[amsat-bb] Re: UHF antenna help

Gary "Joe" Mayfield gary_mayfield at hotmail.com
Tue Nov 30 16:58:18 PST 2010


   Congrats on the move!  What follows is personal experience and may not be
the same for everyone.  I have had very poor luck looping the coax out the
back of the antenna.  I believe it is because I wound up with a conductor
"flapping" around in the breeze close to the antenna yielding unpredictable
results.  What has worked best for me is to run the coax back down the boom
of the antenna and then away from the antenna (at a right angle) at the
crossboom.  This only seems to work with the antenna in the "X" patern and
fails miserably in the "+" pattern.  There are also places along the boom to
avoid when doing this (multiples of 1/2 wavelength).

   Usually when I have had a problem like you are describing it has been a
feedline/connector issue.  It never hurts to make a complete check of that.
I am also assuming you are rotating the "flexible" version of LMR-400.

   The 436CP30 is a great antenna (nicer than any I've ever had), you hear
lots of them on the birds and it should be more than enough for horizon to
horizon coverage.

73 and Let us know what you find!
Joe kk0sd

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of larry
Sent: Monday, November 29, 2010 7:14 PM
To: amsat-bb at amsat.org 
Subject: [amsat-bb] UHF antenna help

Good evening,

   Name here is Larry, N1MIW. I recently moved to a better (higher) QTH and
finally got around to setting up the satellite station "almost" like it used
to be, but am experiencing some reception difficulties on UHF. I'm hoping
someone out here can help me diagnose what I'm doing wrong, or what the
problem is. I am using a Yaesu FT-847 which is computer controlled, as well
as the Yaesu G-5400 rotator. The antennas are mounted on a solid fiberglass
mast only ~17 feet off the ground, and fed with LMR-400. The frequencies are
correct for the satellite I want to use.

   My problem is with the 436CP30 antenna. I cannot seem to find good
results with it since my move - terrestrial or sat related. My SWR is around
1.5:1 at 435MHz, and the polarity switch is working. I tried changing
feedlines and removing the pre-amp, but I still cannot seem to make it work
correctly. I am trying to receive SO-50 D/L, and VO-52 U/L, but both are
just not working like I remember it being before the move. I don't have any
broken or mis-aligned elements (that I noticed - I'll look again). The only
thing I was looking into was instead of having it placed on the boom in a
"+" pattern was making it an "x" pattern - would that make a difference? I
don't remember hearing or reading about that anywhere, so I was looking for
your opinion.

   On a side note, what's your opinion of this antenna? Like I said, I used
to have good luck with it, but I'm not sure what's different, except the new
home. Should I get "horizon" to "horizon" coverage (plus or minus a few
degrees)? Oh, I also looped the coax off the back like the manual states,
but the improvement is very minimal. I checked the "jumpers" at the tuning
box, and they seem OK too.

   I'm running out of ideas, and any guidance would be appreciated. Thanks &
looking forward to working the birds again!

73's... Larry N1MIW

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