Clandestine Crystal Sets - Channel Isles WW2

[unrealdave]

I've been thinking. (took some effort) If you have 2 crystal sets connected to 2 aerials both fed in phase to a set of headphones would you get a approx 3db's increase in sound? Or have I missed something?

I suspect there would have been a proprietary dual crystal/aerial set if it was feasible - lots of experimenter's around back then