-----Original Message----- From: Bob Bruninga [mailto:bruninga@usna.edu] Sent: 29. juli 2002 20:39 To: Uffe Lindhardt Cc: WB4APR@amsat.org; Robert Bruninga Subject: 144.390, An Appology. On Sun, 28 Jul 2002, Uffe Lindhardt wrote: > I understand that you are involved in the PC-SAT project, and that > PC-SAT is the source of the FM Packet interference, that we experience > on 144.390. > > I must submit my strongest protest of this dis-regard for band plans. > Today the French microwave amateurs had their monthly activity day. > Talkback frequency (since years) is 144.390 SSB. This activity has been > seriously impaired by your use of the frequency. It seems > incomprehensible that the Amateur Satellite Service, which has extensive > allocations in proportion to the number of users, needs to take to these > sort of practices. Uffe, Thank you for contacting me. We appologize sincerely. We are very sorry to cause any interference and this interferece is not intentional. It is only a result of a dying spacecraft. I hope I can explain the series of events that has lead to this unfortunate situation.... PCsat was designed with its primary mission and uplinks and downlinks on 145.825 worldwide. This is called the "A side". But it also has a dual redundant backup system, "the B side" for backup commanding and for a secondary experiment for use ONLY over north America. The B side has a downlink on the North American continent wide APRS mobile packet frequency of 144.39 for demonstration of occassional direct satellite- to-mobile emergency communications for the mobile amateur.. ALL normal PCsat operations are conducted with thousands of users worldwide on the satellite frequency of 145.825 on every orbit.. But, the 144.39 downlink has an unpublished secret uplink so that it cannot be used by anyone except the command stations or authorized experimental travelers in remote wilderness areas. To date, the secret uplink to the 144.39 downlink transponder has only been used by COMMAND stations and on the order of 6 or so special wilderness travelers in the Arctic, Antarctic, Northern Canada and a ham operator on a ship in the caribean. And then only for a limited duration of a few days each... As an added measure to assure that the downlink of 144.39 would never be active over Europe, we chose the secret uplink frequency to be on the same frequency as a very powerful published full time amateur radio beacon in Europe. This way, the very high-power European beacon stations which is on the air 100% of the time (CW) would essentially JAM the uplink and prevent it from ever being used in the region... even if the frequency was discovered. Well, this seemed like a good plan until recently. Unfortunately, a combination of other factors is causing us to have a problem as I will try to explain. As a necessity to maximize the ablity to command PCsat after an in-flight anomoly, PCsat was programmed to RESET to SAFE mode whenever it lost its memory or command links. The safest mode for PCsat was thought to be the mode that would Maximize the ability for the satellite to receive commands from the ground. Thus, when PCsat experiences an anomoly, it RESETS and turns ON both backup receivers and it CROSS-CONNECTS the two downlink transmitters. This way, if one transmitter fails, or one receiver fails, we can still command the satellite. The problem is that recently, PCsat is experiencing a RESET on every orbit when it goes into the dark because it runs out of power. As a result, the transmitters become cross connected. This condition remains until a command station can send the command (on every orbit) to again ISOLATE the backup 144.39 transmitter whenever it is over Europe... But by chosing the backup secret UPLINK channel to be always jammed in Europe, this means that the European command station must do all of his commanding on the same channel as all the other users. Sometimes this makes the commanding less reliable and when he is not successful in sending the ISOLATE-transmitters command, then the cross connection takes all of the normal 145.825 downlink and makes it appear simultaneously on 144.39. This is our unfortunate situation that we have been working to solve. We have a dozen command stations around the world that try to send the "isolate-transmitters" command to PCsat on every orbit 14 times a day all around the world. Most of the times we are successful, but sometimes we are not... It is during these few passes when we failed to successfully commmand the isolate-transmitters command that you will hear the interference on 144.39. This situation is not intentional at all, and we appologize that this is causing anyone any inerference. Fortunately there is a limit to how long this condition will last. Let me explain. Since PCsat resets to SAFE mode on every orbit and since the SAFE mode is *not* the low power mode. And since the reason PCsat is resetting is because it does not have enough power to run in the dark, then this means that we are deep-discharging the batteries on every orbit 15 times a day, or about 500 cycles a month. Our analysis shows that these batteries are being deep discharged to less than 0.2 volts per cell (nominal 1.2 volt Nicads) on every pass. As you probably know, a NICAD cannot operate very long under these conditions. So we know that PCsat will die any day now as the battery continues to deterioriate. We do not anticipate that PCsat will remain operational beyond September. In the mean time, we will redouble our efforts to try to maintain a command uplink to "isolate the transmitters" on every orbit over Europe to make sure that this interference on 144.39 will be minimized. If your group has anyone with satellite command experience and especially one with high power packet that would like to assist in this regard, we would be happy to train him to help command the satellite to further help us keep the 144.39 transmitter off the air. Again, we appologize for this problem, and hope that the problem will soon resolve itself. Also, you will notice that PCsat is currently going over Europe in the afternoon and evenings which is probably a busy time for your use of the frequency. This will move earlier and earlier by 30 minutes every day and again, in a month, these passes will again be in the dark when PCsat's batteries are dead and it cannot transmit anyway.. I hope we can resolve this problem to your satisfaction and please send along my appologies to your coleagues who share that frequency. Bob Bruninga, WB4APR PCsat, Command Station PCsat WEB page http://www.ew.usna.edu/~bruninga/pcsat.html ISS-APRS FAQ: http://www.ew.usna.edu/~bruninga/iss-faq.html APRS SATELLITES http://www.ew.usna.edu/~bruninga/astars.html