Okay, now that i have had Geofrancis help me sort out my pile of FrSky r9 equipment, its time to start posting pictures and details in these three "vendor" 915mhz areas.
FrSky is actaully on its third version of 915mhz equipment at this time.
2 versions of hardware, and 2 versions of firmware.
Frsky started out long ago as a clone maker of futuba receivers, then started making its own transmitter modules and receivers, then started making its own transmitters. they had T series receives (futaba fasst clones) then their own V and D series. then they came out with a newer version of the D series, "accst" or D16... at about the same time that they came out with their own transmitters.
when 915mhz became big enough in the Drone world, FrSky decided it was a big enough market to get into. that created the first D series 915mhz equipment, basically the original black jr style transmitter module labeled "r9m" and a full size 8 channel pwm receiver with sport and sbus labeled "r9". they also created two smaller "drone" size receivers that supported primarily s-bus to a flight controller. both of them however did have pins for pwm output. the r9-mini has/had 4 pwm output, and the r9-slim has/had 6 pwm output... but those two just had individual pins, it was left up to the user to build an actual harness that could actually connect real servos to the receivers.
these r9 915mhz devices also used the "accst" protocol.
the problem is that this first version of FrSky's 915mhz equipment had both hardware and software problems. people did not like it. it was so bad that some people figured out that the first batch of r9m modules actually shipped with 2.4ghz antennas. FrSky probably sent out 6 different firmware updates for both the transmitter modules and the receivers in a one year period. people got tired of trying to figure out what version of firmware they needed to make everything work. FrSky was kind enough to change the color of the newer transmitter modules to the orange color, so you could avoid the original black modules that actually had a hardware issue. for a reason that i am not familiar with, they came out with a third version of the transmitter module specifically known as r9m 2019.
some people abandoned FrSky for TBS Crossfire, another 915mhz system, that provided better support, and better performance, but it came at a price. the original TBS hardware was 4 to 6 times the price of the FrSky equipment.
other people took their existing r9 equipment, and wrote new firmware for it. That firmware was/is called ExpressLRS. ExpressLRS is open source, and is now available on hardware made by at least a half dozen different brands.
Then FrSky, for many reasons, most political, and not discussed here, decided to create a new protocol called "access" which did several things. it fixed a bunch of bugs in the original accst protocol, it improved latency in some scenarios, and it extended the capacity, from 16 channels to 24.
you can still get accst hardware from r9m, but all the new radios are made to use access.
FrSky has also decided it wants to go up market. you can still buy a $200 FrSky radio, but they have expanded their line.
they have three basic radio families:
The fundamental difference between the entry level and mid level is that the mid and high level radios now come with FrSky's own firmware, labeled "Ethos", while the entry level radios come with OpenTX.
I bring this up, because the biggest difference between the Tandem upper level and Horus mid level is that true to its name, the Tandem series radios actually have both a 2.4ghz rf deck, and a 900mhz rf deck built into the radio.
I currently own an original Taranis x9d (accst protocol), a QX7 (access protocol), and just recently picked up a Tandem XE (dual access protocol).
In addition to that, i have 3 r9 receivers, an r9 slim, a r9 mini, a single r9-mm (all accst) as well as two r9-mm-ota, which are access. I also have two Jumper r900 receivers, which are basically a clone r9 (accst).
My Posts for R9 hardware will be based on those devices, and any new access receivers i may pick up to use with the Tandem XE