DX Spotting – Which DX Cluster node to choose?

By Mike G3YPP

I watched a recent NARC (Norfolk Amateur Radio Club) Live broadcast with particular interest in the talk on DX Spotting by Kevan N4XL.

At the end, there was a question, “Do you use a different cluster for different contests e.g. SSB, CW, RTTY, FT8 etc. – the answer given was no, but due to time constraints didn’t really go into a lot of detail as to why.  I thought I would add my two penn’orth on why the answer is no.

DX Spots  

Firstly, what are DX Spots?   They are a means of distributing information about a particular station being active on the air.   During day-to-day or contest operation, a spot may be sent by your favourite logging software to a server, known as a node, which you have logged onto.  Spots contain the Callsign, and frequency, of the station heard along with an optional comment.     Your logging software will display spots received from the node you are logged onto, often on a graphical band map or in a table.  If your logging software also controls your radio then “clicking” on a spot will put your radio on the correct frequency.  The screenshot below shows the cluster window in “Ham Radio Deluxe” a popular logging program.   In this case, the software has compared the callsign data in the spot with the contents of the logbook to provide “Worked Status Information” for Country, Band, Mode, and Station.   These are the green ticks or crosses  in the first 4 columns.

DX Spots are a great way to be informed about DX stations on the air but also come into their own during contests and all of the popular logging programs support cluster use.

The Global DX Cluster Network

The DX Spotting system is a cluster of nodes linked together which share spots between themselves and individual users via the internet.   I’ll leave the RBN (Reverse Beacon Network) aside to begin with and just discuss spots from individual users.

A cluster node is just a program running on a computer somewhere.  It collects spots from its connected users and other connected nodes and then serves them to other connected users and nodes.   It’s as simple as that.

There are 2 main DX Cluster software programs in use by nodes these days – CC Cluster and DXSpider.   There are a couple of others but that doesn’t really matter, they all do a very similar job.

All nodes are connected into the global DX Cluster network and therefore share all spots between each other in short time.   Hence, as the spotting data is available across the whole cluster network, it doesn’t matter which node you connect to as an individual user.

So what should influence your choice of node to connect to?  Well, do you want to connect to a node with 1000 other users or just 10 users?   For speed and efficiency, I would say the lower the number of users the better.   The famous VE7CC cluster has over 1000 connected users at any one time and many more on busy contest weekends.   The same holds true for WA9PIE-2 (DXSpider software) which is used by default as the cluster for the “Ham Radio Deluxe” suite of programs and thus has a similar number of users to VE7CC. 

On the other hand, the NCARS node MX0NCA-2 (DXSpider software) has around 10 users connected at any one time.    I had an email from a friend in Devon who commented how fast our node was and how did we do it (he normally used WA9PIE-2).   The answer is few users.   Thus, pick a node with few users.    The Telnet command SH/USERS sent to the node will show all the users connected at any one time.

MX0NCA-2 is connected 24/7 to 6 backbone “super nodes”.    This means that we can be confident that every spot from around the world is available on our node all the time.   We may not necessarily want them so more about that later.

Connection details for all DX Cluster nodes can easily be found on the internet.    All that is needed is the internet address and port number which for MX0NCA-2 is dxc.mx0nca.uk Port 7373.   This is input into your logging software which makes the connection over the internet.

RBN – Reverse Beacon Network

Now, the RBN is slightly different because of the sheer volume of spots generated.    The network consists of automated stations, known as skimmers, which decode CW, RTTY, FT4, and FT8 transmissions on the amateur bands and upload the data on received stations as spots to the RBN relay servers.   For more information see: Welcome! – Reverse Beacon Network

Hundreds of thousands of spots an hour are generated by the skimmers during the major contests.   Sharing those around the DX Cluster network would bring it to a standstill very quickly.   So RBN spots are not shared between DX Cluster nodes.  This means that each node serving RBN spots to users (and not all do) has to connect individually to the RBN.  The node takes a raw feed from the RBN which contains lots of duplicates and “busted” wrong calls.   Fortunately, the DXSpider software has powerful processing capabilities which aim to remove duplicates and busted calls and thus serve quality data to users.   DXSpider actually removes some 90% of what it gets from the RBN as they are duplicates or bad calls.   Therefore, you get a very clean feed of RBN spots from a DXSpider node.  This alone is a good reason not to connect directly to the RBN.

At MX0NCA-2 the RBN feed is not turned on by default for each user.   The telnet command set/skimmer turns it on and the telnet command unset/skimmer turns it off.  Turning it off when you don’t need it reduces bandwidth at your end, and reduces processing needs at your end.     MX0NCA-2 is connected to all RBN feeds so CW, RTTY, FT8, and FT4 skimmer spots are available.   Whilst set/skimmer will turn on all feeds you can mix and match e.g. “set/skimmer cw rtty” or “set/skimmer CW” etc.

 The great advantage of using an RBN enabled node is that you can get both RBN and “normal” cluster spots at the same time. You would not get this if you connected direct to the RBN servers. Note that not all nodes have RBN capability.   This is a choice for the sysop.

Spot Filtering

 Lastly, I mentioned that a user might not want to see all of the available spots anyway.    A spotter in the USA spotting a Canadian on 80m is not much value to us in the UK.   Programs like N1MM have built in filters e.g. to just see spots where the spotter is in Europe.   But that takes up processing power on your PC and logging program as well as wasting bandwidth to and from the node.   Better not to get the spots from the node in the first place.  So, by default MX0NCA-2 is set up to only send out spots (including RBN spots) where the spotter is in CQ Zones, 14,15,16,20 and 33 i.e. Europe and North Africa.   You can add your own individual filters e.g. if you only wanted to see spots from CQ Zone 14 you could send the telnet command “accept/spot by_zone 14”.  That filter stays in place until you change it e.g. with “accept/spot all”.

Filtering at the node level is a very powerful tool and googling “DXSpider filters” will give you more reading material than you could ever want.  Here is a good start: The DXSpider User Filtering Primer

The Last Word

If nobody spots, you won’t see any spots.

Straightforward enough but particularly in contests if you are actively using the cluster to find your contacts then it seems only fair when you are “searching and pouncing” to spot your new contacts.   In N1MM logger there is a “check box” to “Automatically Spot New S&P QSOs”.   You will find it in the config tab menu (see below).   Please set the tick to on.    You don’t need to worry about spotting someone who has already been spotted.  The system and N1MM will take care of that.

Well that is a brief introduction to spotting and the DX Cluster network. You will find plenty of further reading on the internet as well as YouTube videos.