This is all history.. The UHF/VHF DX-cluster was active between 1987 and 1999 and was replaced by an Internet cluster/link SK0BU located at the Technical University in Stockholm

What is a 'DX-Packetcluster' ?


To answer this question, one must understand that DX'ing is a form of hunting involving a high degree of competition as well as being smart and patience. Concentration and other skills are needed that makes a DX'er more successful than just being a radio-operator.
The excitement of getting that very special station from that even more special country that hasn't been on the air in decades, gives such a thrill that there is no way back :-)
To give our closest friends also access to that special one, we used the telephone-line and phone- net's on VHF/UHF or radio teletype links to inform them on the callsign and frequency where the DX-station was located.
In the early 80's a new form of fast information system came to the world called 'Packetcluster'. It's based on the (A)X25 protocol and dedicated to pass short messages over a radio link into a local area ( LAN ).
With this piece of hard/software the problem was solved of informing our DX-society of the whereabouts' of that very special DX station.
Some might say:
" It isn't a sport anymore, you just connect a Packetcluster, wait for the spot (info), tune in the guy and work (contact) him "
Well, my argument is:
"The old times with the selective telephone calls were even more unfair"
Today, we all have the same chance using a Packetcluster. Besides that, to be a successful DX'er, you need more than just a Packetcluster as after all, most of the DX hunting is based on good operator skills.

The LAN of a Packetcluster should still be 'local' to limit the amount of information to relevant info only in respect to local short-wave conditions which might vary considerably. I prefer ca. 150 users connected totally within the whole cluster-group and a radius of ca. 500 Km. ( this applies for Sweden of course)
The 'DX-quality' of the users themselves however is the most important parameter to make the network a success.
Besides the main target of a DX-cluster to pass on messages in a fast way within a LAN, usually the Radio-server contains also local and/or remote databases where additional info can be found on DX related items, e.g. QSL databases, Call books ( CD-ROM ), automated uploaded up_to_date DX info messages retrieved from other sources, sun-spot info, condition forecasts etc. All to make the life of a DX'er a bit easier.
In other words, a DX-Packetcluster looks a bit like a very limited form of the Internet service that you are using right now with the main difference that you can be connected to the network all day long without paying a single penny.

The location of SK0AR-6 at 59 18 N 17 58 E (Stockholm)


The DX-cluster was set-up in 1987-88. The hardest thing was to find a suitable high location within the DX society of Stockholm. As high buildings today have their highest price on the roof ( telephone companies, sat TV etc.), it surely gave us a hard time.
Thanks to SM0HTO, the problem was solved after 6 months of searching. We got one of the highest spots just outside the city centre ( >70 mtr MSL ) with a complete roof-space free of charge.
This gave excellent possibilities to get links to other areas in Sweden and we hooked up 2 other cities ca. 100 to 200 Km away with intermediate nodes. ( Arboga and Gaevle )
Here are some pictures taken from the roof of the Packetcluster on a sunny bright winter day. The left picture is showing one of the link antennas pointing north-west, the right photo shows Stockholm city direction north-east at the base of the LAN antennas.


The hardware


Having industrial design experience, it was easy to understand that amateur- radio stuff can't be used as a full time server without sysop attention. All electrical contacts should be gold plated, power supplies must be heavy duty etc.. Therefore, most of the units you see on the picture below follow ' industrial standards'. The radio transmitter/receivers are basic xtal-controlled modified sets that stands for 24 hour operation. Also high level receiver input will not overload the frontends due to a good set of helical filters in the 70cm transceivers and cavity passband filters between the antennas and the 2 mtr stuff. ( which is a must with radio servers ). Below you see how the hardware looks like. Follow the legends to get more info.


1. The PC . This can be any type of 386 and upwards as the radio-traffic is relatively low compared to the overall CPU speed. It is equiped with a CD-ROM providing an address database as well as a tape backup for local databases stored on the hard-disk. Two DRSI TNC's, with totally 4 radio ports are built-in as well as a tone decoded remote hardware reset switch.
2 and 3. The power supplies of heavy duty type with over-current and -voltage protection, capable of delivering 35 Amps at 12 V
4 and 7. The 2 meter transceivers which are modified 150 MHz phone sets operating as a LAN on 144.575 MHz and a link frequency on 145.300 MHz, giving ca. 25 Watt output power each.
5 and 6. The 70 cm transceivers are modified commercial sets with excellent helical filters at the input. The LAN is operating on 434.575 and a spare link/mail- inbound set is used on 433.650 MHz. Both units have ca. 7 Watts output power.
8. The cavity bandpass filter, currently set on the link frequency of 145.300 MHz.

The software


Today, there are several software packages for a DX-cluster. The original version was designed by AK1A. Below my opinions about the packages known to me.

1. 'Packetcluster'
By Pavillion software ( AK1A ). This is the original software based on a 1986 design by AK1A.
a. MSDOS based
b. Many outstanding features
c. Quite 'buggy' and many work-arounds are needed to get a stable setup.
d. Expensive
e. No technical support since 1993

2. 'Clusse'
This is a design by Hessu Hannikainen OH7LZB, and promising.
a. MSDOS based
b. Better user interface compared to 'Packetcluster'.
c. Stable software.
d. Free !
e. Detailed info from the author can be found at : Clusses homepage

3. 'CLX'
This design is a different approach and probably the most interesting as it is based on an 'healthy' operating system. Author : DL6RAI
a. Running under Linux
b. Stable software
c. Free !

Today, many more DX-Cluster software packages are available. For further info, contact: PCluster

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Last updated April 2002

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