Re: Out of band power
"Thanks for that info, I'm generally ignorant of this tech - it is a bit like doppler but with EMR instead of sound?"
Kind of like Doppler, in the sense that the FMCW radalt measures a frequency shift, and translates that into a time.
The FMCW radalt transmits a chirp waveform (the frequency increases linearly over the duration of the pulse). While that is propagating to the ground and back, there is the same replica waveform running inside the device. Because of the time taken for the transmitted waveform to return back from the ground, it arrives with a frequency shift compared to the replica waveform which has been increasing in frequency during the transmission. The replica and received waveforms are mixed together to produce a signal with a frequency equal to the difference in frequencies of the replica and transmitted waveforms. Because you know the chirp rate, you can easily convert that frequency difference to a time, and thence a distance.
By using a chirp waveform, you can have a longer pulse, which means more energy (not power) in the pulse, which makes it more robust against interference (or, you can trade off transmitted power instead). A fixed frequency pulse has to be a lot shorter to avoid interfering with itself when the ground return comes back (you must stop transmitting before the ground return comes back). The chirp waveform can still be transmitting while the ground return comes back, the changing frequency giving you the discrimination to still see the return signal.
Biting the hand that feeds IT
