[TowerTalk] SWR Problem Balun or lightning protection?

[Jim Thomson]

Date: Tue, 20 Dec 2011 19:41:01 -0500
From: Tony <dxdx at optonline.net>
Subject: [TowerTalk] SWR Problem Balun or lightning protection?

All,

The SWR on my 5 element mono band Yagi rises after I key down for a few 
minutes. The 2:1 SWR bandwidth behaves normally until the problem 
occurs. The SWR goes to normal after waiting a few minutes, but then the 
problem starts again after I key down for a while.

The only things inline are the lightning protection (polyphaser) and the 
balun which is mounted at the antenna. The antenna is made by M2 and it 
uses an M2 balun.

I'm going to bypass the lightning protection tomorrow as a process of 
elimination, but I was wondering if the problem is more likely to be 
caused by the balun?

Thanks,

Tony

##  OK, is this a  4:1  M2 balun???   M2 is not known for quality baluns. 
Their scramble  wound 80m 'rf choke baluns'...and their 6m 'baluns' are
nothing to write home about. 

##  IF  it turns out to be the  4:1  balun...or a 1:1 balun... the fix is easy.   IF it's
a 4:1 balun, replace it with the array solutions 4:1 balun..made for retrofitting 
M2 and KLM yagi's.  You won't blow it up, even with YC-156 power levels.
IF it's a 1:1  type choke balun...and a  20m yagi.  you have all sorts of options.
Everything from W1JR style baluns, wound with 213-U /RG-393  around
4 x torroids, to  17-20 x large style type 43 beads slid over rg-213/ RG-393 coax. 

## 17" worth of the  1.125"  long large type 43 beads will  give you 1500 ohm choke Z. 
[15 x beads used]. You won't blow it up either, even with YC-156 power, if  393 teflon
coax used. 

## check everything else as  folks have already mentioned. IF it is the balun, install a good one.
If a balun can be gotten to  from the tower is  one thing, but when it's  way out on the boom,
I have no patience  for any balun that's  short of bomb proof.   I use Cal-Av  EB-3's  on all
mine. then no chance of water getting inside em, since they are pumped  full of silicone glop
via a  vac chamber. 10 ga teflon /silver pig tails on one end..and a waterproof  7-16 DIN
connector on the other end.   Use Nylocks or similar on the pig tails.  Phosphor bronze
hardware works good too..which is better than SS.  SS + RF is a bad mix. 

##  when I see pix of a crane taking down a huge 40/80m yagi  cuz of a bad balun, it makes
me cringe.....esp when the fellow uses an identical balun for the  replacement ! 

later.... Jim   VE7RF