The GoodWatch is my replacement circuit board for Casio’s modern calculator watches, adding support for 70cm and 33cm amateur bands while retaining three years of battery life and most of the watch’s features. It uses the CC430F6147 chip from Texas Instruments, and the watchband forms an untuned random wire antenna. Source code and CAD files are available on the GoodWatch github repo and documentation is available in the GoodWatch wiki
There is also a Frequency Counter, which helps to quickly identify the frequency of a nearby transmitter without extra equipment. Shown in this photograph, I used my GoodWatch to find the frequency of a walkie talkie that I imported from China, then confirmed its guess by tuning my Kenwood TH-D74 to the correct channel, which was just 50kHz off from the guess.
CW modulation from the radio transmitter was a piece of cake, and the watch will beep the time in Morse if you hold the + key.
Internally, the radio is programmed in C around the RF430 chip’s CC1100 core. Phase shift keying and LoRa modulations are not possible with this radio, but any 2FSK or even 4FSK modulation should be possible to implement with a bit of clever work and the right test equipment. A nice guide for writing OOK Transmitters is available to get you started.