I am disassembling my FR9X stock Iris transmitter and – well isn’t there suppose to be like an antenna inside where this big black nub on top is? It’s hollow. And empty… What in Earth!!!
A stock TH9x looks like the below transmitter;
site.hobbypartz.com/79P-TH9X-R9B … dio-01.jpg
When an FRSKY DJT module is added the TH9x stock antenna can be removed. Probably was ordered that way from the factory and the module is added in the rear with an antenna like below;
3.bp.blogspot.com/-oEk12nQzymA/U … gure+1.jpg
Yeah ok. Got it. Weird but I get it.
Wait, so we only use 915MHz for transmission then? No 2.4GHz???
I found the Contrast menu, btw… System Menu is accessed by LEFT longpress… openrcforums.com/wiki/index.php/ … l_Settings
LCD Backlight is MUCH better now. 
You are still at 2.4ghz and 915 for telemetry. it is just more efficient using this module.
OIC, so the module that snaps on the back with the big antenna spits out 2.4GHz for TX control and uses 915MHz for RX of telemetry data, both using the same antenna?
And then on the Iris, the big black antenna sticking out is the same thing but will TX 915MHz for telemetry and RX on 2.4GHz for control?
Just trying to understand… didn’t realize this… I thought the 2.4GHz was a totally different system and antenna…
I may not be giving you the exact technical answer, but I was told the module allows a better way to connect the receiver to the Iris. It is still 2.4ghz. the 915 is coming from the black antenna on the Iris if you ordered telemetry which it seems you did. Just a note if you are using a gopro. Don’t use the Wi-Fi on the gopro when you are flying as it will interfere with the radio. And if at some point you want to add FPV the safe choice would be the 5ghz system. This way you are keeping all the frequencies separated. This is how my Iris is setup.
Yeah I plan on 1.2GHz or 5.8GHz for FPV… Won’t use 2.4GHz on GoPro (802.11 Wi-Fi). So the black antenna sticking out of the Iris isn’t 2.4GHz but instead 915MHz and the 2.4GHz antenna is coiled up somewhere inside? I have yet to crack my case open but may here soon… 
You have it correct now. the 2.4 is under the top cover.
Thanks! Since we’re on the topic, the 915MHz is bi-directional, yes? Meaning my DroidPlanner or MissionPlanner SW can “control” the Iris (e.g. send commands like alt-hold and throttle %, as well as auto missions)… and the 2.4GHz is only one-way from my hand-held Transmitter to Iris’ receiver? Is that right?
Any idea what the range is on these??
Thanks!
Yes it is bi directional, I don’t have an IRIS but do use a quad with Andropilot. I launch traditionally and enter auto mode via my tablet. I then listen to what its upto. Once complete I land back with the traditional controller. Doing it this way makes it a simple matter of pulling my RTL or stabilize switch if something looks wrong in the mission.
The module in the back is a 2.4GHz FrSky module. more information can be found here frsky-rc.com/product/pro.php?pro_id=8