PCsat2 ARISS COMMS COMPATIBILITY                           20 Nov 2002
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                                                                WB4APR

Since PCsat2 is an amateur radio experiment to fly on the ISS, it must
operate in compatible modes with all other ARISS experiments.  It
consists of dual-redundant AX.25 command/control system and a PSK-31 
multi-user COMM experiment.  Further, it can be configured to agugment
crew voice communications.  The following paragraphs address the ARISS
compatibility of each of these modes.  For a Block diagram see 

         http://www.ew.usna.edu/~bruninga/pec/pecsatcom.jpg

DEFAULTS AND BASIC OPERATIONS:   PCsat2 has 3 receivers and 3 
transmitters.  For NASA EVA requirements the transmitters default to 
OFF.  In addition, their default  configuration if activated are as 
follows:

 145.825 FM RX    ==>TNC==>  435.x TX-A  UI digi normally on
 145.800 RM RX    ==>TNC==>  435.x TX-B  A back up command link

This default mode assures there is no interference to ARISS on 144.49,
145.200 and other unpublished ARISS School contact frequencies in the
two meter band.  Further, PCsat2 antennas will be more than 120 feet 
from other existing ARISS antennas.

PSK-31 COMMS EXPERIMENT MODE:  When mutually scheduled, the PSK-31 
linear receiver can be patched to the UHF-A transmitter for full 
duplex multi-user communications experiments.  Being linear up, and 
FM down, the Doppler rates are on the order of 1 Hz per second and anyone 
with an FM receiver and a sound card can decode all of the 20+ multi-
user data streams with public domain software.  This mode has no 
impact on current ARISS operations on the 2 meter band.  Yet provides
schools with easy 'uncongested' access to an ARISS transponder.

UI-DIGIPEATER CROSSBAND MODE:  In this mode, the 145.825 MHz packet 
receiver digipeats to UHF-A transmitter, again with no impact to
ARISS 2 meter band operations.

UI-DIGIPEATER MODE:  In this mode, the digipeater operates up and 
down on 145.825 in synergy with the existing ARISS packet system.
This mode can be scheduled during hours when the ARISS crew will not
be using 2 meters for voice.  At these times, the best OPERATIONS
PLAN will be for ARISS packet (145.800) to be reserved for MAILBOX BBS 
operations only and all UI digipeater users to be encouraged to operate 
only on 145.825.  This separation of function will lead to greater 
through-put for both.

BACKUP DUAL-REDUNDANT COMMAND/CONTROL MODE:  This mode is always
active as a backup command channel.  WIth a 2 meter uplink and UHF
downlink on UHF-B, it also has no impact on current 2m ARISS operations.

FM-CREW-COMMUNICATIONS SUPPORT MODE:  In this mode, the PCsat2 can
be configured to act as a full-duplex crossband voice repeater with 
2-meter uplink and UHF-B transmitter downlink.  This permits a
vast improvement in crew-to-ground ARISS voice operations because
it eliminates the total congestion on the uplink by allowing
everyone in the footprint to hear the uplink as well as the downlink
and thus avoid collisions.  The uplink has been chosen to be 145.800 
for several reasons.

1) Uplinking on the existing published 145.200 and 144.49 voice
uplinks is problematic and wouild require changing frequencies two
times per orbit.   Thus, using the internationally cleared ARISS
voice frequency of 145.800 is the next best choice.

2) By operating the FM repeater with a receiver on 145.800, normal 
operations of ARISS are not impacted and yet any crew operations of 
opportunity will be heard on the UHF-B downlink.

3) To take maximum advantage of this capability, crew operations
will best operate simplex on 145.800, with everyone monitoring
the process on UHF-B to avoid collisions with others.

4) In the future, the presence of a full duplex repeater on ISS
will allow HT operations by the crew from anywhere within the
ISS (if it were ever possible for such emissions within the ISS).

CONCLUSION:  This PCsat2 configuration is felt to offer the best
possible design which minimizes any conflict with current ARISS
operations, while still offering distinct ARISS advantages of
improved voice communications, improved packet throughput, and
something new (PSK-31) for students to learn about.

Bob Bruninga, WB4APR
US Naval Academy Satellite Lab