Category Archives: Packet

Playing with packet radio in the CRD

The Capital Regional District (commonly referred to as the CRD) is the name for the region that contains and surrounds Victoria, the capital of BC. The CRD is made up of a number of municipalities, and through Emergency Management BC, each municipality has its own Emergency Operations Centre, or EOC. Part of each EOC usually includes some kind of communications facility, which is run by licensed amateur radio volunteers, and the facility normally has a packet station that can be used to pass messages back and forth.

What this means is that if packet radio is something you’re interested in, Victoria has plenty to keep you occupied.

Connecting to a node

First, pick a node from the CRERCC Packet Station page. For this example, I went with VE7SEP-7, which is located at the Saanich EOC.ve7sep7

For anyone familiar with packet nodes, the above should look pretty familiar. If you’re not, then the basic functionality is that you can connect through to another node, list the other nodes that this node has heard, and disconnect.

I hit J (or Heard) to see the other nodes than VE7SEP-7 had heard, and you can see that my call is the latest in the list:-

ve7sep7-2

Connecting to other nodes

While you’re connected to a node, you can usually use the C (or Connect) command to connect to another node that’s on the same frequency. This is useful if you can’t hit the other node directly, but the node you’re connected to can hit you and the other node.

For example, from Langford I can’t connect to VE7PEP-7 directly, but I can – as we saw above – connect to VE7SEP. When we looked at the nodes that VE7SEP-7 has heard recently, we can see that VE7PEP-7 is in there, which means there’s a good chance VE7SEP-7 can connect to it. To try it, we can type C VE7PEP-7, and cross our fingers:-

ve7sep7-3

Success! We’re now connected to VE7PEP-7 and can use it as if we were connected directly. This also means in theory that we could jump to yet another node, although this is not always a good idea, which I’ll touch on later.

Using digipeaters

The above method for reaching packet nodes that we can’t hit directly works, but is a bit cumbersome. What if we could connect to our intended node via the closer node, but without having to manually connect to the closer node first? We can, and it’s known as digipeating.

In this example, I can’t connect to the packet station VE7RAH-7:-

term-ve7rah-1

(I’m using Linux for these examples – AX25 is well maintained, relatively easy to set up and simple to use, and I’ll cover it in a future post)

As you can see, I tried to connect using the axcall command, but I didn’t get a response and eventually aborted the connection attempt. As before, I know I can reach VE7SEP-7 directly, so let’s adjust our command:-

term-ve7rah-2

 

ve7rah-digi

…and we’re connected!

There is a subtle difference at work here, and that’s that in our first example, we were creating separate connections first to a nearby node, then from the nearby node to a distant node, while in our second example we’re creating a single connection to a distant node, but relaying it through a nearby node . The configuration needed to support these two different methods is different, so while one may work, the other may not. From the examples above, we can see that VE7SEP-7 supports both.

A further example to highlight this is that although I can connect to WF7W-7 (and, although not shown, I know WF7W-7 can see VE7RAH-7):-

wf7w-7

…trying to use it as a digipeater fails:-

wf7w-digi

 

A word about too many hops

As fun as bouncing around different nodes can be, it’s best to keep it to a minimum. For starters, for each hop you add to the connection, the more delay there will be when issuing commands to the intended node. This is because each node in the path has to retransmit your packet and wait for a response before it can reply back to you. Add other stations into the mix or any sort of interference and having any more than 1 or 2 hops can be unusable.

The second – and perhaps bigger – problem is that all these additional packets being generated will tie up the channel, making it more difficult for other users on the same channel.

What next?

What I’ve shown above is just scratching the surface, and in future posts I’ll cover setting up AX25 on Linux, and how a tool call RMS Express is used to provide worldwide e-mail services over packet radio networks!