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Remote Baluns:

Richard Borgioli (KE4ZHN) on May 30, 2003
View comments about this article!

As we all know, many hams are forced to run compromise antennas, myself included. While this is much better than the alternative of not having ANY antenna, it also presents challenges to amateurs' technical abilities to come up with a design that's reasonably efficient while not being overly obnoxious to the neighbors. While at the same time providing you with a decent signal. I live in a so-called antenna restricted area (no towers) and after some squabbling with a homeowners association; I managed to put up a 40 ft push up mast for my limited antenna farm. While most amateurs in this situation can't even go this route, I was lucky in this regard. Now, faced with the challenge of being able to operate HF on 80-10 meters on one antenna is another matter... Since I could not push my luck by running cut to the band wires all over the yard, and risking further grief, I had to make due with an old stand by from the 30's, the 135 ft centerfed doublet. I strung this up in a typical inverted V configuration apexed from the top of the push up on a small homebrew PVC yardarm so as to get the feedpoint of the V away from the metal pipe. This antenna is fed with your garden-variety 450-ohm ladderline twin lead. This works pretty well on the lower bands as I ran the feedline directly into my shack and fed the line right off the internal tuners balun (4:1) All was well till one fine day wanting to work some DX on ten-meters, then I discovered that I had RF in my rig something terrible.

No matter what I tried, the RF was getting into my rigs audio circuitry and wreaking havoc. Discouraged, I had to find a solution to this. The answer is simple. Remote mount the 4:1 balun outside! (a current type is preferred for this) I purchased a balun and ran a short run of RG-8 coax outside to the balun and from there it feeds my 450-ohm line which runs straight up to my dipoles feedpoint. Now, there isn't any RF on any band at full power. While this is no news for veteran hams who have been around for awhile, I posted this article for new hams who are having the same problems with running open wire feed into the shack, or forced to run a single antenna for all bands. My problem was, I had no way to directly run the 450-ohm line into my shack without bends and close proximity to wiring and objects that most certainly caused the line to become unbalanced and radiate into my shack. This is lost power and highly undesirable for one seeking a decent signal!

Also, by remote mounting the balun, you get the best of both types of feedlines. You get the excellent shielding properties of coax inside, while keeping the multi-band capabilities of ladderline with very little loss. Sure, it's not perfect, but it sure beats RF in your rig, computer, phones etc. There are a couple of tricks for maintaining an easily tunable doublet using this system to keep in mind. For instance you run out of roller inductor on 80-meters all you need to do is add a short piece of ladderline to the existing run. Yes, I know, splices aren't exactly desired, but the loss of ladderline is so low, you wont even know it's there. Keep the line lengths on both conductors as close to identical as possible! If you do not, the line becomes unbalanced and you defeat the purpose of using it. If possible, try to run your ladderline at least a quarterwave long on the lowest band you operate on between your balun and feedpoint. This seems to help it tune up a lot easier and you will have lots of roller inductor left to play with on your tuner.

I have also read that many tuners internal baluns leave much to be desired. They aren't built heavy and many have very poor current balance on the higher bands. If you have an RF current meter available, just try and measure the current in your ladderlines conductors on higher bands and you may see as much as a 50% difference in current! (Several amateur antenna websites all agree on this.) Not very well balanced at all!

There are specific 4:1 baluns made for this type of application, (coax to ladderline) but I'm not going to endorse any products here; that's up to you to find one. If you read the product reviews section on this website, you can find some suggested baluns to try. While I admit that this isn't the worlds best set up, it does do a good job on the bands and I have no trouble working DX or anyone I can hear on any band, including the WARC bands. I believe that this system works well enough to suit most any ham who is stuck in the antenna restricted areas and can maybe sneak one up across a couple of trees for support. I also believe this outperforms the G5RV especially on 80-meters. Not that the G5RV is a bad antenna, but its short length on 80 degrades it somewhat on that band.

I would imagine a system like this could work well on full wave loops that are installed far from the shack. You could use this approach to limit feedline losses over long runs without running open wire into your shack and risking RF in your rig. Many of the audio experimenters would really benefit from this feed system to keep any stray RF out of sensitive audio equipment. A word of caution for Windom users -- a Windom is NOT a balanced antenna even though some use open wire for feeding them, the line actually acts as part of the antenna. The unbalanced condition would destroy a balun if used in this manner. Remember, a BALUN is for unbalanced to balanced feed, NOT unbalanced to unbalanced! I hope that any of this is helpful to hams both new and old.

73's DE KE4ZHN

Member Comments:
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Remote Baluns:  
by LA1SJA on May 30, 2003 Mail this to a friend!
I certainly agree with KE4ZHN.

My general experience is that ladderline dipole for multiband use is really the Swiss Army Knife of HF.
Better antennas give higher signals, but quite often the ladderline dipole will get you through.
Multiband loops fed with ladderline seem to give good results as well, exept that you have to get used to the low signal levels in receive.

There is a remote balun inverted V in my garden, and there is one ready to go for the next Field Day.

For dipoles with remote balun, there are normally three considerations; achieving the signal balance
with respect to earth to supress local noise in urbania, having a core in the balun thats large enugh to handle the mismatches that will leave lagre voltages over the balun on most frequencies, and the lenght of coax from the shack and the length of the actual dipole that will determine the lowest usable frequency.

Although the current opinion seems to be that current baluns have a lot going for them, I would like to advocate the use of straight voltage baluns wound on
ferrite, or iron dust cores. Especially for their superior signal balance.

For signal balance, the ideal would be to have the balun case connected to a metal rod in the garden, with the coax buried in the ground.
You can check the actual balance in your setup with a 50 ohm signal gererator and a battery powered oscilloscope connected over a 200 ohm resistor at the balun output, and making a 2-channel balanced measurement with respect to ground. This extra effort really helps in areas with high local noise levels.
Most small commercial baluns will only be barely usable on 80m, and wery few will do anything useful
om 160m. This test will show that as well.
Generally, the more ferrite or iron masss in the balun core, the higher chances are that they will work on the lower bands.
(Of course, if conditions are less ideal you just do what is practically possible and have as much fun as you can.)

Another discussion would be whether to use 1:4 or 1:6 ratio. Since there is going to be no perfect 1:X match at any frequency anaway, you choose what makes it most likely that your tuner will give a good match on all bands. This seems to be 1:4 for dipoles and 1:6 forloops fed via ladderline and used for multiband
operation.

Everyone will tell you that the coax should be short, 25 feet or so max.
In practice, if you need to use 150 feet or even more there is no coice.

Building high quality baluns that cover all HF bands in a single unit is not easy.
I would like to recommend one product for dipoles, the MFJ 912 1:4 balun. Because of its multi-core design it works fairly well on all HF bands, even on 160m.
Although it is rated far higher in power handling capacity for an exact 1:4 match, you should not run above 100-200 watts on it if you intend to have the large levels of mismatch over it as will occur using a ladderline dipole for several bands.

For the lower bands you can build an exellent high power balun for a few tens of dollars. Get a red painted iron dust core so large that you can just put your hand though it. Wind a standard 1:4 balun on it using wire with high voltage insulation. Put it in a
fairly large metal box with some distance to the box metal on all sides.

So, the ladderline dipole with remote 1:4 balun and coax tuner is really my "desert island antenna". Since such cartoon islands normally ony have a single palm in the middle, it would be perfect for the inverted V.
 
RE: Remote Baluns:  
by K0BG on May 30, 2003 Mail this to a friend!
I see two potential problems with this.

You didn't say how long the RG8 piece was. A 10 foot chunk would only have an additional 2 db of loss with an VSWR of 20:1. However, the VSWR in your case could be 50:1 and perhaps more. Now your 10 foot chunk would have more than 8 db of loss.

This brings up the other possibility. The voltage rating of good RG8 is about 3,700 (a lot less for some of the cheap stuff) and with a ±50:1 VSWR, this voltage rating could be exceeded.

Alan, KØBG
 
RE: Remote Baluns:  
by K3UD on May 30, 2003 Mail this to a friend!
I freely admit that the whole subject of VSWR and additional line losses has always been a bit of a mystery to me and I am more limited in my understanding of it than I should be.

I may not be the only one as there always seems to be a lot of controversy and differing opinions among those who actually do the measurements and the math on these forums and the usenet antenna forums. However, 8 db of loss at 50:1 VSWR in a 10 foot section of RG8 sounds a bit excessive.

There is a nice calculator online at: http://www.ocarc.ca/coax.htm that shows what additional line losses will result from different SWR values. A 10 foot section of RG8 at 50:1 on 28 mHz was shown to have an additional 1.8 db loss due to the mismatch.

Of couse it is possible that calculators like this one only add to the confusion.

Personally, I have always found that if I could make an antenna take power, I could make contacts with it. I have also never had much luck with bringing twin lead or ladder line into the shack because of the RF problems mentioned in the original article, usually on 40 or 15 meters, even when I had what would be considered decent grounding. Running 10 to 20 foot piece of coax from the tuner to a balun on the outside of the house usually tamed the RF problems.

73
George
K3UD
 
RE: Remote Baluns:  
by KE4ZHN on May 30, 2003 Mail this to a friend!
Hi Alan, In my situation, the RG-8 run is only about 20 ft. I strongly recommend keeping the coax run as short as possible. If you need more feedline, thats what the 450 ohm is for. It doesnt care about swr loss,(to a degree) thats what makes it so desirable. Coax on the other hand, frowns on 20:1 mismatches as we all know. The purpose of remote mounting the balun is only to eliminate routing the open wire into the shack, which in many cases is just not feasible without upsetting the line balance and causing it to radiate in your shack. I will agree with you that this is not exactly a perfect set up, but it seems to work extremly well for me. It not only solved my RF in the shack problem on the higher bands, but all my reports on signal are up too. My theory for this is, that I was obviously losing signal due to it not being radiated by my antenna, but instead it was floating around in my shack not doing anything good at all! While this may not be ideal for all, it sure can help the ham who is forced to run one wire for all bands. 73`s
 
Remote Baluns:  
by K5DVW on May 30, 2003 Mail this to a friend!
Interesting article.

But, always being one to over analyze things, I'd be leary of using coax in a situation where the VSWR was much above 5:1, especially on the higher HF bands or with any appreciable power. Your losses in coax can be tremendous in this type of setup.

One way to use the antenna you mentioned with coax and never have to worry about high VSWR is to remotely tune the antenna. There are a few automatic antenna tuners on the market that will do the job and you might then find that your so-so performing antenna comes alive with signals. They cost money, but so did your HF rig and your antenna system is 99% of your signal on HF.

One good test of an HF antenna setup is how much atmospheric noise you can hear with it. In other words, how high does the noise floor come up when the feedline is attached. If you can hear a decent amount of background noise, your antenna is reasonably efficient, and then you can most likely work any station you can hear.

K5DVW

 
RE: Remote Baluns:  
by WB2WIK on May 30, 2003 Mail this to a friend!
Nice article.

Propagation lately has been pretty poor so it's a difficult time to judge how anything works without a standard of comparison; conversely, when propagation is great (as it was only 2-3 months ago!), almost *anything* can work the world.

Sometimes lacking a second home station antenna for comparative analysis, I often use my mobile as the standard! I have a mobile rig for HF, with the Hustler 54" fold-over mast and various band resonators/whips. The Hustler base is on the trailer hitch of my wagon, and is additionally grounded by several large copper straps to various parts of the auto chassis, and it works pretty well. And of course it's sharply resonant for each band and in the center of each band matches a coax feedline perfectly (VSWR <1.5).

I run coax out to the car in the driveway, and use a coaxial antenna switch in the shack to compare the Hustler whip system to my "new" HF antenna, for whatever band. I expect any home station antenna to outperform the Hustler whip considerably, but have been surprised at times to find that some *seemingly* wonderful antennas aren't any better than the car-mounted whip!

When that happens, it's time to take it down and try again...

But at least if anyone asks how my new antenna works, I can say, "better than a mobile whip!" Or, I hope so.

WB2WIK/6
 
RE: Remote Baluns:  
by W8JI on May 30, 2003 Mail this to a friend!
It's interesting to see this, because I was just in the lab measuring balun performance at high load impedances. This will be my work assignment for the next few weeks. My work assignment for the past few months was designing high power baluns that worked very well over wide bandwidths under matched conditions (300kHz to over 100MHz)!!

We'd better pick the open wire feedline and antenna length with great care and planning, unless we are very lucky people!

Consider a 1/4 wl feedline on 80 meters feeding a 1/2 wl dipole at modest height.

On 80 meters, the feedpoint will be around 50 ohms or so. SWR is about 9:1 on the ladder line. With 450 ohm line, the balun end will have 9*450= or about 4050 ohms.

On 40 meters the same antenna could have 5,000 to 10,000 ohms of center impedance! The line would be 1/2 wl long on 40, and the balun would see a load of 5,000-10,000 ohms!

If the same antenna is used with a line 3/4 wl long on 40, the balun impedance is a much more managable 450 resistive with 450 ohms reactance on 80 meters, and 20 to 40 ohms resistive on 40 meters.

The best balun is actually a 1:1 ratio current balun, NOT a 4:1 balun and especially not a voltage balun of any type.

I couldn't find any commercially manufactured 4:1 balun that are more than a few percent efficient at 10,000 ohms! On the other hand 1:1 current baluns might lose balance, but efficiency remains very good even with extreme impedances. 1:1 current baluns are voltage breakdown limited in wire insulation, not core limited (except as the core affects balance).

Voltage baluns, by necessity of construction and design methods, have much worse performance when operated into mismatched loads. Voltage baluns of any ratio subject the core of the balun to substantially more core flux density than 1:1 current baluns.

1:1 current baluns handle much more power with VERY much less loss than 4:1 baluns, and do so over much wider impedance ranges. The only thing a properly designed 1:1 current balun looses is balance when the load impedance gets very high.

73 Tom
 
Remote Baluns:  
by K5UJ on May 30, 2003 Mail this to a friend!
Thanks for the article; it is timely for me. I recently put up a smaller center fed wire at a low height (see http://www.cebik.com/88.html). I am feeding it with 600 ohm open wire feedline which enters the shack through a small plexiglass window in which I have two receptacles for quick disconnect banana plugs. On the other side of the window I have a balanced transmatch, the Bliss Z MatchMaster and from it, a 15' run of 1318 RG8 to the transmitter. I have not had time to use it very much but it has worked well on 75 meters so far with good signal reports close in. I expected this since it is a cloud burner. I have been able to run 1 kw p.e.p. with no rf getting back in my tx audio. The ladder line is a good idea but I suggest readers consider open wire feed and a balanced transmatch. The b.t. design puts the balun (a current balun) on the transmitter side of the transmatch where it can function as a 1:1 balun. You can make one (see Rich Measure's Balanced Balanced Tuner article http://www.vcnet.com/measures/bbat.html) or buy one. They are now made by Palstar and Bliss. Open wire feed is available from W7FG or you can make it yourself.

73,

Rob Atkinson
K5UJ

p.s. two other interesting articles related to this topic: About a year ago QST ran A Balanced Approach to All Band Bliss (sorry, can't recall the author's name) which covered balanced tuners, ladder line and horiz. loops. Earlier (1994?) Steve Ford published in QST an article on ladder line with the title The Lure of the Ladder Line. Information on Palstar, Bliss, W7FG and the articles should be found with google searches.
 
Remote Baluns:  
by K5UJ on May 30, 2003 Mail this to a friend!
Forgot to mention this: PVC pipe with T sections on top is great for suspending open wire feed on a run across the ground. You can cut it to any length you need to keep it several feet high. Drive a pipe in the ground to make a hole for the PVC and stick it in. Pull one end of a feedline spacer off its wire and stick it through the T section, refasten the spacer to the wire, and jam the bottom of the T on the top of the pipe. Do this every x no. of feet as needed for acceptable slack, and height above ground (or snow) and choose a pipe diameter that allows for a moderate amount of flex.

K5UJ
 
Remote Baluns:  
by KE3HO on May 30, 2003 Mail this to a friend!
If you feed a symetrical antenna (such as your center feed dipole) in theory the current in the two legs of the ladder line should be equal in magnetude. In the real world this is not the case, as each half of the dipole is in a physically different area so each half has different coupling to the ground and nearby objects. The main problem with RF in the shack comes from the current imbalance in the ladder line. Most (if not all) commercial tuners have a voltage balun which will do nothing to keep the currents equal in magnetude. This is what allows the RF in the shack, not the fact that you have ladder line in the shack. If you were to run coax to a remote voltage balun, you would probably still have a RF in the shack. The current balun is the way to go. If your tuner had a current balun, you would most likely be able to run the ladder line right to the tuner without any RF in the shack. I have to agree with others that a 4:1 balun (even a current type) is not a great solution for connecting 50 ohm coax to 450 ladder line, especially when using a non-resonant antenna where the SWR is likely to be high anyway.
 
Remote Baluns:  
by AC7GO on May 30, 2003 Mail this to a friend!
Thanks for the interesting and informative article.

I have just put up a sloping dipole fed with 300 ohm TV line. I have not had RF in the shack, and the radiation pattern is about what I would expect. But I think my good fortune to this point in that regard is because the angles of the dipole arms relative to the feedline are such that the dipole arms induce approximately cancelling RF currents in the feedline. I am sure there will arise conditions which disrupt the balanced condition I have it in. For example, I will probably at some point in time want to rotate the dipole so that one leg is parallel to the feed line.

I am aware of the complexities of running baluns or bal-bal transformers at large SWR conditions. To avoid that, my thought is to get some large, high permeability cores, and wind several turns of the 300 ohm line through them. My thought is to space the cores such that the distance between them is something less than 1/2 wavelength at the highest ham band I plan to use. The inductance of the cores should do a good job of limiting induced RF currents, and thus prevent disruption of the dipole pattern and also prevent RF in the shack.

I would appreciate any comments you might have on the scheme I have outlined.

Thanks & 73

Max Nielsen AC7GO
 
Remote Baluns:  
by K5UJ on May 30, 2003 Mail this to a friend!
p.p.s. For the mother of all verticals fed with open wire feedline go to
http://www.fybush.com/site-020424.html
You thought the 50 kw pros had abandoned it? Think again and check the vswr on the DX50 display.

Rob Atkinson
K5UJ
 
Remote Baluns:  
by W5LXG on May 30, 2003 Mail this to a friend!
As aways, post article contributors provide a variety of high and low level engineering data. I have the same architectural controls and ended up with almost the identical antenna as Richard's.

I run 450 ohm ladderline directly to a old Heathkit KW tuner, with roller inductor and internal 4:1 balun. The results(performance) of the antenna are superior to any other wire antenna I have used in 46 years of hamming, at least on 40 thru 10 meters.

Now the reason I write: For both 160 and 75/80 meters, I tie the ends of the ladderline together and feed the antenna as a random wire, or if you prefer, a single fed "T" antenna. Performance is adequate for the limited time I use those bands. Don't worry about losses and math. If an antenna works, use it and have fun.
 
RE: Remote Baluns:  
by W8JI on May 30, 2003 Mail this to a friend!
>my tx audio. The ladder line is a good idea but I suggest readers consider open wire feed and a balanced transmatch. The b.t. design puts the balun (a current balun) on the transmitter side of the transmatch where it can function as a 1:1 balun. You can make one (see Rich Measure's Balanced Balanced Tuner article http://www.vcnet.com/measures/bbat.html) or buy one. They are now made by Palstar and Bliss. Open wire feed is available from W7FG or you can make it yourself.>>

Actually moving the balun to the input does nothing at all to improve system balance!!! It does reduce differntial mode stresses, but that usually isn't a problem anyway.

Roy Lewallen gives an analysis of this at his web site:

http://www.eznec.com/miscpage.htm

Balance is a common-mode problem. Moving the balun to a network input does not change the common mode impedance seen by the balun.

73 Tom
 
Remote Baluns:  
by KF4VOP on May 30, 2003 Mail this to a friend!
"Balanced Everday Approach to All Band Bliss"
Apr 2002 QST
Kirk Kleinschmidt,NT0Z
http://www.arrl.org/members-only/tis/info/pdf/0204047.pdf

"Lure of The Ladder Line"
Dec 1993 QST
Steve Ford, WB8IMY
http://www.arrl.org/tis/info/pdf/9312070.pdf

"Balanced Balanced Antenna Tuner"
Feb 1990 QST
Richard Measures,AG6K
http://www.arrl.org/members-only/tis/info/pdf/9002028.pdf

"Loop Skywire"
QST November 1985
Dave Fisher, W8MHS
http://www.arrl.org/members-only/tis/info/pdf/8511020.pdf
 
Remote Baluns:  
by WA9OIG on May 31, 2003 Mail this to a friend!
I run a center fed dipole with 450ohm twinlead to a Icom AH-4 auto tuner remoted away from the shack. I'm using RG213 to feed the tuner. The feedline from the shack to the tuner is matched so I have minimum loss in the coax. I have had very good results with this setup 80m - 6m.
 
Remote Baluns:  
by AC5UP on May 31, 2003 Mail this to a friend!
For what it's worth, I've had an Off-Center fed Dipole (often called a Coaxial Windom) on the air for better than two years with no problems. This is the 136' version with the feed point 46' feet from one end. At the feed point I have a two core Guanella style 4:1 'current' Balun feeding 50 ohm coax. The toroid cores are #43 mix and the windings are #18 stranded silver Teflon.

No RF in the shack, excellent SWR bandwidth, and it works the world on all HF bands except 30 and 15 Meters. Dr. Jerry Sevick, W2FMI has a Balun book in print that should be standard issue for those who experiment with antennas as broadband matching does involve a bit of art with the science. Sevick claims the Guanella style Baluns can be used effectively as UnUns, and I agree...

- AC5UP

 
Remote Baluns:  
by KE4ZHN on May 31, 2003 Mail this to a friend!
You can do the math, analyze it, reanalyze it, reengineer it.....all I know is, it works! I said I wouldnt endorse any products in my original post, but just for the record, the remote Balun I use is the Centaur B41LW10-50. After hours of ragchewing on 75 mtrs. at power levels of 1kw or at times legal limit, this balun never even gets warm to the touch. The swr never rises, and it just seems to do its thing. Like an earlier poster said, to heck with the math, use it and enjoy it.
 
RE: Remote Baluns:  
by LA1SJA on May 31, 2003 Mail this to a friend!
I hope there still is bandwidth available for a few remarks on a different note.
Since writing my first remarks above I have been on a hike in a large nature reserve on the border between Norway and Sweden. On bike and on foot. No radio, not even the K2 or a HT. No cellular coverage.
Early this morning, the Sun was obscured by the Moon up here to a degree not seen for 50 years.
The day saw clear sky and perfectly shining sun. The temperature was such that you could just barely dip yourself into a lake for the first time this year.

So, what on earth is the relevance of all this to remote baluns ?

Well, in the afternoon my thinking went like this:
I all the years, when has the signal balance or the common mode rejection of my remote baluns stopped me from making radio contacts? Never.
(Even in spite of this bordering on an obsession after years in telephone and ISDN egineering.)
When has 150 feet of coax losses prevented me from receiving a 599 from Bejing? No idea, but there is a QSL card at home. It probably was a 478 contact, but most people send you 5nn anyway.
Had any high voltage sparkovers? Yes, once. Changed to a larger tuner.
How often has this antenna saved me from getting in the way of the cars on family gatherings at my mother in law? Every time.
How often have I enjoyed this antenna setup? Every time exept once when the moskitoes spoiled the fun.
Need I say more?
 
Ladder Line - length *is* important  
by KF6IIU on May 31, 2003 Mail this to a friend!
I did not have RF problems until I took 10 feet or so off my ladder line (feeding a 135 ft doublet) and tried operating in the CW part of 10 meters. I added about 8 feet (1/4 wavelength at 10 m) back in and now no RF. The antenna still won't tune up at the very bottom of 80, but he ladder line is very short - 60 feet - about 1/4 wavelength at 80m.

Ladder line cannot radiate RF unless it is unbalanced by coming too close to a conductor. If there is a high voltage (or current too?) point on the line close to a metal object (in my case probably the connection to the transmatch or the transmatch itself) the line will radiate. Adding (or subtracting) 6 feet will move the high voltage point out of the shack.
 
Remote Baluns:  
by G3RZP on June 4, 2003 Mail this to a friend!
In my last house, the centre fed antenna was about 80 feet long - that was all that would fit. The open wire line was 24 feet long , because that was the maximum length of wire I could stretch out through the living room and kitchen, and the antenna was only 20 feet high. The balun was 10 turns of RG213 about 12 inches in diameter, hung on the fence. Fed with a homebrew 'Ultimate Transmatch'tuner, it wasn't brilliant on 80, was useless on 160 (surprise!) and went pretty well on the other bands with about 150 watts or so from a Drake TR3. This must be as cheap as you can get.........

Losses in the coax aren't that bad at HF if you use decent coax, while the maximum voltage you can get is twice the matched voltage. But I wouldn't go much above 150 watts of RF, especially if the coax is small stuff, such as RG58.
 
RE: Remote Baluns:  
by W8JI on June 4, 2003 Mail this to a friend!
<Losses in the coax aren't that bad at HF if you use decent coax, while the maximum voltage you can get is twice the matched voltage. >

I don't understand that statement, maybe something was unintentionally omitted? I've melted 300 ohm twin lead with an single 807 tube as a Novice because of unwise antenna length/ feedline choice!

The maximum voltage on a mismatched line fed with a tuner can be terribly high even at low power when the mismatch causes high impedances, just as maximum current could be terribly high when impedance is very low.

While some people dismiss suggestions we use a little care picking feedline lengths, it really isn't all that difficult or complicated if you know what an even or odd number is! When using open wire or ladder line with a dipole on multiple bands:

1.) Avoid ODD-multiples of 1/4 wl feedline on the band where the antenna is a 1/2 wl long. (ie NEVER use a 55-70ft ladder line between the balun or tuner and antenna when feeding an 80 meter dipole.)

2.) Try to make the feedline an ODD-multiple of 1/4 wl on bands where the antenna is an EVEN multiple of 1/2 wl long. (ie TRY to use a 20-30ft or 80-90ft feeder to feed an 80-meter dipole operating on 40 meters.)

This will ensure maximum system efficiency and prevent subjecting a balun, feedline, or tuner to extreme voltages (even at low power)!!!
 
Remote Baluns:  
by N4KIT on June 5, 2003 Mail this to a friend!
My antenna is a G0FAH design, described in a QST article some years back. It is a doublet design, 94' total length, fed by 41 feet of 450 ohm ladder line with a 1:1 balun at the bottom. The length of the ladder line is carefully chosen to give a near 50 ohm impedence at the bottom of the ladder line on several bands. The 1:1 current balun (mine is a RadioWorks B1-2K) transitions the 50 ohm coax to the antenna.

The match is of course not perfect by any stretch, but I get the best match at 20 meters, very little tuner to bring it to 1:1. 160 of coarse is out of the question, but I can get a workable match 80 thru 10. 80 and 40 typically take a good bit of inductance from the tuner, but the EZNEC model predicts that.

Bottom line, I have one antenna for HF, which satisfies my XYL restrictions and yeilds QSOs on 80 through 10. My next project will be to lengthen the elements to 135' and try to determine a good comprimise length for the ladder line in the same basic setup.

73 de Chris N4KIT
 
RE: Remote Baluns:  
by G3RZP on June 6, 2003 Mail this to a friend!
If you have an open circuit on the end of a transmission line, you can only get double the matched voltage at each point of maximum voltage. Not usually enough to break the dielectric down - unless you're up at very high power.

I use a quarter wave of open wire line to feed an 80m dipole, with no problems. I don't use a commercial tuner, but a home brew one with a 'toast rack' two section variable capacitor and link coupling with a series variable cap. That works very well on 80, 40 and 30 - and I don't run QRP. No balun needed.

To avoid confusion, my open wire line is hard drawn #14 copper, spaced 3 inches apart by ceramic insulators (Dayton flea market the other year, 50cents each, surplus), spaced along it every two feet or so.

No plastic insulation.

73

Peter G3RZP
 
RE: Remote Baluns:  
by W8JI on June 7, 2003 Mail this to a friend!
<If you have an open circuit on the end of a transmission line, you can only get double the matched voltage at each point of maximum voltage. Not usually enough to break the dielectric down - unless you're up at very high power.>

That isn't true at all Peter! When a transmission line is open terminated, the peak voltage can be almost any voltage at voltage maximums. It can be thousands of volts with only a few volts applied at the line input!

My old open wire line feed antenna, feeding two halfwaves in phase, would arc across 1.5 inches of insulator with only 1500 watts PEP in wet weather. It also had corna problems even in dry weather at the antenna feedpoint. I could see where the little strands of pointed wire were rolling up into balls from corona, so I had to install a larger antenna center insulator.

Power formulas do not lie. The 7MHz feedpoint impedance of the antenna was 6000 ohms, I had 30 feet of 600 ohm feedline. The source end had 60 ohms j0 and with 1500 watts it had 300 volts (424v peak) and 5 amperes RMS. The load end had 3000 volts (4200v peak!)and .5 amperes RMS. Line SWR was only 10:1, it wasn't even an open circuit case.

Anyway the ratio of maximum voltage to minimum voltage is equal to the SWR, just as the ratio of maximum current to minum current is equal to SWR. It can be MANY times the matched voltage on a transmission line.

That is why impedance mismatches are sometimes defined as "VSWR" even when the instrument measures true forward and reflected power.

73 Tom
 
Remote Baluns:  
by N0SP on June 11, 2003 Mail this to a friend!
I am glad that your article of remote baluns also includes the idea that using parallel conductors in open wire line does NOT assure that the currents in the feedlines are, in fact, balanced. This kind of feedline is certainly "low loss", but that all goes out the window (and RF comes IN the window!) when the currents are not equal and 180º (degrees) out of phase. The line radiates and other nasty things happen.

The first rule is to be highly suspect of almost every commercial antenna tuner that has a "built in balun" for feeding balanced line. Nearly all of these tuners use a rather mundane voltage balun at the output of the tuning network to balance the currents. These baluns do a very poor job when confronted with a highly reactive signal (which is almost always the case in this application) and can easily saturate at even fairly low power levels. When they do they can spray parasitics all over the place. Voltage baluns are at home with a well matched, non-reactive, balanced signal to a low impedence matched line. And a given balun only works well over a fairly narrow frequency range. Depart from this senario very far and you're asking for trouble. Be advised, your SWR meter will NOT give you any hint of problems in this area! It may eventually when the balun gets hot and begins to destroy itself if you're using high power. But short of that, you'll never know it by reading the meters.

But take heart, there are ways to avoid these problems. There are a few antenna tuners, both new and old, presently available that can provide a true balanced signal. Starting with the "old"... the venerable old Johnson Matchboxes will do it fine. So will the Nye Viking tuners that came later. They are frequently available on Ebay and hamfests. The only caveat with them is that they have fairly limited tuning range and can't quite match an extremely high or low impedence signal to ladder line, but will work in most settings. Often just adding or subtracting some feedline will allow them to work. Also, there are some easy mods that can extend their range.

As for NEW tuners, there is only one company I can find that solves this problem. Some articles mentioned Palstar, but it should be noted that they make two tuners that do it well. Palstar (Palstar.com) makes a tuner (the AT4K) that uses an internal balun. HOWEVER, it is located between the radio and the tuning circuit so the balun never sees the highly reactive signal coming down the line. Instead the balun is always treated to a non-reactive load and therefore is extremely resistant to saturation. It is a high quality high power balun. The other, and perhaps the best, tuner for this purpose is the newer Palstar AT1500BAL that uses syncronized dual roller inductors for a true balancing act. It also has switchable impedence ranges for low impedence loads like loops and short dipoles. This is the ultimate tuner for this application. It should be noted that this tuner is designed for balanced output ONLY, not coax. It's main advantage is that it's a high power tuner at a very reasonable price since it doesn't need the multi-hundred-dollar bandswitch that the big coax tuners need, yet it has the large silver-plated roller inductors and high voltage capacitors of the more expensive dual-output AT4K.
Another excellent balanced tuner mentioned about is the Bliss Match Master. However, I cannot find any retailer that sells this anymore and the last Eham product review submitted for this model was in 2001. I believe plans are available at the ARRL to home brew this. A Google search shows TomsTubes.com as a dealer, but his website no longer offers it.
Typical tuners are absolutely awful when used this way. Also, they all put the balun on the antenna side of the network where it sees sometimes extreme voltages and highly reactive loads. If you're lucky and the feedline happens to be close to the right length you might do alright, but it's something you certainly should not count on.

Hold on.. there is one more way to do it well without going out and buying a new tuner. RADIO WORKS (RadioWorks.com) makes a product called the "Remote Balun" that is a very high quality CURRENT balun. (not a "voltage" balun) that is specifically designed to handle high SWR without saturation. You can put this at the coax output end of any good tuner and get a very good result. I've used these extensively and have put lots of power to them and they never get the slightest bit warm. They are a 4:1 balun, so you probably don't want to use it with a very very short dipole (less than 1/8 wavelength) or smallish loop. They work very well. I've sent several of these to friends who had tuning and RFI problems on balanced antennas and in all cases the problems were solved.

Pardon the verbosity, but after all the discussion here and elsewhere on Eham about the feedlines, baluns, and loss, I thought it best we talked about how to efficiently balance a signal in the first place. I've spent 30 years on the bands fighting and dealing with balanced lines and had my share of microphone bites. The line just won't do it's job well if it's not given a balanced signal to work with.

73,
Dennis
NØSP
 
RE: Remote Baluns:  
by W8JI on June 12, 2003 Mail this to a friend!
<<<As for NEW tuners, there is only one company I can find that solves this problem. Some articles mentioned Palstar, but it should be noted that they make two tuners that do it well. Palstar (Palstar.com) makes a tuner (the AT4K) that uses an internal balun. HOWEVER, it is located between the radio and the tuning circuit so the balun never sees the highly reactive signal coming down the line. Instead the balun is always treated to a non-reactive load and therefore is extremely resistant to saturation. It is a high quality high power balun.>>>

How discouraging to see incorrect technical analysis without verifying measurements make it into amateur radio so well!!!

Moving a balun to the input of a common T or Pi network tuner does nothing to improve balancing of the system!!! It is a myth, started by poor theoretical analysis and perpetuated by people who never actually check things they do and verify results. The common mode impedance of a pi or T matching network is very low, only the differential impedance is changed.

I've measured it in many cases, and have found a balun move to be a total waste of time and effort. Might as well put the balun at the output, assuming it is the more proper current balun and not a useless voltage balun (which hardly works with any mismatch, and will never guarantee balanced currents anyway in the real world)!

Because the common mode impedance is virtually unchaged, the stress on the balun core and the requirement for high common mode impedance is NOT noticeably modified by moving the balun.

Read Current Baluns at:
http://www.eznec.com/miscpage.htm

Lewallen also recently e-mailed me this in a recent exchange:

"On another subject, Jack Belrose VE2CV recently brought up the issue of
a balun at a tuner input vs output. I realized that I'd never done any
actual measurement to verify the contention that moving the balun to the
input doesn't help the balance. So I ginned up a simple experiment. The
results were spooky -- if I were to publish it, I'd fiddle the numbers a
little. As they are, they're so close that it'd be hard to convince a
reader I hadn't cooked them. Description follows.

I just finished running a simple experiment as a further test of the
premise that putting a balun at the input of a tuner doesn't help the
transmission line/antenna balance. I'm sorry, but I don't use graphical
drawing programs very often, so it would take me a while to get together
a pretty presentation. I'll try to describe in words what I did. If it's
not clear, I'll take the time to draw it up.

There are three components in the model:

1. The "antenna". I loosely based the 14.15 MHz impedances on your 30.1
meter dipole up 9.1 meters, so I'd be working with a set of values that
could happen in practice. I purposefully chose a frequency where the
impedance was fairly high, although not so high as to make accurate
measurement difficult. And to simplify matters, I made my model antenna
purely resistive, with resistance values about equal to the magnitudes
of the impedances of the antenna you modeled. I did an EZNEC analysis of
the antenna with the transmission line conductors tied together
(actually, I used a single wire of equivalent diameter) and driven
against ground to determine the common mode impedance. The end result
was a differential mode impedance of about 300 ohms and a common mode
impedance of about 315 ohms. In my experiment, I represented this with a
tee network having 150 ohms for each of the two series resistors and 240
ohms for the shunt resistor. The shunt resistor was connected to the
common ground point for all measurements. ("Ground", incidentally, is
essentially one point on a small copper board for these tests.)

2. The balun. I purposefully made a balun which would be quite effective
at 50 ohms, but not very good at a 300 ohm level. The longitudinal
impedance was 317 + j407 ohms (516 ohms magnitude) at 14.15 MHz. It was
made by winding about 25 cm of RG-174 type coax on a small
high-permeability ferrite core.

3. The "tuner". Because I made the load purely resistive, I could
represent an unbalanced tuner with an autotransformer. The transformer
had a 5:12 turns ratio to match the 300 ohm differential load to 50
ohms. With the output loaded with 300 ohms resistive, the input measured
46 + j8.5 ohms with a GR bridge. So it does a reasonable matching job.

Test 1: Balun at the "tuner" output.

I connected a 50 ohm signal generator from the transformer tap to the
transformer bottom. The transformer bottom was grounded. The balun was
inserted in the conventional manner as a 1:1 current balun between the
high-Z side of the "tuner" (top of the transformer) and the antenna.
That is, the center conductor of the balun input was hooked to the
transformer top, and the shield of the balun input was connected to
ground. Each output side conductor was connected to one of the 150 ohm
resistors. The bottom of the 240 ohm common mode resistor was connected
to ground, as it was for both tests. The 150 ohm resistor to which the
balun center conductor was connected is called the "hot" end of the
antenna, below, and the resistor connected to the balun output shield
the "cold" end. Of course, if the balun were perfect, both sides of the
antenna would be equally "hot".

Result:

Signal generator output voltage: 352 mV p-p
Voltage at "hot" end of antenna: 540 mV p-p
Voltage at "cold" end of antenna: 298 mV p-p
Voltage across 240 ohm resistor: 105 mV p-p

So you see there's considerable imbalance. If balance were perfect, the
voltages at the "hot" and "cold" sides of the antenna would be equal in
magnitude (but opposite in phase), and the voltage across the 240 ohm
resistor would be zero.

Test 2: Balun at the "tuner" input.

I moved the balun to the "tuner" input, between the signal generator and
the transformer primary. The bottom of the transformer now connects to
the balun output shield and one of the 150 ohm resistors (which I'll
call the "cold" end), but not to ground. The top of the transformer
connects to the other 150 ohm resistor (the "hot" end). The 240 ohm
resistor still connects to ground.

Result:

Signal generator output voltage: 434 mV p-p
Voltage at "hot" end of antenna: 544 mV p-p
Voltage at "cold" end of antenna: 289 mV p-p
Voltage across 240 ohm resistor: 105 mV p-p

Hard as it might be to believe, I did *not* "cook" these results! One
really curious thing I don't have a ready explanation for is why the
"antenna" resistor voltages came out nearly identically for the two
tests despite the different signal generator output voltage. (The
generator level was the same for both tests -- the different measured
voltages were due to the different impedances presented by the test
circuit for the two tests -- 32 - j4.9 and 46.5 + j12.7 ohms
respectively -- and the generator's fixed 50 ohm output impedance.) I
suspect that the transformation caused by the short balun transmission
line is involved, the transformation being different when the balun is
connected at the input of the "tuner" than when at the output. Possibly,
the different voltage transformation just compensates for the different
input impedance, since they're both caused by the same effect. But I
haven't gone through an analysis to see if this seemingly exact
compensation should be expected, or whether it's just a coincidence.

The conclusion from the test is clear: The balance is the same (exactly
so, within measurement precision) when the balun is on the input as it
is on the output.

Of course this single simple experiment certainly doesn't constitute
proof that the conclusion is always valid. However, the tests were set
up in a way that should have shown a difference if there were inherently
some advantage to putting the balun at the input. And it does tend to
confirm the same conclusion drawn earlier from theoretical
considerations. I encourage you or anyone else to duplicate the
experiment, then extend it to other models, and share the results."

73 Tom


 
Remote Baluns:  
by K6XR on July 20, 2003 Mail this to a friend!
My antenna is 130 ft long center fed with 450 ohm ladder line to a mfj-912 balun with 10 ft of 9913 coax to my mfj-986 tuner. the system works very well. In fact, my internal tuner in the ts-570 will tune all bands 160-10 excluding 30 meters. My k1 internal tuner will also tune the antenna 40,30,20, and 15 meters. doing the math for attenuation and swr losses computes to 98.175 watts delivered to the antenna for radiation. This is the best wire antenna I have ever used and I do not consider it "compromise" but a good antenna. I am not sure if the 912 is a current or voltage balun, but think It may be a voltage type. I have no problems 160-10 meters.
 
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