My packet radio email address is OH3QN@OH3RBC.FIN.EU


WHAT IS PACKET RADIO?

Packet radio is digital communications via amateur radio. Packet radio takes any digital data stream and sends that via radio to another amateur radio station. Packet radio is so named because it sends the data in small burst, or packets.

WHAT IS AMATEUR RADIO?

Amateur radio is individuals using specified radio frequencies for personal enjoyment, experimentation, and the continuation of the radio art. Amateur radio operators must be licensed by their government. Normally, a test on operating practices, radio theory, and in some cases morse code proficiency test is administered. Amateur radio is not to be used for commercial purposes. Also, amateur radio operators are restricted from using profanity and using amateur radio for illegal purposes.

WHAT ELEMENTS MAKE UP A PACKET STATION?

1. A TNC (Terminal Node Controller)

A TNC contains a modem to decode the audio signals into digital signals. It also contains a micro-computer handle to convert the digital signals into text that can be sent over RS-232 port to the computer. The CPU also handles the protocol overhead of the packet station. When you send data, it takes the text, puts error checking on it (CRC) and also puts it in envelope for sending. When receiving a signal, it takes it out of the envelope, and sends the message to the computer.

2. Computer or Terminal

This is the user interface. A computer running a terminal program or just a dumb terminal can be used. For computers, any phone modem communications program can be adapted for packet use or customized packet radio programs are available.

3. A radio

For 1200 baud operation (normal user access), a standard voice radio cab be used (9600 baud requires a special data radio). For UHF or VHF packet, Narrow band FM is used, normally on simplex channels. For HF packet, 300 baud data is used over single side band modulation (SSB).

AND LAST; WHY PACKET OVER OTHER DIGITAL MODES?

Packet has one great advantage over other digital modes: automatic operation. Packet TNC's are very advanced as far as automatic control go. Just simply connect to the other station, type in your message, and it is sent automagically. Any packet TNC can be used a packet relay station, or a digipeater. This allows for greater range by stringing several stations in a row. On HF, this allows for contacts with stations normally not in propagation range.

Packet radio provides error free transmissions because of built in error detection schemes. If a packet is received, it will be correct.

Also, on VHF/UHF packet, packet operators are allowed to operate in automatic control mode. This means that you can leave your packet station on constantly. Other users can connect to you at any time they wish to see if you are at home. Some TNC's even have Personal BBS's (sometimes called mailboxes) so other amateurs can leave you messages if you are not at home.

Another advantage of packet over other modes is the ability for many users to be able to chat simultaneously using the same frequency.


One of my best packet radio (AX.25) contact so far has been with Russian space station "Mir" in 1991...

Mir, the Russian space station, was in space since February 1986 till March 2001. The word 'Mir' is usually translated in to English as 'peace', but also means 'world' or 'an autonomous community'. A popular Russian greeting is 'Mir o Mir' - Peace on Earth. In 1988 a handheld amateur radio was added to Mir for crew recreational use, and it was a popular activity. Many other pieces of amateur radio hardware followed, and Mir had an extremely impressive ham station. Ham radio was a popular activity for many of the Mir crewmembers. The Mir Amateur Radio EXperiment (MAREX) turned out to be one of Mir's most visible activities, and an enjoyable leisure time activity - both for the cosmonauts and the hams who have the opportunity to talk to them.

Finding out when Mir is going to be over your horizon was fairly easy if you've got almost any microcomputer. There are dozens of satellite tracking programs which predict when a satellite will be over your location. Mir's radio was set for 145.800 Mhz. (space to ground) and 145.200 Mhz. (ground to space). For most hams it's easy to set your radio to listen to 145.800 Mhz. with a - 600 Hz. offset - similar to operating with a local repeater. Mir's packet system used the same frequencies - 145.800 Mhz. Mir to ground, 145.200 Mhz. ground to Mir. For a relatively low altitude spacecraft like Mir and 2 meter transmissions the maximum doppler was 3.3 Khz. In effect not adjusting for doppler is the equivalent of using a radio which is slightly off frequency. That isn't too bad, and many folks don't even bother compensating for doppler. If you do compensate for doppler your signals will be clearer, and easier to understand.



During my contact packet radio communications were carried out between the Russian Mir space station and many ground stations on 145.550 MHz. Callsigns of U2MIR and U2MIR-1 were used by the amateur radio station on board Mir. Space station Mir had a fully operational packet radio bulletin board system, complete with a "standard" PBBS command system capable of supporting mail exchanges between users as well as disseminating news bulletins to all users of the system.

The U2MIR-1 BBS system was compatible with standards 1200 baud 2-meter FM packet stations. No special TNC's or external PSK modems were required for access. Downlink signals from Mir were strong. Even operation with indoor antennas did seem possible. Some lucky hams were successfully contacted Mir while watching Mir go across the sky - a simultaneous visual and radio contact!

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