[OKDXA] The weak spot in my dipole

[Roger Simpson]

===========
John:

I had some erratic problems once with a beam. I tried all kinds of 
stuff. Finally, I did stuff which seemed to help but then the problem 
would come back. Finally, out of desperation, I cleaned up the 
connections, where the gamma match hooked up. I also replaced the balun, 
and put in new coax run between the xmitter and the beam. I don't really 
know which of these fixed the problem, but once I did all of this the 
problem with intermittent high SWR was solved. When you have 
intermittent problems you just have to change stuff until the problem 
goes away and stays away.

73     Roger   K5RKS
============

------ Original Message ------
From: "John Geiger" <af5cc2 at gmail.com>
To: "Oklahoma - DX news and information" <okdxa at mailman.qth.net>
Sent: 6/30/2016 2:22:38 PM
Subject: [OKDXA] The weak spot in my dipole

>  spot" in my dipole
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>« *on:* *Today* at 11:45:32 AM »
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>------------------------------
>I have a homebrew G5RV type dipole that I made around 18 years ago.
>Overall it has been a very good antenna for me and I have worked lots 
>of DX
>with it.  It is around 100 feet of copper wire, joined to a run of 
>300ohm
>Radio Shack twin lead, maybe 25 feet or so.  At the twin lead to coax
>junction I have a Unidilla 4:1 Voltage Balun, and then 20 feet of RG11
>75ohm coax.
>
>A couple of years ago I was using a MFJ 918 1:1 current balun, and on 
>some
>of the lower bands, I couldn't keep the antenna "tuned".  I am using a 
>MFJ
>941D tuner, and I would tune the antenna tuner on 40 or 80 for the 
>lowest
>SWR, and once I started transmitting the SWR would jump up to infinity, 
>so
>I would transmit a carrier, retune it, and once I transmitted again, 
>same
>problem, the SWR would jump up.  A few months ago I replace the MFJ 
>balun
>with the Unidilla 4:1 Voltage Balun because when I originally built the
>antenna, I had a Van Gordon 4:1 voltage balun, and it worked fine.
>
>Changing baluns seemed to fix it for a while, but now I am having the
>tuning problem again, but it happening on all bands, not just 40 and 
>80.
>Luckily I have a miniquad for the higher bands, but I tried the dipole 
>on
>20 and 17 today with the same losing tune problem.
>
>Before I go climbing around on the roof changing stuff out, does anyone
>have an idea of where to start-what might be causing this tuning 
>problem.
>Same thing as before, I would load up the dipole to a 1:1 SWR, using a 
>less
>than 100 watt carrier, but once I go and start transmitting at full 
>power
>the SWR quickly jumps way up.  I go retune it,which just requires a 
>slight
>adjustment, and the SWR jumps up again, and it just keeps doing this.  
>I
>don't think it is the MFJ tuner because it doesn't have this problem 
>with
>the miniquad, which also goes through the tuner.
>
>Also, the dipole shows a low SWR (2:1 or less) on 12 and 15 meters, and
>when I put the tuner in bypass mode I can transmit on the dipole with 
>no
>problems with losing its tuning.  On 80m the SWR is also low, and
>transmitting on bypass mode to the dipole usually works but once in a 
>while
>it will its tuning.  On 30m it will show a low SWR initially but once I
>start transmitting (in bypass again) the SWR quickly goes to infinity.  
>On
>40m when I tune the antenna and then transmit at 10 watts it seems to 
>stay
>tuned.  Going up to 25 watts detuned it again.
>
>So, any ideas or guesses as to where the problem in my system is?
>
>73 John AF5CC
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