The Truth About the G5RV antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W0BTU, Apr 7, 2011.

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  1. W0BTU

    W0BTU Subscriber QRZ Page

    Although the G5RV is often promoted as an antenna that works well on all bands from 80 through 10 meters, that is absolutely NOT the case.

    To make a long story short: There are some bands where the SWR on the coax is out of sight and the feedline losses are astronomical.

    There is a better design, which involves shortening the antenna and lengthening the section of ladder line. G0GSF came up with a similar design that is a significant improvement over the G5RV.

    Even that design still doesn't cover all the HF bands, but it's certainly a worthwhile improvement.

    Before you buy or build that G5RV, do yourself a favor and Google ZS6BKW|G0GSF.

    This is not to say that the G5RV doesn't work well on SOME bands. But it does NOT work well on ALL HF bands. That's my point.

    http://www.karinya.net/g3txq/g5rv/ See the note at the end
    http://www.nonstopsystems.com/radio/G5RV-1.pdf See Part 3 at the end!
    http://www.nonstopsystems.com/radio/ZS6BKW.pdf
    http://www.nonstopsystems.com/radio/ZS6BKW-2.pdf
    http://www.nonstopsystems.com/radio/ZS6BKW-3.pdf
    http://www.w8ji.com/g5rv_facts.htm It works great on 75 meters!
     
    Last edited: Apr 7, 2011
  2. G3TXQ

    G3TXQ Ham Member QRZ Page

    Mike,

    What you say is certainly true of one implementation of the G5RV. But we should remember that Varney also recommended using open-wire feeder "from the centre of the aerial right back to the transmitter output or atu."

    With the assistance of computer modelling, Brian Austin (ZS6BKW) certainly came up with a superior design - superior in the sense that it covers more bands at low VSWR. The biggest "grumble" I hear about his design is that it doesn't cover 80m, which is disappointing for a dipole that is only 11ft shorter than the G5RV.

    73,
    Steve G3TXQ
     
  3. W0BTU

    W0BTU Subscriber QRZ Page

    Ah, yes! That's what I've always used. But I think that when people think of the G5RV, that's not what they think of. Do you?
     
  4. G3TXQ

    G3TXQ Ham Member QRZ Page

    I don't know - I've given up trying to guess what folk mean when they say: "G5RV", or "G5", or just "I'm running a G" ;)

    73,
    Steve G3TXQ
     
  5. W5DXP

    W5DXP Ham Member QRZ Page

    I worked out a modification (on paper) to the 90'/40' ZS6BKW that allows a SPDT relay to be used to obtain operation on 80m. Using 40' of 450 ohm ladder-line, EZNEC sez the impedance at the ladder-line/coax junction is 12+j109 ohms at 3.8 MHz. For that value of impedance, in the following diagram, C1=1487 pf and C2 = 481 pf for a near-perfect 50 ohm match at 3.8 MHz. Obviously, that impedance will vary from system to system and therefore so will the actual values of C1 and C2 - so this is just a conceptual idea for which I have not calculated the SWR bandwidth.

    Incidentally, this modification will also work for a G5RV to give a perfect 50 ohm match on 75m - only the values of C1 and C2 change and C2 may not be necessary. There is a way to use the coax to deliver the DC relay coil voltage to the relay.
     

    Attached Files:

    Last edited: Apr 7, 2011
  6. N4MXZ

    N4MXZ Ham Member QRZ Page

    A Born of necessity and time constraints (one weekend) 'hack' antenna.
    in 1992 I came up with my own implementation of the G5RV in order to solve space problems at my beach house for 160m. Basically it's 3/8 wave (linear loaded shortened dipole) at the lowest operating frequency (about 190' on 1850), with 1/8 wave 450 ohm ladder line. I found that the impedance on 160 was approx 25 ohms, depending on height and apex angle, if any (your installation may vary). I had a W2FMI 2:1 unun/balun combo sitting around, so I opened it up and reversed the unun. This configuration works quite well on 160m and 75m with no tuner, although 2:1 bandwith is <60khz on 160 and <150khz or75m.
    I also use it very successfully on 40m with a tuner.
    As a 3/4 wave dipole on 75 it is quite potent.
    Even on 160, It works well enough that, I use one at home off season as my 160 horizontal. I get nationwide coverage, with some DX (obviously no match for my vertical on DX).
    W2CYA named it the N4MXZ Zapper, and you may still find some write ups on the internet about it.

    At the beach it is set up as a "corner" horizontal vee with the apex about 100 degrees, and a height of about 30' (radio shack poles in the sand)
    Here at home it is horizontal at about 60' in height.
    In the mid 90s I had 3 of these up in a triangle at about 70'. Even at this height there was a substantial amout of bi-directional directivity on 75m . It was a terrific array.

    Cecil, a shortened version of this 3/8 over 1/8 configuation works on 75/40.
    There are bands above 7MHZ?[​IMG]
     
    Last edited: Apr 7, 2011
  7. G3TXQ

    G3TXQ Ham Member QRZ Page

    Cecil,

    Building that network into my EZNEC model of the ZS6BKW produces a 2:1 VSWR(50) bandwidth of 50kHz, a 3:1 bandwidth of 88kHz, and a 4:1 bandwidth of 116kHz.

    73,
    Steve G3TXQ
     
  8. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    The truth is, any antenna you erect will have some drawback(s). Whether you're willing to put up with the drawback(s) is the real question. The old adage about any antenna is better than no antenna is also correct. However, some very popular designs have major drawbacks, as these pages attest to. What is more amazing to me, at least, is the yardsticks used to measure antennas (number of DX contacts, input SWR, etc.), and the over reliance on antenna modeling software; After all, they are only as good as the data they're fed.
     
  9. N4MXZ

    N4MXZ Ham Member QRZ Page

    Although "linear loaded" may not be quite accurate :rolleyes:
     
  10. W5DXP

    W5DXP Ham Member QRZ Page

    That's what 33' rotatable dipoles are for.:)
     
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