Self Contained VHF Packet
Recently, I’ve set up a Packet Radio node. This receives what is affectionately called ‘Packet Nonsense’ in the form of bulletins and personal mail. The APIs and availability of data around this is fairly limited and somewhat archaic. I started poking at various bits of code to see if I could improve that. Mostly with the somewhat redundant aim of checking my Packet Mail from my phone.
This meant that I needed a test node in order to develop against while the main node still received the latest Nonsense from around the world. I was using my Kenwood TH-D75 which has an inbuilt TNC, but that seemed like a waste of quite an expensive radio - and it only supports the basic ‘1200’ and ‘9600’ bps modes, none of the newer implementations.
Looking around for cheaper options I found there’s a mod for the ubiquitous Baofeng UV-K5, but it’s a fairly involved hardware mod and involves replacing a bunch of surface mount components in a way that I’m not entirely sure my current skill level is appropriate for.
Then someone in OARC pointed out the TalkPod A36plus mod from the M17 project. This looked like it fitted the bill nicely and is designed with the same aim in mind. It’s also a significantly easier mod and only requires the removal of a couple of components. The Hot Air rework station made quick work of that.
The only problem was locating a couple of the components that are mentioned. The last capacitor removal isn’t in the pictures.
The next breakthrough was discovering that you can in fact power the radio from 5V through the battery connectors. It makes it complain that the battery isn’t charged but fortunately we can ignore that.
The new ‘standard’ hardware modem/TNC for Packet at least in the UK is the NinoTNC. This is a pretty nice board and an easy build. Investigating the board I found that there’s a 5V / GND output where the serial connection is. If you have the USB MCP chip fitted they become powered. I don’t think that’s an intended use or even what the maximum current draw would be - but initial tests prove we an power up the TalkPod from it at least. I doubt we’d get 8W from it now, but it’s enough for a dummy load and the 3 metres range I need.
The connection cable is the standard ‘K1’ connector, the same as the UV-K5. I made it up following the diagram from the OARC wiki.
I printed a mount to hold the two parts together and plugged it into the test node. It holds 1200bps reliably, 9600 also works. I’ve not fully tested the newer NinoTNC modes yet, but it’s definitely sufficient for now and frees up the Kenwood for other things.