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Re: FM satellites (was: Re: SUNSAT OVER EUROPE)




At 01:13 PM 7/26/99 -0400, you wrote:
>This may sound really off the wall, but if single-channel
>FM satellites work so poorly, why do people launch them?

I have been working on the Weber State University CAST ACP experiment
to be on JAWSAT. It has an experimental 3 axis stabilization system.
In order to upload code to improve and fine tune the system it needed
a digital link. Receivers, transmitters and modems were available 
"off the self" that can upload at 9k6 and download at multiple rates
(4k8 to 38k4). They are FM and use GMSK modems.

The group and myself were also interested in faster data rates and using
S-Band.  The ACP will have a 2-watt S-Band transmitter on 2403.2. It and one
of the UHF transmitters (0.1 to 8 watts) 437.175 can both downlink at 38k4.
The amount of time we can run these is unknown because of heat build up.

I am very active on AO-27 and enjoy working it while away from home.  I had
hoped for more satellites that could be on at night and available for more
passes.  This project gave me the chance to do my part in getting at least one
more FM bird up in the sky!

I joined the project and worked with the
vendor to get a FM audio mode with access tones added to the modem. This added
few parts to the design and since I am helping on the software I can make sure
this mode can get turned on.  We have two UHF (both 9K6+Voice) receives. When
we change the data rate higher than 9k6 on one of the modems it receiver
(145.960) can not be used for 9K6 digital. I had a jumper option added that
will let it be used for audio and link to the other transmitter creating
a FM bent pipe. I had hoped to have two variable power UHF transmitters but
funding did not allow it. The second transmitter (if it flies) will be a 
2 watt data radio (437.075) and can only be used when the S-Band is not on
and it also can not have a 100% duty cycle.

The original designed had more options (including data rates greater that
38k4) but some had to be cut short since time and funding did not allow it.

I found someone else to be the satellite licensee since I was getting too
involved with the CAST group and OSSS. The modes and schedule will not be
up to me. I have tried hard to configure the satellite to keep it amateur
radio friendly.

There are times when AO-27 is over used. Is that worse than FO-20 and FO-29
being under used?  As I have stated many times not all passes of AO-27 are
chaos.  Passes over the West coast are nice and friendly during the work
week and for most of the weekends.

I would not say "FM satellites work so poorly" but rather say they
"work too good" in getting people to use them. I am not sure that having
just a few more in orbit will change what happens on those weekend passes
over the center of the USA.  Each of the voice satellites have there own
following and operating methods.  For now I accept that and will put up with
those crowed weekend passes.

When at home with my OSCAR antennas I strive to pull those week signals out
of the air and call them to give them a chance to be heard. I have 
received may thanks from them for doing that and for there first
satellite QSO. I have e-mailed help to those who are having trouble
hearing the bird and many of those have gone on to work the satellite
successfully.  I am not the only one who does this and I encourage others
with good receivers to do it also.  I try to wait to see if someone
else will call them before I do, so please others jump in there.  In doing
this I have lost a few new grids and counties but at least someone else gave
the new station the thrill of working a amateur satellite.

Maybe that is part of what has kept me on the birds since 1992.

>Surely there is a better (not to mention less frustrating) way
>to introduce newcomers?

I do not consider AO-27 to be easy to newcomers.  It takes some work and
practice to hear the bird well.  It does allow many to work a satellite
with the equipment they have!

I wish someone would make a HT SSB rig that could be used to work FO-20
and FO-29 with an arrow antenna.  It could have few feature but should
include built in Doppler control. It could also have a tracking program
built in to tell where to point the arrow antenna and when the next pass
will be.  Two meters SSB up and 70 cm SSB down. An internal GPS unit would
be nice.

I have worked FO-20,FO-29 and RS-13 portable but the problem is that during
the work week out West no one or very few people are on! Often there are more
FM simplex QSOs on FO-xx going on between hams on the ground than between
SSB satellite users.

Well I need to get back to working on that Pacsat download protocol. I hope
this has been more positive than my other posts in the last month.

Good Luck on the birds!!!

Randy N7SFI

I hope to have some breathing time before JAWSAT gets into orbit to
describe more its configuration.  I will be in New England in the first
part of August so look for me on AO-27. I will be "rubber duck" sans arrow
for some of the passes. My family does not like to be seen with me when I
wave a "full arrow" in the sky.


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