Interference from PCSat-2

In August of 2005 a project called PCSat-2 was installed outside, on the P6 Truss, on the International Space Station. PCSat-2 is a Department of Defense project that also has an Amateur Radio project as part of the telemetry system.  PCSat-2 was uninstalled and returned to Earth in September 2006.  During its year of operation we did have a frequency conflict between the Voice/Packet operations with the D700 and the PCSat-2 project.  

We hope that better frequency coordination will be used in the future to avoid these issues.

http://eng.usna.navy.mil/~bruninga/pcsat2.html

PCSat-2 operate on the following Amateur radio frequencies, at approximately 2 watts.

Transmit and Receive Packet 145.825 mHz
Transmit and Receive Packet 435.275 MHz
Receive PSK-31 29.401 MHz

The problem we have is that when PCSat-2 is transmitting on 145.825 mHz, it will interfere with Amateur Radio Voice and Packet operations with the D700 transceiver. Both projects are on the same radio band and their externally mounted antenna are less than 100 feet apart. 

In order for these two project to be active at the same time you either need to separate the Radio channels by several megacycles of radio spectrum or install large heavy cavity filters on both systems. Neither solution is practical at this time. The good news is that PCSat-2 is tentatively scheduled to be shutdown and returned to Earth Q3 or Q4 2006.

The PCSat-2 project has a constantly changing transmit channel schedule. The only way to know what channel they are transmitting on is to check the PCSat-2 web page or listen on 145.825 down link frequency.

Packet Interference:
If the ARISS D700 packet project is active, it is listening for Earth packets on 145.990 mHz. When PCSat-2 transmits on 145.825 mHz, the short bursts of packet data from PCSat-2 will momentarily block reception to the D700 Packet system. The same is also true when the D700 Packet system sends data down to Earth on its assigned transmit frequency 145.800 mHz. The amount of interference is dependent on the amount of data and the number of users on each system.

Voice Link Interference:
Astronaut Bill McAurther has been very active on 2-meter voice using the ARISS D700 system. In voice mode the ISS crew will switch between two different receive channels, depending on what part of the world they are over. For Europe they will listen to 145.200 mHz and for North America they will listen to 144.490 mHz.

When PCSat-2 transmits on 145.825 mHz, the short bursts of packet data from PCSat-2 will momentarily block reception to the D700 in Voice mode. Both voice receive channels will be affected, 145.200 and 144.490 mHz. The amount of interference may be less on the 144.490 frequency, however no interference data has been published.

The same is also true when the D700 transmit Voice down to Earth on its assigned transmit frequency 145.800 mHz. Stations using the PCSat-2 will have their data blocked while the crew is talking on 145.800 mHz. What the ISS crew may hear while listening to the receiver will vary depending on the strength of the transmitting Earth station. A weak voice signal will have audio gaps in the conversation. The gaps are caused by the short packet bursts coming from the PCSat-2 Transmitter. The amount of interference is dependent on the amount of data being sent down to Earth by the PCSat-2 transmitter.

The frequency conflict was caused by a simple miss communication between the project designer and ARISS hardware team.  Steps will be taken by ARISS in the future to prevent similar conflicts with ARISS projects.

School Voice links:
ARISS is aware of the problem and has issued instructions to the PCSat-2 team the shutdown the PCSat-2 transmitter on 2-meters during school schedule and special event days.