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Re: [amsat-bb] Re: Why FULLDUPE On is good? (Re: iss)

To get a feel for what the ISS radio is hearing, just tune in on
UO-14 when it passes over your area when ISS is in range. The
downlink on UO-14 is 435.07 MHz.  The uplink to UO-14  is
145.975 MHz which is a mere 15 KHz away from the ISS uplink
frequency on 145.99 MHz.  The receiver on UO-14 is probably
a little broad which accounts for it picking up transmissions from
the ground stations trying to uplink to ISS when it is in range.
Of course, some of the packet uplink stations are transmitting
in excess of 5 KHz deviation as well.

The packet attempts going up to ISS were starting to annoy
some of the users trying to talk on UO-14 since there were a
lot of packet bursts coming through the satellite around 05:00 UTC
over the US.

Taking the Doppler into account I guess a station uplinking to ISS
could effectively be transmitting 6 KHz closer to UO-14 (145.975 MHz)
if they were at the beginning of an ISS pass transmitting 3 KHz lower
in frequency to compensate for Doppler and UO-14 was just
coming in range with a Doppler of 3 KHz on the high side.  This
would effectively make an ISS uplink transmitter appear 6 KHz
closer to the uplink channel used by UO-14.  Since a common
IF filters used on FM receivers fall in the 12-15 KHz range, the ISS
uplink channel would be right at the edge of the bandpass for the
UO-14 uplink.  I suspect the UO-14 IF filter could be a little broader.
This is why we hear packet signals intended for ISS coming through
the UO-14 satellite.

As the ISS came over the US right behind UO-14 early this morning
you could hear the level of activity start to build very quickly.


Tim - N8DEU
Huntsville, Alabama

----- Original Message -----
From: "Bob Bruninga" <bruninga@usna.edu>
Cc: <sarex@AMSAT.Org>
Sent: Tuesday, April 17, 2001 8:17 AM
Subject: Re: [amsat-bb] Re: [sarex] Why FULLDUPE On is good? (Re: iss)

> > > But if we could get everyone down to say one
> > >packet per 2 minutes, then there would be a 90% chance that more than
> > >100 people PER PASS WOULD be successful... (or so)
> How was everyone's success last night?  I heard one station in our
> area transmitting his packets every 3 seconds for the entire duration of
> the pass.  THus, effectively jamming everyone in the country.  Since our
> area is just one of 5000 such areas in the footprint at the same time, it
> gives an idea of the scope of the problem.
> Yet when I talked to one of the others (not the 3 second guy) trying also
> with over 2000W ERP, he didn't see it as any problem, figured he had as
> much right to try as everyone else...
> Actually, he's not wrong.  Its human nature.  About all we can hope for is
> user education as to what is going on and hope that users will lower their
> retry rate, pray that everyone else will, and once someone is successful,
> then say something useful/interesting to the group and back off... That is
> about all we can hope for...
> de WB4APR, Bob

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