PK-88 TNC Hardware Modifications

As is typical for stories on here, through a long series of events I ended up in kind of the perfect position to build APRS infrastructure supporting Northern California. On the APRS side, I had (more than a freaking decade ago now!) put together my Masters thesis on APRS and the protocol design of it. While working on that, I played around with a few different Terminal Node Controllers, which are essentially APRS’ version of external modem (plus optionally a lot of the network protocol intelligence as a historical artifact of the early days of packet radio pre-dating the ubiquitous home personal compute). I had developed affection for the AEA PK-88 in particular for a few reasons; primarily that its modem performance seemed quite good in testing, the circuity is Z80 based and well documented, and finally that with a little patience obtainable on eBay for less than $50. On the Northern California side, I’ve gotten to know several of the repeater infrastructure folks who own and/or…