ORIGINAL: daveosoar
Just as amatter of interest. Here in the UK, where we fly on 35Mh., we can change both Tx and Rx Xtals at will which is very handy on busy sites. The 'unwritten law' is for power to use odd nos., gliders even. Of course, over the English Channel, in the smaller part of Europe a different frequency band is used. Some sites insist on the local but I have found that "visitors" are able to use their own frequencies with the local bosses sayso.
Just to throw in some more international stuff. Australia has specific frequency ranges for R/C equipment. For aircraft the most common band is 36Mhz although 40Mhz is also permitted. 27Mhz is OK for park flier stuff and 29Mhz tends to be an older aircraft range more commonly used by R/C cars.
In general, aircraft run on 36Mhz using odd numbered channels. We peg frquencies using one of two standardised frequency boards. Two inch wide keys cover 20Khz and one inch keys cover 10Khz. There are different boards for 10 and 20Khz separation.
When I peg my frequency of 629 the two inch key blocks off 628 and 630. This ensures no-one flies on the adjacent channels. The reason for this is to ensure any frequency drift doesn't wander into someone elses channel. Hence my key blocks an effective 20Khz wide band. You'll understand why odd channels are preferred now, it minimises the risk of overlapping into the blocked range of someone elses key.
In Australia the national MAAA requires that most member clubs/fields follow their frequency guidelines, which means that every TX must be tested and certified for the freq it transmits on. You can change crystals to get onto another channel but you need a certification test and approval sticker. Not sure how they deal with synthesised stuff theses days but I'm sure there is a rule.
I also believe our 36Mhz band does not use positive or negative shifts as seen between different brands of radio. At least, that's what the experts tell me BUT most people stick to matching brand receivers.