POCSAG Paging with the P2

ke4pjw

This is a project I started way back in 1996. I was working at a 2-way radio shop and learning all about radio. Reading in the back of a Zetron Paging Terminal it showed the POCSAG protocol is detail. I learned a lot about the protocol, how pages are sent in batches, how power saving is achieved by turning the receiver on only during the part of the batch where the pager's CAP code window is, etc. I set off to write a basic program that would generate a wav file that could modulate the soundcard. I failed because I did not understand the wave file format. I just had a raw stream of data that should have been sent at 512 or 1200 bps. I never knew if my code was correct, or if the NZRI code I wrote actually worked, etc. If I had money at that time, I probably would have found success with a Basic Stamp. I was too broke, financially irresponsible, and unfocused at the time to afford one.

So, over the weekend, on a lark, I asked Claude to write a POCSAG encoder for the P2. Last night I had an opportunity to give it a shot on real hardware. First thing I noticed is that Claude didn't do the FSK output correct. I am unsure of what it was trying to do (NCO-tone generation? ), but once I was explicit that it would be driving a FM modulator directly, and it updated the code, the output "sounded" correct. After a couple of tries and inverting the output, I was able to set off the pager. It received garbage, but I was able to give that info to Claude and it corrected that as well. Fun stuff. Demo video and code attached. Includes the Claude markdown and other files used by Claude. I did have to reference the V54 Spin2 documentation, but is too large to place in the ZIP.