G5rv configuration and performance problem

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0BXN, Mar 9, 2018.

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  1. WA7ARK

    WA7ARK Ham Member QRZ Page

    ...but the arc will only form if the PL259 is disconnected from the radio. Any ham rig I have ever owned always has either zero Ohms or less than a few hundred Ohms internally across its antenna connector, which bleeds off the static. With the PL259 disconnected, the charge between the center conductor and the shield of the coax builds to the point where the air gap breaks down, and a little arc forms to discharge it.

    btw- this is why I always discharge an open coax by shorting across the fitting before connecting my expensive antenna analyzer.
     
  2. WA3QGD

    WA3QGD Ham Member QRZ Page

    Dont believe? try placing a meter across the pl259 on a day when large white cumulous clods are serenely drifting by,and observe voltage gradients from a few millivolts to several hundred as those Harmless clouds go drifting by,Experience is what one gets after passing the test.or for fun try a neon bulb and watch as the charge density builds up and one or the other electrode starts to glow then a sudden discharge.
     
  3. K8JD

    K8JD Ham Member QRZ Page

    Static Stopper
    If I lived in a dry windy area I would add a 100K 2W resistor across all my dipoles, at the point where the feedline attaches to the antenna wire !
    This would cure all static buildup.
    Here it is humid enough to stop any static buildup most of the year !
     
  4. AB8MA

    AB8MA Premium Subscriber QRZ Page

    Forget that G5RV and use the Yagi on your backyard tower instead?

    From your QRZ lookup:

    upload_2018-3-9_12-27-25.png
     
    KE0BXN likes this.
  5. KE0BXN

    KE0BXN Ham Member QRZ Page

    I have a force 12 c4 that should have been up last year, but finding help to put it up is easier said than done :(
     
  6. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    A proper G5RV, in good shape, should exhibit a very high SWR on 15m, certainly much greater than 4.5:1!

    As hinted at by Roger, we need to know if this is a "true" G5RV - 102' of flat-top fed with about 32' of balanced line - or a home-made G5RV "clone" with a more or less random length of 300 ohm teevee line.

    This is because a "true" G5RV produces a very reliable SWR curve, which should show SWRs similar to these:

    [​IMG]

    In other words, on 15m the SWR should vary from about 10:1 to almost 50:1 (which is too high for many of us to measure reliably), across the band. If your SWRs are in line with the above, your antenna is probably ok. If not, you may have a problem, perhaps in the balun.

    A possibility is that the arcing you saw was accompanied by arcing you did not see inside the balun unit.

    Of course, if yours is not a "true" G5RV, the impedances looking into the balanced line section might not match those given above.

    Finally, two quick notes:

    (1) If you want to use SWR readings to troubleshoot problems such as this, take a number of readings across each band, and draw an SWR curve.

    (2) Generalized statements such as "I am getting mostly 3.5:1 or less on most bands with the exception of 40 and 15 where I am ~4.5:1" don't really tell anybody much of anything. Please give actually observed readings for specific bands.
     
    Last edited: Mar 9, 2018
  7. W1VT

    W1VT Ham Member QRZ Page

    The solar flux numbers have been very low, which means that 80M is more of a DX band in the evenings than a ragchew band. This is great if you have a vertical that works well, but not so good if you are using a typical G5RV at a modest height.

    Zak W1VT
     
  8. W5DXP

    W5DXP Ham Member QRZ Page

    Don't know about any other rig, but it didn't seem to hurt my IC-745.
     
  9. KE0BXN

    KE0BXN Ham Member QRZ Page

    I will reply tonight with the specifics for the bands from the analyzer.
     
  10. KE0BXN

    KE0BXN Ham Member QRZ Page

    Good thing my rig was unplugged at the time. I think I do have videos somewhere.
     

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