MIREX 70cm Packet Mir International Amateur Radio Experiment (MIREX) will be conducting a three week 70cm experiment with the Mir PMS station. The PMS station will be switched from the 2-meter band to the 70cm band on 437.650 MHz FM simplex world wide.
Information they expect to gain from the three week experiment:
1.Is the 70cm band interfered with by the existing commercial VHF equipment?
2.How many stations around the world have access to 70cm FM capabilities?
3.Do the 70cm Mir operations cause any interference to any of the equipment
on Mir?
4.Can simple ground stations compensate for 70cm Doppler and work Mir
on voice?
5.Can simple ground stations compensate for 70cm Doppler and work Mir
on packet?
MIREX will be running the test from September 6 until September 28,
1997 world-wide. After the completion of the test, they will switch the
Mir PMS frequency back to the current 2-meter frequency on September 29th.
Interference from Mir's VHF Commercial Communications Links
In 1993 the MIREX team began to hear there were problems with 2-meter packet, when Mir was transmitting on their commercial channel 143.625. The rumors indicated the 2-meter station on 145.550 would become deaf. The information that MIREX received about this problem was very limited, and the problems only happened over Europe. They did not have problems with 143.625 over the USA and were not able to analyze the problem until 1996. Then NASA began to install remote communications links with Mir in 1996. Now Mir was active on 143.625 as it flew across the USA. More ground links were being added world wide. Soon many populated areas of the world would have remote Mir VHF ground links.
MIREX began testing with the Mir crews in late 1996. It was confirmed that when the commercial link was active on 143.625, it was impossible to work the Mir space station on any frequency below 145.900. The frequency 145.940, was barely usable when the ground station was transmitting more than 3000 watts ERP.
These uplink power levels are just not realistic. A better solution needed to be found. MIREX is working on a filter project, that if approved, will solve the comm link interference problem. The MIREX filter project is still waiting extensive paperwork approvals, etc. No date has been confirmed for delivery of the filter. MIREX still encourages stations to use as little power as possible. Another possible solution is to try to use the 70cm equipment already on board Mir. The existing external antenna is a dual band 2-meter/70cm antenna. The existing radio, a Kenwood TM-733 (European version) supports both 2-meters and the 435-437 MHz portion of the satellite sub band. MIREX began testing of the 70cm operations for voice and packet during the spring of 1997. The equipment appears stable enough to allow access to the general public. They originally had planned to operate both bands simultaneously, but they have run into equipment and power limitations. So the test is being scaled back to test just the 70cm band for a limited time. For the duration of the 70cm test (up to 3 weeks) the 2-meter operations will be turned off. After the 70cm test is completed the frequency will be moved back to the 2-meter band.
MIREX believes that 2-meter mono-band operations should always be the primary system because it allows the greatest access to the most users. Other modes should be experimented with, and if successful additional equipment could be installed, just as long as you never permanently turn off 2-meter mono-band support.
[ANS thanks Miles Mann, WF1F, and Dave Larsen, N6CO, MIREX President for this information.]
The ERP requirements on 70cm are a little higher for this band. Stations should try for an ERP rating of greater than 25 watts. Doppler will be the biggest challenge. The Doppler on 70 cm is + and - 10,000 cycles. Most radios made today can only make tuning steps in 5 kHz channel steps.
To work Mir on voice, a station will need to get within 3 kHz of the receiver frequency on Mir. To work Mir on the packet frequency, error must be less than 2.0 kHz. A 5 kHz radio is not recommend for running 70cm packet during this test. The Doppler change is not linear. What this means is that during the first 3 minutes of the pass the Doppler will be approximately 10 to 9 kHz and will drift 1 kHz in three minutes. However during pass minutes 4 to 6, the Doppler will swing 14 kHz in 3 minutes. A radio which can step in 2 kHz or less can program in a set of 11 channels.
MIREX has tested this configuration for both voice and packet with good results. Use channel 1 at the beginning of the pass. Then monitor the FM signal meter for discriminator center tuning on the radio and change channels to keep the FM discriminator center tuning meter centered.
On 70cm both the TX and RX MUST change!
Program in these 11 channels in this order:
TX Channel RX Channel
Doppler
1 437.640
437.660 +10
2 437.642
437.658 +8
3 437.644
437.65 +6
4 437.646
437.654 +4
5 437.648
437.652 +2
6 437.650
437.650 0
7 437.652
437.648 -2
8 437.654
437.646 -4
9 437.656
437.644 -6
10 437.658
437.642 -8
11 437.660
437.640 -10
Dave Larsen N6CO and Mile Mann WF1F have been conducting many packet upload and download tests on 70cm with Mir. If a station can compensate for Doppler correctly the reliability should be equal to 2-meter packet. The Mir receiver seems to work better if the uplink channel is a little lower than or equal to the calculated RX channel. Going above the calculated RX channel may cause packet performance to drop off more quickly. Based the testing using the listed 2 kHz channels steps, it has determined that a mobile radio (with 5 kHz steps) can not work 70cm packet with any amount of reliability and should be avoided.
[ANS thanks Miles Mann, WF1F, and Dave Larsen, N6CO, MIREX President for this information.]
The following is from the September 6, 1997 ARRL Letter
Starting on or about Saturday, September 6, and continuing no later than September 29, ham radio voice and packet operations aboard the Russian Mir spacecraft will shift from 2 meters to 70 cm. An "experimental" worldwide FM simplex frequency of 437.650 MHz will temporarily replace the current 2-meter operating frequencies. Operations will return to 2 meters after the experiment ends.
In the meantime, the shift could make it a bit more difficult to work Mir. For starters, power requirements will be higher than on 2 meters -- 25 W ERP or greater -- although contacts using an H-T are not out of the question. Also, some transceivers do not cover the satellite subband (435 to 438 MHz).
The Mir International Amateur Radio EXperiment (MIREX) is conducting the 70 cm test based on suggestions from several Amateur Radio satellite groups who are interested in the feasibility of operating Mir and the International Space Station on 70 cm. MIREX hopes the experiment will determine whether the 70-cm frequency receives interference from the existing commercial VHF equipment on Mir and whether 70-cm operation will interfere with onboard equipment. More important for simple ground stations, however, is whether they'll be able to compensate for 70-cm Doppler shift on voice or packet.
MIREX President Dave Larsen, N6CO, concedes that Doppler will be the biggest challenge for earthbound hams trying to work Mir on 70 cm. The Doppler on 70 cm is plus or minus 10 kHz. Most radios include 5-kHz tuning steps, and to work Mir on voice you will need to get within 3 kHz of the Mir receiver frequency. To work Mir on packet, the frequency error must be less than 2 kHz.
Miles Mann, WF1F, of MIREX reports he talked to Mike Foale, KB5UAC, aboard Mir on 70 cm on Thursday, September 4. Mann was mobile at the time, running 35 W. He reports very good signal quality during the 10-minute pass, which was at close to 60 degrees. Mann said he compensated for Doppler by programming odd-split channels in advance. He reminds users that both the transmit and receive frequencies must change, if you program channels in advance.
Larsen said this week that if the experiment does not work out, "it will be cut short." He said he hopes a filter that could be sent to Mir as early as October will minimize desensing of the 2-meter transceiver by Mir's commercial equipment on 143 MHz.
The Mir Personal Message System (PMS) currently consists of a Paccom Handi packet terminal node controller (TNC) connected to a Kenwood TM-733 2m/70cm transceiver. The antenna is an externally-mounted dual-band antenna, similar to a mobile antenna. To comment on the experiment or for more information, contact Dave Larsen, N6CO, [email protected] or Miles Mann, WF1F, [email protected].