Usually 41 MHz transmitters are used in France where the 40MHz is not legal (the 40MHz is normally used in the rest of Europe and also here in Italy).
However before the introduction of the 2.4Ghz I know of some guys that runs their 40MHz equipment using 41Mhz crystals (without any problem), in order to avoid any possible interference
Probably if you use the 40MHz channels more close to the 41MHz (eg. 40.8XX, 40.9XX ) everything will works fine
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Bye
Ema