MIREX Current / Pending Projects

Mirex Proposal for reconfiguring the existing Amateur Radio Equipment on Mir
October 21, 1997

Modem replacement and reconfiguration plan

Mirex would like to experiment with a configuration to allow the simultaneous support of both 2-meter Mono band 1200 packet and 70cm mono band packet operations from the Russian Mir Space Station. With the addition of the new Modem, there should be enough equipment on board the Mir station to support simultaneous dual band operations.
The existing 2-meter 1200 baud Mono band PMS station is working very well.
The Mir PMS is the most popular Amateur Radio satellite in the world. Because of the popularity of the 2-meter 1200 baud Mono band PMS, there is just not enough memory or general capacity to support the large number of users.
We would like to expand the Mir Amateur Radio projects, by adding support for a second radio band. And at the same time, keep the 2-meter 1200 baud Mono band PMS fully functional.
We believe it is very important to the future of Amateur Radio Satellite operations to always keep a place for beginners to start experimenting. The Russian Mir 2-meter 1200 baud Mono band PMS is the perfect place for beginners to start. Over 90% of all new Satellite Amateur Radio operators, start by learning how to use the successful Mir 2-meter 1200 baud Mono band PMS.

Benefits of two simultaneous band operations:

The 2-meter station operations will not change very much. The crews will still have voice and packet access via the 2-meter station. The equipment configuration suggested for the 2-meter station will consist of the Icom 228 Transceiver, connected to the PacCom HandiPacket II Modem.
This combination of equipment has already been tested for three years on Mir very successfully.
The memory mail box capacity of the PacCom modem is very limited, and is currently configured for 13k of message storage. Ground stations using the Mir 2-meter PMS, will not see any changes in the mode of operation.

The 70cm portion of the project will have over 100k of message storage capacity. Since fewer people have access to 70cm, the amount of competition will be lower.
The success rate of the station using the 70cm PMS will be much higher.
Mirex will transfer their daily messages to the crew members from their family, from 2-meter to the 70cm modem. This will help reduce the amount of traffic on the 2-meter side.
Initially the modem will be configured for 1200 baud.
This data rate will be extensively tested to verify the equipment operations.
After a successful test period, the modem will be switched over to 9600 baud RF packet data rate. Under strong signals conditions, 9600 baud data should be almost as reliable as 1200 baud.
Mirex will conduct extensive testing of the 9600 baud configuration.
The data rate of 1200 baud has limitations on the Size of a file which can be transferred during an 8 minute pass.
To calculate the amount of data which can pass, you need to take into account the Acknowledgment times for packets, and Transceiver Switch-over delays of the radio.
Mirex has measure this value to be between 40-80 characters a second at 1200 baud or 35% to 65% efficient , when signals are good. During an Ideal 8 minute pass, you can upload a file of 38,000 characters.
However, this file would require the whole pass, and signals must be perfect. Mirex has tested upload files sizes in the range of 5,000 - 10,000 characters, with good results during average signal conditions.
During Mike Foale's stay on Mir, Mirex sent up JPG images of Mike's family via Packet radio.
The JPG files were carefully edited to make the files as small as possible.
A 2cm by 2cm image usually required 5kb of data. Because of the editing, the images were of poor quality, but it proved that images could be send, if we can find a way to increase the amount of data transferred.

After switching to 9600 baud FM 70cm, Mirex expects to find similar efficiency results. The table below will show, that even if 9600 baud signals are corrupted more frequency than 1200 baud signals, the throughput will still be much higher.
If 1200 baud is 65% efficient, and 9600 baud is only 35% efficient, then 9600 baud will still be able to deliver 4 times as much data during the same time period.
During an 8 minute pass, at 9600 baud, 35% efficiency, the Kantroncis Modem will be able to receive over 160,000 characters of data.

Efficiency in Characters per Second for Mir packet operations
                       35%        65%
    1200          42         78
    9600         336        624
Efficiency in Characters per Minute for an 8 minute pass
                 35%        65%
    1200      20,160     37,440
    9600     161,280    299,520

The primary reason we have delayed the implementation of 9600 baud packet, is because of the expense of the equipment and limited availability. Most Amateur Radio equipment built before 1995, was not capable of supporting 9600 baud data rates.
Now most new equipment comes equipment to support higher data rates. The cost of building or purchasing the newer modems has been reduces and is now affordable by many more Amateur radio stations.
The number of stations using Mir 70cm 9600 baud packet is expected to be approximate 50 to 100 users initially. This number of stations will gradually grow as more people discover the benefits of 9600 baud satellite packet.
The number of different stations using the 2-meter PMS is over 400 stations. This huge number of stations is causing problems with saturation and reliable access.

  1. Can we support both 2-meter Mono band packet and 70cm mono band packet at the same time with minimal interference. If there is any interference, we will have the opportunity to design filters which can be used on both Mir and ISS.

  2. Can we support 9600 baud mono band packet on Mir.

  3. What is the approximate efficiency rate of 9600 Mir 70cm satellite packet.

  4. How many different stations around the world can currently support 9600 baud 70 cm packet. Mirex has already determined from previous experiments, that over 120 stations world wide have access to 1200 baud 70cm packet.

  5. Is it possible to upload and download large files to Mir (20 - 50k files sizes).

  6. Transfer some of the 2-meter users, over to the 70cm band. When 70cm Packet is in operation, does the success rate on 2-meter packet improve because there are now two packet stations for people to use.


The information we learn from this experiment, can be used to help us design better systems for the ISS program.

Modem connections:

Connect the PacCom II modem to the Icom 228 2-meter radio.
Set the Icom to the Low, 5 Watt power level.
Configure several channels into the Icom, and use initially the 145.985 FM Simplex channel for both Voice and packet operations.

Connect the new Modem to the Amateur Radio power supply.
Connect the new 1200 baud Data cable to the modem and to the Kenwood TM-733 Data port. There are labels on this cable to help identify the cable and usage. The 6 pin DIN connector goes to the Kenwood TM-733, and the DB-9M goes to the matching port on the KPC-9612.

The PC serial port on the has been pre set to 9600 Baud. This rate should be the same as the existing PacCom II Modem.
Connect a Laptop PC to each Modem, one at a time and verify that both modems can be access and the mail on the modems, listed and read.
The command set for both modems is very similar.

Antenna connections:

The existing externally mounted antenna on Mir is designed to support both the 2-meter and 70cm Amateur Radio bands. The antenna connections are very important. If the connections are made incorrectly, one or both of the Amateur radios may be damaged.
According to conversations I had with Mike Foale, the radio needs to have the Antenna connected to the radio before the power is turned on.
If the Antenna needs to be disconnected for any reason, make sure the power supply is turned off and the radios power cable is then disconnected.
If the power supply is turned on, while the antenna is disconnected then a raw unfiltered 28 volts DC may surge through the radio.
These radios are designed for a 12 volt DC system (12 -14 volts).

Diplexer operation:

The Diplexer Filter is needed to connect both radios to the Externally mounted Dual Band Amateur Radio Antenna. Make sure all power is turned off to the radios and the power supply is off, before changing any antenna coax cables.
The existing Diplexer on Mir works in the following manner:

Filter Mode

  • VHF: In the filter position, the filters in the Diplexer are enabled. All VHF signals coming in from the antenna port will be pass throughout to the VHF Radio port. All other signals on the VHF Radio port will be attenuated. Do not try to transmit a UHF signal through the VHF Radio port when the switch is in the Filter or Bypass position.

  • UHF: In the filter position, all UHF signals coming from the Antenna port are passed to the UHF port. All other signals are attenuated. Do not try to transmit a VHF signal thought the VHF Radio port when the Diplexer is in the Filter mode.

Bypass Mode
The Bypass mode turns off the VHF Radio port and directs all Unfiltered signals to the UHF Radio port.

  • VHF: Do not Transmit any signal from a radio connected to the VHF Radio port when the Diplexer is in the Bypass position.

  • UHF: In Bypass mode, the filter will pass all Antenna signals, UHF and VHF to the UHF Radio port. If the Kenwood TM-733 is connected to the UHF port, and you want to transmit on 2-meters from the Kenwood, the switch must be in the Bypass mode. If the switch is set wrong, damage to the radio could result.

Antenna Connections:

Connect the Icom 228 to the VHF port of the Diplexer.
Connect the Kenwood 733 to the UHF port of the Diplexer.
Set the Diplexer switch to the Filter position.
The 2-meter transmitter on the TM-733 can be disabled to prevent accidental transmission on the 2-meter band. Use the following command from the Kenwood manual on page 30.

UHF Operations only.
1. Press the left [Band Select] to select the 144 MHz band. The left control select indicator will light.
2. Press the [VFO] button, then the [MR] button
3. Press [F] Function button, then the [CONT SEL] button
Look for the 'U2' to appear on the left Display, repeat step 3, until the Letters 'U2' are on the display.

Power Consumption:

The existing power supply for the Amateur Radio equipment is rated for 150 watts at 12 volts (approximately 12.5 amps). This value is sufficient to provide the power required for the Dual band operations providing specific settings are used.
Even if the transmitter output power settings are set incorrectly, there is still a small safety margin.
Since the Amateur Radio power supply will be at its maximum load, it is important that all other equipment be removed from the Amateur Radio power supply.

                          Minimum      Transmit        Max Transmit Load
                          Full Duty    Intermittent    Intermittent
2-Meter Station
Icom 228 A
Low Power setting          300 ma          3000 ma
High Power setting         300 ma                           6000 ma

PacCom Modem                50 ma            50 ma            50 ma

70 cm Station
Kenwood TM-733
Medium 'M' power setting   300 ma          4000 ma
High power setting         300 ma                           8000 ma

New Modem                   45 ma            45 ma            45 ma

Total Loads                695 ma         7,095 ma        14,095 ma

Safety Margin            >11.5 amps          >5 amps         1.5 amps over
Design limit
Conversion Date schedule:


Crew Work Load:

In conversations with Mike Foale, all of the wiring of the coax cables has already been completed. The only installation required would be to wire the new Modem to the Amateur Radio Power supply.
David Larsen N6CO and Miles Mann WF1F would be on hand to talk the crew though any configurations issues.
Mirex schedule times are flexible and most of the work can be carried out on weekends. I do not expect more than a 1 hour initial cable configuration time and 30 minutes of crew assisted test time to complete the project.


It is important to carefully pick the proper frequencies to support all of the existing Mir Amateur Radio projects and to try to avoid any interference problems to or from Mir commercial equipment.

There are currently two operational Mir Amateur Radio projects and one proposed.

2-Meter PMS    145.985 FM   Simplex
SAFEX II       437.950 TX - 435.750 RX

70-Cm PMS      437.900 TX - 435.025 or 050 or 075 RX

70cm PMS Transmit Frequency:
The 70cm PMS transmit frequency 437.900 was chosen specifically to reduce the possibility of interference to the SAFEX II repeater. The SAFEX II repeater has a set of build in Cavity filter. These existing Cavity filters will be sufficient to block any signal from the 70cm PMS from causing any interference to the SAFEX II Repeater.
This transmit frequency was also chosen because there are no other satellites using this frequency.

70cm PMS Receive Frequency:
The 70cm PMS receive frequency was chosen to be as far as possible away from the SAFEX II repeaters transmit frequency. The spacing between the channels is almost 3 MHz. This wide spacing between the two channels is required to allow both projects to operate at the same time.

By using the proposed frequencies, both the SAFEX II Repeater and the 70-cm PMS should be able to operate at the same time, with out any noticeable interference.

Crew Work Load:

The additional crew work load to support three (3) Amateur Radio Experiments will not be significantly higher than it is currently for two (2) Amateur Radio Experiments.
To help prevent crew intervention new rules will be posted for the 70cm PMS.

Review of existing 2-meter PMS rules.

The public is allowed to send mail to the 2-meter PMS, as long as the Mail is address to the Mir crew.
The public has been asked not to use the 2-meter PMS for Third-Party-Traffic.
The public should not send mail to other terrestrial amateur radio stations, or publish messages to ALL.
When the crew has free time, they may read and respond to some of the messages.
The public knows the crew is very busy, and does not have time to answer all of the mail messages.
These rules are good and they should stay in place for the present 2-meter PMS system.

The 70cm PMS will operate under different rules.

The 70cm PMS will be designed to operate as a Third-Party-Traffic Public-Mail-Box (PMB).
Amateur Radio stations around the world, who can afford to operate 70cm will now have an FM orbiting Public-Mail-Box.
Third-Party-Traffic will be allowed (biased on rules for the country of transmission).
The Mir crew members will not read any traffic from the Public on the 70cm PMB.
The Mir crew members will not send any mail to the public (except possible bulletins by the crew).
The mail box will be maintained by the Mirex team and other specific volunteer organizations. This Sysop support of the Public-Mail-Box will reduce the need for any crew involvement with the 70cm PMB.

Additional Benefits:
  • Many Amateur Radio stations want to find a simple affordable FM Public-Mail box.
    The existing Amateur Radio PMB satellites (F0-19, FO 22) require expensive SSB radios and PSK Modems. The Mir 70cm PMB will cost less for Amateur Radio Stations around the world to use. I expect 200 - 300 different users per month during the initial start of the 70cm PMB.

  • Reduced load on the 2-meter PMS.
    Many stations are still trying to use the 2-meter PMS to send Third-Party-Traffic.
    This traffic load can now be transferred to the 70cm PMB.

  • Replacement Satellite.
    Old existing Amateur Radio satellites are beginning to Fail. We have fewer working satellites this year than last year.
    The following satellites have all stopped operating recently A0-10, AO-13, RS-12.
    The future Satellite Phase-3D, will not fly until the year 2000.
    The Russian Mir Stations can help keep interest in Amateur Radio Satellites by added a third mode of operation.

We need to prove that multiple amateur radio experiment can be supported from a single orbiting space station.
When ISS is flown, it will not have one amateur radio experiment, but it will eventually have a dozen.
The information we gain from the experiments run on the Russian Space Station Mir, can be used to help develop new hardware for ISS. Success or failure we will still learn valuable information. But if we do not experiment, will never learn.


Back To Home