MB7PMF is the POCSAG Paging transmitter we deploy at the biannual EMF Camp
- Call Sign: MB7PMF
- Location: EMF Camp – Eastnor Castle (IO82TA)
- Mode: POCSAG
- Band: 70CM
- Output Frequency: 439.9875 MHz
- Output Power: 3.7 dbW (2.3 W)
- Network: DAPNET
- EMF programme announcements on RUBRIC 67 during festival
Pager technology, once the bane of anyone on call, has been reinvented by the amateur community in a distributed system which can be used to push alerts and other useful messages in the form of DAPNET (Decentralised Amateur Paging Network).
At the last EMF we had fun paging out the event programme and have decided to bring the service anlong again for 2024.
Hardware
MB7PMF is largely the same as the transmitter described on the DAPNET wiki here. The notable differences being the use of a Motorola GM900 instead of a GM1200, the addition of hardware to remotely disable the radio and a very over-engineered software/infrastructure deployment.
Full details of just how over-engineered this transmitter is are available here.
Pagers
This page on the DAPNET wiki has a good overview of compatible pagers that will work with DAPNET. SDR based options and the protocol spec are also easy to find for homebrew solutions.
The wiki also details how to program Skyper and non-Skyper pagers to receive pages both directed to you and containing rubric news.
Fof those who cant find suitable second had pager harware and/or are wincing at the cost of an Alphapoc there is an alternative using a Lora board. The one I had to hand is a TTGO T3 V1.6 which is an ESP32 based device but boards based on AVR should work just as well provided you add the correct mods.
The LoRa chip cant demodulate POCSAG pager protocol directly so you need to add a couple of jumpers from the raw I/O pins on the LoRa module to a suitable pair of inputs on the microcontroller, fortunately on this board the LoRa pins are brought out on the main board so a simple pair of jumpers will suffice from Lora1 -> IO35 and Lora2 -> IO34:
If you want to add an audible alert you will need to connect a passive sounder or small speaker between IO14 and GND (note that the version i used looks very similar to an active beeper so be careful with your selection unless you want to alter the code so it outputs DC rather than PWM)
You will now need some firmware, the one I used came from:
https://github.com/ManoDaSilva/ESP32-Pocsag-Pager
I updated my ric and callsign in config.h (line 33 or thereabouts) and left everything else alone since the frequency was already correct @ 439.9875 MHz however if you use a different microcontroller you will need to adjust perip.h. Also see the EMF camp rubric number in the next section, you will want to add a line for that so you get the EMF site announcements (note that rubric 67 translates to ric no 1067):
ric[RICNUMBER]={
{[your ric], “[your callsign”,2,0,0},
{1067, “EMF”,0,0,0},
};
Now test it out, and print a neat little box (i used this one from Printables):
Thats it for now. If i get a chance id like to extend the firmware to store say the last 10 messages and scroll through them but right now it seems more important just to get this published so folk can prep for EMF.
Data
MB7PMF is in the uk and uk-all transmitter groups on DAPNET, so anything targeting those groups will be transmitted.
There is a rubric (number 67) for EMF Camp specific traffic and it is anticipated upcoming talks/events will be announced through this in real time as per the 2022 event. It is worth pointing out that no license is required to receive amateur traffic so anyone can buy/build a pager and receive the general information.
If you want some scheduled messages beyond the event schedule (e.g. wake up call?, have you had your daily Club Mate yet?) give Dan/M0NXN a shout or submit a PR to the appropriate place here.
