Using the Moon as an Echo [video]

This is the main plot from 3 body problem using the moon to magnify the signal!

I've successfully used moon bounce one way, with my signal from California on a simple 8el yagi being heard by a big station in Italy. -- using a digital mode, of course, getting phone through requires a BIG station on both sides since there is about 250dB of path loss.

I haven't managed a two way contact because there is some broadband noise on 2m in the same direction that the moon rises that raises my noise floor in that direction by more than 10dB.

I've made a fair number of contacts via meteor scatter, however.

I am out of my depth here

What they are beaming at the moon are not mechanical sound waves (which obviously won't cross the vacuum that separates earth and moon) but radio waves (= electro magnetic radiation)

Since we are talking about audio waves at both input and output of the demonstration ...there is presumably a conversion of audio waves to radio waves -- possibly using some form of modulation like AM or FM to encode the audio information.

Assuming it is FM modulated, given that the return signal has all kinds of doppler effects due to relative velocities ... we can't simply tune into the base frequency of the FM Modulation carrier wave ... but need to correct it with each passing minute maybe.

And the frequency modulation encoded on top of the carrier wave should also be scaled back proportionally based on doppler correction.

Once we do that though...why wouldn't the echo sound identical to the origibal?

I didn't quite follow why there is still a change in pitch of the audio between input and output.

Did they simply skip the second step of error correction described above and are showing the resulting distortion in recovered audio after FM demodulation?

They're using single sideband. Effectively their audio is just being shifted up to the moon frequency and back down again. (or, alternatively, like AM but with no carrier or secondary image)

The amount of doppler depends on what frequency they are at and where the moon is. One can set an offset between RX and TX frequency, but one doesn't have to.

You can skip the elevation if you don't mind being limited to working when the moon is near the horizon. You don't need to deal with polarization if the far side can handle it.