In the States, the FCC (Federal Communications Commission) who controls and distributes the whole spectrum of radio frequencies, have said that changing the transmitting frequency by changing the crystal alone, is not allowed.

This is because just changing the crystal doesn't guarantee the frequency doesn't bleed outside the prescribed narrow band without the factory fine tuning the transmitter after the crystal change.

That's how the FCC sees it. In fact in Europe and probably elsewhere, any bleed over isn't actually a problem like it can be in the States. Our frequencies have other users between some of the channel frequencies. Some earth-moving equipment, for example use the frequencies between a couple of our frequencies and it's best not to confuse them at all!!

Changing the frequency using a module (like the Spectra module in the Hitec transmitters) controls the frequencies tighter and is therefore allowed. Also, you can send the transmitter back to the manufacturer for them to fine tune the frequency after a crystal change.

So, whereas it's technically possible to change the channel by changing the crystal, it isn't allowed in the States, as the FCC who control these things have decreed it will interfere with other users of the nominal 72 meg bands. They may or may not be right about the bleed over, but they are the ones to decide so we should comply.

-David C.