[TowerTalk] frustrating rain and connections... also Noalox?

[Grant Saviers]

I'd bet with Joe, maybe the DE insulator is cracked or holding water.   
One "used" antenna I own had ABS pipe as the insulator. ABS pipe is foam 
core can hold water and worse has a lot of creep with age so the U-bolts 
loosen.  I replaced the ABS with custom UV resistant nylon split clamps.

Grant KZ1W

On 4/2/2016 6:14 AM, Joe Subich, W4TV wrote:
>
> How is the driven element constructed/insulated and matched?
>
> The downward shift indicates increased capacitance across the feed
> point when the antenna is wet.  Look for moisture to be trapped in
> the DE insulator ... for example, if you are using split PVC is the
> split *UP* in one antenna and *DOWN* in the other?  If you have a
> rod of some kind in the element to stabilize the feedpoint is it
> completely sealed to moisture?  Are the balun feed points completely
> sealed?  If there is a support for the beta match (if one exists)
> is it designed so it will not absorb water/allow water to stand on
> it?  If there is a coil across the feed point, does the construction
> allow water to accumulate on supports, etc.?  If the antenna is an
> OWA design, check the insulator of the *FIRST DIRECTOR* as well as
> that element has a significant impact on antenna tuning.
>
> It only takes a very few picofarad change in shunt capacitance to
> move the "resonant point" quite a bit.
>
> 73,
>
>     ... Joe, W4TV
>
>
> On 4/2/2016 8:21 AM, StellarCAT wrote:
>> I’m testing a yagi... I can raise it to ~37’ for testing and lower it
>> to about 8’ for adjustment ... it was made as a duplicate to another
>> one and testing showed it to be just that – a duplicate. Until it
>> rained! The SWR shifted downward. At 21425 it was ~1.35:1 ... and it
>> would go over 2:1. I’m at a loss as to what is causing this. It is a
>> used antenna reassembled... but I find it very difficult to believe
>> that water could get in to the mechanical joints and cause this kind
>> of a problem. The balun doesn’t appear to be taking on water – there
>> wasn’t a drain hole in the bottom – there is now – I went out early
>> this morning just after it rained – SWR up high – and there was
>> nothing coming out of the drain hole. I have checked all connections
>> – they’re tight. Oh – and the strange thing – it goes back to normal
>> after only about 4 – 5 hours without rain. It has done this 3 times
>> now. It is now – 45 minutes after checking it this morning where it
>> was at 2.33:1, its now down to 1.8:1 and continuing its decent. And
>> further note the SWR seems to be about the same – its just shifted
>> downward when wet. Also I hosed it down – the balun/coax connection,
>> hairpin for a good 5 minutes – no change. I hosed down the elements
>> at their joints – no change. It rains: changes! The fact that it
>> shifts seems to be independent of height – it does this if at 37’ or
>> at 8’.
>>
>> Also: is Noalox the same as penatrox? It is the No AL OX sold by HD
>> ... it says it is for increased conductivity as well as anti-seize...
>> perhaps IT is the problem at the joints ... unless someone knows it
>> to be fine (or KNOWS it to be bad).
>>
>> thanks – I’m hoping someone has personally seen such a thing and has
>> an idea. Its holding up the testing of the other antennas.
>>
>> Gary
>>
>> ps: the first one had no problems when it was rained on.
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