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Author Topic: G5RV - A FEW QUESTIONS ?????  (Read 411 times)
GM1ZVJ
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Posts: 152




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« on: July 22, 2002, 06:19:02 PM »

HI,
   Looking for some more kind help from anyone that can help !! have purchased a full size 80 -10 mtr g5rv antenna,its fitted with "30 feet 6" inches off 450 ohm ladder line feeder.have the antenna mounted with the centre at about 25 feet with both 51 feet sides sloping down to about 10 feet above the ground either side.the antenna is situated just outside the main operating shack which means there is more than enough off this feeder to reach the actual radio.what now ?? attatch a very small length off coaxial cable to the end off this feeder ?? say 1 or 2 feet in length ?? or take a longer run off coax from the radio to outside to the laderline feeder ??
Also as this ladderline is coming near to the actual tower is it neccesary to insulate this from the tower itself ?? with say some plastic tubing or is there anything else I could use ?? suggestions please ??

As always thanks to all who help with advice its always very much appreciatted.

                                 kind regards,
                                              john

                                       scotland
                                        - uk -  
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WB2WIK
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Posts: 20536




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« Reply #1 on: July 22, 2002, 06:32:55 PM »

This is a less than ideal installation to be sure.

The G5RV is intended to be installed at a height greater than 31 feet above ground, thus the entire length of ladder line should be vertically bisecting the doublet and all hanging in free space, for the antenna to work as intended.

It's also rather guaranteed to be detuned by the fact that you've installed it as an inverted vee with the ends so low.  As such, its normal 20 meter resonance is almost undoubtedly lost.

You do need to support the antenna and its ladder line away from conductive surfaces including towers.  Using a "standoff arm" made of PVC is a fine idea, and works well provided the tubing is strong enough.

If you have a tuner capable of directly attaching balanced line, I'd use no coax at all and simply attach the ladder line to the tuner.  But don't expect this particular G5RV to be resonant on 20m, as per the design, because it likely won't be.  It's too low, and the capacitive coupling to earth at the ends will likely lower its resonant frequency quite a bit.

I've never really gotten a G5RV to work properly until it's up about 40 feet above ground.  At lower heights, it's still an antenna, but doesn't work as G5RV intended, and results will vary with earth conductivity and proximity of surrounding objects.

WB2WIK/6
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KO6NG
Member

Posts: 2




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« Reply #2 on: July 29, 2002, 12:40:25 PM »

I use a similar G5RV extensively.  I found that until I got the bottom end of the ladder line up to about 15 feet or so, nothing worked very well.  This required that I hire a tree-climber to get up above 50 feet into my tallest trees to tie it off at each end. since then, I have been amazed at the DX performance.


Regards,

Steve, ko6ng
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