As for TX's, it takes some history and I may be missing a few points or even be wrong.
Initially lower freq was used and a dedicated channel was needed since there was no encoding with the signal commands. Therefore you could loose control because somethingoperatedon the same freq.
Hence the move from 29 mhz to 72 mhz, more channels and less potential for someone operating on the same frequency, but still unencoded.
Fast forward to spread spectrum (frequencyhopping). JR and Spektrum are the same and are made by JR. Original DSM was frequency hopping on the 2.4 ghz band but it did not use multiple channelssimultaneously. DSM2 brought 2 channelssimultaneouslyand DSMX brought true (opinion) spread spektrum. Futaba used fasst which always used multiple frequenciessimultaneously. All of these are encoded which makes it unlikely to to get channel interference as the TX/RX communicate a good freq on power up.
However there are issues with 2.4 ghz. Line of sight is best and in reality you should always have line of sight. Reflections of the signal can cause strange things to happen, i.e potential loss of control so best to be away from building etc and this shouldn't be a problem. 2.4 ghz in an urban area is very noisy (everything uses it!) but ideally you shouldn't be flying in a crowed urban area and those devices (routers, phones, video, microwaves...) don't check for what channel they will be using. 2.4 ghz is also more attenuated (weaker signal and less distance) from environmental factors but shouldn't be an issue if you can see your bird.
Now there are UHF systems that use spread spectrum and improve many of these issues. However, they have a longer antenna andtechnicallyyou may require a license to operate on those frequencies.
For the most part this is notrelevantto most folks and is partially my research/needs into FPV. But I have had some unexplained spektrum things happen as I think a few of you have also.
So, with a TX that is modular, you can put in manydifferentmodules that operate atdifferentfrequencies to satisfy yourdifferentneeds (if you have diverse needs).
But your doing the right thing, researching
Hope I haven't sounded like a git from another site...