Hi all, I had a quick look a at the Radiometrix 27MHz RF module datasheet and whilst not entierly clear (I would have to go through in detail with example frequencies) it looks as if it has 10kHz RF channels, so setting a specific RF channel within the model band shouldn't be a problem, but it looks as if they might only support a limited number for each s/ware version programmed in.
Similarly, since the modulation input is DC to 4kHz CMOS so a straight digital signal, PPM would be no problem as PPM is pulse position (time) not pulse amplitude. You might have to work on the antenna matching since no details of the RF port impedance are given as far as I can see.
Assuming a standard 2ms servo at 50% gives a 500Hz signal (ignoring sync pulses etc.) so with an assumed channel bandwidth of 4kHz there might be some jitter since if the channel bandwith is too low it effectively slows the switching edges making them sloping, so any noise gets translatted into timming jitter.
A 4kHz bandwith would convert a 4kHz square wave to a 4kHz triangle wave (sort of) with a 'rise time' of 125usec, so the max timing jitter could be +/-62.5usec due to noise
Probably no worse than the old 'analogue' systems though, since they probably had a similar signal bandwidth.
If noise or interference is an issue then going digital allows the use of digital message coding techniques that basically use multiple message bits to define each servo command bit, so you can use a majority decision system to allow for corrupted bits. If you had a max channel bandwidth of 4kHz, then that gives a max bit rate of 8kbits/sec, so spreading 8 servos of 10 bits each accross 4 bits (320bits per frame, say 500bits per frame) then that would allow 16 frames/sec (500 x 16 = 8,000).
The 27MHz probably has the advantage of less volume, as the antenna is just a wire, as opposed to the rigid 'rubber duck' antennas that are probably not waterprooof, so have to the inside the WTC.
Digressing slightly, I was interested in the commesnt about the origins of the openLRS, I did look at it but it seemd as if over time it has grownw to be more flexible and complex, but it seemed quite complex to configure and using an arduino mini-pro I had to go back to basics to fit the s/ware in the memory provided, hence my version of s/ware.
Going to any commercial system, or even a new open source I think the trink is to be clear up front what is required, and to prevent the 'wouldn't it be nice if....' (professionaly known as WIBNI or creeping elegance!) for even more niche ideas.
Even more of a digression, has anbody tried the new RaspberryPi pico instead of the Arduinos? This looks as if it has way more memory, 3 x anlogue inputs and 16 PWM channels .. and < £4
That processing power might allow the use of a software radio module, I think been mentioned before here, such as
That claims to cover 24MHz to 1.8GHz all for £22 or so, but it still needs a transmitter design. Once I've finished my current project .......!