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RE: ISS downlinks today?



The ISS is currently using the ECOM (Early Communications) system for
communications.  The ECOM operates in the S-Band range (2.1064 GHz up,
2.2875 GHz down) via the Tracking and Data Relay Satellite System (TDRSS).
The TDRS Satellite relays the signals to/from White Sands, New Mexico.  It's
not likely you would hear these transmissions from the ISS to the satellite,
and from the satellite to the ground it uses spot beams, so unless you live
near White Sands (WSC), you probably won't hear the TDRS-to-WSC signals
(plus, I believe the S-band frequencies are translated to Ku-band between
the TDRS and the ground).  And since the ISS transmissions are to the TDRS
satellites (East or West, depending on where the ISS is in its orbit), you
couldn't use them to verify that it's overhead even if you could hear them.

Once the standard S-band and Ku-band equipment are launched (STS-92, with
S-band being activated on STS-97), the ECOM system will become the back-up.
The S-band system normally uses a horn antenna (with an omni for backup at a
much lower data rate), so the problem will become even greater.  On top of
that, the data is transmitted using a packet protocol defined by the CCSDS,
and the data is encrypted.  The S-band frequencies are 2.0857 GHz up, and
2.265 GHz down.

The Ku-band (13-15 GHz) uses a 6' dish on the ISS at a data rate of 50 Mbps.
How big is the Ku-band dish in your back yard?

Pete Greene, N2LVI
L-3 Communications System - East
ISS Communications & Tracking System contractor


-----Original Message-----
From: Chris Elmquist [mailto:chrise@n0jcf.com]
Sent: Monday, March 06, 2000 10:54 AM
To: amsat-bb@AMSAT.Org; sarex@AMSAT.Org
Subject: [sarex] ISS downlinks today?


Just curious if anyone is aware of any downlinks (probably not amateur
yet) from the ISS that one might tune into with equipment accessible
to the average guy??

A number of coworkers are interested in visual sitings of ISS and are
encountering alot of trouble in actually spotting it.  I thought it
would be cool if we could also "hear" it to increase the confidence
level that what was seen and heard was really ISS...

It would not be neccessary to actually demodulate some complex downlink--
just sufficient to detect some signal on a known frequency and
run with that.  VHF, UHF, S, C, Ku band are all condidates...

Thanks.

Chris N0JCF

-- 
Chris Elmquist
chrise@n0jcf.com
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