This has been sent to me from Miles as was included in the SpaceNews Zine which was sent in December. MIR REFRESHER COURSE * >======================== >Speaking of Mir, have you ever tried to contact the Cosmonauts on the Mir >space station on packet radio? In this issue of SpaceNews, G. Miles Mann, >WF1F presents some useful hints and friendly advice for those who would >like to improve their communications success with the Mir space station. > >Mir Personal Message System (PMS) Tutorial de WF1F: > >If you plan on sending mail to one of the Mir crew members, keep your >message short (2 or 3 lines). Long messages seldom upload successfully. >The Mir PMS only has room for approximately 22,000 bytes of information. >Make sure you kill any messages that may be addressed to you on Mir and >try not to upload too many messages to the Mir PMS at one time. When you >are sending messages to the cosmonauts, phrase your questions carefully >so they can be understood, and try to use the Russian language whenever >possible. This will often speed your response. Remember, English is >not the cosmonauts' native language. > >The Russian crews have asked users NOT to use their Personal Message >System as a maildrop between terrestrial stations. If you think having >a monoband FM packet satellite or a simplex digipeater in space is a good >thing, then build one. Please try not to download Mir's help file. The >commands are similar to most Personal Message Systems available on packet >radio TNCs. A copy of the help file is reproduced below: > >B(ye) B [CR] disconnects you from PMS. >H(elp) H [CR] or ? [CR] displays this help file. >J(log) J [CR] displays a list of callsigns heard (optional date/time) >K(ill) K n [CR] deletes message number n (only to/from your callsign). >KM(ine) KM [CR] deletes all READ messages addressed to your callsign. >L(ist) L [CR] lists the 10 latest messages. >M(ine) M [CR] lists the 10 latest messages to/from your callsign. >R(ead) R n [CR] reads message number n. >S(end) S (callsign) [CR] begins a message addressed to (callsign). > Subject: max 28 characters ending with [CR]. > Text: End each line with [CR]. > End message by typing /ex [CR] or CTRL-Z [CR] at the beginning > of a new line. >SR(eply) SR n [CR] Sends a reply to message n prompting only for text. >V(ersion) V [CR] displays the software version of the PMS system. > >[Info via Miles, WF1F @ K1UGM.MA.USA.NA] > * MIR REFRESHER COURSE * >======================== >Ever tried to contact the Cosmonauts on the Mir space station? In this >issue of SpaceNews, G. Miles Mann presents some useful hints and friendly >advice for those who would like to improve their communications success >with the Mir space station. > >Mir Refresher Course - Part 2 of 3 de WF1F. > >When is it appropriate to call the MIR Packet BBS? > >First, configure your TNC to be able to monitor all packet information >during transmit and receive, and turn Time Stamp ON. Setting the correct >TNC parameters will assist you in a successful connection with the minimum >amount of interference. By monitoring the control packet information at >the end of each packet header, you can tell if the packet information is: >C-Connect request, D-Disconnect request, DM-Disconnect mode, UA-Unnumbered >Acknowledge, UI-Unconnected Information frame or I(n)-Information frame >(n=0-7). > >This is a sample of suggested TNC parameters for a KAM. Your actual >parameters may vary: > >AUTOCR OFF >LFADD OFF >MCON ON >MCOM ON >MONITOR ON >RETRY 8-10 >TIME STAMP ON > >Set your terminal program to save all data to disk. This will help you >look back at what was captured after the Mir pass is complete, and even >if you are unable to connect to Mir, you can read what other people were >sent. > >This is a sample of a station logging off from Mir: > >R0MIR-1>WF1F/V [05/01/95 03:50:57]: <>: - Logged off > >R0MIR-1>WF1F/V [05/01/95 03:50:57]: <>: >*** DISCONNECTED [05/01/95 03:50:57] > >R0MIR-1>CQ/V [05/01/95 03:50:59]: <>: - Logged off >"NOW YOU MAY BEGIN CALLING MIR, C R0MIR-1" > >Look for the "<>" Disconnect frame. This is different from the "<>" >Disconnect Busy message. If the station connected to Mir goes our of range, >then an idle timer will force a log out after 8 minutes. The Mir PMS will >send 15 <> messages, then MIR resets and sends out the desired "CQ, ><>" packet (UI = Unconnected Information frame). > >In part 3, we will discuss how to format your messages for upload to the Mir >Personal Message System. > MORE MIR OPERATING HINTS * >============================ >The Mir operating hints that have been carried in SpaceNews over the past >several weeks have received wide acclaim from all corners of the world. >It is hoped that these tips will help make contacts with Mir more practical >and rewarding for all those involved. Many thanks go to G. Miles Mann, >WF1F and Dr. Dave Larsen, N6JLH for contributing their sage advice to >those recent articles. As a follow-up, I thought I'd throw my hat into >the ring and offer some comments on the effect that Doppler shift plays >in communicating with a simplex communications satellite such as the >Amateur Radio station on Mir. > >Doppler shift is nothing new in satellite communications, but it takes >on an interesting "twist" when a simplex communications link is employed. >Doppler shift is the apparent frequency change observed as the result of >the motion of either the transmitter or the receiver in a communications >link. Both the satellite's motion and the Earth's rotation contribute >to Doppler shift, with the satellite's motion playing the larger role. >Doppler shift's magnitude is determined by the rate of motion, while >its polarity is determined by the direction of motion. The polarity >is also determined by whether the transmitter or the receiver is in >motion. > >When Mir is approching your ground station, the spacecraft appears to >be moving towards you at a high rate of speed. This motion causes the >signal received from Mir to appear about 3.5 kHz ABOVE Mir's actual >transmitting frequency of 145.550 MHz. At the same time, while Mir >races toward your ground station, it receives signals from your uplink >transmitter about 3.5 kHz ABOVE your actual transmitting frequency. >No Doppler shift compensation is performed on the Mir spacecraft. >All compensation must all be handled by individual ground stations. > >In order to compensate for the effects of Doppler shift, ground stations >wishing to communicate with Mir must tune their receivers several >kilohertz ABOVE 145.550 MHz at the time of acquisition of signal (AOS), >AND their transmitters several kilohertz BELOW 145.550 MHz. This involves >transmitting and receiving on separate (split) frequencies approximately >7 kHz apart. Most ground stations use transceivers that transmit on the >same frequency on which they receive (simplex), and if they tune their >transceivers 3.5 kHz (or 5 kHz if their equipment tunes in 5 kHz steps) >above 145.550 MHz at the start of a pass, their uplink signals are >received 7 kHz (or 8.5 kHz) ABOVE what the Mir space station receiver >is tuned to. The chances of establishing a radio contact under these >conditions are extremely remote, even if there are no other ground >stations competing for Mir's uplink receiver. > >Around the time of closest approach (TCA), which also occurs around the >time of maximum elevation for satellites such as Mir in circular orbits, >the Doppler shift between Mir and the ground station approaches zero. It >then quickly reverses polarity as Mir recedes at an ever increasing rate >away from the ground station. At TCA, it is safe for ground stations to >set their transceivers to 145.550 MHz and not worry about Doppler shift. >As Mir recedes however, stations should tune their receivers several >kilohertz BELOW 145.550 MHz, and their uplink transmitters several >kilohertz ABOVE 145.550 MHz to compensate for the increasing Doppler >shift. Failure to properly compensate for the Doppler shift on the >uplink would, again, result in the ground station's signal falling >outside the passband of the narrowband FM receiver on Mir shortly after >TCA. As Doppler shift increases, so must the split between the ground >station's transmitting and receiving frequencies. As DOWNLINK signals >drift DOWN in frequency during a pass, UPLINK signals must drift UP. >T/R offset is zero at TCA, and maximum at AOS and LOS. > >The effects of Doppler shift play a greater role in packet radio >communications than they do in FM voice communications. 1200 baud >packet radio communications (1 kHz shift AFSK on a narrowband FM carrier) >occupy a much greater signal bandwidth than does FM voice, 1200 baud >Manchester encoded FSK, or even 9600 baud FSK packet. If an uplink signal >isn't properly centered within the passband of the FM receiver on Mir, it >will be received with severe distortion if it is received at all. Tests >have shown that a 1200 baud FM packet signal must be strong enough to >produce at least 25 dB of receiver quieting for an acceptable bit error >rate performance. Along the same lines, if other stations are competing >with one another on the uplink frequency, it would take a signal strength >at least 25 dB above the SUM TOTAL OF ALL OTHER SIGNALS on frequency to >be received reliably on Mir because of the capture effect of FM. If just >one bit of a packet frame is received in error, then the entire packet >frame is damaged and must be re-sent by the transmitting station until >it is received cleanly without error. Incidentially, a signal 25 dB >(300 times) stronger than the sum total of all others is an ASTRONOMICAL >signal level even if only a few other ground stations are colliding with >one another on Mir's uplink frequency. That's why QRM is so damaging and >following proper operating procedures is so important when communicating >with Mir. > >While it may be possible to successfully pass a short connect request >packet to Mir and receive a connection acknowledgement in between >interference bursts, it's much more difficult to go much beyond that >and transmit longer information frames to issue PMS commands and >send a message to Mir in the midst of heavy interference. > >In closing, please keep in mind that the Personal Message System on Mir >is a single-user BBS with very limited storage capabilities. Only ONE >station may connect to Mir at a time. ALL OTHERS MUST WAIT. PLEASE >DO NOT connect to Mir unless the PMS is open and transmitting CQ frames. >PLEASE DO NOT connect to Mir unless you have a reason for doing so. >PLEASE DO NOT use Mir for passing terrestrial packet radio traffic. >PLEASE DO NOT use Mir as a digipeater, and PLEASE DO NOT connect to >the keyboard port (R0MIR) unless it is in active use by a Cosmonaut >wishing to make a contact. PLEASE LISTEN carefully to Mir's downlink >frequency to avoid causing interference to other stations who may already >be in contact with Mir and to determine what mode of communications the >Cosmonauts are using on the Mir spacestation. * DOPPLER SHIFT REVISTED * ========================== The following is a follow up to John's good article on Mir and the problems with Doppler shift. Many of us have transceivers that are "channelized" (tuned in discrete steps of several kilohertz each). This means you cannot make any fine tuning adjustments to your receiver or transmitter frequency. Most Mobile/HT transceivers are limited to the smallest frequency change of 5 kHz or 2.5 kHz channel steps. Doppler shift will cause the Mir transmit frequency (145.550 MHz) to appear as if it is 3.5 kHz higher in frequency. If you tune to 145.555 MHz, you may improve you reception (for a 5 kHz rig). Consult your transceiver's operating manual for information on establishing "odd-splits" and program in the following consecutive frequencies into your transceiver's memories: For transceivers with 5 kHz steps: Channel 1 145.550.0 TX 145.555.0 RX Channel 2 145.550.0 TX 145.550.0 RX (simplex) Channel 3 145.550.0 TX 145.545.0 RX For transceivers with 2.5 kHz steps: Channel 1 145.547.5 TX 145.552.5 RX Channel 2 145.550.0 TX 145.550.0 RX (simplex) Channel 3 145.552.5 TX 145.547.5 RX When Mir is approaching your QTH, use channel #1. Then when Mir is over head, use channel #2. When Mir passes your QTH use channel #3. For best results, use a satellite tracking program that displays Doppler shift in real-time. InstaTrack, available from AMSAT-NA, is one such program. This information will assist you in determining when it is best to change memory channels. As you may have noticed, I do not recommend adjusting you uplink frequency for the 5 kHz transceivers. This is because you may have better results if you leave your receiver tuned to 145.550 MHz. The Doppler shift is only at the +3.5 kHz setting for a short period of time at AOS prior to an overhead pass. Shortly after AOS, the downlink signal will drift lower, and in five minutes or less when the spacecraft is overhead, the Doppler shift will be zero for a brief period of time. The downlink signal will then drift lower, down to -3.5 kHz over the next five minutes. The receiver on Mir can work ground stations when the ground station is off frequency by as much as 3 kHz. This is because the receiver on Mir has a relatively wide passband. In some situations, a wide receiver is good, and we are lucky to have such a receiver on Mir. If the receiver on Mir had better selectivity, it would actually make it harder for ground stations with channelized transceivers to access Mir. The following are specifications for the transceiver on Mir along with a few others for comparison: Selectivity at Rig -6dB -60dB =============================================================== ICOM 228 15kHz 30kHz Existing equipment on Mir Yaesu 736R 12kHz 25kHz Typical Base station Yaesu 2400 12kHz 30kHz Typical Mobile transceiver What makes the Mir transceiver work so well is the wide -6dB @ 15kHz receiver passband. This helps the receiver copy signals that are off frequency by as much as 3 kHz. The bad thing, however, is that Mir requires a wide, clear channel. The normal channel spacing required for 2-meter FM is 20 kHz, but because of the Doppler shift, the Mir station requires 25 kHz channel spacing. This means that during a Mir pass, courteous stations should not run other modes between 145.525 MHz and 145.575 MHz to avoid interference with communications taking place with Mir. Remember, only 1 station can connect to the R0MIR-1 PMS at a time. ALL others must wait. [Info via G. Miles Mann, WF1F]