Radio Channels

[E69_VonPepofen]

Acording to what I have read, fighters radio  (and probably bombers too) had only one channel in WWII. They could only communicate with their own squadron and control tower. Changing the channel ment changing the cristal (physically) that vibrated at a certain frequency. Thus they could not communicate with other fighter or bombers which were not using the same frequency and for obvious reasons each unit used their own frequency.

[56RAF_Roblex]

That is true for the Spit Vs in 1940.   They had four channels and to change frequency meant changing the crystals on the ground.  The same sort of system was used in the  early P39 but the later ones had,  I believe,  three receivers and two transmitters with preset frequencies for different ranges.