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Thread: Balun Mystery ...

  1. #1

    Default Balun Mystery ...

    I'm not exactly clued up on baluns. Which is why I buy, rather than build them. A few years ago, longer than my failing memory can clearly recall, I bought one for a 1:9 end fed long wire install. But we then moved house. This morning, looking through my box of bits for a 1:1 balun to put between the coax and the ladder line of a half-size G5RV, I found a grey box that claims to be a balun - the one I used for the 1:9 install. It's got an SO239 plug into which I clearly plug the unbalanced end of the coax. But its also got three wing nuts, one on the right and two on the left. The ones on the left are respectively marked Ant 4:1 or 1:1 and Earth. The one on the right is marked Ant 9:1 or 1:1. And no instructions or wiring diagram.

    Now, to which two of these three wing nuts do I connect the two ends of my ladder line in order to achieve a 1:1 balanced / unbalanced connection? I am assuming that I connect one side of my balance line to 9:1 and the other to Earth if I want if I want a 9:1 balun. And by the same logic, I assume I connect to 4:1 and Earth for a 4:1 balun. So does that mean (by deduction) that if I connect one side of the ladder line to 4:1 and the other to 9:1 I get a 1:1 balun? Seems a bit odd to me...

    Can anyone cast light on my darkness?

    Thanks for reading.

    Richard G4JJP

  2. #2

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    A pic would help!

  3. #3

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    Thanks for reply. OK. Here are a couple:
    balun1.jpg
    balun2.jpg

  4. #4

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    OK, similar to one I have owned in the past though not exactly. When an end fed wire is hooked to 9:1 or 4:1 that's what you have. Connected across both in a dipole configuration should give 1:1. The Earth always goes to a counterpoise for end fed or earth ground in dipole configuration. At least that's the best my memory comes up with.

  5. #5

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    Here's the place it came from:
    http://ham-radio.urbasket.eu/balun-unun-c-11.html

    Maybe you can find a datasheet, or email them for one.

  6. #6

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    Thanks. That makes it absolutely clear - and obvious when you realise it. Actually, just what I need for a G7FEK antenna.

  7. #7

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    NONe - throw away the G5RV, build yourself a Fan Dipole antenna..

    The internet here is your friend, do a little reading, you will discover that the G5RV and G5RV jr are pieces of crap - and their design does not lend itself to the use of a balun, because it is a non resonant antenna.. Baluns, either current or voltage is used to connect a balanced load to coax.

    In the case of the G5RV jr - it is an unbalanced load - just like the end fed wire - which didn't work or work well - which you surely discovered when you tried to use it.

    How Lou Varney tried to make the G5RV work was by making it non resonant and using a Johnson Matchbox to tune it to resonance.

    Of course back then the radios were all tubes and they were not particular on what you fed it as long as the impedance was more than 50 ohms.. Low ohms are a lot harder to tune than a high impedance. To match the antenna to 20m - Lou used about 65 feet of RG-8 coax, hoping that the coax would be capacitive and would absorb the reflected power, for low power applications even Mini 8 would work - since all you are using it for is to act like the element inside of a toaster.

    If the coax is very lossy - all the better, because then it might trick the user and the swr meter into believing that the antenna is actually resonant - just by looking at the almighty swr meter and seeing a low SWR doesn't mean that it is resonant, just that it is lossy.

    A friend of mine uses a G5RV jr - he is a real dumbass - college educated idiot that you can't teach anything to and his only objective is cost.
    As soon as a person makes a couple of contacts - and they are cheap, they justify their antenna as being " Good Enough"!
    It must work because I talked to (Xy1za) in ( Spain, England, France - enter your country in here) and they gave me a good signal report!

    If you really want to test your balun to see how good it is, connect it to a true 50 ohm dummy load, feed it with 100 w and look at the SWR meter.
    Then connect it to an antenna analyzer and sweep the bands you plan to use it on. If the impedance moves around - according to the frequency, then the balun is not a good choice. Invest your money in a real antenna, i'm not even saying that you have to buy it, but buy yourself a good Guanella-Balun...

    Most peoples problems stems from the fact that they don't understand how a antenna works... They don't understand feed lines, and they don't understand how antenna (trickers) tuners works - or doesn't work.. they try to compensate with more power - like Tim The Toolman Taylor - now also a licensed amateur.

  8. #8

  9. #9

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    https://www.eham.net/ehamforum/smf/i...;topic=61669.0

    (Quote) - poor Mr Varney is turning over in his grave. The real G5RV was 102' flat top, not inverted "V", fed with 34' of 525 Ohm parallel feeders and 72 Ohm coax. It was designed as a 20 meter antenna that could be used on other bands when nothing else was available.


    If you have the tuner with a balance output, save yourself the money on the g5RV and use ladder line to a dipole cut to half wave on your lowest operating frequency. If will most likely tune on all bands above the lowest using the balanced output of your tuner. It won't cost any more than the G5RV and it will work better.

    If you insist on paying MFJ, then I think they have some doublet antennas, with ladder line and wire and insulators you can buy. Go with that.

    The problem with the G5RV is the feed line, balun losses and the common mode current problems due to offcenter feed. Why the G5RV has developed an almost mystical cult following is beyond me.

    If you go back and actually read the articles writen by Lou Varney, G5RV
    himself (several are available on the internet) his prefered feed system
    was balanced line all the way to the shack. This generally is the lowest
    loss option and allows the antenna to be used efficiently over a wider
    range of frequecies. The common feed system with a mix of ladder
    line and coax gives a reasonable match on some frequencies, depending
    on how much loss you are willing to tolerate. It was originally designed
    to be used with 75 to 90 ohm coax, which still may be a better option.
    Here is a good analysis of loss vs. frequency for a full sized G5RV:

    http://www.vk1od.net/G5RV/index.htm

    Doubling the frequencies will give you a rough estimate of the losses
    of the half-sized version, but in practice you'll find the coax losses
    will be a bit higher (feedline loss increases with frequency) and the
    tuner losses will drop a bit with reasonable-sized components. He
    also has a page on optimizing the match for your specific components
    and frequencies. Figure 12 of this article shows the losses with balanced
    line all the way to the shack. (The problems with radiation from balanced
    lines in the shack is often overestimated. I've seen more problems
    with RF from coax feed than from balanced line - If you don't use a balun at the bottom of the matching section, you can
    get RF flowing on the outside of the coax (and back into your shack
    if you aren't careful.) The amount of RF will depend on the length of
    the coax, how your station is grounded, etc. Perhaps a worse problem
    is when the coax is laying on the ground: the lossy dirt will attenuate
    the RF before it reaches the shack, but unfortunately that is simply
    wasted power that doesn't get radiated.


    So if you run balanced line all the way to the shack you can use the
    balun on the back of your antenna tuner. (It may work better to use a
    1 : 1 balun on some bands, depending on the feedline length.) If you
    use coax feed you need some sort of balun/choke at the junction
    between the coax and twinlead.

    http://www.karinya.net/g3txq/g5rv/

  10. #10

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    Quote Originally Posted by Sixmeters View Post
    A friend of mine uses a G5RV jr - he is a real dumbass - college educated idiot that you can't teach anything to and his only objective is cost.
    According to EZNEC, a 51 foot dipole at 35 feet fed with 16.5 feet of 300 ohm twinlead with a VF of 0.85, has a 15.9-j4.4 ohm impedance on 7.2 MHz looking into the twinlead with an SWR(50) of 3.2:1 on the connecting coax. It is 27.3-j21.2 ohms on 14.2 MHz with an SWR(50) of 2.3:1 and 110+j71.8 ohms on 28.4 MHz with an SWR(50) of 3.3:1

    Assuming 70 feet of Belden RG8x and using TLDetails, the coax loss on 40m is 0.328 dB with an efficiency of 92.7%. Coax loss on 20m is 0.296 dB with an efficiency of 93.4% and coax loss on 10m is 0.407 dB with an efficiency of 91.1%. Efficiency would be even higher using RG-213.

    A standard S-unit is 6 dB so the total coax loss on 40m is 5.5% of one S-unit. On 20m, it is 4.9% of one S-unit and on 10m, it is 6.8% of one S-unit. A rule-of-thumb is that the human ear can barely detect a 1 dB change so the losses in 70 feet of RG8x coax feeding a G5RVjr are undetectable by the human ear. Does one need a tuner for a G5RVjr? Of course he/she does, but a lot of built-in tuners can handle those SWRs and a wide-range external tuner will certainly match those impedances with small tuner losses.

    Quote Originally Posted by Sixmeters View Post
    The problem with the G5RV is the feed line, balun losses and the common mode current problems due to offcenter feed.
    The G5RV is a balanced center-fed 102 foot dipole fed with ~33 feet of balanced tuned feeder. A good 1:1 choke balun at the coax to twinlead junction virtually eliminates common mode current on the coax. The 1:1 choke balun adds about four feet of coax loss which is negligible on the bands on which the G5RV performs well, i.e. on 80m, 40m, 20m, and 12m. It is a multi-band antenna but not an all-band antenna.

    It is neither a gift from the gods nor the work of the devil. It obeys all the laws of physics.
    Last edited by W5DXP; Thu 10th May 2018 at 13:25. Reason: added second response and comment

  11. #11

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    Thanks for the detailed advice, much appreciated. My biggest problem is available space. I have a rectangular brick built house that is 27 feet long, and this extends along a brick built garden wall that is a further 23 feet, giving me a straight run of 50 feet, but with 23 feet of that on a slope as I can't erect a pole at the end of the wall (covenants). The highest available point is under the eaves of the house at fractionally over 16 feet high. A random length dipole of 50 feet fed by twin lead (not ladder line - too visible) would be the easiest option, and possibly tuneable on some bands with a balanced output tuner. The reason for opting for a half-size G5RV is that I can just about squeeze it into the available length, the ladder line can run behind a plastic drainpipe, with a 1:1 balun I can reduce RFI issues, and it may tune better than a random 50 foot dipole. No room for a fan dipole, and it has to be stealthy(ish) because of covenants on what I can and can't erect.

    The alternative is a loft antenna, and with 27 feet to play with, I can just about squeeze a 20m dipole into the space if I let the last few feet of each arm drop vertically. But that precludes 40m, and certainly 80m. So not a lot of choice, really.

  12. #12

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    Quote Originally Posted by G4JJP View Post
    The reason for opting for a half-size G5RV is that I can just about squeeze it into the available length, ...
    The 51'/16.5' G5RVjr will work on 20m and parts of 10m without a tuner. A tuner is required on 40m. It does not work as is on 80m, 30m, 17m, 15m, or 12m. If you want 80m operation, you could try feeding it Marconi style by shorting the coax at the tuner output and using the single "wire" output to see if it will tune to a "match". But feeding it like that no doubt requires a good ground and results in RF-IN-THE-SHACK.

  13. #13

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    The old G5RV was one of my earlier antennas, bit limited, but when I introduced a length of 470 ohm twin feeder at the centre (centre fed zepp ?) it became a great antenna.. When one 'leg' went down , I now utilise is as an OCFD, with an S band, Z match, or T match , home brew coupler I still work 7 to 28 fairly good

  14. #14

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    I could tune both my 1/2 size G5RVs on 15m. A quick look through my logbook shows 5/9 reports in QSOs as far away from the UK as Haifa and Newfoundland. But my initial tests on the G5RV on 15m state 'no go' in the book. Tests a bit later were OK, but I can't tell you what I did. It may be that the auto ATU in my TS930S couldn't tune it but my external Daiwa CN419W could. It did also tune on 40m according to the log, but not 80. For 40 and 80 I used the ex CB 1/2 wave vertical that I'd shortened to be resonant on 10m. Tuner required, of course.

    When I (eventually) get my shack back from my son, a 1/2 size G5RV will probably go up again.
    Current radios: VHF/UHF: 2 x Baofeng 2/70 Handhelds. VHF: Kenwood TR9130 2m multimode. HF: Kenwood TS930S-AT
    Home antennas planned: G5RV / G7FEK / end fed wire. 1/2 wave vertical for 10m. 6 element beam for 2m. Vertical collinear for 2/70
    Website for the 'day job': www.andrew-gilbert.com

  15. #15

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    Quote Originally Posted by W5DXP View Post
    According to EZNEC, a 51 foot dipole at 35 feet fed with 16.5 feet of 300 ohm twinlead with a VF of 0.85, has a 15.9-j4.4 ohm impedance on 7.2 MHz looking into the twinlead with an SWR(50) of 3.2:1 on the connecting coax. It is 27.3-j21.2 ohms on 14.2 MHz with an SWR(50) of 2.3:1 and 110+j71.8 ohms on 28.4 MHz with an SWR(50) of 3.3:1

    Assuming 70 feet of Belden RG8x and using TLDetails, the coax loss on 40m is 0.328 dB with an efficiency of 92.7%. Coax loss on 20m is 0.296 dB with an efficiency of 93.4% and coax loss on 10m is 0.407 dB with an efficiency of 91.1%. Efficiency would be even higher using RG-213.

    A standard S-unit is 6 dB so the total coax loss on 40m is 5.5% of one S-unit. On 20m, it is 4.9% of one S-unit and on 10m, it is 6.8% of one S-unit. A rule-of-thumb is that the human ear can barely detect a 1 dB change so the losses in 70 feet of RG8x coax feeding a G5RVjr are undetectable by the human ear. Does one need a tuner for a G5RVjr? Of course he/she does, but a lot of built-in tuners can handle those SWRs and a wide-range external tuner will certainly match those impedances with small tuner losses.



    The G5RV is a balanced center-fed 102 foot dipole fed with ~33 feet of balanced tuned feeder. A good 1:1 choke balun at the coax to twinlead junction virtually eliminates common mode current on the coax. The 1:1 choke balun adds about four feet of coax loss which is negligible on the bands on which the G5RV performs well, i.e. on 80m, 40m, 20m, and 12m. It is a multi-band antenna but not an all-band antenna.

    It is neither a gift from the gods nor the work of the devil. It obeys all the laws of physics.
    I've beat this horse to death, don't really care if you want to listen.

    For the so called experts that claims that it is a universal do all antenna - I say Bull S. All you have to do is to do the math..
    I'm not on my personal computer, so I don't have my notes handy, but if you do the math, you will discover - yes it is semi resonant on 20 m, the rest of the bands - it is resonant - somewhere outside of the amateur radio bands, using an antenna tuner to move the resonance into the amateur radio bands is like trying to haul 10 gallons of gasoline, 10 miles, in a 12 oz wax covered paper cup. Even if you do get there, by the time you move all 10 gallons, you will only end up with 1 or 2 useable gallons of gasoline, the rest will either leak out, evaporate, or be spilled while you walk.

    The only way to compare two antennas is to put up both antennas on the same day - within 1 hour of each other and compare what you can hear at that site at that time.
    You will quickly discover that you will hear a heck of a lot more on a simple dipole than you ever will with a G5RV or RV jr.

    An educated person would put up separate dipole antennas, cut for the specific frequencies they desire to operate on and would never use an antenna tuner, especially if using a 1000 watt plus amplifier.
    Last edited by pmh; Tue 15th May 2018 at 18:37. Reason: Civility costs nothing!

  16. #16

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    Matching Problems - MFJ 949E User Manual

    Most matching problems occur when the antenna system presents an extremely high
    impedance to the tuner. When the antenna impedance is much lower than the feedline
    impedance, an odd quarter-wavelength feedline converts the low antenna impedance to a
    very high impedance at the tuner. A similar problem occurs if the antenna has an
    extremely high impedance and the transmission line is a multiple of a half-wavelength.
    The half-wavelength line repeats the very high antenna impedance at the tuner. Incorrect
    feedline and antenna lengths can make an antenna system very difficult or impossible to tune.
    This problem often occurs on 80 meters if an odd quarter-wave (60 to 70 foot) open wire
    line is used to feed a half-wave (100 to 140 foot) dipole. The odd quarter-wave line
    transforms the dipole's low impedance to over three thousand ohms at the tuner. This is
    because the mismatched feedline is an odd multiple of 1/4 wavelength long. The line
    inverts (or teeter-totters) the antenna impedance.
    A problem also occurs on 40 meters with this antenna example. The feedline is now a
    multiple of a half-wave (60 to 70 foot) and connects to a full-wave high impedance antenna
    (100 to 140 foot). The half-wave line repeats the high antenna impedance at the tuner. The
    antenna system looks like several thousand ohms at the tuner on 40 meters.

  17. #17

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    From EHam.net

    If our G5RV is really 104, 108 or 112 feet long instead of 102 feet long, we won't detect much of a difference on 75 or 80 meters but we will definitely see a large difference on the 10 meter band.

    The standard G5RV has trouble on 30, 17, and 10 meters. On other bands where this problem exists with the 30, 17 and 10 meter bands, arcing within the antenna tuner will happen, causing damage to the tuner.

    Years ago in 1940 and years before there was the Center Fed Zepp the same identical antenna as the G5RV and could vary the antenna length and the open wire line length as well. However no problem to the 30, 17 or the 10 meter bands occured because the tuning system was different than what is being used today. The tuning unit of years gone by consisted of a link coupling system whereby the coupling could be varied and also a series or parallel tuning arrangements could be accomplished.

    The input impedance to the G5RV antenna will vary from band to band, going from higher to lower and lower to higher impedances which the tuner cannot produce within a certain range of impedances or cannot take the high voltages developed. I will show written just what takes place with the G5RV antenna:

    At a antenna length of 102 feet and a feeder length of 34 to 38 feet on 3.5 Mhz will require "parallel" tuning. 7 and 14 Mhz will require "series" tuning. 28 Mhz will require to experiment with both series and parallel tuning. This, because of the antenna height above ground and ground reflections.

    I never could understand why the G5RV became so popular, it is after all just a piece of wire, and a feeder, and its a called a dipole, so what's special about that.?

    Since the original 102 ft long dipole, along came the half size model, completely useless, unless the radio conditions are right. Then someone in the States thought about selling double size G5RV at 204 ft.!
    Double size G5RV, I ask ya !

    Forget all about the G5RV, get yourself a piece of wire 33 feet long, solder it to the 102 ft. make yourself a 135 ft dipole, feed it with open wire feeder, 300, 450 or 600 ohm, a 4:1 balun and a good tuner and you will be able to transmit anywhere between 10 metres and 80 metres with an SWR as flat as ya momma's pancakes.

    Over the years, the G5RV has been thrusted into the limelight as the "magic bullet" of multiband, single 50 ohm feed antennas.

    In actuality, it is quite the opposite, probably because of shear convenience and desire.

    As AI4CB stated, the best thing you can do to solve your G5RV blues is to a) cut off the balun - which is being mis-used because the impedance it is driving is unknown, maybe with the exception of 20 meters for the 102 ft version - and b) the coax.

    What you are left with is a dipole (add 23 feet and it will be resonant on 75) fed with 450 ohm balanced line. Couple it to your rig with a good quality balanced tuner and you have a much more predictable system.

    I would also stay away from tuners that use 4:1 baluns to couple to balanced line. Again, this is a misapplication of the balun as it is meant to operate at its designed port impedances: 50 ohms resistive in and 200 ohms out. Since the SWR can vary widely on balanced feeders (which they can typically handle without being lossy, the major reason for using them), that means the impedance will vary as well, which is highly unlikely to be 200 ohms resistive. The balun is therefore not running under the conditions it was designed which can result in it's failure as well as lost efficiency - or less radiated power.

    Now if you say, "hey, it's easier to use the coax to get the feed into the shack", well, you're right, it is easier to route coax. But there are lots of ways to get 450 ohm line into the shack and it will be worth the extra effort.

    In terms of cost, an 80 meter dipole fed with 300 or 450 ohm line and a good quality balanced tuner is definitely cheaper than buying a G5RV.

    You get a better antenna without paying for the all the hype.....

    The G5RV was never intended to be an all band antenna.

    When Mr. Varney (G5RV) came up with the design, it was intended to be three 1/2 wavelengths on 20 meters and to exibit some modest gain on 20 meters. Now, if you want to use it on other bands, that's fine, but just understand that it was never intended to be an "all bander" to begin with.

    From calculations I find:

    3.5 Mhz 102 feet too short. Should be 133 feet.

    7.0 Mhz 102 feet too long and short. Should be 66 feet for half wave or 133 feet for two half waves fed in phase.

    10,1 Mhz 102 feet close to two half waves fed in phase. 92 feet would be a full wave or two half waves fed in phase.

    14.0 Mhz 102 feet is a long wire on 20 meters, should be for a extended double zepp 85.57 feet which will give a 3 db gain. at any height above ground.

    28 MHz: On this band, the antenna acts as a 3-wave, center-fed long wire.

    The pattern is similar to 21 or 24 MHZ, but with additional gain due to the colliner effect obtained by feeding two 3/2-wave antennas in phase. The load is high-Z, with low reactance.



    14.150 MHz, and the dimension of 102 ft is derived from the formula for long-wire antennas which is:" LENGTH (ft) = 492(n-.05)/f(MHz).

  18. #18

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    Quote Originally Posted by Sixmeters View Post
    You will quickly discover that you will hear a heck of a lot more on a simple dipole than you ever will with a G5RV or RV jr.
    Our modern receivers have a dynamic range in the ballpark of 100 dB so for your statement to be true, the "simple dipole" would have to be 100 dB better than a G5RV. W8JI ran some A/B comparisons on the air between a G5RV and a "simple dipole". The hams on the listening end preferred the simple dipole even when W8JI lied about which antenna he was using. If he told the listeners that the resonant dipole he was using was a G5RV, they gave it a bad report. If he told the listeners that the G5RV he was using was a resonant dipole, they gave him a good report. Sounds like that's what you would do.

    An educated person would put up separate dipole antennas, cut for the specific frequencies they desire to operate on and would never use an antenna tuner, ...
    I'm an educated person (an Electrical Engineer). I use a ZS6BKW antenna which is a close relative of a G5RV and I don't use a tuner. I've managed to get my SWR below 2:1 on all HF Bands without a tuner. Here's how.

    http://www.w5dxp.com/ZS6BKW80/ZS6BKW80.HTM

    Here's a photo of what happens when I switch that antenna from 40m to 20m on PSK31 without changing anything but the frequency.

    40m-20m.png
    Last edited by W5DXP; Wed 16th May 2018 at 03:02.

  19. #19

    Join Date
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    Quote Originally Posted by Sixmeters View Post
    I've beat this horse to death, don't really care if you want to listen.
    ................................................ snip ..............................................
    An educated person would put up separate dipole antennas, cut for the specific frequencies they desire to operate on and would never use an antenna tuner, especially if using a 1000 watt plus amplifier.
    With the continuous projected arrogance and attitude like this, I'm shocked you get anybody to pay attention to your otherwise occasionally pertinent information.

    You're right, I don't care to listen to condescension. This isn't the CB. Or the Sixmeters show.

    On ignore you go. Bye bye.

  20. #20

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    Sorry to see you go - dont' let the door hit ya where the good lord split ya..

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