Connecting a Spektrum DX7 to long range radios is not documented well as most of the LRS manufacturers only explain how to connect their TX to Futaba radios. The DX7 has a trainer port that sends out PPM signals and some have tried to use this port for their LRS connection. The benefit of using the trainer port is that the DX7′s 2.4 radio is automatically cut from power and does not transmit any longer.
However, measuring the PPM’s signal power of the trainer port reveals that the signal is a lot weaker compared to the internal PPM bus signal. In theory, you want to provide your LRS system with the strongest PPM signal available, which means you have to use the internal PPM bus. This manual describes how to hook your LRS system directly into the PPM stream of the radio and also provides power (which the trainer port does not). While it requires you to open up the radio, cut some wires, make some solders, and drill a hole in the case, it’s really not that bad of a mod and provides a great solution that makes switching between LRS and 2.4 easy. Thanks to Ian for coming up with this solution and for writing it up!
This isn’t a detailed ‘how too’ manual, just a quick overview. But looking at the photos should hopefully make clear what I’ve done. Any questions though, please just ask. It’s very straight forward and once complete, switching the DX7 from 2.4GHz to 433MHz could not be simpler. Although this is written with the DragonLink in mind (as that’s what I have), this technique would work equally as well for either the EzUHF or TLRS (Thomas Sherrer).
The only parts needed are a SWITCHED 3.5mm stereo jack-socket, a 3.5mm stereo jack-plug, oh and some wire.
You can buy the switched 3.5mm stereo jack in the USA here.
- Cut the RED and YELLOW wires going to the 2.4GHz TX module and wire the SWITCHED 3.5mm stereo jack-socket inline with these. Leave the BLACK wire.
- Attach a wire from the ground pin on the SWITCHED 3.5mm stereo jack-socket to a ground point in the DX7. I used the charger socket.
- Drill a hole in the DX7 case and glue the the SWITCHED 3.5mm stereo jack-socket in place. I used Araldite.
- Wire a stereo plug to the DragonLink 3-wire lead. (GND to the top band, POWER to the middle and PPM to the tip).
Once finished you can use your DX7 as normal, but then when you want long range, just switch OFF, plug in the DragonLink and switch ON again! It will automatically cut the power and PPM signal from the 2.4GHz TX module and re-route these to the DragonLink. It works a charm!
IMPORTANT: ALWAYS ensure your DX7 is SWITCHED OFF when inserting/removing the 3.5mm stereo plug.
Disclaimer: Performing the instructions described in this manual will void your manufacturer’s warranty! Proceed at your own risk!