Packet Radio

Packet Radio is yet another data mode used for sending text messages in digital form from one station to another. There are two things that separate Packet from other data modes. One is the fact that full error correction is used, and the second is that more than one contact can take place on one frequency at one time. These two advantages have led to a network over the world of real-time and non-real-time contacts. Packet can be used in the same way that RTTY or PSK31 is used on HF, but is slower by comparison.

The REAL advantage is the non-real-time use for the mode. If you look at Packet as a container for a message with an address along with it, then the data is contained within the Packet and if the data, or message, is long, then it is broken down into smaller parts called frames. These are sent sequentially, and each frame consists of a start "flag", an address, the text and an ending "flag". Each frame is identified by the receiving station by a unique number and if this co-incides, then the receiving station sends an acknowledgement and the next frame is then sent. If the two numbers are different, the receiving station asks for a repeat. You can therefore see how more than two stations can exist on one frequency at a time, with this type of corrective sequence. It is not necessary to go into lengthy technical discussions of the operations of the TNC, so I will merely explain the setting up of a typical station.

A typical installation for a user would be a computer, a TNC (Terminal Node Controller or Modem) and a transceiver. Using the equipment rather depends on what the user wishes to do. However, since a simple installation can cover most uses, I will describe these as we go along. The "typical" installation I just covered is not strictly true in the year 2003. When packet radio was first introduced, a TNC was essential, but now there are software solutions that have taken over as a cheaper way to obtain the same, or better, results. So, the PC with a sound card is the basis of a packet ( or any data mode ) station. The software to use is written by SV2AGW and is available to download on the Internet. Once installed, it will allow you to run 300 baud packet for HF operation, 1200 baud for local use and also 9k6baud for local use, if there are any other similar users.

One of the first things to do is to read as much as you can. There are several books available to introduce you to all the advantages of Packet Radio, and the following would be a good start:

Packet Radio Primer by Dave Coomber G8UYZ and Martin Croft, G8NZU
Your Gateway to Packet radio by Stan Horzepa WA1LOU
Digital Modes for All Occasions by ZL1BPU

These are readily available and will be a worthwhile investment.
Do a search on the Internet, and probably one of the best places to start would be the BARTG Web Site. In any case, if you are serious about Data communications, you should join BARTG. I think there are some tutorials on there but a check would be a good idea.

Setting up the station has to be done properly in order to gain full advantage of the system. One of the most important things to check is your deviation. Assuming you are using an FM transceiver, set up your deviation so that it is not more than 2.5kHz for a 12.5kHz channel. Most channels on two meters should be 12.5kHz now. Then check your tone frequencies and make sure they are accurate, and lastly the various parameters on the TNC or in your software program. The most important of these are the timing parameters. If these are not set correctly you will not connect to the other station.

TXD 65
MAXFRAM 1
RESP 15
DWAIT 4
Ppersist 60
Frack 7
Slottime 120
Retries 10
Paclen 200

These are the most important to get right in the first place. Once you have these set correctly then try a connect with another station. If all works, then you are set to proceed further.

One of the most common uses for the mode is the accessing of the local Bulletin Board System or BBS. This is run by a volunteer, who leaves his equipment running 24/7 with a PC and a Mailbox program. This is where the non-real-time use comes into its own. It's a bit like posting a letter. You compose it, either off-line or on-line and then send it, addressed correctly to the BBS. The BBS then routes it to the address you have given it and -hopefully - delivers it to your correspondent. If the route is within the UK, then it follows a terrestrial network around the houses until it ends up at the nearest BBS to your correspondent. He then reads it, and replies and the reply comes back via the same route.

If the mail is for abroad, say Australia, then your mail is routed via the UK Network to GB7LDI, the Satellite Gateway. It is then automatically up-loaded to an amateur satellite, UO-22 carrying store and forward software, and is downloaded when the satellite is above Australia, by a VK Satellite Gateway. It then follows the VK terrestrial route to its destination. This routing has been spoiled lately by BBS changing over to Telnet, an Internet based telephone forwarding system, non-amateur. The Internet has been responsible for a decline in the interest in Packet Radio, but having described the journey of mail destined for VK, using an amateur RADIO based network, surely this should be supported instead. There is more satisfaction from talking to a VK on the air than phoning him!
You can find our more about the Satellite Gateway system from another article I have written, also on here.

The BBS has all sorts of servers, all to make your use of it much more interesting. You can ask to have your mail sent and collected by the BBS, and by leaving your gear on as well, you can have bulletins of just your interests, sent to you too. Conferencing is possible using the BBS, with several stations on at once this can prove quite interesting, just like chatting.

There are various means of asking for all sorts of information, from a histogram of the use of the BBS to orbital data for about 40 different satellites.
The teletext server has lots of interesting articles and up to date information on all sorts of subjects. The Library is another place where you can spend a few hours just reading. There is a full call-book server on CD ROM, and also an up-to-date QSL manager server.

If you get fed up with the BBS, then take a look at your local DX Cluster. If you are interested in HF DX-ing this is the place for you. You don't have to listen on the bands for hours on end any more. Just monitor the DXX Cluster and watch the spots come up. Then just tune your transceiver to the frequency given and - hopefully - work him! Propagation can be checked and the latest solar data found here. You can even use your packet station to connect to the International Space Station!

It is far too complex a subject to cover it in full here so take my advice and invest in a book or two. Software is all important and if you are an end user of a BBS, take a look at Winpack or TPK, or as I suggested above, the SV2AGW program. Above all, enjoy it, and if you don't understand something, never be afraid to ask. We all had to start and we all had to ask. If the person you ask takes offence or laughs at a simple request, then he is not worth talking to. Just ask somebody else. A genuine Radio Amateur will always help.

Above all, enjoy Packet Radio - whatever you decide to do with it.

Tweet