Fourpak Packet Radio Group

The following is aimed at radio hams who want to know what packet radio is and what it can do.

Packet radio is a text-based form of communication between Radio Hams using computers and radios. It allows simultaneous error-free two way communication, and allows several conversations to co-exist on the same radio channel at the same time.
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Why is it called "Packet" radio?

The information being transmitted is broken up into discrete blocks or packets of data, with typically a hundred or so characters in each packet. These packets take between 1/2 and 2 seconds to transmit, and the radio transmitter is only active during the transmission of a packet, which is why the radio channel can be shared with several other Packet users. Each packet contains source and destination callsigns, so packets are routed to the right people.
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What can I do with it?

Keyboard-to-keyboard chats.
OK, so you can chat with a microphone, but Packet allows you to go and make a cup of tea, or answer the phone without missing anything, because it's all there in print. You can have extended chats in which each party only says something infrequently, while you're all getting on with other things, like operating HF, watching TV, mending a rig...

And these chats needn't only be with locals. Packet allows you to converse with people far away, even if you're only running basic equipment. This has obvious advantages for Class B licensees, but even for class A's it can be useful, as it doesn't need high power and doesn't use fickle propogation modes. Low power also means less TVI !

There is a worldwide network of Packet relay stations, called nodes. You can "connect" to your local node, then instruct it to connect you to any other node. In this way, you can "visit" far away places, and the exploration and charting of the network is great fun in its own right. From any node you can escape from the network and contact the local users in that area, either by calling a specific user, or by calling "CQ".
Exchange Electronic Mail
In intimate relation with the network of nodes is a worldwide network of mailboxes (also called Bulletin Board Systems, or BBS's for short). These allow you to send messages to other packet users anywhere in the world, either individually ("private" messages) or collectively (bulletins).

These messages can contain any sort of data, not just plain text. People send each other pictures, computer programs, sound samples and so on. And you can join special interest mailing lists, where people share information on a common interest.

Using the mailbox network, you can have leisurely conversations with other Hams which may last days, weeks or even months, the modern equivalent of correspondence by letter, but faster. You're not tied to specific "sked" times, and can communicate at your leisure.

There is a wealth of experience and knowledge amongst packet users, and you can send a bulletin asking for help on any topic, or you can distribute information which may benefit others. You can take part in nationwide discussions on a wide range of topics such as: (A VERY small sample!) Amateur Satellites, Land Rovers, Satellite TV, winemaking, Motorbikes, rig mods, Star Trek, Raynet, DX, propogation, TCP/IP, space, Television, scanning, recipes, football, UFO's......
Exchange Data
Many mailboxes have file areas containing a wealth of useful (and not so useful) data, such as rig mods, satellite data, UFO reports, antenna designs, programs, pictures, poems, recipes, technical reference and so on. You can "download" the files from your local mailbox, or request files from other mailboxes.

Taking this idea one step further, there are specialised "databases" connected to the network, in which the data is indexed and stored in a logical manner, and upon which searches can be performed to find the data you want. These databases are themselves networked together, so that they can share data.
Chase the DX
Another useful Packet service is the DX-Cluster. This is like a bulletin board, but works in real-time. DX chasers connect to this service, and leave it running in the corner of the shack. When someone finds some rare DX or spots an opening, they can type in a short message which is instantly flashed to all other users connected to the system at that time, so everyone gets a chance to work the DX.

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What CAN'T I do with it?

You can't yet browse the Web via Packet Radio. It is technically feasible, albeit a little slow, but the main problem is that the UK licencing conditions forbid the interconnection of Packet and the Internet, except as the medium between two ham stations. However, we hope licensing will eventually become more liberal. For the moment we're restricted to browsing amateur radio sites only.
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Why Packet, why not just TALK, with a microphone?

As mentioned above, you can do things on Packet that you can't do on Voice. There's no reason why you can't do BOTH - and at the same time too! For example, you could be having a Voice ragchew on 70cm, while having a Packet contact with someone hundreds of miles away on 2 metres. Or you could be reading bulletins from the local mailbox while chatting on your local repeater. Or watching out for DX "spots" from the DX cluster, while operating on HF.

Many people make the mistake of putting all their eggs in one basket and going completely over to Packet, thinking it will allow them to do everything they could do on Voice, and they get disillusioned because the two are complementary, but very different.

Some people however prefer Packet, and are much more active on that mode than they would ever have been on Voice.
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What would I talk about?

Anything and everything, as you would in a normal Voice contact. Packet tends to be a lot more informal, and you can have in-depth conversations with people. You don't really experience "microphone shyness" in the same way as you would on Voice, and the written word allows you time to think carefully about what you want to say.
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Do I need any technical knowledge?

Absolutely not. You can get on Packet by simply plugging a few pieces of equipment together, then you can take it as far as you want, either just USE the system and enjoy it, or delve further into it's workings if you want.

You could choose to build your own equipment, either from kits or from scratch, from published designs or your own. You can use ready made software or even write your own. As with any other branch of radio, you can build or modify radios, antennas and power supplies, and solve EMC problems.

Packet gives tremendous scope for self-training. Once you're on Packet you have access to packet experts worldwide, many of whom will be only to glad to help you learn more.
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Isn't all this computer stuff killing the art of Radio?

Emphatically NO, it is doing quite the reverse. Because you don't need state of the art rigs for Packet, many people are encouraged to adapt or modify ex-PMR radios. Suddenly, all those old, simple, crystal controlled radios are back in demand, to leave the main rig free for Voice operation. When people operate simultaneous Voice and Packet, they may need to learn about filtering and optimum antenna placement, in order to minimise mutual interference. And once you're on Packet your horizons expand, so you have access to the expertise of other Amateurs worldwide, with whom you can share technical know-how.
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Do I need special equipment?

You will need something on which to type and display text, such as a computer or a "dumb terminal", a radio, and an "interface" to connect the two. The complexity (and cost) of the interface depends mainly on the type of computer or terminal used and the frills required, ranging from a couple of transistors and a few passive components to a full TNC (Terminal Node Controller). All the interfaces are available ready-built. See below for a more detailed disucssion.
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What is a TNC?

TNC stands for Terminal Node Controller, and it used to be the "heart" of a Packet Radio station, although these days computers are increasingly taking over that role.

It is usually a little box, four or five inches square and an inch or less deep, although there are much bigger TNC's which include other modes such as RTTY, FAX etc. The front panel usually has a row of LED's giving status information, and the back panel houses sockets for 12V DC power input, RS232 (connects to the computer), and a lead to the radio, carrying audio in/out and PTT connections.

Its function is to accept text from the operator's keyboard and break it up into discrete blocks or "Packets" of data, which it sends over the air by keying up the radio at the appropriate time. Packets received from other stations are assembled back into text and presented to the operator's screen. All the error detection and correction is done automatically, invisible to the user.

All TNC's have the ability to act as a relay station, receiving and retransmitting other peoples' packets upon request. This is called a "Digital Repeater", or Digipeater for short.

Most TNC's also include a Personal Mailbox System (PMS for short), which is like an automatic answering machine. Other Packet users can contact your PMS and leave you messages, which you can read at your leisure. You can also leave messages for other people in your own PMS, so that they can be read when the recipient calls your PMS.

A few types of TNC have a built in KA-node. This is a more efficient type of digipeater, allowing Packet users to send their packets all over the country, by directing the output of one node to the input of another and so on.
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Do I need a special licence?

You only need a special "Notice Of Variation" (NOV) to your licence if you intend to operate a full service mailbox. And you need special permission called "site clearance" in order to operate unattended on certain frequencies, such as those at the top and bottom of the 70cm band.

You need to inform your local RIS branch if you operate your station unattended. This is so they know how to close your station down in the event of interference to vital services, and is not necessary if you turn off the station when you're not there.
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Do I need to leave it on all the time?

You can do so if you wish, but there's no need these days. If yours is the only Packet station for miles around, you may wish to leave it on to act as a "relay station" for other users, either as a normal digipeater, or as a node. If you want others to be able to drop messages into your personal mailbox at any time of day, you will need to leave the equipment switched on. But with so many full service GB7 mailboxes, it's just as easy to log on once a day to collect your mail, or have the mailbox deliver/collect mail automatically at a certain time of day.
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On what frequencies do I find Packet Radio?

On HF, Packet is usually found just above the CW allocations, along with RTTY, FAX, AMTOR etc.

The main activity on VHF is to be found on the two-metre band, between 144.800 MHz and 144.975 MHz, with 144.950 MHz being the most popular frequency in sparsely populated areas.

The second most popular band is 70cm, with activity between 432.625 and 432.675 and between 433.625 and 433.675 MHz. In sparsely poulated areas, 432.675 MHz is the most likely frequency on which to find activity.

On 4 metres, activity tends to be on either 70.325 MHz or 70.4875 MHz, with 70.3125 and 70.3375 MHz in less common use. 50.650 MHz is the main channel on 6 metres, which isn't a popular band. The allocations at the top and bottom of 23cm are used by site-cleared network stations for interlinking, and there is generally no user access up there.

On HF, Packet uses FSK (Frequency Shift Keying), whereas the predominant mode on VHF is standard FM.
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Is mobile Packet feasible?

Yes. In fact many organisations such as the AA and the gas board use a form of Packet Radio to exchange data with their mobiles. Amateur Packet stations have been established in cars, and on motorcycles and pedal cycles. Even pedestrian portable packet is possible, using a handheld radio, a palmtop computer, and one of the latest low- consumption TNC's which runs off a PP3 battery. Or better still, there are mobile rigs and walkie-talkies with inbuilt TNC's.
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What equipment is needed?

Firstly and most obviously you need some sort of radio, capable of use on the main packet frequencies. Most activity occurs on 2 metres FM, but the 70cm band is also gaining in popularity. For listen-only, a scanner will suffice, but a transceiver or a transmitter-receiver pair is needed for full operation. Ex-PMR gear is ideal, because most packet activity within a given area tends to congregate on one or two frequencies, and you can get away with just a single channel xtal controlled rig. Radios with solid-state transmit/receive switching are preferable, because they are quieter in operation and more reliable in heavy service, but relay switched radios are perfectly acceptable.

Secondly you will need something on which to type and display text, such as a computer, a dumb terminal, or even an electronic typewriter. Virtually any computer will do, as long as it has a "serial" or "RS232" port to communicate with the outside world, and can run a program called a terminal emulator. Some computers, such as the Commodore 64 and Sinclair Spectrum do not have built-in serial ports, nevertheless there are adaptors and interfaces available, and many of these machines are in use for Packet Radio. Any IBM compatible computer will be ideal, as there are many powerful shareware Packet programs available for this platform, which offer facilities beyond those provided by terminal emulators. Dumb terminals can generally be obtained for next to nothing, yet for some applications they are ideal.

Lastly you will need an interface to connect the radio and the display unit together, and the type of interface depends on the type of display unit. If you use a dumb terminal, or a non-IBM compatible PC (other than Commodore 64 or Sinclair Spectrum) you will certainly need a proper TNC. If you use an IBM-compatible PC, a Commodore 64 or a Spectrum you can use a much simpler interface, in conjunction with a omputer program which does much of the work normally done by the TNC, such as the German BAYCOM program. You can choose to use a TNC with any type of computer, provided the computer has a serial port. Many people choose to use TNC's, because they enable you to leave a Packet station on 24 hours a day without having to run a computer all the time, but a growing number of people are entering the Packet scene using the much cheaper Baycom system.

Software now exists (e.g. "FlexNet" and SV2AGW "Packet Engine") which will allow you to run Packet on a Windows PC using the inbuilt sound card.
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What would it cost?

Assuming you already have a suitable radio and an IBM compatible PC, all you need is an interface and a suitable program. The simplest interface can be built for a pound or less. An interface for the more popular Baycom program can be built for under ten pounds, obtained as a kit for around twenty, or ready made for anything up to fifty pounds - it's worth shopping around! The programs are generally shareware or freeware, so can be copied from a friend or obtained for a couple of pounds from any shareware company. Registration fees are not expensive. A suitable second-hand computer shouldn't cost you more than about 5 pounds these days.

The Commodore 64 interface is virtually identical to the BAYCOM interface used on the IBM-compatible PC's, and can be built or bought for a similar price. The DIGICOM program for the C64 is shareware, and was in fact the forerunner of BAYCOM. Alternatively, you can build an RS232 interface for the C64 and use a TNC (see below), with a terminal program such as KERMIT. Commodore 64 computers can be obtained from rallies for as little as a fiver.

If you choose the TNC route, it is going to be more expensive. TNC's generally start around the 120 pound mark for the "basic" models, which nevertheless are very suitable, up to several hundred pounds for the "all-singing-and-dancing" models which include PACTOR, AMTOR, FAX, RTTY etc.

Second hand TNC's are like gold dust, and where available they tend to hold their price. Nevertheless, if you're in the right place at the right time, you may be able to obtain one for around fifty pounds.

Use of the network is free, but the operators are always grateful for contributions towards its running cost.
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If Baycom is cheaper, why does anyone use a TNC?

Baycom is a relatively recent arrival on the Packet scene. Many people started on Packet before Baycom was written, and a TNC was an essential item. These people carry on using TNC's, although they may have additional Packet stations on other bands using Baycom.

Early editions of Baycom did not include a PMS, a facility which many people find useful, so if anyone wanted a PMS they had to use a TNC. Later versions do include a PMS, but the main disadvantage is that you need to leave a computer on all the time, with the attendant fire risk, energy consumption, wear & tear, noise and so on. A TNC consumes only a few watts, and can safely be left on all the time. A TNC makes no noise either!

If you only have one computer, you may want to use it occasionally for purposes other than Packet Radio. A TNC will carry on working without being connected to a computer, so it allows you to keep your Packet station on air while you do other things with your computer.
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Where is it going?

In the future, as data bandwidths increase and compression techniues improve, Packet Radio will be able to carry real-time voice communications, and beyond that, even moving pictures. And beyond that, who knows?
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Where can I find out more?

The RSGB sell a couple of beginners guidebooks to Packet Radio, at around eight pounds each, and while these can be very useful there is no better way to learn than hands-on experience. So go and see a friend who is running Packet Radio, and maybe operate his station.

If you don't know anyone who uses Packet, your best bet is to contact your local Packet user group, who will be glad to help you.

FOURPAK, the Four Counties Packet Radio Group, is the group covering Herefordshire, Worcestershire, Gloucestershire and the West Midlands, and they are responsible for the provision and maintenance of the network in those counties.