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Author Topic: G5RV; Can It Be Shortened?  (Read 1217 times)
K3ZL
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Posts: 139




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« on: December 09, 2009, 10:53:07 AM »

I have a g5rv jr (40-10 mtrs) that about 1.5 inches has been cut off each end.  What effect will this have on the antenna's performance on the jf bands, 40-10?  Also, will this antenna work on the WARC bands?
tnx
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KI6LXT
Member

Posts: 13




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« Reply #1 on: December 09, 2009, 11:04:35 AM »

In my experience the precise length of a G5RV is not critical. You will never notice the loss of 3 inches although I would not shorten it by more than a foot or so. I have used my G5RV from 160 to 10 meters with success including the WARC bands.
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VK1OD
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Posts: 1697




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« Reply #2 on: December 09, 2009, 11:29:42 AM »

It is widely held that a G5RV is not dimensionally critical, and that it is very tolerant of the installation environment.

This might account for the perception that G5RV is a poor performance antenna. I remember hearing a couple of OM in QSO, one saying to the other "There are a lot of G5RVs in use these days" and the rapid retort "Hmmm, probably accounts for the weak signals".

I don't think that the G5RV is installation independent, especially on the lower bands. I wrote an article on optimising the G5RV at http://www.vk1od.net/antenna/G5RV/optimising.htm .

Whilst I have not done the same analysis on the G5RV junior, experience tells me that the issues that exist for the G5RV on 80m pretty much exist for the G5RV Jr on 40m.

At this point, many users would rush to propose otherwise, that they have the QSLs to prove it. Unfortunately, QSLs do not prove that an antenna is working as well as it should, citing them proves the person is too easily convinced by weak evidence.

Owen
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WB6BYU
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Posts: 13569




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« Reply #3 on: December 09, 2009, 12:44:30 PM »

Owen VK1OD has a lot of good information about the G5RV
and the losses over frequency on his site, and I suggest
you start here:

http://vk1od.net/antenna/G5RV/index.htm

and double the plotted frequencies, which will give you an
idea of the performance of the G5RV Jr., even if it isn't
exact.  (So, for example, the losses plotted for 10.6 MHz
on VK1OD's graph would apply to 21.2 MHz on the Junior.)

Generally a difference of a couple inches won't make a big
difference, but if you are worried about it and don't want to
go through the optimization method that he described, just
tie up the antenna as it is and splice on a couple extra inches
of wire to the ends, letting them hang downwards.  That will
restore the original length and it should work as well as it
did before.

While the basic radiator of the G5RV can be used on all
bands from 40 through 10m, the specific twinlead length
will give a low SWR only at a few frequencies in that range.
The most common problem with the G5RV is losses in the
coax due to the high SWR, as the plots in Owen's article
show.  If you have a very short length of low-loss cable,
or if you can tolerate higher losses in the feedline, you
can use the antenna on more bands.
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W5DXP
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Posts: 3639


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« Reply #4 on: December 09, 2009, 01:10:05 PM »

The G5RVjr's design frequency is somewhere in the 10m band, where the 51' dipole length is 1.5WL. Chopping off 3 inches will slightly raise the 10m resonant frequency. The G5RVjr will work relatively well on 40m, 20m, 10m, and 6m.

The G5RVjr will not work on the WARC bands without a matching network at the coax/twinlead junction.
--
73, Cecil, w5dxp.com
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K3ZL
Member

Posts: 139




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« Reply #5 on: December 09, 2009, 06:00:28 PM »

Thanks to all.  I will follow the links provided and get up to speed on this antenna.  
I am also considering putting up a Horizontal Loop antenna instead of the g5rv. Any thoughts aappreciated.
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WB9JOX
Member

Posts: 103




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« Reply #6 on: December 26, 2009, 02:35:31 PM »

I read your question regarding Q5RV. Im late , but you never cut wire off just fold it back and tape it.That way if things dont work out you can go back to old measurement. 73
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