PCSAT2 - PSK-31 Tests

On Saturday morning there was an initial test of the PSK-31 transponder onboard PCSat2 which is attached to the International Space Station (ISS).

The PSK-31 transponder takes all the signals in a 2.4 kHz segment from 29.401 to 29.4025 MHz and retransmits that segment as audio on an FM transmitter at 435.275 MHz.

The initial test showed signals going through the transponder and further tests will be taking place.

Below is an email from Bob which describes how to operate through this inovative transponder.

Use the Online Satellite Predictor to find out when PCSAT2 on ISS is in range:
http://www.amsat.org/amsat-new/tools/predict/
Select Show Predictions for ISS and enter your approximate Lat and Long co-ordinates or IARU QTH Locator.

73 Trevor M5AKA

PSK-31 Saturday morning over USA...

OK, lets do it. I can come to work and turn on the PSK-31 over the East coast of USA for a few passes. It will not be on, but about 5 minutes max in the middle of each pass. I see these at about...

1225z, 1405z, 1540z and 1715z

PSK-31 stations should Spread out between 29.401 and 29.4025. Remember that Doppler will start your signal about 600 Hz higher and move your signal down the passband to end 600 Hz lower from beginning to end...

Transmit the entire pass. Listen on 435.275 FM donwlink +/- 9 KHz doppler. The more signals the better. (You probably have to run two PSK-31 programs so you can RX on UHF FM while tansmitting on HF uplink)...

There are two means of control of PSK xponder. The one we are using during checkout is the backup method which is ON/OFF by direct sysop command. The ultimate one will be by a user packet connecton to the "PC2PSK" callsign.

The ON/OFF one is really a backup and so it also has a backup fail-safe timer that at least turns it off after 20 minutes. So even if I miss the turn off command, it will cycle on and off every 20 minutes or so until I next get a shot at it...

Turns out, that if it is the one orbit that goes from USA, over Europe, then africa and then AUS NZ, this 20 minute cycle will keep it on to about the central of Europe then off
over central africa then on over southern AUS and NZ, then off, and then back on for the west coast... maybe. But we dont know the exact timing of the 20 min timer...

Lots to test the next several days.

When we activate the USER access method, then any
station that wants to command on the PSK-31 can just connect to the callsign of PC2PSK. His packets from then on do nothing and are NOT welcome, but simply the CONNECT LED is the circuit that turns on the transponder. His TNC and the PCSAT2 TNC will occassionaly exchange CHECK packets to verify he is still connected. Once the user station is lost, the TNC connection will timeout 7 minutes later and the CONNECT LED will go out, and this will drop the PSK-31 transponder.

We chose that so that it will timeout when the satellite goes out of view of that station. Such a station will have to have his TNC set for FULL DUPLEX, because once the PSK-31
xpoonder comes on, this will open his squelch and his TNC will not complete the connection, because it will hear the channel busy...

With full duplex on, his TNC will ignore the PSK noise and will let his TNC transmit to complete the connection. Unfortunately, you cannot use a D700 for this purpose since it does not have a way to turn off the channel busy on its internal TNC. But the D7(g) does. Use the DCD menu.

Remember, this satellite has no command processor other than a pair of simple KPC-9612 dual port TNC's, so we had to be a little creative to find ways to command things...

Bob, WB4APR

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