An update to my post on rain and connections for those that might be
interested...
I’ve had beams since 1978... I was off the air from 1990 through 2005 and when
I returned it was in Arizona where rain is rare and when it comes, generally
during the summer monsoon, EVERYTHING is disconnected. I don’t remember seeing
the sort of effects I’ve seen with both the 15 and the 20 yagis here. And that
I remember no one in their replies said “that’s normal” ... except one private
email I received from an antenna manufacturer that asked to be unnamed...
he said indeed it IS normal and it is caused by the dielectric change with the
rain acting as a covering (impartial and uneven thickness) and thus changes the
tubings velocity factor and in essence lowers the antenna resonant frequency.
That is what I saw on the 15 – not what I saw, or at least I wasn’t able to
confirm it since my rig (and my license) won’t allow operation lower than 14.0
which is where I saw the SWR’s worse change on the 20... I found it difficult
to believe ...
so ... now I have the 20 on the test tower and the 15, now with a run of new
coax (common suggestion – replace the coax, even though coax can’t change
properties off and on in a matter of a few hours) on saw horses... it rained
last night and BOTH antennas indeed saw the same increase in SWR high in the
band. And both after a number of hours (about 5 again) returned to normal.
So it rained again a little while ago and the 15 went up again ... so this time
I went out and I dried all the elements with a towel. Before drying it I
noticed that all of the elements had water beading along their bottom along the
whole element length. Didn’t do a great deal – just ran a towel over the
elements. And lo-n-behold the SWR returned to normal! This over a matter of 4
minutes from the test showing it was high to the test showing it was back to
‘normal’ after I had dried the elements.
So ... that to me is proof positive it is normal. I’m not sure why I don’t
remember seeing it before – or why no one else mentioned it (many comments with
many yagis/antennas) ... but now I know definitively that there is a direct
relationship between water on the elements and high(er) SWR. [note – the SWR
shifts downward so indeed it might lower the SWR on the low end of the band
thus in that case being beneficial]
Thanks again to all that replied. (And my apologies for doubting! )
Gary
K9RX
From: StellarCAT
Sent: Saturday, April 2, 2016 5:03 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] frustrating rain and connections... also Noalox?
Thanks for the comments – it is a hairpin design. It is an M2 6 element 15 that
was built using their 15M6-125 antenna and converted to their 15M6DX ... so I
refer to it now as a 15M6DX-125. Anyway it has a fiberglass center insulator
with thick donuts to ensure there isn’t any creepage along the fiberglass...
and if it were anything related to that it should have done it when I hosed it
down (lowered to 8’)... I couldn’t really get it to change with a hose.
Its off the tower now – had to move on (take advantage of clear days) to
testing the 20M5LGS made from a 20M5 ... its now on the tower at 8’ up with
high winds so its not going up any higher until the hills are calm.
I’ll continue to test the 15 on saw horses. What I was seeing I’m sure will
show even at that height. And once again: whatever design wise might be
suggested it has to be remembered this is a near exact duplicate of another one
that didn’t have this problem. So I’d guess it has to be either related to
construction or possibly a deficiency caused by being used. The latter
shouldn’t be a problem – I’ve dealt with used antennas before and never had a
problem... but it could be. Please write direct if you have any other thoughts
that come to mind.
Gary
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