Retekess pagers

Out of pure boredom I got my hands on a Retekess T119 pager from Amazon. My idea was being able to interface it with a PC, and get notifications whenever anything important happened.

Here's the documentation on how those pagers work.

Protocol

The pagers use on-off keying, with the center frequency set at 433.92MHz, which is an unlicensed ISM part of the spectrum.

Each transmission is composed of 50 repetitions of a packet, with a separation of 7.5ms:

Each packet is conformed by 25 bits:

These packets are formed by two parts: a 13-bit restaurant ID, and a 12-bit pager ID. These parts are sent LSB-first as-is, with no preamble, header nor footer:

The restaurant ID is random, and is only used internally to avoid one restaurant triggering the pagers of another restaurant. The pager ID, on the other hand, is displayed on the LED panel of the pager.

This T119 pager admits IDs up to 999. If an ID of 1000 or higher is attempted to be memorized, the pager beeps indicating an error and ignores it.

The transmission of each bit is reminescent of the Princeton Tech PT2262:

• Each bit takes 1300µs to send, for an effective symbol rate of about 770 symbols per second.

• A zero bit is represented by the the transmitter being on for 1/4 of the symbol duration.

• A one bit is represented by the the transmitter being on for 3/4 of the symbol duration.