[NLRS] loop yagi driven element corrosion

[Dr. Gerald N. Johnson]

I just looked at my 1296 Spectrum International looper that I've had 
since some time in the 70's. It was in the air for a couple decades. The 
driven element and rigid coax is gray now. I don't remember if they were 
coated after assembly, there's a slight chance I have the assembly 
instructions in a file cabinet somewhere.

73, Jerry, K0CQ

On 9/14/2016 9:40 PM, Chris Elmquist wrote:
>
>
> Hi Guys, thanks for the input.  The elements appeared all the same when the antennas went up roughly 8 yrs ago or so.  They have turned this dark color over time so it is some sort of aging process.  Could be a coating that is discoloring and maybe the DE and the feed line were all sprayed with the same stuff and so a call to the maker makes good sense.  The DE being brass has been mentioned before too so maybe mother nature is just doing her thing on it.
>
> Big pain to take these babies down though so I will plan carefully.
>
> Thanks again.  73, Chris N0JCF
>
>
> On September 14, 2016 9:26:24 PM CDT, "Dr. Gerald N. Johnson"<geraldj at netins.net>  wrote:
>>
>>
>> If not copper the driven element is sure to ba a copper alloy since
>> soldering to aluminum is difficult. The rigid coax is sure to be copper
>>
>> or tin or silver plated copper. What the feed and driven element needs
>> is a cleaning to bare metal and a coat of clear Krylon or Rustoleum to
>> protect them from corrosion. There is a chance that the black is some
>> sort of protective coating. I wouldn't prefer a black coating because
>> most black pigments are based on carbon that is a poor conductor. I
>> prefer clear to be an insdulator.
>>
>> 73, Jerry, K0CQ
>>
>> On 9/14/2016 8:56 PM, Chris Elmquist wrote:
>>>
>>>
>>> I've mentioned this to a couple guys and am kind of perplexed about
>> this
>>> issue...
>>>
>>> I have two DEMI / Directive Systems loop yagis on my tower at about
>> the
>>> 35' point.  One is 33 elements on 902 and the other 45 on 1296.
>>>
>>> While doing some work on other antennas on the tower, I noticed that
>>> the driven elements on both of these yagis are extremely discolored
>>> (ie, black).  All the other elements on both yagis are nice and shiny
>>> aluminum color.
>>>
>>> The little rigid coax that comes down to meet the N feedpoint
>> connector
>>> from the driven element is also black on both yagis.
>>>
>>> The yagis a fed with a length of Superflex that goes down the boom to
>>> the mast, down the mast a few feet forming a rotor loop, and then
>>> meet a run of 7/8" Heliax (air line under positive pressure).
>>>
>>> These antennas seem to still work as well as when they were put up
>> but
>>> I'm concerned about the discoloration since it suggests some kind of
>>> dissimilar metal action or some other kind of active attack against
>> the
>>> metals--  but I'm not sure where or how that would be happening.
>>>
>>> And no, I'm not running 1 KW+ on these bands :-)  30W on 902 and 60W
>>> on 1296.
>>>
>>> Tower is aluminum and all these feedlines are copper of course but
>>> all jackets are still intact and no copper is meeting the aluminum.
>>> Everything's taped and sealed really well and so I'm having a hard
>> time
>>> explaining what process would cause the entire element to turn black
>>> with no similar situation occuring on the other elements, boom or
>> other
>>> non-loop yagis on the tower.
>>>
>>> Any ideas?
>>>
>>> Chris
>>
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