[OKDXA] Antenna issue really puzzling me

Sun Apr 21 10:25:00 EDT 2013

I do plan on replacing the coax run with another piece I have that is 
50ohms, and the balun with a 1:1 current balun.  Will also clean and resold 
the copper wire to twin lead connections.  That should take care of it.

73 John AF5CC

----- Original Message ----- 
From: "Kim Elmore" <cw_de_n5op at sbcglobal.net>
To: <okdxa at mailman.qth.net>
Sent: Sunday, April 21, 2013 1:09 PM
Subject: Re: [OKDXA] Antenna issue really puzzling me

> I'm with second what everyone else has confirmed. I've seen the same thing 
> and it's always either a corrosion issue or a connector. In one very 
> memorable case, it was due to a crack inside of a 90-deg coaxial fitting 
> (UG-646/U is the Amphenol number) for use with garden-variety PL-259 
> coaxial connectors.
>
> This one was NOT an Amphenol fitting, but instead a Rat Shack cheapie. 
> Inside was a threaded fitting that had cracked. That was the source of my 
> problem. It took days of tinkering to track it down and, even then, I 
> found it hard to believe because this particular one had been inside all 
> its life and never subjected to hard use. Along with everything else 
> that's been suggested (all excellent), I suggest you check any and all 
> coax fittings while you're rummaging about looking for the problem. Flex 
> them and move them around, even if they seem tight. You might get lucky 
> and find the problem right under your nose.
>
> 73,
>
> Kim N5OP
>
> On 4/20/2013 8:52 PM, John G. wrote:
>> Hi Bob,
>>
>> I have thougt of that and do plan on cleaning and redoing all of the 
>> connections, and replace the balun and feedline.  Would the oxidation 
>> make it affect some bands but not others?
>>
>> 73 John AF5CC
>>
>> ----- Original Message ----- From: "Robert Redmon" <k5sm.bob at gmail.com>
>> To: "Oklahoma - DX news and information" <okdxa at mailman.qth.net>
>> Sent: Sunday, April 21, 2013 12:27 AM
>> Subject: Re: [OKDXA] Antenna issue really puzzling me
>>
>>
>>> John,
>>>
>>> You have oxidation on some contact or connector between your rig and the 
>>> antenna. My remote antenna switch uses relays to switch between 
>>> antennas, and from time to time I have the same symptoms as you....and 
>>> the same temporary fix...just hit a dit or click the mic switch. That 
>>> tiny amount of rf is enough to blow through the microscopic layer of 
>>> oxidation and all will then be well until you let it set for a 
>>> while....and the oxidation returns. I clean the contacts in the switch 
>>> using brown paper as a mild abrasive, pulling it between the contacts. 
>>> This fix lasts for a few weeks (or months), but the problem always seems 
>>> to eventually return.
>>>
>>> Bob
>>> On 4/20/2013 6:24 PM, John wrote:
>>>> This is DX related in that it involves my antenna, which allows me to 
>>>> work
>>>> DX,
>>>> and you can reply to me off the list if you like also to keep the 
>>>> reflector
>>>> from
>>>> getting too far off topic. I am hoping I can rely on the collective 
>>>> wisdom
>>>> of
>>>> list members who know far more than I do about antennas and 
>>>> electronics.
>>>>
>>>> Here is my antenna system-105 feet or so of copper wire, attached to 
>>>> Radio
>>>> Shack
>>>> 300 ohm twinlead, about 20 feet or so of that. The twinlead runs to a 
>>>> 4:1
>>>> voltage balun, which transitions to RG-11 75ohm coax, which then runs 
>>>> to the
>>>> shack. I then use a MFJ949D manual antenna tuner.
>>>>
>>>> About a year ago I noticed the receive level in my Icom 706 was 
>>>> starting to
>>>> dropping down, first on 12m, and later on on some other bands, and 
>>>> coming
>>>> back
>>>> after you click the mic or key putting the rig into transmit. That 
>>>> first
>>>> suggested to me that it might be a relay problem, specifically on the 
>>>> low
>>>> pass
>>>> filter board since it wasn't happening on all bands. I did go through 
>>>> and
>>>> try
>>>> to test things in the antenna system after a friend say he had had a 
>>>> similar
>>>> problem once with a connector going bad in the feedline. I tested the 
>>>> coax
>>>> jumpers, low pass filter, tuner, and they all looked ok.
>>>>
>>>> One test I also made was to switch over to the 6m yagi and see keying 
>>>> the
>>>> rig
>>>> would bring the receive back, since it is on a different feedline from 
>>>> the
>>>> dipole I am running. It did, which is one reason I concluded it must be 
>>>> a
>>>> rig
>>>> problem. I now see that there probably was a little energy making it to 
>>>> the
>>>> dipoles feedline anyways, since both antennas were on an antenna switch 
>>>> in
>>>> the
>>>> tuner, and I know that isolation isn't perfect. I sold the rig as a 
>>>> fixer
>>>> upper
>>>> and got a good deal on a replacement. Well it has the same problem! 
>>>> Same
>>>> symptoms, same bands (different brand and model of rig) everything! 
>>>> Talk
>>>> about
>>>> frustrating!
>>>>
>>>> Tried hooking the 6m antenna straight up to the rig and didn't witness 
>>>> the
>>>> receive level dropping at all. That tells me it must be something in 
>>>> the
>>>> antenna system. Given this system, where is the problem likely to 
>>>> be-and
>>>> more
>>>> importantly, why would it occur on some bands and not others. It 
>>>> happened
>>>> mainly on 12m and 15m, and was starting to happen more on 17m and 30m. 
>>>> I
>>>> never
>>>> saw it occur on 10m or 20m, and only very rarely on 40m.
>>>>
>>>> Anyone have an idea as to what might be going on?
>>>>
>>>> 73 John AF5CC
>>>> ______________________________________________________________
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>>>
>>> -- 
>>> Robert Redmon K5SM
>>> AMA 58073
>>>
>>> ______________________________________________________________
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>>
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>
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