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Radio amateur activities

Kenwood TH-F6A, TX: 144/220/440 MHz with 5 W, RX : 0.1-1300 MHz

Clusters and Packet Radio

If you want to succeed in trying to work a rare DX or a special call sign, it is sometimes very useful to read news about current DX-peditions and other activations, the ones to come, and to log their period of activity in your logger calendar in order to be alerted once they will be QRV.

Your national ham radio magazine as well as 425 DX Network can provide you such an information and much more. But this information is rarely available in real-time.

Can you, just now, get "DX spot information", I mean to know what DX-pedition or DXer is currently in QSO on the 15-meter band, in SSB mode, and what is his QSL info ? Some decades ago (before the '80s) it what not easy to find the information, all the less in real-time.

Today this spot information is available at your fingertips via a connection to a cluster. Born in the 1980s, this technology is today used by practically all amateurs who can't no more ignore this tool when they work on the air as it provides them a very useful assistance.

Definitions and requirements

A cluster is a network of dedicated computers called "nodes" connecting amateur radio operators. This cluster serves an area which size is ranging between a small city and a country, but sometimes it connects amateurs at international and even at trancontinental level. The objective of a cluster is to provide and share information pertaining to amateur radios.

The most common usage of a cluster is to provide spot information : a licensed amateur (only) heard or worked a station and would like to share the information with the ham community. The information shared on a cluster include DX spots, WWV spots, beacons, announcements, message, and mails. In some countries, weather and emergency services are also available on clusters. Most of them also provide utilities like a call sign lookup, a QSL database, great circle heading and sunrise/sunset calculations.

A DX cluster is a cluster network while an AR-cluster is a software using an Internet link to connect with other AR-cluster nodes ("AR" meaning Amateur Radio). In facts, there is no difference between a DX and an AR cluster, and a cluster network can combine DX and AR clusters.

There are two types of connections : TNC that uses an external packet interface linked to a RF device (a V/UHF transceiver), and Telnet via an Internet connection to a dedicated website like DXHeat, DX Summit or HB9DRV among others clusters. Note that the Telnet access requires a login, usually the amateur's call sign.

"CC User" program developed by VE7CC is an example of client interface running under Windows supporting DX and AR clusters among others. "AR-cluster" program developed by AB5K is another example of client application. Both software replace a TNC if the amateur has an Internet access.

Telnet connection via Internet

The simplest way to connect to a cluster is using Internet as it is already installed in most residences or available close to your home via a Wi-Fi connection. However, if you are not connected to Internet by any mean, in this case you need to use a TNC linked to an external V/UHF transceiver.

Telnet is the session layer of TCP/IP protocol in the OSI model used by Internet and wide and local area networks (W/LAN). In fact, TCP and IP frames are encapsulated in AX.25 packet frames.

TCP/IP is available by default when you subscribe to an Internet Service Provider or ISP (operator). TCP/IP is supported by all Internet browsers and by most electronic logbooks (loggers) like DX4WIN or Ham Radio Deluxe displayed below.

Two examples of loggers linked to an AR cluster. At left, DX4WIN version 8.05 supporting packet and telnet connections. This printscreen shows the user interface (at left) completed with an external connection via Internet to DXHeat cluster (upper right), itself linked to U.Twente SDR receiver in NL (middle right window). The window displayed below right and highlighting lines in red and yellow is the packet connection established by DX4WIN to VE2CC cluster. At right, Ham Radio Deluxe version 5.2x showing the telnet (Internet) window (below the log) connect to HB9DRV-9 cluster (selected by the system according to my QTH but that can be modified) displaying DX spots in real-time. In both programs, only the Internet connection was used. Documents T.Lombry.

Sometimes, some loggers disconnect from the DX cluster without warning. In this case, the solution is using a program between the logger and the cluster like "CC User" or "AR-cluster" described above that keeps that connection.

This kind of software is placed between the logger and the DX cluster node : in the case of DX4WIN, this logger connects to localhost (syntax for DX4WIN : LOCAL>CC User,localhost:7300) and the "CC User" program connects to the node.

As reliable as a wired Internet connection, this kind of program can stay connected to the node for days or weeks if needed, even by Wi-Fi (that you need to protect with a password for security reasons). That said, if disconnections remain, most of the time it is either a local issue linked to your computer (OS or hardware) or to your ISP.

More interesting, when a cluster is connected to your logger software via Internet or through a TNC, if you keep the default settings, the program will automatically highlight all DX and WPX that you have not worked or listened yet, DX in a new mode or new band, etc, as displayed below (left and center windows). This is a very useful assistance to get new points in the DXCC palmares or during contests or simply to know what are new DX that you could work.

Check DX spots on clusters:

DXHeat - HB9DRV - DX Central - DX Summit - eHam DX Cluster Spots

Three ways to display DX Spot information for the same date and time, tools classified as "assisted QSO" in contests. At left, the packet windows interface included in DX4WIN showing the connection process to K2UT cluster in Medford, NJ ( DX4WIN also accepts a connection via Internet by typing either the IP and port or the full URL of the server. At login prompt, the sysop will ask you a valid call sign that you can enter in a programmed key (bottom left in pressing Alt-E). Once in the system you can explore the cluster and its links, show DX spots (SH/DX), spot a DX, filter data, request information or execute services (send mail or message to the cluster, to a specific amateur, etc). Most commands are case sensitive and use one of the three existing packet languages (mots command are the same but there are exception, specially using VE2CC custer lmocated at Maple Ridge, BC ( At center, the DX4WIN DX spots window that automatically opens at startup if the packet option is activated and the connection established using the packet window at left. Specific colors are programmed checks comparing the logbook entries vs. new DX spots, new bands, new awards, etc. Color are user-defined. Take care entering these data in your setting files because most servers are case sensitives and could refuse your connection if typed in uppercases, displaying simply "connection closed". Using Internet, if you enter the IP address alone, without specifying the port number, you make a FTP connection directly to the Linux node. The system will ask you for a call sign, then nothing more. You will have to type DX to get the cluster login prompt. At right, the web interface of DX Summit provides DX spots information in the continuity of OH2AQ Radio Club that ceased its activities in 2008. Similar information is accessible at no cost using a TNC connected to a VHF handheld transceiver that you will dedicate to this activity. Documents LX4SKY.

How to setup a cluster?

As explained, a cluster or node is a computer system (sometimes several) connected to Internet on one side and to RF (shortwaves) the other side using a V/UHF packet connection.

In the field, this computer is connected to a dedicated transceiver, itself connected to a TNC (e.g. Pakratt, Rigblaster, see below), 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.

This computer is linked to the global network via the AX.25 (Amateur X.25) and Telnet protocols.

This cluster manages information about amateur traffic, mails sent between hams and provide many other interesting services that we will describe below.

Once the connection established, a prompt requests the user to enter his call sign to be authenticated and to receive his personal profile. At this point only amateur radio call signs are accepted, no SWL, CB, Hamsphere or nicknames.

Once in the system in using standard commands the amateur radio simply sends his message for immediate release. Thousands hams proceed this way every day and every minute. It 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 saved in huge databases often managed by a Linux server that can be queried remotely either in command mode or user a client interface. It allows you to search for specific information : to confirm a call sign 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.

A typical packet radio installation : a dedicated 2m hand-held transceiver and its antenna, a TNC interface supporting the AX.25 protocol, and a computer linked to the web in TCP/IP, completed with all the required cabling system. In some models, the TNC includes a sound card. Usually the mic and speakers are used when the remote repeater works in VoIP mode (e.g connected to Echolink or IRPL network linked to the Internet). The mic and speakers are thus optional but can bring much comfort in communications or when one play with multimedias (CD, DVD, etc).

Of course the data updated today in databases can be obsolete tomorrow because e.g. the QSL Manager will change according to the amateur who will use the same call sign during the next special event. Therefore it is always useful to ask during the QSO all the information you need to get the QSL of your contact. However, today most DX stations will answer that you can get all these data and much more on 

How to set up a TNC connection to a cluster ?

As explained above, in a packet connection using a V/UHF link, there is a TNC device between the computer and the transceiver which function is to establish an AX.25 connection to a cluster in order to share spot information or to work in digimodes as we are going to see hereunder.

If you use a TNC like the famous Timewave PK-232 DSP or the smaller AOR AR-210, knowing that hundreds of messages are sent each second to all clusters, there are two very important parameters to set in that device : the baud rate (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 e.g that you type <Ctrl-C> to enter in command mode, and as long as you don't enter these two keys, the system will never switch in command mode and will never accept your new settings...

The AOR AR-210, this is not a regular and multimode TNC but one of the smallest AX.25 TNC able to connect to packet clusters.

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 connection 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 connections.

We now understand better why outside the limitation of about 11 or 15 ms many connections to clusters are usually refused (without any message or at best "connection 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.


Last but not least, you can also use clusters to communicate in all digimodes by the intermediate of your TNC interface and keyboard with other hams using similar ham equipments.

Indeed,  in 1986 the company Advanced Electronic & Applications, Inc. (AEA) introduced the venerable PAKRATT PK-232 controller or packet interface displayed below. It does packet at 300 and 1200 bauds or bits/sec (bps), RTTY, AMTOR/SITOR, PACTOR, and CW.

This TNC includes a maildrop that works in Packet, PACTOR and AMTOR modes so that you can access to a personal mailbox from anywhere in the world. This model was withdrawed 1996 and the patent sold to Timewave. However this TNCs can till be purchased on secondhand for about $50.

Since 1998, Timewave provides a similar model, Pakratt PK-232 DSP (below) supporting RTTY-Baudot, RTTY-ASCII, AMTOR/SITOR, PACTOR, Packet at 300 bps HF and 1200 bps VHF, FAX HF, GPS, NAVTEX, TDM, and CW. See this page and these audio files to listen to the variety of digimodes.

To read : The History of Amateur Radio

The invention of Packet radio and TNC (1977-1980)

Above, the venerable PAKRATT PK-232 TNC or packet interface introduced in 1986. It does packet at 300 and 1200 bauds, RTTY, AMTOR/SITOR, PACTOR, and CW. Below the Timewave PK-232 DSP replaces the old model. It supports most digimodes including SSTV. A true Rolls at $535 !

PK-232 DSP includes a DSP filter to reduce QRM and a sound card to work in PSK31 or SSTV. Since 2011, it includes an USB port too and other models are also available.

Today packet radio can interface with many other services than DX Clusters, like chat bridges, networking, emergency communications, satellite operations, APRS, and much more.

Working with clusters

There are usually several clusters per country, some managed by radioclubs, others by private amateurs. 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, managers of clusters can restrict the usage of their packet network to local amateurs 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.

At last, there are clusters like VE7CC where some services are charged.

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 on 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 !

If you have not needed of a local system and test various clusters adresses, e.g. from Canada, U.S.A. Europe or Asia, you will see that the list of DX spots is at 90% common; they are not many differences (not more than comparing lists displayed on two web clusters). So if you live in Europe for example, you can connect without problem to a US cluster if you want.

But as soon as you want to send a message to amateurs living close to your QTH, in this case you need to connect to the cluster on which these amateurs are connected (or use commands to jump from one cluster to another until you reach the local cluster, see below).

Among the most used clusters, reliable and fast there are HB9IAC-8, K2UT and VE7CC. Others, listed in old files created ten years ago are no more active like the famous EA7URC-5 ( or ON4DXB (

Cluster info

Clusters (syntax for DX4WIN)

K2UT : Medford (NJ),

VE7CC : Maple Ridge (BC),

DX-Central : DX-Central,

VHF Packet Frequency

LX0PAC : 144.650 MHz

F6KWP : 144.850 MHz

FTP clusters

Web clusters

DXHeat - HB9DRV - DX Summit - LOTW Online - DXMaps - Ham Radio Deluxe - eHam

Some TNC commands

<Ctrl-C> : to get the TNC prompt and be able to enter commands

HB 1200 : set the baud rate to 1200 on the TNC

MYCALL LX4SKY : load the TNC with LX4SKY's profile

TX 11 : set the emission delay to 11 ms

NB. Usually all TNC use a small lithium battery to keep these parameters in memory.

Some cluster commands

There are at least 3 systems in packet, each using a specific language. So some commands that work for one cluster can be without effect on another one. VE7CC for example selling some of its services, uses a slightly different syntax than the others. Here is the syntax of VE7CC and HB9IAC-8 (in French).

HELP command : give help on command "command"

BYE : close connection

SH/DX/10 : list the 10 last DX (all bands if no filter is set)

SH/DX/10 21 : list the 10 last DX on 21 MHz. If you sent prior the two previous commands, only the HF QSO worked in SSB mode and worked on 21 MHz will be displayed.

REJECT/SPOTS 1 ON 50000/2500000 : reject from the display all DX spots from 50 MHz and up

REJECT/SPOTS 2 ON HF/CW : reject from the display all DX working in HF and CW mode

SET/FILTER DXBM/PASS 6 : add spots for 6 meters (on VE2CC)

SET/FILTER DXBM/REJECT VHF,UHF : add filter to reject VHF and UHF spots (on VE2CC)

SET/FILTER DXBM/REJECT 80-CW,40-CW : reject CW spot on 80 and 40 m  (on VE2CC)

ACCEPT/SPOTS ON HF : only accept HF spots

ACCEPT/SPOT 0 info CW : only show spots with "CW" in command

ACCEPT/SPOTS BY_DXCC K,W,N : only show spots by K,W? N stations

ACCEPT/SPOTS BY_ZONE 29,30,31, 32 : only show spots in Zone 29 to 32 (VK-ZL)

SH/WWV : list the last propagation conditions (solar indices RFI, K, A, etc)

SH/USERS : show all users currently connected to your cluster

WHO : same as SH/USERS but list also users's nickname and their IP address

SH/QSL LX4SKY : show the QSL info of LX4SKY

SH/QRZ LX4SKY : show the QSL info of LX4SKY on

DX LX4SKY 14120 gud opening to SE Asia! : You announces on the local cluster a DX spot : on 14120 KHz, LX4SKY has a good opening to SE Asia stations

A message : Announce, send the "message" to the local cluster to the attention of all connected users

ANN/FULL message : Announce, send the "message" worldwide to all clusters (to use only if your information is relevant !!)

S LX4SKY ur phone pls : Send a mail to LX4SKY with message "your telephone please"

T LX4SKY available ? : Talk in private with LX4SKY to ask him if he is "available ?". LX4SKY must be connected in real-time on the same cluster as you.

LINK : show all clusters connected to yours

CONN HB9C-14 : Connect to a cluster named "HB9C-14" discovered using the LINK command. Some clusters can be temporary closed or can refuse to connect you (message "Not Allowed").

NB. Some of these commands can slightly differ from one cluster to another. But there is always a help command available (h or hlp, help, h/?, etc) that you can use to get more information on any command. Some others are undocumented to avoid misuses. Most are UNIX compatible.

If you are in trouble with a cluster, try to identify his manager (see this list maintained by F5GIT) or try to connect to another cluster. They are many, some can be down.

If he wants to work a specific Zone or entity, thanks to the "link" command you can jump from one cluster to another. Once on the destination cluster, thanks to the "talk" command you can for example ask to a specific connected amateur if he is interested in a QSO with you.

 If this amateur 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 !

From Europe to USA is a few keystrokes

c LX0IST-14 (You are connected to a cluster in LX)

LINK (To display all active links among them 9A0TCP-5)




A QRV to work counties award on 21300. Plse call.

You are now face to all users connected on WB0TAX-7 cluster !

NB. Some clusters will reply "Allowed", others "Not Allowed", and the list changes as time goes by. To test.

At last, if you have some difficulties to find information about some call signs or their QSL info (the way to reach a station by post or bureau) on a cluster, do not try because the cluster queries also the QRZ database. Try rather alternative databases like HamCall (ex-Buckmaster) or Pathfinder, hence the importance to create a profile on one of these databases as well.

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, there are many chances that you did a mistake in working this station, "you are not in log"...

For more information

Loggers (in the download page)


Web clusters

FTP clusters



DX Summit

eHam DX Cluster Spots

Ham Radio Deluxe



LOTW Online


AR-Cluster User Manual (PDF)

Cluster syntax : VE7CC, HB9IAC-8 (in French)

Maillist AR-cluster :

Maillist DX4WIN :

Hope this helps !

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