[TowerTalk] Rain drops noise on Yagi (dipole)

[Jim Thomson]

Date: Thu, 6 Dec 2018 01:22:23 -0000
From: "David Robbins" <k1ttt at verizon.net>
To: <towertalk at contesting.com>
Subject: Re: [TowerTalk] Rain drops noise on Yagi (dipole)

<As far as preventing it, that can be difficult.  Telrex tried adding rounded balls to the ends of their elements for a while, but didn't round off corners of t-match shorting straps or even the screws connecting the element sections so did not solve the problem on <their antennas.  I think most of the quads that claim to be quite probably had insulated wire, which combined with relatively few pointy things like screws or hose clamps would reduce or prevent most corona.  Dipping a driven element in liquid rubber might be <an interesting experiment, but I would like to see a UV camera used on a Yagi during a storm to see just where most of the corona is first, there may be simpler solutions, or maybe not.


<David Robbins K1TTT

##  Back in 1977-1981   I tried some experiments with  general Electric  ....  high voltage  acrylic  plastic,   It came in a spay bomb.   A local buddy had arcing on the air variable on his  gamma matched, shunt fed 50 ft tall tower,
he used on 160m..which was top loaded with a tri band, trapped yagi.  The air variable would arc across the stator and rotor plates, once power output exceed   aprx  80 watts.   I completely un meshed the plates.... and doused it 
with the GE spray.   After it dried, cap was tweaked for the normal  1:1  swr.     No more arcing..even with 120 watts out.   So far, so good.   The fellows amp did not have 160m...so I brought my..at the time, Dentron amp over, which did have 160m.
I stuffed  1100  watts  though the gamma matched tower, and  zero arcing.    I was  convinced I was onto something.   Another buddy had a yaesu  FL-2100 B  amp, with tiny spacing  on the load cap. One rotor plate and one stator plate  touched 
at one point of the rotation of the load cap... which of course, shorted out the  load cap.... which also happened to be on the band he used the most.   With almost zero spacing between plates, it was impossible to realign the plates, if anything,
we made matters worse.  So ran the load cap  totally un-meshed   and doused it with the GE  HV spray.    After it dried,  no more problems !   In fact, the plates were STILL  touching, right where load cap peaked for max output.
Ran like that for another  15 years that I am aware of.   At that point I was convinced the GE spray was a miracle cure.

##  In 1980,  I built a hb  5 el  10m yagi, all eles  dc grounded to boom, and gamma matched with a hb gamma match..consisting of  polystyrene  tubing, slid over   .5 inch OD  al tubing.   Extremely tight fit.   Had to turn down the .5 inch tubing with a file,
while  .5 inch   tubing spinning away in my  500 rpm heavy duty drill.    For an experiment,  all the els, which were  6061-T6  were cleaned with scouring pads.   Middle portion of each ele was a 12 ft length  of  1.00 OD  tubing.  Each tip was 
.875 inch OD tubing.  One  SS hose clamp on each ele half.  Dead simple.  26 ft boom used,  made of  2 inch OD  tubing, with center   6 ft  being double walled.    Since I had loads of  GE spray left over, I doused  all 5 els with  the GE spray. 
Boom was not sprayed.  Els  stayed shiny until  1999.   It was up  76 ft  at top of tower, back in  1980-1982.   This was when I was up in northern BC.    Loads of snow,  8.5 ft per year,  sometimes wet,  but mostly dry powder.   One bad ice storm,
with .375 inch  of ice on everything.   Fair amount of wind  from time to time.  10m Yagi was fixed on EU, no other yagis on the tower.   That was a long time ago, but I dont recall a single instance of   rain / snow / wind static.

##  I believe  GE has discontinued the HV  acrylic spray, as I cant find it on their site.    I did note, that in 1982, the  10m yagi came down, replaced by a hb  4 el 20m yagi.   Same dc grounded els, and similar gamma  match.  No GE spray on the 20m eles,
as I had run out.  The  20m yagi was also at top of the 76 ft tower..and also fixed on EU.    20M  yagi did  have precipitation static from time to time, but not often. 

##  If GE, or somebody else, makes a similar product,  Id be interested, it has a multitude of uses, as a cheap way of HV stand off.   perhaps just the last  3-6 ft of each yagi ele  needs to be doused with it,  along with each end of the boom, dunno. 

Jim   VE7RF