G5RV (JR) High SWR when wet

Discussion in 'General Technical Questions and Answers' started by 2E0RPS, Dec 27, 2009.

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  1. 2E0RPS

    2E0RPS Ham Member

    In common with many G5RV users i've noticed that the SWR on my half size (inverted V) goes high when wet by rain etc.

    My external ATU can still handle it however the fwd RF power is much lower.

    As far i understood this is happening due to the feeder ladder arrangement typical of the G5RV.

    What would be the best solution or modification to minimize this issue? (if any)

    many thanks in advance

    73 de Rod / 2E0RPS
     
  2. AG3Y

    AG3Y Ham Member

    Move to the desert, or put up a coax fed antenna !

    Not being smart, just stating an answer !

    Ladder line is going to have losses when wet, and really cannot be avoided. I have spoken out against G5RV style antennas for a good while, since they are a compromise, at best, and a terrible compromise at worst!

    You would be far better off with antennas tuned for each band of interest, or at least a "Fan dipole" arrangement being fed with coax, if you are in a very wet and humid situation.

    Just my 2c worth ! 73, and good luck. Jim
     
  3. K7SGJ

    K7SGJ Ham Member

    NOT TRUE

    It rained here about three years ago.
     
  4. AG3Y

    AG3Y Ham Member

    We had about 18 inches of snow on the ground a couple of days ago. Got above freezing, the rain came ( thank Goodness, not ICE ! ) and almost all the snow is gone !

    I'm sure my Johnson Matchbox could handle the difference in impedance, but I haven't had the radio on for the past three days. Too much family activity with Christmas, and all.

    "White Christmas" is a thing of the past, and so is most of the snow, for that matter!

    73, Jim
     
  5. 2E0RPS

    2E0RPS Ham Member

    QSL and many thanks for support .. all understood
     
  6. G0GQK

    G0GQK Ham Member

    Some wire antenna's go out of tune in wet and damp weather, others don't. A half size G5RV can be "tuned" on other bands with a good ATU, but its so short, and its not always the feeder which causes the problems.
    Some vertical antenna's are like this, I have two, one is badly affected by wet conditions, the other one isn't.

    G0GQK
     
  7. 2E0RPS

    2E0RPS Ham Member

    QSL,

    i wonder if Hams using doublets are experiencing similar SWR issues on wet condition?
     
  8. AC0FP

    AC0FP Ham Member

    That sounds normal here for both of my doublets. However, just a minor adjustment of one of the capacitive tuning elements usually corrects the readings and the output power returns to where it normally measures.

    Of course right now when we have a larger amount of snow than normal (highest in at least 20 years), one of the window lines is behaving poorly because it is under a "snow bank" where it enters the house! :eek:

    73,

    fp :)
     
  9. G8ADD

    G8ADD Ham Member

    Yes, its normal, and due to water sitting on the ladder line. One way to reduce the effect is to replace the ladder line with old-fashioned open wire feeder, you can make this up using spacers purchased from Waters and Stanton.

    73

    Brian G8ADD
     
  10. KC9AXZ

    KC9AXZ Ham Member

    I propose you put up two antennas. Tune one for dry weather and the other for rain. Problem solved. :D
     
  11. W5ALT

    W5ALT Ham Member

    I use a doublet about 100 ft long, center fed with ladder line that goes to a tuner. I live in Houston, so we generally have plenty of rain. I don't notice much change in SWR or performance, but then I tweak the tuner when changing bands, so maybe there is a small effect I haven't noticed.

    73,
    Walt, W5ALT
     
  12. 2E0RPS

    2E0RPS Ham Member

    QSL and many thanks for all the replies,

    I can spot the change in SWR simply because I use an Automatic AMU.
    This unit memorize the impedanc of specific frequencies so basically when you return to that freq. it will take a split second to find a match, this obviously doesn’t happen when the antenna is wet meaning that the SWR has changed.





     
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