So over the last few weeks a couple of friends of mine have been talking about how they’ve been getting some old packet radio gear working again, with a view to starting up a new network. They’ve been sharing screenshots and photos of various different events including a couple of converse QSOs they’ve made, with each other and with other stations having sent out e-mails to a couple of local clubs encouraging activity. It’s something I’ve never yet played with, but with the APRS node I run (MB7UDJ), it feels like joining the packet network and setting up a node for that might be the next logical step. Sadly I can’t join the others on 2m as my APRS node already runs there and the two would deafen each other, but that’s a story for later on.
As luck would have it, during a particularly interesting discussion/breakthrough for the others, an advert appeared on a second-hand site I follow for some gear from an SK. Amongst the other items was an AEA PK232 packet TNC, for which the son of the SK was asking a mere £13. I promptly fired off a quick e-mail and with a price adjustment to cover the postage costs, the sale was agreed. It transpired from the photos I was sent that it was the better spec AEA PK232MBX, which has the Mailbox functionality on board too, and with a serial number in the 56,000s, had this all on one board. It also has multicolour LEDs rather than all red, and this one’s running firmware from 1991. A couple of days later the unit landed at my office, with a familiar “old electronics” smell to it, in pretty reasonable condition for its age.
Of course it was never going to be that easy. On first inspection the unit looked good, but once plugged in, nothing happened. The first thing I checked was the internal fuse (as I’d seen this documented with a few other people’s experiences), and as expected it had blown. Luckily with the help of M0BLF’s handy page, I had the RS part number to hand so could order some fuses easily. That wasn’t going to stop me testing the TNC though, so I promptly soldered a wire across the fuse terminals and having checked for some kind of resistance across the DC socket (there was plenty), I powered it up. Success… kind of.
On boot, a single amber LED – BAUDOT – lit up. From some research and discussions with a couple of people, it looked like this meant the system was waiting for its auto-detection sequence for the serial port baud rate. In itself perfectly normal, except I was getting no responses at all from the PK232 over my serial terminal software. I spent an hour or so trying various different settings combinations, three different USB-Serial adaptors and various reboots of the unit, and nothing was working. I then tried desoldering the CR2032 battery from the motherboard (unnecessarily, it transpired) to perform a full factory reset. This didn’t help, and I found out shortly afterwards that this was because the battery wasn’t actually connected. The two pins appeared to be missing, and I then realised they were present and correct on the underside of the unit, accessible through a hole in the lower casing. Naturally I promptly dug a jumper out from an old IDE hard drive and pushed that across the pins. Still nothing, except frustration at the lack of progress. Out of a little desperation and some crazy thought, I decided to try swapping the straight-through serial adaptor (9 to 25 pin) for another I had, which was coded as a null modem adaptor. All the evidence I had seen on every website, and in every manual, suggested this was not going to work, and that the PK232 uses a straight serial cable, but I hooked it up anyway, just on the off-chance. Hey presto! The serial console woke up and gave me the message I was expecting, asking me to send a single asterisk character so the baud rate auto-detection could do its thing.
At this point everything started to go rather smoothly. I was able to hook up a loopback wire as per the self-test instructions in the user guide (yes, I read it, as the amount of space on these units is very limited so there’s little to no embedded help), and perform a full set of tests including connecting to itself and echoing back its own messages. A few RF tests with FM voice have shown that I can’t reach any of the other users nearby on 70cms (I have a spare Motorola GM360 which works on that band), or on 6m (my FT8900R is also currently idle so can be pressed into service there), so unfortunately that’s as far as I’ve got. As mentioned at the start, 2m is not an option due to the proximity to MB7UDJ, but with any luck I can persuade some of the other locals to add 6m to their stations and link me into the 2m network running around Berkshire/Hampshire once it picks up.
Anyone else with kit around the Buckinghamshire area, or further South but with a decent shot over the Chilterns (which curtail my RF activity to the South), feel free to hook up a rig on 50.525 and call me – who knows, we might even get a QSO out of it!
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