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Whilst rummaging about up in the loft the other day, looking for… I can’t remember what, I stumbled upon my old AEA PK-88 Packet TNC.

You remember them, right?

All the big boys were running PK-232 units, but they were too costly for me. The cheaperPK-88 served it’s purpose well, though.

Back in the late 80’s, I’d gotten very interested in the X.25 protocol used to send data packets around a telecoms network and so, when some bright spark developed a version that could be used in amateur radio in the early 90’s – AX.25 – I of course decided to get involved.

Back then, packet communications was all the rage and hundreds of us set up nodes and digipeaters at home, forming a radio mesh that allowed packets to travel up and down the country, in much the same way as companies like BT were doing.  Our packets tended to be just routine messages (like an email), rather than the commercial data that travelled over X.25. Of course, our amateur network lacked the millions of pounds that the telecoms companies were able to pour into it: it was slower and prone to failure… but it was fun and we learnt a lot about network routing.  Looking back at it now, I realise just how much I have forgotten, over the years.

But anyway…  amateur packet was pretty much killed off by the internet and so I wondered what I could use my old TNC for.

Not much, according to Google.

But, a version of amateur packet is still alive, in the form of the Automatic Packet Reporting System.   Unlike the old system, APRS tends to be more localised, with guys broadcasting beacons, detailing local weather and shit like that.  All a bit pointless, but I wondered whether I would be able to use my ancient TNC to pick up APRS packets and decode them.

And so, after much fiddling about with RS232 cables and PuTTY and a bit of soldering, I was rewarded with the picture on the right.  Success!!

I am pretty chuffed at having figured out how to get it to decode the packets, after nearly thirty years.

Next step is to see if I can actually transmit any.

Watch this space… if you can be arsed.

I was gifted a lovely little radio a while back – a Yaesu FT-270R.

It’s an old 2m model, dating back to the late eighties, I’m guessing.  As such, it lacks CTCSS capability, which limits its use somewhat.

However, there is a space inside to fit a FTS-8 subtone encoder board. And so I thought I’d fit one of these and give it a new lease of life.

Sadly though, the FTS-8 board is no longer available and secondhand ones command a hefty price tag.

What to do? Well, make one of course!

I found an elegant design on the web and built it onto a piece of veroboard. Plugging it into the radio, changed some of the available functions, so the radio obviously detected the board.

It allowed me to choose the subtone from the front panel. Excellent.

But it didn’t work.  Checking  the output with my scope, the tone just wasn’t there… or rather, it wasn’t what it should have been.

I spent ages fiddling with it, but ultimately could find nothing wrong.

And so I passed it onto Dave, who – being a clever bugger – worked out pretty quickly that the board I had built actually worked perfectly. Unfortunately, the radio didn’t. It was giving out the wrong signals to the board.

This wasn’t something that could be easily fixed – possibly a microprocessor issue. And so, I figured a workaround, that would allow the tone to be selected manually, using a combination of switches to produce the binary equivalent of the hexadecimal value that the board was looking for in the tone lookup table.

This worked perfectly and when I tested it, I was successfully able to open several different repeaters, all using different subtones.

And then I found a bug, where the tone would only change after five minutes and not whenever the PTT was keyed.  This looked to be a fault with the MCLR on the PIC… possibly damaged by putting in 7.6 volts from the radio (datasheet states that Vpp shouldn’t exceed Vcc). Not having another chip available, I made a slight mod and fitted a miniature relay, which only allowed the board to be powered when the PTT was depressed.  This seemed to work nicely and I was able to switch tones easily and on-the-fly.

So, I put a call out on a repeater. “Your audio is awful!”, I was told.   I replaced the mic ( a new one from ebay cost fifty quid! Yes, fifty quid for a 30 yr old mic!) with an old YM-47 from an FT-290 and it worked perfectly… once I had figured out the differing wiring scheme.

And so, after many weeks of working on it, on and off, it is ready to be put to use.

Not that I need another radio at the moment, so a friend is going to borrow it.

Many times I nearly gave up on it and was going to throw it away. But, I had invested a lot of time and a reasonable amount of money on it and so I wanted to see it through.

I’m pleased that it is finally finished and working… because that means I can now move onto my next project 🙂