In 1837, Samuel Morse developed his first telegraph system and his code of dots and dashes to be used with it. This was refined into what became known in the 1850's as the International Morse Code.

  So, what has this to do with Data Communications? More than you might think!

  Modern digital communications essentially began in 1837. "Digital" in this sense refers to passing information in binary form, that is, by converting the information to be sent in ones and zeros. Morse code fulfills this requirement and is thus a digital mode.
 
Why did it Develop Further?

  One of the problems with Morse code is that it is relatively slow. By hand, sending speeds of 35 WPM (Words Per Minute) can be achieved by experienced operators. However, that is fairly hard work and is very slow when you consider that most people could read to an audience at in excess of 130 WPM without rushing (local TV news readers at more like 300 WPM!).

  Another major problem is that operators effectively have to learn two new languages to communicate efficiently. Why two? Well firstly, they need to master the code itself and become sufficiently conversant with it that they can think in it rather than trying to simultaneously translate it. Secondly, they need to learn a comprehensive set of abbreviations designed to speed up traffic flow with the limited transfer speed (an early "compression" technique - more about this later).

  Various techniques were developed. One was an automatic sending device where punched tape was produced on a special teleprinter and then fed through a Morse sending machine. These devices were still in limited use as recently as five years ago. Additionally, a receiver aid was designed whereby the received characters could be reproduced as inked marks on a paper tape (Samuel Morse's original method - only later did receiving operators realize that they could decode the incoming messages by ear). Not only did this provide a permanent record of the received information, it also allowed for high-speed hand or machine-sent Morse to be read at a slow speed by less experienced operators or to be archived for future reference.

What Came Next?

  Morse code (CW - Continues Wave) has one real limitation - speed. As mentioned previously, a large library of abbreviations developed to improve the effective "data rate". This had two side effects. An advantage was that CW became effectively an international language where a given abbreviation meant the same thing in every language, thus allowing effective communication between people with no common spoken language. On the minus side, it entailed learning a new language in order to be able to communicate effectively and at any speed.

  In essence, therefore, in order to provide effective communications, specialist training and skills were required by both transmitting and receiving operators.

The Typewriter - and RTTY.

  CW is, as stated earlier, a digital mode. This means that intelligence is represented by two levels. Morse generally uses an on-off keying system, in other words, a one and a zero.

  Prior to the development of telegraphy, the typewriter was invented as a means of producing the written word more efficiently. A logical conclusion of this was to combine the principle of the typewriter with a method of on-off keying - the result being the teletype or teleprinter.

  This overcame various problems. Firstly, much higher speeds were possible by experienced senders. In addition, unlike CW where the speed of the transmitting station is limited by the skill of the receiving operator, the signal received in a teletype system is telewriten text on a sheet of paper and thus the speed of the link is only limited by the mechanical limitations of the technology.

  In addition, the RT. system is limited to 33 characters - the English alphabet and numbers and a few punctuation's and special symbols. Although it was necessary to employ skilled typists to maintain accurate high speed links, in practice, any one-finger typist could be called upon in an emergency with an absolute minimum of training to maintain an albeit slow link.

  Another advantage of RTTY was that, with the development of the punched tape punch and reader, messages could be produced off air at low speed and then transmitted at a higher speed than that of the best manual operator. In addition, text could be formatted and proof read before transmission thus producing a clear and accurate result at the receiving end.

  It did not take long for CW and RTTY techniques, originally designed for wired telegraph systems, to be employed as part of radio links. However, this is where another major problem developed. Samuel Morse had discovered that his electric code receiving equipment could not cope with the signal level on a link over about 32 km in length. To get around this problem, repeaters were installed at regular intervals so as to receive and automatically retransmit the signal.

  However, with the incorporation of this equipment into radio links, this repeater technique was not possible. Where as the accuracy of CW wire systems was limited only by the skills of the operators, and that of RTTY by that of the sender, radio links suffered from interference and fading. At best, the gist of a plain text message could be derived from the context of the received text. At worst, the received message would be totally indecipherable. What was needed was some means of error detection and correction.

* RTTY (Radio TeleTYpe).

TOR.

  Basic error detection and correction is very simple in principle. Imagine that you are talking to somebody on the phone and giving them a list of items that you want them to buy. Each time you read them the next item on your list, they write it down and then read back to you what they have written. If it is correct, you tell them the next item. If what they tell you is not what you expected to hear, you can repeat this item until they correctly report it as having been written down at which point you can proceed to the next item. This is the basic technique of error detection and correction.

  In a CW or RTTY system, this is very difficult to achieve. A radio link is likely to be as poor in one direction as it is in the other. If the receiving station repeats received messages back to the originator, errors may occur during this process although the original message may well have actually arrived intact. This would require that the message be resent providing two more opportunities for errors to creep in.

  What developed were two similar error detection and correction systems. Based on the RTTY system, the first method involved sending each character twice. The receiving station would expect to see each letter twice in sequence, and if this was not the case, it would request a resent of the offending character until it correctly received the pair. The second system was similar except that only one letter was sent, but the receiving station would repeat the letter back and the transmitting station would resent it if it was not what it had sent.

  Again, these systems suffer from the problem that the repeated-back check could be received by the transmitting station as being an error even though the receiving station had read it correctly.

* TOR (Teleprint Over Radio).

What is Packet Radio?

  Packet radio is a digital mode. It is a method by which information can be passed between users in 1s and 0s by means of audio tones. It permits users access to personal and bulletin E-mail facilities (both exclusive of and integrated into the internet system), personal one-to-one contacts, access to DXCluster DX spotting facilities, satellite communications, GPS systems and contact with orbiting spacecraft.

Packet Switching Systems.

  With the advent of digital computer systems, the data rate at which information could be passed increased dramatically. Because of this, it became necessary to develop more efficient error correction systems and technically possible to do so. What actually developed was a protocol now known as X-25.

X-25.

  What happens here, at the simplest level, is that data is transmitted in "packets". In essence, each packet contains a start marker, a block of data, a checksum and an end marker. The checksum is a number which is effectively a mathematical representation of the data within the packet and is generated by the transmitting station. The receiving station performs the same calculation on the received data and produces its own checksum. If the two checksums match, the packet is deemed to have arrived intact. If it does not match, a resent is requested. The system used in Amateur Radio is an Amateur variation of X-25, "imaginatively" referred to as AX-25.

AX-25.

  Packet systems rely on a technique called handshaking. What happens is this: The originating station issues a connect request. On hearing it, the receiving station issues a confirmation of the request and announces its preparedness to establish a link or that it is busy. If the transmitting station has not received either of these messages within a preset time, it again sends a connect request. This process is repeated for a preset number of times after which it stops attempting to connect if it has heard no reply.

  After a connection has been established, assuming that no traffic passes between the two stations, one will poll the other after a preset period of time and ask if the other is still there. The one being polled will hopefully reply that it is and the link will go silent again until the time of the next check when the process will be repeated. As before, if no response is received to the request, the requesting station will try for a preset number of times until it receives a reply. If it does not, it terminates the link.

  In each case, a failure to receive a reply to a request or message will prompt the sending station to retry for a preset number of attempts after which, if it does not get the reply that it expects, it will drop the link.

  If it becomes necessary to pass data, the transmitting station first asks if the receiving station is there and ready to receive a sequentially numbered packet. Assuming that it gets a positive response, it will transmit the first packet. The receiving station will check the checksum. If it is correct, it will tell the transmitting station that it has received it correctly and is ready to receive the next. If the transmitting station receives no message, it will ask the receiving station if it is still there and if it has correctly received the packet. If it gets a message that the received packet was incorrect, it resents it until it has been told by the receiving station that it is correct at which point it sends the next one.

  When the traffic session has been completed, one of the stations sends a disconnect request to the other. The receiving station acknowledges this and confirms that the link has been terminated and that's that.

In Practice.

  This all sounds very complicated - and it is! However, the good news is that, as a packet user, you do not have to worry about all of this as the Terminal Node Controller (TNC) handles it all for you.

TNC.

  The TNC is essentially a radio modem. It is a means of converting the 1s and 0s that your computer uses into two tones which can be transmitted over the radio. It also contains other software which handles the link control functions in response to simple textual commands.

  Most commands can be abbreviated to one or two letters. The manual that comes with a TNC lists all of these commands, some of which differ between different models of TNC. In addition, the built-in software usually contains a list of these commands, often accessed with the "HELP" or "?" command.

  To connect to another station, e.g., 5B4QRM, the command is:

CONNECT 5B4QRM <RET> (where <RET> means hit the RETURN key).

  This can be abbreviated to:

C 5B4QRM <RET>

  This assumes that the other station is on the same frequency and within simplex range. Of course, this is not always the case, so strategically placed repeaters are used to increase the range. These are of two types - digipeaters and nodes.

Digipeaters.

  Every TNC can operate as a digipeater, often known as a digi. If the TNC's owner switches the digi function on, other users on the same frequency can connect to each other by having their signals repeated by the digi.

  In this case, the digi acts like a simplex voice repeater. Everything it hears from a specific station to be directed to another specific station is repeated immediately after it is received. As discussed earlier, packet works by one station transmitting a packet and another receiving it and acknowledgment back to the sender via the digi.

  This is a potentially useful method of extending your range, but on a busy channel it is slow and inefficient. For this reason, nodes where developed.

Nodes.

  A node is a normal TNC which has had its usual software replaced with node software and might be regarded as an "intelligent" repeater. Networks of nodes have the facility to be able to recognize each other and establish routes between them.

  Unlike the situation with a digipeater when one station connects to another using the digi just to increase the range, stations actually connect to a node and then request the node to connect to the next node or to the destination station.

  Because of the "intelligent" manner in which the nodes talk to each other, they can create large networks.
Because each node has a unique identifier (its call sign and often an alias), it is often possible to connect to the first node in the network and then issue a connect request to a station at the other end of the network, and the nodes will work out the correct route automatically.

BBS's.

  So what's the point of all of these systems? In their simplest form, they serve as repeaters to allow remotely sited stations to connect to each other for one-to-one chats. However, this would all be a little bit boring. This is where bulletin boards (BBS's) come in. For those familiar with telephone bulletin boards, the principle is virtually identical. Individuals can connect and leave personal messages for other users or can read and send bulletins - messages readable by any user - on almost any subject. It's also possible, if the particular BBS supports it, to send and receive software and other digital files.

Personal Mail.

  The SP (Send Personal) commands allows a connected user to send a message (E-mail) to another user on that BBS or, in theory, any other Amateur Radio BBS in the world. Messages for local users are held on the BBS (which periodically transmits a beacon which includes the call signs of any stations for whom mail is waiting) until they connect and read them. Messages for users of other BBS's are automatically forwarded through the network to the destination station's home BBS where they again held for collection.

Bulletins.

  The closest analogy to the bulletin is that of the Internet news group. However, instead of having specific areas where all messages on a particular subject are held, the `subject` field of the message describes, by definition, its subject. Wild cards similar to those in DOS commands can be used so that only those subjects in which the reader is interested can be listed and read/replied to, or the user can view all of the received messages.

  The geographical area of distribution can be set as appropriate. In Cyprus, three locations exist. Local mail distribution to the Cyprus BBS's only is sent @CYP. Mail intended for European (and slightly beyond) BBS's is sent @EU. In order to theoretically reach all users worldwide, messages are sent @WW.

Cyprus Network.

  At present, the main BBS is in run by Costi, 5B4TX, in Limassol. This operates primarily on 2m (144.675 MHz) operating at 1200 Bd (Baud) - the most common data rate. The BBS maintains a regular VHF link with several BBS's in Lebanon and, when summer conditions permit, with Israel. In addition, the BBS links to several BBS's in Russia, Lithuania and UK on HF at the much lower speed of 300Bd. These links allow personal mail and bulletins to be passed into and received from the worldwide network. This BBS operates from approximately 0700 to midnight  each day (local time).

  The second BBS is operated by Ian, 5B4YX, at Episkopi. This BBS only has VHF links and acts as a backup BBS in case of a failure of the 5B4TX BBS. In addition, this BBS collects mail from Lebanon (and sometimes Limassol) during the night and then passes it to 5B4TX the following morning.

  In addition, there is one 2m node (5B4CYA-1 - or ONE) situated just above Lefkara Mountain which covers most of the island (Paphos is still in a bit of a hole!) and has good links with Lebanon and Israel during the summer.

Compression.

  As you can see, the maximum basic data rate of 1200 Bd is very slow when compared with the typical Internet link speed of 28.8k or higher. Unlike land line modems, TNCs are not in themselves usually capable of compressed data transfer. In order to speed traffic between BBS's, most BBS software now permits data to be compressed (similar to PKZipping) before being transmitted.

9K6.

  The latest step forward in data transfer has been the increase to 9600Bd. This produces a dramatic increase in flow rate but requires specially modified equipment, a very good link, and is often very difficult to get working properly. At present, the BBS of ZC4ZL at Akrotiri is being used as a 9k6 link test bed with a link to 5B4TX on 70 cm (UHF) and this is working very well. It is hoped to establish a permanent 70 cm 9k6 link between 5B4TX and 5B4YX in the next couple of weeks and this will remove the inter-BBS forwarding from 2m making user access easier.

  In addition, the 9k6 equipment at ZC4ZL (known as also 5B4ZL) will become the island's second node this summer where it will operate on 70 cm band at 9k6 (9600 Bd).

  In the future, we may see links of 19k2 (19200 Bd) and better. However, the faster the data rate, the better and quieter the link has to be. Higher rates such as this will, in practice, probably be limited to point-to-point microwave links.

World Wide Network.

  So how do your messages get to their destinations? Well, in addition to the HF and VHF links previously mentioned, there are various Amateur Radio satellites which carry BBS's. These are regularly accessed by ground-based satellite gateways (Sat Gates) which allow for very rapid transfer of mail.

  I have previously mentioned that worldwide distribution is theoretical. The reason for this is that most intercontinental links involve some HF element which is, of course, dependent on propagation. If conditions cause a link to fail for an extended  period, the message may arrive very late or may even expire and not arrive at all. However, it is usually fairly reliable.

Equipment Required.

  This is all very well but surely it must be very difficult and expensive to get started on Packet? Not at all. Most shacks will already have most of the elements required to operate - a computer and a 2m FM transceiver. The only other item required is the TNC - the modem.

  Typically, a basic Packet TNC will cost a little over 100 Cyprus pounds ($200). This is connected to a COM port of the computer in exactly the same way as a modem. It is then connected to the transceiver, typically requiring a lead to the external speaker socket (receive audio) and one to the microphone socket (one line for transmit audio, one for PTT and a common earth).

  In addition, you would require some terminal software. The TNC is an "intelligent" modem and it contains all of the commands required to operate Packet in firmware. Any program that can be used with a modem can be used for Packet. However, many software packages exist from very basic and free to quite complex commercial programs.

  At 1200 Bd, it doesn't matter whether the transceiver employs true FM or phase modulation - it will work just as well. However, if you later decide to operate 9k6, you will need to add a high-speed modem (it usually just plugs in), and your transceiver, which will have to be true FM, will need to be slightly modified. In practice, many Amateurs use ex-PMR commercial FM transceivers specially modified for the purpose.

  There are many other digital modes such as RTTY, AMTOR (AMateur Teleprint Over Radio), and G-TOR, and many other Amateurs opt to buy a more complex TNC, such as a PK-232 MBX from PAKRATT (such as my own modem equipment), which incorporates many if not all of the common digital modes, including CW!

PMS.

  All TNCs contain within them a small mailbox known as a Personal Message System or PMS, typically about 32k (RAM) in size. If a user has his system on the air but is away from the keyboard, they can leave this switched on. Anyone who connects to them for a chat will instead be connected to the PMS and will be able to leave a message to be read later.

  In addition all TNCs have a digipeater function which can be switched on to allow weaker stations to operate using your TNC and transceiver as a repeater. This does not affect the TNC's owner's ability to operate at the same time.

  Almost any TNC can be made into a node simply by changing one EPROM, and software exists for the PC to create a node in the computer which looks, to the other users, just like a normal node.

Other Software.

  I mentioned earlier that pictures and programs can be passed over Packet. This is true, but a single problem has to be addressed. Like RTTY, Packet can only transmit ASCII characters although it can handle all of the printable characters. Software and pictures contain unprintable characters and Packet cannot handle them. In order to pass these, they need to be encoded using UUEncode or 7 Plus (a similar package) which converts them to pure ASCII characters. Once received, they can be decoded back to their original format.

  In addition, a format called YAPP (Yet Another Packet Program) allows binary transfers to be carried out similarly to ZMODEM with land line transfers. In this case, ASCII encoding is carried out automatically.

IP Gates.

  Another development has been the interfacing of Packet radio with the Internet forwarding system. In many countries, and here soon also, TCP/IP BBS's are set up as a permanent node of an Internet provider. Using the speed and reliability of the Internet system, personal mail can be swapped between packet users world wide, equipped only with their normal Packet equipment, at Internet speeds. In addition, if so configured, the IP gate can permit Packet DXing to foreign BBS's.

  As an aside, the TCP/IP system employed by the Internet system is exactly the same as ours - it was designed by a Radio Amateur. I wonder how many Internet users appreciate this!

DXCluster.

  This is a system whereby people finding DX on HF (or elsewhere if appropriate) can inform the rest of the Amateur community who are equipped with Packet. They put the frequency and other details onto the system and other users are alerted to the activity. Some modern software can interface with the user's transceiver and even automatically tune it to the correct frequency.

GPS.

  Many of us are familiar with Global Positioning Satellites and their associated equipment. This equipment can now be interfaced with many TNCs to allow appropriately equipped stations to graphically monitor the positions of other active stations.

Conclusion.

  Packet radio is a simple mode to use. It is versatile and allows similar facilities to Internet E-mail and news groups at no operational cost. The local network is expanding with more facilities being added and it welcomes new users.