Installing a G5RV

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB0NDS, Apr 2, 2011.

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  1. KB0NDS

    KB0NDS Ham Member QRZ Page

    Greetings all, I am going to install a MFJ-1778 (G5RV) wire antenna and have a question. If I install it as vertical I will have to run one of the legs between two of my towers guy wires (one above & one under). Can I do this without causing any problems. The two wires are about 10-12 feet apart. Thr other option is to use it as an inverted V. If I do this I won't be able to place the two wires straight across from one another. Can I go at a 45 or a little less (not quite a right angle) as long as I keep it in a V and keeping the ends less than 25 feet below the center as the instructions state? Thanks.
  2. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    From my experience and what has been written on multi band use of non resonant doublets such as the G5RV they do not perform very well on the higher bands installed as an inverted vee. It may work OK on 80 meters and somewhat on 40 meters if you keep the apex angle at least 90 but preferably very preferably 120 degrees or more. I doubt that it will have any really useful radiation patterns above 40 meters.

    A G5RV is a good antenna when installed properly.
  3. KB0NDS

    KB0NDS Ham Member QRZ Page

    Sorry I should have mentioned that this on the is 10-80 102' version.
  4. K5PO

    K5PO Ham Member QRZ Page

    I think you'll have much better luck in an inverted vee versus a vertical configuration.

    The concern with the vertical dipole is the feedline radiation. Are you going to be able to keep the feedline perpendicular to the dipole component as it moves away?
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    You would normally not want to install a G5RV or any other inverted vee from a tower that uses metallic guy wires; the interaction with the guys is guaranteed.

    I'd either change the guys to Phillystran, or make the G5RV a flattop with one end supported by the tower and the other end supported by something else 102' feet away.

    I use self-supporting towers (no guys) and this is one of the main reasons I go out of my way to do that: No interaction with wire antennas hanging from the towers.
  6. K1DNR

    K1DNR Ham Member QRZ Page

    Steve is right. There is really no practical advantage to mounting vertically unless you simply don't have the horizontal space. The interaction with the tower and guy wires will give you trouble.

    If I absolutely couldn't make it horizontal from the tower, I'd do the inverted V and try to replace the guy wires with non conductive Phillystran.

    As for the G5RV itself, any dipole that is significantly longer than a half wavelength develops peaks and nulls in the pattern. This has nothing to do with resonance, it is a function of the current distribution on the wire. A 15m signal on a 40m dipole has the same effect, and it is resonant. The patterns of G5RVs at various heights are all over the Internet. Better yet, download and install 4NEC2 or EZNEC (both free) and load one of the pre-made models. Antenna modeling software is like crack. Once start playing with it, you can't stop.

    A G5RV at 70 feet works as a good bi-directional antenna on 40 meters. It is ok on 80 but a little short. On 20 it has some "gain" over a half wave dipole in some directions, pattern like a clover leaf. As you go higher in frequency the pattern becomes more and more star-like with lots of peaks and nulls in different directions.

    (the assumption is that one is using a tuner of some kind...)
  7. KB0NDS

    KB0NDS Ham Member QRZ Page

    Thats the problem I am faced with. I may not be able to stay perpedicular with the ends. I do have an option of doing a V shape but at a bit of an angle vs straight line. The shape will still be in a V and I can attain the minumun angle of 120 degrees.
  8. K1DNR

    K1DNR Ham Member QRZ Page

    If you must make a compromise, go for symmetry. Try to make one side the mirror image of the other, including nearby masses, etc.
  9. KB0NDS

    KB0NDS Ham Member QRZ Page

    That would be no problem to do.
  10. W5DXP

    W5DXP Ham Member QRZ Page

    A vertical 102' G5RV is limited to 80m and 40m operation. The take-off-angle on 20m is too high to be very useful.
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