Re: [amsat-bb] Newbie needs help with AO-40!!

["Bill Klebes" <wa8efc@xxxxxxx>]

Before you waste any more time trying to figure out why your uplink is so
poor let me tell you about
my findings on the Cushcraft 738xb with default RHCP. I purchased one also
thinking it would be a way to save a few bucks.  When assembled and verified
according to directions it was consistently 15-20db
weaker than a FO-22 22 el yagi on the downlink.  SWR measured at the antenna
was about 3:1.  The lengths of the matching/phasing harness did not seem to
be reasonable for the frequency and feed type of the antenna.  It was
verified on a network analyzer and found to be totally incorrect.  OK that
being determined I built another harness and eliminated the switching box.
SWR at the antenna now 1.2:1 but still at least 10db less than the 22
element linear yagi.  Note: my installation is close to the ground and
antennas can be swapped with a step-ladder in about 5 minutes so comparisons
were made on the same pass within a few minutes of each other.  Manually
changing polarization had virtually no effect on the very poor performance.
At this time I modeled the antenna on one of the available modeling programs
and found with the dimensions out of the box its gain was somewhere in the
neighborhood of 5db.  Thinking
maybe the modeling program was in error it was modeled on two other programs
which essentially confirmed the original findings.  I contacted Cushcraft
and after several strongly worded emails finally got a response which was
basically "Where did you get that antenna, we quit making it over 5 years
ago?"
Like yours it did appear to work on the LEO's but I did notice the very poor
pattern when manually moving the antenna across the satellite, very close to
what the modeling programs predicted.  The 738xb
now holds a place of honor in the junk in the attic of my garage.  The
linear yagi still continues to perform
satisfactory on AO-40 and the LEO's.

Bill WA8EFC
----- Original Message ----- 
From: "Thomas B. Turner Jr." <thomasturner@centurytel.net>
To: "AMSAT BB" <amsat-bb@AMSAT.Org>
Sent: Thursday, January 08, 2004 2:52 PM
Subject: [amsat-bb] Newbie needs help with AO-40!!


>      I subscribed to the board yesterday to seek help. I don't have an
Elmer
> so all I learn is through reading books and the internet.
>      I got interested in working satellites a couple of years ago when I
got
> back in Ham radio after being inactive for abt 20 years.  I bought a used
> Yaesu 5400 and a couple of Cushcraft yagis that were new but old stock.
The
> 2 meter is a 22XB and the other is a 738XB. They are on a 24ft. tower with
> 150 feet of 9913 and a Landwier pre-amp on each and each has polarity
> switching. I bought them because they were a lot cheaper than M2 and
> others.(I also know you get what you pay for.) I have used them to work
the
> low sats with great success. I can work FO-29 from horizon to horizon.
>      Over the holidays I built downlink antenna for AO-40 using a .75
meter
> offset dish, an AIDC 3731AA from K5GNA, with a helix feed. It appears to
> work fine. The last couple of nights the beacon is S7-S8. The noise floor
is
> S0-S1 and most QSOs are S3-S6 on the meter of my TS-2000X. The antenna is
on
> the ground until I get through fiddling with it, then I will put it on the
> tower.
>      Now for the problem. I have been reading that 50W with an antenna
such
> as mine(19 ele./15 dB supposedly) should make Leila scream!! For the last
> two nights I have tried to hear my signal and finally heard it but it was
> barely audible. I thought I was looking in the wrong place for my return
> signal, but I was doing it right it was just weak. I swept the sky to see
if
> my antenna might be off a few degrees, I went outside with a compass and
> protractor, and I switched polarity. Nothing helped!!
>      I have been trying so hard to make a good receiving antenna while
AO-40
> has been inactive and I never thought my uplink antenna might stink.  I
have
> heard from a couple of sources that some older Cushcraft Sat antennas were
> junk, but I thought mine might have been an exception. The 738XB receives
> the low sats well, but I have not used it to transmit very often(AO-7 a
> couple of times).
>      Where should I proceed? 1.Sell the Cushcraft on E-bay and get an M2
or
> another brand. 2.Get set up to use the 1200mHz module on the TS-2000X for
> uplink. 3. Buy an amplifier for UHF(how big?). 4. Something else.
>      Thanks for any help that ya'll can give me and I'll be back for more
> help in the future I'm sure.
>      Thomas
>      KA5YJJ
>
> ----
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