RE: Tx Rx crystal/freq mystery
Dustoff
Yes it is perfectly legal to switch your Tx frequency with a single frequency module or a synth module without retuning. The reason is and the reason this type module was first delveloped for use in our Tx's is that the module contains all the Frequency determining circuitry within the module and therefore when changing the module there is no need to retune. In fact a module by itself can be sent to a sevice facility for a checkup and alignment without even including the Tx.
If I may I would like to address the reason why crystal swapping (crystal only, not modules) in Tx's is aginst FCC regulation in the US and if I am not mistaken I beleve in Canada also. As unlisensed users of the 'hobby bands' we are listed by the FCC as secondary users. Now we have a situation in North America that many other parts of the world do not have to contend with. You see the hobby bands are shared by lisensed meaning paid exclusive users of frequencys that are interspersed between the hobby channels. They are half way between each of the channels. This is precious little spacing.
These commercial users are listed as primary users which means if we intrude on them we have to cease and desist. I don,t beleve the FCC cares if we shoot each other down but watch out should we step on the toes of the commercial users. This could even impact our future free and unlisensed use of the band. Now I don,t beleve those folks in many other parts of the world have quite this situation and true for instance crystal swapping in the UK is freely practiced apparently. A simple crystal swap certainly can have the potential to detune the Tx sufficiently to impact the primary users while still not apparent on a range check or even impacting an adjacent hobby channel.
As to the reason many non module Tx's may have accessable crystals is with the world market where swaping is freely practiced it would be uneconomical to produce different case designs just for the North American market.
Just one last thought: When it comes to the RF environment in North America, there is no "middle of nowhere".
John