Date: Tue, 20 Dec 2011 19:41:01 -0500
From: Tony <dxdx@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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|