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Re: Sunsat this weekend




Good morning,

> Ib Christoffersen writes:
> > Perhaps it would be a good idea to have a controller at least over
> > Europe (NO - I am not a candidate).

Richard W L Limebear counters:
> I am against this idea. The HF bands are full of "policemen" and it usually
> makes things worse; I suggest we don't want this regime on the satellites.

Mike, KF4FDJ adds:

I can't speak about the European passes of SUNSAT, but I suspect a
similar phenomenon to one I am noticing here is at work there also.

We've been told the SUNSAT receiver passband was built intentionally
wide.  This allows many signals to be detected by the satellite
receiver, even if they are NOT centered in the passband.

Advance notice, anticipation, and infrequent schedules all contribute to
unprecedented load on this satellite.  Allow me to explain what I think
is happening here.

Early in the pass, before hundreds of operators are trying to reach the
bird, the operators farthest south have successful QSOs, using low power
uplinks.  As the orbit proceeds north, and many more operators are in
the footprint, when one QSO clears, we hear several seconds of hash and
noise, until one or more operators crank up their power to capture the
bird.  Now we've reached the second tier of operation, where the strong
stations prevail.

What is all the hash we're hearing?  I believe that many of the same
operators used to working AO27, using mode J uplink, which nominally
doesn't require the operator to compensate for doppler on the uplink,
are trying to work this bird without having their uplink signal centered
in the receiver passband.  I also believe this is an inherent weakness
of a mode B bent pipe device.  The less Doppler tuning an operator has
to make on the uplink, especially on an easy sat, the better.  I think
mode J is superior for this reason alone.

I've seen conflicting posts regarding the frequencies for SUNSAT, which
only serves to exacerbate the problem.

So, here are several hundred operators, all trying at the same instant,
with many signals only on the edge of the receiver passband.  All those
signals, spread across the receiver passband, activate the satellite AGC
circuitry, but there is no coherence, hence, noise and hash.  And as the
pass progresses, the hash and noise persist for longer seconds until a
successful operator (centered in the passband I should add), cranks up
the power still farther.  Now we've reached the third tier of operation,
where astute operators, carefully tuning for Doppler, AND running
excessive power prevail.

What's the answer?  I don't have a clear answer.  More air time will
help, as the satellite becomes less novel.  But there is one clear way
to lessen the problem using common sense, and science.

Doppler shift on the 70-cm uplink is roughly 3 times as great as the
2-meter Doppler shift.  Maximum Doppler shift on the 70-cm uplink can be
a little over 9 kHz!  If you DON'T tune the uplink, you probably WON'T
be one of the successful operators.

I respectfully submit the following tables of frequencies as a guide to
working SO35.  I have been monitoring the actual frequencies over North
America, and these are close to what should keep you centered in the
passband.  I also respectfully ask all operators to give good operating
practice a chance, and lower your power.  If you are centered in the
satellite receiver passband, less power will be required, and your
signal will be more clear than a signal which is several kHz off
frequency.  Here are the tables:




If your rig is capable of tuning in small increments, use this table as
a guide.  Tune the downlink until your discriminator meter, or S meter
shows you are tuned to the correct downlink frequency.  Look across the
table and make certain your transmit frequency is close to the
associated 70-cm table entry.

Downlink  --  Uplink
--------------------
145.828      436.282
145.827      436.285
145.826      436.288
145.825      436.291  Satellite directly east or west of you
145.824      436.294
145.823      436.297
145.822      436.300





If you are using a scanner to listen, or an HT which only tunes in 5 kHz
increments, use this table as a guide. Since the downlink frequency will
be closest to 145.825 during most of the pass, break the pass into a
little over 3 minute chunks, and increment your programmed pairs during
the pass for best centering in the passband of your uplink signal.


Downlink  --  Uplink
--------------------
145.830      436.280
145.825      436.285
145.825      436.290  Satellite directly east or west of you
145.825      436.295
145.820      436.300


73, Mike in Fort Myers, FL

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