The stumper here, however, is when he said a five-minute deluge from his garden
hose produces zero change. It’s only rain that changes it.
Would acidic rain be more conductive than tap water? But then, why wouldn’t the
rain affect the other?
Must be some difference between the antennas Gary can’t identify, hairline
cracks, or something, in an insulator.
73, kelly, ve4xt,
> On Apr 2, 2016, at 9:51 AM, Grant Saviers <grants2@pacbell.net> wrote:
>
> 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.
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________ TowerTalk mailing
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>>>
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