Dipole with Ladder Line and Tuner

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N1ETL, Dec 3, 2018.

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  1. N2EY

    N2EY Premium Subscriber QRZ Page

    No.

    G5RV started off with a 3/2 wave 20 meter antenna, because it gives a nice four-leaf-clover pattern, and would fit in the space available. He then noted that a particular combination of dipole length and open-wire line would present a "low" 72 ohm SWR on 80, 40, 20, 15 and 10.

    But it must be remembered that, in those days, "low SWR" meant "less than about 5 to 1", and "can be matched by a tube transmitter with a wide-range output network". To the hams of those times, it did NOT mean "less than 2 to 1" or anything close.

    Also, to G5RV, "80 meters" was 3.5 to 3.8 MHz and "40 meters" was 7.0 to 7.1 MHz.

    It should also be remembered that the G5RV came of age during Cycle 19.

    73 de Jim, N2EY
     
    W7UUU, W9AMM, AG5CK and 2 others like this.
  2. AG5CK

    AG5CK Ham Member QRZ Page

    I've never heard of that but will look it up.

    Thanks. I had read that somewhere before and have also read that he was shooting for a 20m antenna with gain. That's the interwebs for you.

    If Varney was running the ladder line straight to a transmitter with a link coupled final I think he had a very good idea. A 20m gain antenna is also a good idea but I don't agree with how it is used and advertised today.

    When I got on HF a few years ago and was trying to decide on an antenna I read the description of some premade g5rv antennas being sold online. Some manufacturers suggested using at least 70 to 80 feet of coax for the magic to happen.

    When it isn't installed under ideal conditions the feed point impedance changes and throws everything off. Throw in a long run of coax and you have a lot of loss.
     
  3. N2EY

    N2EY Premium Subscriber QRZ Page

    Why not go right to the source and ask the horse?

    http://forums.qrz.com/index.php?threads/should-i-use-a-balun-for-a-g5rv.631136/page-4#post-4832561

    has the original 1958 G5RV article by the man hisself. There's also a 1966 followup which is left as an exercise for the reader to find.

    Why? That's not what he did. See the article.

    A 3/2 wave dipole has a tiny bit of gain, but that's not what G5RV was after.

    70 feet of good coax won't have a lot of loss on most HF bands, though. But it will have some - and just a few dB of loss is enough to "improve the SWR" at the feed end. \

    In addition to earlier notes, it should be remembered that 60 years ago he didn't have access to antenna models, analyzers, nor high-precision test gear. The G5RV design is basically sound but, like many things, is based on a bunch of assumptions and compromises.

    Read the article and see what G5RV himself said and did.

    73 de jim, N2EY
     
    WN1MB likes this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I'd say it works fine for what it is, after all it's just a 102' doublet with a cleverly selected section of matching line that gives an OK (,but not necessarily great) match on several HF bands such that coax losses aren't too high back to the shack. But for those bands where you get a reasonable match it's a decent antenna but no better or worse than any other 102' doublet hung in the same place. Sure on the bands where you can't get a decent match to 50 ohms there are better choices including minor variations on the same theme like the ZS6BKW but for what it is, the antenna works.

    I'd also say the antenna gets a really bad rap for reasons that aren't great. Sure it doesn't cover 80-10m including all the WARC bands (which didn't exist when G5RV invented this antenna) with the less than 2:1 SWR that folks expect for their solid state rigs (which also didn't exist when he invented this). But in the end it's a 102' doublet and works as well as any other 102' piece of wire up in the same location once you match a signal into it. Seems some hams really hate this antenna and arguing that it doesn't cover ALL HF ham bands is a bit like saying a 20m halfwave dipole fed with coax sucks because the match isn't good on 17 meters. It does what it does and that aint half bad for a pretty simple antenna but for someone after a multi-band antenna that provides a great match into all HF bands there are better choices.

    But sure, like a lot of things there are folks over selling these antennas compared to what they actually do but that isn't the fault of the Louis Varney or the antenna he designed as much as folks stretching the truth to try to sell something.
     
    W2AAT and N2EY like this.
  5. N8AFT

    N8AFT Subscriber QRZ Page

    It doesn't get much better than a doublet, open wire fed, and a proper balanced line tuner.
    Run with 2 True Ladder Line antennas here.
    G5RV is OK but way over rated. Mystery Antenna? Wouldn't mess with one.
    Put up something with decades of performance history.
    The only thing you'll need to set correctly is the feed length.
    I run 6' of TV twin lead through the window to the tuner. Works FB QRO too.
     
  6. PA1ZP

    PA1ZP Ham Member QRZ Page

    Hi

    The G5RV is a good solid antenna but needs a tuner, now in the modern days of transistorized rigs (already 35-40 yrs hihi).
    I do agree with N8AFT use it as a doublet or make it a bit bigger and use it as a doublet.
    But if you place any dipole wrong to low or otherwise compromised it will not work very well, so also concentrate on the placement on the antenna.
    I like true ladderline and know its limitations, if you do and have the tuner to operate it, its a wonderfull way to feed an antenna.
    I think window line or 300 ohm TV line could be rather well, but that is very depending on the quality you buy , because I have seen a lot of junk beeing sold.

    The design of the G5RV is old, nothing wrong with old but as said in the time before antenna modelling etc.
    Problem with balanced antennas is the knowledge you need and the tuner you need.
    Here lots of hams still use "old fashioned balanced" fed dipoles, delta-loops, quads, extended dipoles even vertical zepps or normal zepps.

    But knowledge is getting less and less.
    For antenna tuners look at PA0FRI website.

    73 Jos
     
  7. K8JD

    K8JD Ham Member QRZ Page

    My Experience with A Non-Resonant Antenna

    I made a 20M EDZ antenna, it's two 5/8 wave wire segments in-line and center fed with (in my case) 450 Ohm balanced line. Since it's non resonant I had to use high Z feedline and a balanced line going to a tuner in the radio room. I used the MFJ 974 balanced line tuner, and that can match the 20 M EDZ antenna on other bands from 60M t0 17M pretty well !
    The mismatched Z from whatever band I am on passes thru the balanced line with little loss, and the strange variety of Z and X from the different bands is tuned to 50 Ohms in the tuner and the radio is happy.
     
  8. W5DXP

    W5DXP Ham Member QRZ Page

    The purpose of an antenna tuner is to cause the maximum amount of available RF current to flow through the radiation resistance that exists at the antenna. A properly adjusted antenna tuner causes a Z0-match to 50 ohms at its input. In a low loss system, the result of that Z0-match is a near conjugate match at the antenna feedpoint. If it weren't for tuner and feedline losses, achieving a Z0-match at the input of a tuner would guarantee a perfect conjugate match at the antenna feedpoint no matter what impedance mismatch exists at that point.
     
    WA9UAA likes this.

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