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Re: Help with problems

Problem #1

Don't worry Jerry, no problem is 'easy' until after it is solved.  This may
sound strange, but I'm betting you have too much gain! and something is
getting overwhelmed along the way.  Try this experiment, if your IC-820 has
an attenuator put it in line.  Then try cranking the RF gain down , and the
AF gain up.  Remember the radio was designed to pick a weak signal out of
even weaker noise,  If you give the radio a lot of noise and moderate signal
it will probably have trouble.

I'm using the TranSystem down converter, and get my best results with about
20dB of attenuation between the down converter and my radio.  Anyway it
won't hurt to try!

Problem #2

After you solve problem number one, number two should be easier to solve.
Here are a couple of thoughts on #2.

A. You need to be really sure you are hearing your self through the bird and
not a spur of some kind from the radio, this will be easier after #1 is

B.  Doppler is considerable on S-Band (especially during certain parts of
the orbit).  Your 'track' function will compensate for tuning up and down
the band, but it will not compensate for Doppler.  For example:  Let's say
I'm a good operator and I tune up out of the way near the top of the band.
I discover that transmitting on 435.570 puts my downlink on 2401.455 (The
actual numbers are not important).  My radio shows this as Up on 435.570 and
down on 145.455.   I punch the 'Track' button and make sure the tracking is
for an inverting transponder.  Yaesu calls this reverse tracking, I don't
know what Icom calls it.  I start tuning down the band and hear a nice CQ at
2401.375 (the radio says 145.375) if I haven't changed anything else my
radio will transmit on 435.650 MHz.  Depending on how long it has been since
I "found myself" at the top of the band I may or my not hear myself answer,
but normally you will need to tweak your transmit frequency to hear yourself
answer the CQ.  This is okay!

C.  The dreaded AGC.  There are times when I have heard my signal just
disappear.  A quick check of the telemetry usually shows the AGC has been
driven up.  There is nothing you can do about this (except turn on the juice
which is bad practice).

Conclusions:  If possible get in touch with some of your locals.  I am sure
there are several active stations in the metroplex who would like to drop by
for an eyeball and help (I understand the desire to do it on your own, but
help is better than towel throwing)

Email me when you want to confirm South Dakota on AO-40 (or any other of the
analog birds for that matter).

I hope I helped.


----- Original Message -----
From: "Gerald Payton" <n5gpc@earthlink.net>
To: "AMSAT-BB" <amsat-bb@AMSAT.Org>
Sent: Tuesday, September 04, 2001 10:36 PM
Subject: [amsat-bb] Help with problems

> Last time I was admonished for saying it was a "stupid question."
> I should rephrase it and say, "a question from a stupid person."  I REALLY
> feel inapt for having to ask these questions.
> Yes, I know that everyone on the BB has had to start sometime, but these
> problems seem like they "should" be relatively easy to overcome.
> (Setup= IC-820 H, Andrew 26T-2400 Grill antenna, DEM 13ULNA Pre Amp,
> Millicon MC-251 d/c and LMR-400 coax.)
> Problem One:   The signal to noise ratio seems that it should be better.
> >From my previous post, I'm told that my setup is nominal.
> I receive the MB very well, but the QSO's are very weak and down near the
> noise level.
> Adjusting my SHIFT helps some, but the majority are still not good enough
> for contact.  I believe that if I cannot hear the audio, I should not try
> contact!  Therefore, I'm still unable to attempt a contact.
> I am just wondering if a newer radio with DSP and better filtering and
> adjustment might be the cure.  Of course, I'm sooooo
> frustrated now, I'm about ready to throw in the towel and sell everything!
> Problem Two:   I have been able to adjust my uplink signal (70cm) and hear
> it returned.  However, it too was very weak on return.  And, then with
> additional tests, I no longer hear my downlink signal.  I don't know if I
> have an "tracking" problem with the IC-820 or not.  It appears to be
> operating OK when looking at the radio (LSB up, USB down and reversed
> transponder).
> Analyzing all this in my mind, I can't help but believe that some sort of
> selectivity (DSP, Shift or something) would help reduce the noise to a
> which I could hear well.  I realize that preamps and such amplify BOTH
> and noise and separating the two is difficult.
> I hate to be so close and have spend money that I can't really afford and
> then give up.  I'm not an experienced SSB operator and am not familiar
> operating SSB and adjusting for same.
> Sorry for the "crying towel", but I am really frustrated............
> 73 to ALL,
> Jerry  N5GPC
> ----
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