[OKDXA] Antenna issue really puzzling me

Sun Apr 21 08:24:48 EDT 2013

John,

No, I can't think of a scenario where this might be band specific. If 
your anomaly is band specific, consider whatever band switching that you 
might be doing, e.g. capacitance switched into the tuner circuit for 
some bands but not others. Also, I think the 706 uses diode switching, 
but some rigs use small mechanical relays for band switching (low pass 
filter switching).

Bob
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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-- 
Robert Redmon K5SM
AMA 58073