Remote control leaf blower to blow the water off the elements.
or
Remote control small semicircular squeegee.
or
Eccentric weight on a motor's shaft to shake the mast to vibrate the
elements of the antenna
or...
On 4/12/2016 11:09 PM, Bob K6UJ wrote:
I have always noticed a slight change in the swr with hf yagis when it
is raining. Just a
minimal change though. Nothing like what Gary, K9RX reported.
Bob
K6UJ
On 4/12/16 7:36 PM, Gary Huber wrote:
So if the SWR returns to normal with a towel, what would a gentle
shaking of the antenna using the rotor to rock the antenna back and
forth do? I'm sure some of those rain drops would drop....
73 ES DX,
Gary - AB9M
On 4/12/2016 7:02 PM, StellarCAT wrote:
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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