[amsat-bb] Re: UHF antenna help

Tue Nov 30 06:08:06 PST 2010


A couple of others things to check after working through all the other great

You did not mention how you moved it.  Assuming you only broke it down to
the boom sections, are the various phasing cables still good?  There are a
couple of places where you have to pull them very tight, and with a sharp
bend, to get them to fit.  Those could use checking.  As someone else noted,
the SWR is not that high, and if one of those were broken, I would expect
things to be more obvious.

The other area to check is the aluminum blocks which are the folded dipole
feeds.  About two years ago, I noticed that rear driven element was slightly
but obviously crooked.  The SWR measured by my Bird was about 1.8:1.  I
brought it inside and opened the aluminum box.  Sure enough, that was the
problem.  One of the connections was loose, and the element was not
internally supported or connected.  (Best theory is a bird flew into it.  I
have had 2 other such incidents over the years, complete with blood and
feathers, and in one case a dead hawk.)  However, what surprised and
appalled me was that the broken connection was a solder bridge, and a very
obvious one!  We are talking something which even MFJ "quality control"
would reject.  However, it would have been possible for the mechanical
connection to be good, with the electrical connection still bad.  I am
thinking there is a possibility, slight though it is, that yours might have
gotten bumped in transport.  It is not robust at all.  I repaired the
connection better than new, and all is well.  The next time I take down the
antennas, I will crack them all open and check.

Something to check if all the probable stuff fails.

73s es gud luck!


-----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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