Actually it's not a Gunn diode. It's a transistor Dielectric Resonant Oscillator (whatever that is).
These guys have been hacking it extensively. By itself, it has VERY little range, the transmit power is quite low. Probably due to the need to be cheap and also not cook the heads of kids staring into it.
https://www.austech.info/showthread.php?t=135840&page=1
They replaced the DRO board with a real Gunn diode, upped the voltage with a new battery, and got pretty nice performance!
It's pretty mind-blowing that these are real.
I do have a project in mind where I need to detect not only the velocity of a projectile, but more importantly the change in velocity (in relation to its instantaneous velocity) to calculate its drag coefficient. Doing that would require a Gun diode for range, new processor (no problem) and a new display (probably a serial port for data transfer for display on a laptop).
But now I'm starting to think since I'd throw out the DRO, processor, battery, and display,
is anything left in this device that is worth getting? I'm not clear on what would stay and how hard it would be to make something of my own that did the same job.