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+----- Thread: RF module for spectrum? (/showthread.php?tid=151)
RE: RF module for spectrum? - erhard52 - 04-03-2026
learnt this one from gemini - looks like i did not appreciate this before fully.
https://gemini.google.com/share/8745774cd611
RE: RF module for spectrum? - flyingw - 04-03-2026
That's interesting Erhard.
It reminds me of what would have been so nice about the infamous proposed XPS transmitter. I reckon it would have directly spoken native XPS protocol to the XPS receivers (without converting from either PPM or XJT-D16 first) and as a consequence would likely have been one of the most efficient and reliable systems out there.
If, knock on wood, my existing Futaba and Taranis transmitters with their respective XPS transmitter modules last for another decade or two (I'm 70), I should be good. But just in case I am learning ELRS and EdgeTx.
Jim Drew wrote in an earlier post here that his new proposed version of the X10+v3 would be able to take CrossFire (CRSF), the standard ELRS protocol, as an input. If that comes to pass, then that would be a real nice way to use inexpensive ELRS receivers with the X10.
I saw in the forums and in the configuration tools that ELRS receivers can output SBUS so I tried using it with the X10. It sort of worked, but I wouldn't trust it to fly. The servos worked, but it turns out that ELRS "robs" a frame each time it needs to send telemetry back to the transmitter. It uses a spot in the SBUS data stream that standard SBUS and the X10 do not expect. As a consequence the X10 led flickers each time it sees this non-standard frame. I was actually ok with that because the servos worked, but it also had the negative effect that it prevented the ability for the X10 to program the failsafe positions while this non-standard stream was in effect.
An X10 that takes CRSF officially should not have this problem. The peril with open source stuff is of course, that the ELRS development team could change the CRSF protocol at any time and XPS would have to accommodate the change.
In the meantime, I want the New Jersey weather to get better so I can go flying without freezing and or fighting the winds.
Paul
RE: RF module for spectrum? - erhard52 - 04-03-2026
(04-03-2026, 02:16 PM)flyingw Wrote: That's interesting Erhard.haha i am 73 and debating if you should switch to mode 2 from mode 1 (germany) in my old days. i am trying to interest some kids in flying and for them it would only make sense to learn mode2.
It reminds me of what would have been so nice about the infamous proposed XPS transmitter. I reckon it would have directly spoken native XPS protocol to the XPS receivers (without converting from either PPM or XJT-D16 first) and as a consequence would likely have been one of the most efficient and reliable systems out there.
If, knock on wood, my existing Futaba and Taranis transmitters with their respective XPS transmitter modules last for another decade or two (I'm 70), I should be good. But just in case I am learning ELRS and EdgeTx.
Jim Drew wrote in an earlier post here that his new proposed version of the X10+v3 would be able to take CrossFire (CRSF), the standard ELRS protocol, as an input. If that comes to pass, then that would be a real nice way to use inexpensive ELRS receivers with the X10.
I saw in the forums and in the configuration tools that ELRS receivers can output SBUS so I tried using it with the X10. It sort of worked, but I wouldn't trust it to fly. The servos worked, but it turns out that ELRS "robs" a frame each time it needs to send telemetry back to the transmitter. It uses a spot in the SBUS data stream that standard SBUS and the X10 do not expect. As a consequence the X10 led flickers each time it sees this non-standard frame. I was actually ok with that because the servos worked, but it also had the negative effect that it prevented the ability for the X10 to program the failsafe positions while this non-standard stream was in effect.
An X10 that takes CRSF officially should not have this problem. The peril with open source stuff is of course, that the ELRS development team could change the CRSF protocol at any time and XPS would have to accommodate the change.
In the meantime, I want the New Jersey weather to get better so I can go flying without freezing and or fighting the winds.
Paul
what can i say here in the bay area we have no complains about weather at least not from me. i think your NY weather is closer to the german weather.
yes i agree that XPS should be a leader in the RC systems.
it is an amazing job to have spoofed the M-link system so successfully.
so if you are also a electronics guy then i wonder how could we really measure RF output power with the hopping stuff. maybe just a broad band filter and my tiny SA.
i also ordered the ELRS parts for my tx16s - want to explore it too. i am getting used to the edgetx open source. maybe need to learn LUA scripting too
on the side FYI
https://www.youtube.com/watch?v=ueA7riyLH4M&t=26s
RE: RF module for spectrum? - flyingw - 04-06-2026
Hi Erhard,
I am primarily a flyer who has learned enough about the RC products I use so that I can limit my mistakes.
I do not know how to measure the RF output power of a spread spectrum frequency hopping signal. It's a good thing Jim Drew does and I trust that the XPS products work well as required for our RC hobby.
More than a decade ago Jim Drew produced a product called the DivBee. The DivBee is a 2.4GHz transceiver module intended to be integrated by other manufacturers into their products that need wireless communications. The data sheet, which I found informative, has a table 5.1 that summarizes the RF power and duty cycle for the range of frequencies used in the 2.4GHz band. I found the data sheet by looking at the website: www.divbee.net
I think similar technology as used in the DivBee may be also used in the XPS RFU receiver. Also, at some point Jim said he was investigating using RFU-like components as a possible replacement for new XPS transmitter modules (in light of the fact that many of the original components are no longer available).
With ELRS the transmitter RF power can be set anywhere from 10mw to 1watt (!). So far I have been using 50mw and that gives adequate range. I don't know how it is FCC legal to transmit more than 100mw (including the antenna gain) in the ISM band.
Paul
p.s. Nice transmitter stick extensions. I have some of those rubber tips and I will try that out. Thanks for sharing that.
RE: RF module for spectrum? - XPS - 04-06-2026
I am pretty the ELRS won't pass at 100mW. The maximum radiated power allowed on the ISM band is 200mW. The average radiated power allowed is even less, but depends on the exact frequency.
The Gemini info certainly simplifies what was required. The data stream to the EVO module is encrypted. Once that was figured out, the entire protocol (which can actually change based on the number of channels and frame rate) had to be reverse engineered and the replicated.