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How does work a cluster ? Here you enter in the world of digital communications. You probably know OH2AQ and his team who, among other hams, provide on their website what we call "spots information" displaying in real-time a summary of QSO established on various bands and modes. In the 1980s such tools were not available yet.
A cluster or node is a computer system connected to the Internet on one side and to shortwaves the other side using VHF (2m) or UHF (70 cm) packet connexions. In the field, this or these computers are connected to one or more dedicated transceivers, themselves connected to a TNC (e.g. Pakratt, Rigblaster), a sort of multimode modem able to process hig tones if its bandwidth is large enough. The information is transmitted in small packets, hence its name. These computers manage information about ham traffic (QSO), mails sent between hams and provide many other interesting services that we are going to review hereunder. Licensed hams (only) that heard or worked a station and who want to publish the information to the attention of the ham community have first to contact to a near cluster using the TNC connected to their 2m or 70cm transceiver or using their Internet connexion to a dedicated website like OH2AQ.
Once the connexion established, a prompt requests the user to enter his callsign to be authenticated and to receive his personal profile. At this point only ham callsigns are accepted, no SWL, CB or nicknames. Once in the system in using standard commands the ham simply sends his message for immediate release. Thousands hams proceed this way every day and every minute. This is this huge collection of messages that you can read in real-time on clusters and many websites dedicated to ham activities. These data are all saved in huge databases that can be queried remotely if you are for example searching for some information (i.e. to confirm a callsign worked on a specific date, to confirm a frequency, a QSL manager or any other data that would have been sent by another ham this year or a couple of years ago). Of course the data updated today can be obsolete tomorrow because i.e. the QSL Manager will change according the the ham who will use the same callsign during the next special event. Therefore I suggest you to ask during the QSO all the information you need to your contact in order to get the QSL without trouble as any other useful information. The same day check on QRZ too. If a callsign is assigned for a few days only, the concerned ham has practically no time left to update his website with the new information. So we could say that clusters have limitations from the moment you don't find the information you want but there are not the fact of the technology. Let's question rather the ham himself who didn't publish the information on his cluster in due time. TNC setup
Knowing that hundreds of messages are sent each second to all clusters, there are two very important parameters to set in a TNC : the baud rate (between 300 and 6400 bauds, e.g. HB 1200) and the duration of each emission (usually 11 or 15 ms, i.e. TX 11). If you forget these two commands and some others, your TNC will look like dead and it is possible that you will consider it as broken... But it is not. You have only to type the good commands in order that it "understands" you !! Some request i.e. a <Ctrl-C> to enter in command mode, and while you don't enter these two keys, the system will never switch in command mode and will never accept your new settings... Some amateurs may be surprised to learn that a TNC uses a so short delay to send a message that we have sometimes difficulties to type, don't we need more than 11 ms ? Technically speaking, whatever the time you need to type your message, once you pressed the <Enter> key the CPU of your computer is able to process hundreds of operations (and as much messages) in a few millisecondes. This is its main function due to the high integration of its components. But there is another reason to select such a short delay. We cannot imagine occupying the 144.850 MHz frequency or any other one dedicated to packet radio during e.g.10 sec or more to send a message because during that time hundreds or thousands of other messages will be queueing, waiting to be processed and transmitted live on the cluster. Admit that you set the TNC with a 10 sec delay. The server will open its connexion for you during 10 sec but you can be sure that your short message will be for long processed, probably already 5 ms after you depressed the <Enter> key. But during the 9.9 sec reminding the TNC will wait you for nothing, while all others messages will be pending. In other words the cluster will not be able to answer to any other user querying the database of wishing to post a message. So the shortest is the delay, the best is the cluster response. So usually these clusters work with the fastest CPU, much fast memory, and huge disks spaces in order to handle the high rate of connexions. We now understand better why outside the limitation of about 11 or 15 ms many connexions to clusters are usually refused (without any message or at best "connexion closed" or "not allowed"). Therefore some hams think sometimes that their TNC is broken because they cannot connect to the cluster. In fact they have not enter the good commands or parameters. Hopefully usually there are LED on the TNC front panel that display the current status of the system. None of them is menu-driven and this lack of ergonomy is somewhat a pity. To read : The History of Amateur Radio The invention of Packet radio and TNC (1977-1980)
More interesting, when a cluster is connected to your logger software (e.g. DX4WIN) through your TNC or via your modem/DSL connexion, the best programs automatically highlight all DX and WPX you have not worked or listened yet, or DX in a new mode or new band, etc, as display below. This is a very useful assistance to get new points in the DXCC palmares or during contests or simply to know what DX is currently on the air, on what band and what mode. At last you can also use clusters to communicate digitally by the intermediate of your keyboard with other hams connected to the same cluster as you. This is also an easy and fast way to communicate with hams at no cost using the air in place of taking your phone and to receive the bill one month later, Hi !
Working with clusters There are usually several clusters per country, some managed by radioclubs, others by private hams. Using a 2 m or 70 cm transceiver, the distance at which you can connect to a packet cluster is physically limited by two parameters : first by the distance to your QTH, second by the position of the cluster antennas. In some countries like in LX, managers of clusters can restrict the usage of their packet network to local hams and you cannot always hear these clusters a few kilometers outside the borders of the country. In most cases these networks are managed by private operators like you and me who share their personnal computer with the ham community. To avoid misuse, spamming and other denial of service on their system some ops do not hesitate to filter the raw information or to cut links to other clusters. This way they reduce the risk that pirats enter from abroad on their cluster but in the same time they limit drastically the amount of information available of their cluster. The less used systems receive sometimes only one message each dozen of minutes. They are useless when we learn that during a contest in the same time you can work hundred of stations ! Among the biggest european clusters there is EA7URC. This is also the fastest one !
You can connect to any one of them, preferably in a near country in order that QSO displayed are of your concern. Indeed, e.g. from Europe it is useless to connect to a cluster on the US West coast, in Japan or Brasil as there are few chance you hear easily these stations, and vice versa. However a licensed ham can connect to a foreign cluster, jumping from one to another if he wants to work such or such entity. Indeed, thanks to the "talk" command you can ask a specific user connected if he or she is interested in a QSO with you. If this ham is very distant he will be very surprised to receive for example on his US or JA cluster a personal message (e.g. TALK K1A Please QSO with me for CA award ?) from someone living on the other side of the world. When he will receive this message, he will surely ask you : "How did you find me" ? Now you can answer him : "was ez, used links btw clustr and asked to show users". This way to sked QSO is very smart if you want e.g. to work a far DX in special conditions or for any other reason. It is also convenient to work this way in place of waiting like many others OM that a DX appears on the cluster, because once published it is often too late to work him cool and relax... Clusters offer you also an excellent opportunity to increase your score if you want to get awards. With so many services and commands and your disposal, you will without any doubt regularly work with clusters !
At last if you have some difficulties to find information about some callsigns or their QSL info (the way to reach a station by post or bureau) on a cluster like EA5URC-5, do not try QRZ.com because the cluster queries also the QRZ database. Try rather Buckmaster, DX-CENTRAL or Pathfinder. These websites or tools gather currently the most complete ham databases available online. QRZ is probably better known in the U.S.A., and in a lesser extent worldwide (essentially in english-spoken countries) but some information are only available on Buck's (e.g. some email addresses). If none of them provides you the information, and if queries on OH2AQ databases give no better results, there are many chances that you did a mistake in working this station, "you are not in log"... Hope this helps ! For more information The History of Amateur Radio (the invention of Packet radio, on this site)
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