[NLRS] loop yagi driven element corrosion

[Dr. Gerald N. Johnson]

In VHF Communications for 1/1978 an article on loop yagies suggested the 
driven element and feed along with the screws be coated with 
polyurethane lacquer and when it dried, the entire antenna be coated 
with ordinary lacquer. Somewhere I have a vintage RSGB microwave 
publication with a chapter on loop yagis, but I haven't turned it up in 
my first search this evening.

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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