[TowerTalk] Rain drops noise on Yagi (dipole)

Wed Dec 5 19:28:29 EST 2018

Hi Rich,

Taking the worst case rain static situation – very heavy rain for say, about 30 minutes, the Top antenna is ~ @ S9, the 2nd @ S6-7, the 3rd @ S3 and the bottom antenna quiet or almost quiet.

Phasing any two of these antennas gives you close to the arithmetic average of the two noise levels.

So the limiting factor is,  what is the signal strength of the target area on each antenna at that point in time?  And which antenna has the best s/n ratio?

If it is at night and I am trying to run JA’s on 10 near the top of the cycle, an S9 noise level will effectively end the run, whereas if it is in the daytime and there is a good opening to EU, it may be possible to continue the run depending on qrn level, signals strengths of callers, signal strength dropoffs with different stacking combinations, etc.

In one DX contest, JA’s were fairly loud on 10 but the rain static on the top antenna @ 100’ was louder and was killing the run.  However, the 3rd antenna,  @ 37’, had signals about 2 s-units weaker than the top antenna but about 4 s-units lower qrn, allowing me to sustain a slower run with fewer callers (because I was 2 s-units weaker!).

I quickly realized that I had only one option given how short 10 meter JA runs are in New England.  I had to transmit on the top and then immediately switch back to the 37’ to listen and then immediately switch back to the top when transmitting.  I did this for about 30 minutes – a real PITA! – until the rain became so intense that the qrn rose on the 37’ to S-9 as well.  That was the end of the run, but I had gotten another 30 minutes out of it.

I remember working K5P on 10 meters the same way – qrn (from power line noise) was S6-7 on the top and S2-3 on the  37’ footer. K5P was maybe S3 on peaks on the top antenna but was completely buried in the qrn.   At the peak I barely heard K5P on the 37’ footer but he heard me transmitting on the top antenna and came back to me – which I didn’t realize until I switched back to the 37’.  After two tries we had a good qso on 10 thanks to FB operating and patience on his part and rather novel operating on my part.  You do what you have to do.  :-)

This is fairly typical for all types of qrn whether from power line noise or rain static – the only difference is that the power line noise is mostly directional where as the rain static is omnipresent regardless of the direction to where the antennas are pointed.

While there are some differences from 10 to 15 to 20, the relative qrn level differences between antennas in the stacks on 10, 15 and 20 are pretty similar.  

I had not thought about the possible effectiveness of putting an antenna on the mast above the top 20 @ 130’.  I’ll have to give that some thought.

73  

Bob KQ2M

From: Richard Smith 
Sent: Wednesday, December 05, 2018 6:41 PM
To: towertalk at contesting.com 
Subject: Re: [TowerTalk] Rain drops noise on Yagi (dipole)

Hi Bob,
What would you say that the S-Meter differences would be, on the average, between the top, second, and third yagis?  I'm guessing that they are not always consistent, depending on a particular storm, but are we talking generally about a 1, 2 or 3 S-Unit difference?
73, Rich, N6KT

    On Wednesday, December 5, 2018, 1:18:14 PM PST, Bob Shohet, KQ2M <kq2m at kq2m.com> wrote:  

I have had difference experiences than Jim.  When the rain static is horrible (at the level where is sounds like the drumming section in a large marching band  ;-)  the the top yagi is always the loudest in Ierms of hearing rain static, it is NOT the only one that gets it and that has been true whether it has been 10, 15 or 20 meters.  What happens at my qth is that the top is the loudest by far, the 2nd one down is moderately loud, the 3rd one down has some static and the 4th one down (bottom) is quiet.

With lower levels of rain static, the top is still the loudest but the 2nd and 3rd one down may not experience any.

I use 5L Hygain HG205CA, 155CA and 105CA’s.

73

Bob, KQ2M

From: Jim Thomson 
Sent: Wednesday, December 05, 2018 12:50 PM
To: towertalk at contesting.com 
Subject: [TowerTalk] Rain drops noise on Yagi (dipole)

Date: Wed, 5 Dec 2018 11:03:12 -0500
From: "john at kk9a.com" <john at kk9a.com>
To: towertalk at contesting.com
Cc: guidoted at gmail.com
Subject: Re: [TowerTalk] Rain drops noise on Yagi (dipole)

<The rain static solution is in the towertalk archives 1 Apr 1997 http://lists.contesting.com/_towertalk/1997-04/msg00023.html

<John KK9A

##  Its always the very top  yagi,  regardless of how many yagis on the same tower.  The lower yagis never seem to be affected. 
Perhaps the..fix is to  install the smallest yagi you can get away with..at the very top of the tower..or mast above the tower...
that will kill the rain and or  wind static..or st elmos  fire..or whatever the heck is actually causing it.  The top ant does not need coax either.
Perhaps something like a 1-2-3 el 10m yagi..or  TA-32, TA-33, or just enough aluminum  at the very top to kill the noise to the actual
yagis below it, that are  being used. 

##  I have heard the same story at least a doz times now..even if they are  DC  grounded eles... like a Hy gain  204BA. . 
Its always the very top yagi that gets the noise..and never the lower yagis. 
Some type  of sacrificial top...yagi /  al  may well do the trick.  

Jim  VE7RF 

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