[NLRS] loop yagi driven element corrosion

[Dr. Gerald N. Johnson]

Some European authors about antennas have advocated covering the entire 
antenna with an epoxy paint for weather protection. There is a chance 
the dielectric of the coating could change the antenna performance by 
adding losses and changing the resonant frequencies of the elements.

In constructing the looper it would be nicest of the directors could be 
cut from extruded tubing to have no joints, but that would be difficult 
to get the right dimensions without starting with heavy wall tubing and 
a metal lathe and converting most of the aluminum to scrap shavings. I 
would  stick with the single end holes on the director (and reflector) 
loops but would put a drop of Alnox electricians aluminum wire 
connection grease (filled with zinc crystals that break through aluminum 
oxide to get to the bare metal) and I'd put a nut against the loop to 
squeeze that grease tightly not depending on the stiffness of the boom 
for that contact pressure. I'd be temped to insert a stainless steel 
internal or external shake proof lock washer too that will bite through 
the aluminum oxide that is always present. I've run aluminum jacketed 
CATV coax for decades outside with Alnox at my home made connector 
adapters covered with Scotch #33 or 88 and not detected any changes.

I'm sure the latest International Microwave Handbook has several pages 
on building loopers which should include the knowledge of old timers. It 
suggests making welded directors of stainless steel welding wire, same 
for the driven element using acid core solder to get the ends tinned. 
Then coating the driven element, solder connections, and screws with 
polyurethane varnish, and finally paint the entire antenna. Mostly on 
page 57 in the antenna chapter. The paint type isn't specified.

I have a direction systems looper in the basement but would rather not 
open the packaging to read their instructions.

73, Jerry, K0CQ


On 9/15/2016 8:33 AM, Chris Elmquist wrote:
>
>
> OK. Thanks again guys.  I have received a couple other replies that suggest
> this discoloration is happening elsewhere too and so that is a data point
> I was looking for.   That's the good news/bad news piece that says it's
> probably not some dissimilar metal action or magical mystery currents
> eating away my loopers and just the elements doing their thing on the
> elements ;-)
>
> Am making plans to overhaul the whole setup here next year so will just
> leave them alone until then and hope that Santa brings me a new tower
> this Christmas and then I can clean them up and move them a lot higher
> in the air where they really belong.
>
> 73, Chris N0JCF
>
> On Thursday (09/15/2016 at 06:34AM -0500), Ray Johnson wrote:
>>
>>
>> Hi All
>>
>> In a later RSGB publication, Radcom I think, it was suggested that
>> the original design was not the best for long term reliability.
>>
>> The claim was that the bottom of the loop is a high current point
>> and having an overlapping  joint there is bad for the long term.
>>
>> The revised design would rotate the overlap point by 90 degrees and
>> require 2 fasteners for each element: A long fastener to hold the
>> element to the mast and then a short fastener to handle the overlap
>> point. The claim is that this improves the reliability.
>>
>> I am sorry I don't exactly remember where I read this.  A friend
>> gave me some 20+ years of Radcom back issues and it would take a
>> while to find that article
>>
>> Worth the extra effort when you build a looper ?..........I will
>> leave that discussion to the pontification crowd......
>>
>> rayj  WB0EBG
>>
>>
>> On 9/14/2016 11:19 PM, Dr. Gerald N. Johnson wrote:
>>>
>>>
>>> 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:
>>>
>>
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