning arrestor at the entrance to the shack. I use arrestors made for balanced line from www.iceradioproducts.com mounted on a ground rod at the entrance of the antenna wires into the shack. 2) For a multi-band wire antenna the SWR on some bands like 30m and 15m are so high (50:1) that using any kind of coax will reduce both transmitted and received signals by a huge amount. That is why the G5RV doesn't really work well on these bands. Check out the math in the articles by Cebik. Run as MUCH ladder line as you can and as LITTLE coax as you must with the balun at the shack wall on the outside. In my case the coax from the balun to the antenna switch in the shack is 6 ft. 3) The best balun could very well be 1:1 current type depending upon your other factors. With the feed point impedance of a multi-band antenna varying all over the map between bands in some cases it could be so low that reducing it further by using a 4:1 balun could make it very hard for the tuner to match it. Thus, it seems that using a balun just to make the transition from balanced-to-unbalanced without any impedance transformation is the best solution. That is what DXengineering recommends and they (of course) sell baluns for just that purpose. 4) If one is going to use a tuner designed for coax lines and a balun between the tuner and the feedline of a multi-band antenna, look for those that are rated for 1K even if you never plan to run anything near that power. The larger components used therein will have lower losses at the 100W and QRP levels. After all my research I converted my G5RV coax fed antenna to a 110 doublet by replacing the coax feed with 450 ohm ladder line into a DXEngineering balun (type AT). I liked the pattern of this length antenna based upon its direction and height above ground. It's working very well with 170 countries confirmed with 100w (about half of them since I made the change) and, most notably, it works much much better on 30m. I have sense added a 2nd wire antenna at about 45 degrees fromt the first one to get different azimuth angles from other parts of the world. Both have their own balun by DXE which is a little pricey but makes switching them easy using a coax switch inside the shack. It is easy for me to keep them separated except where they connect to the arrestors at the shack wall. A few lessons I've learned. First, any antenna is better than no antenna and a carefully researched and understood antenna (direction, pattern, feed point impedance) is better still. Second, if I had it to do over again I'm sure I would use a coax tuner with the baluns. Instead, I would have either built or bought a balanced tuner. While I like having coax from the arrestors into the shack I'm not sure how much the baluns are reducing the received signal (have to measure that some day). I will say this: the baluns are built like a tank! (Full disclosure: I have absolutely nothing to do with DXE except that I am a happy customer!). _______________________________________________ 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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