Sorry if this has been mentioned before but I had not realized this problem until I read Robinson´s "Invasion 1940".
Also from
Spitfire on my tail || kuro5hin.org
Steinhilper was the communications officer for his gruppe, and has some interesting insights into the Luftwaffe´s radio communications. Bombers and fighters used incompatible systems and could not communicate with each other at all during a flight. The radios they did use were crude and unreliable. It's generally accepted that the radio problems were a significant handicap for the Luftwaffe.
Also it is certain for German fighters it was never possible to talk to ground control, or the fighters and bombers to communicate with Air Sea Rescue Units.
Radio discipline was often sadly lacking. During combat, so many German pilots were talking that "the frequency would be swamped and all that could be heard was a high-pitched whistling as the receivers became overwhelmed."
Two years passed before the Luftwaffe´s air-to-air and ground-to-air radio communications finally caught up with the rest of the war. " Operationally speaking", Heinz Knoke told in his diary in June 1942, " it will now be possible for our fighters to be located and directed by ground control at all times." Something that Fighter Command was doing competently in 1940.
Also some fault is put on the "Spaniards", the Luftwaffe pilots who had served in Condor legion.:
Steinhilper came to the conclusion that, because the Condor Legion was clandestine, it had avoided using radio in case the transmissions betrayed its existence. Pilots communicated by hand signals or wing-wagging. Back in Germany the Spaniards disliked the whole idea of radio: It smacked of direction from the ground;they preferred the freedom of sky. After a Luftwaffe exercise which included an experiment with ground-to-air radio, Adolf Galland blamed Stenhilper´s unit for "bothering" his men : "...it would be best to throw out all these damned radios! We don´t need them. We didn´t need them in Spain and without them we could fly higher and faster!"
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The radio for RAF did not work perfectly though at all times:
RAF entered the war with the TR9D set. It had a limited range. When Sergeant Pilot Ginger Lacey took his hurricane to France, he found that above 15,000 feet his HF radio could receive only BBC;he made his first attack on an Me109 with the music of Jack Teagarden and his orchestra in his earphones.