Interfacing Spektrum DX7 to either DragonLink, EzUHF, Thomas Sherrer, or ChainLink LRS

 

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!

Manual

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).
  • Done!

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.

Solder the cables in a 90 degree angle so the cables won't be in the way when you close your TX.

The cables seen from the top -- 90 angle solder joints.

Move the hole for the mini plug as far to the outside as possible so that the mini plug won't bind with the internal components.

Connected to a DragonLink.

 

Connected to an EzUHF

 

Disclaimer: Performing the instructions described in this manual will void your manufacturer’s warranty!  Proceed at your own risk!

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28 Responses to : Interfacing Spektrum DX7 to either DragonLink, EzUHF, Thomas Sherrer, or ChainLink LRS

  1. Ray Campbell says:

    I was thinking about buying a Chainlink LRS from BEVRC, but wasn’t sure I’d be able to use it with my DX7. Concerns resolved!

    We’ve needed a place like this for a while. I agree that the forums are great, but relevant information can be difficult to find.

    Thanks for getting this going!

  2. jimmaplesong says:

    I want to do this, but have a DX8. What are the chances that I’d be able to figure out the equivalent procedure?

    • Tim Nilson says:

      @Jim – if you figure this out, please come back and post a manual on how you did it here. I am sure you’re not the only one trying to do this.

  3. Ian Davidson says:

    Agreed. Although I’ve never seen inside a DX8, my understanding is that it is very different to the DX7. I think the best route for the DX8 is to try and tap into the PPM signal via the trainer port.

    • jimmaplesong says:

      Hi Ian, yeah… the trainer port has the signal we need, but it sounds like it’s just a little weak. I think the solution there would be a line level converter… I happen to have a couple handy…

      In order to use the line level converter, I need a reference voltage (something that’s the same as the logic high from the trainer port) and another voltage which is where we _want_ the PPM signal hi to be. I’ve read that this is 4 volts, I’ve also read 8V and 12V.

      There’s just a little too much misinformation out there on the nets for me to know exactly what to do yet.

      • Ian Davidson says:

        I thought the PPM signal on the DX8′s trainer port was slightly higher than that on the DX7′s trainer port and so perhaps could be used, but I might have misheard on this.

  4. jimmaplesong says:

    No need to void my warranty on my DX8!

    http://fpvlab.com/forums/showthread.php?543-Zephyr-in-Vermont&p=7788&viewfull=1#post7788

    The EzUHF (according to the manual) can accept PPM signals as low as 3.3v. I don’t have my oscilloscope yet, but I made a SVideo mono audio mini jack, and it works great.

    Ian, you were right, the DX8′s trainer port has plenty of signal power.

  5. Pingback: Updated DX7 to LHR Manual — fpvmanuals

  6. Pingback: Anonymous

  7. ilovslavo says:

    I want to do this, but have a DX7se (special editions).
    http://www.spektrumrc.com/Products/Default.aspx?ProdId=SPM2731

    Because the DX7se- Special Edition operates at the faster 11-millisecond frame rate,and has not a trainer port,the trainer system is no longer compatible with other transmitters.

    I would like to ask you,to know your opinion.Please help me!!

    If I Connecting a Spektrum DX7se to ChainLink LRS as show
    in this dokument,through internal PPM bus signal,so If I hook my LRS system directly into the PPM stream of the radio
    (through RF module pins and new 3.5mm stereo jack).

    IT WILL BE WORKS ??? on my DX7 special edicion TOO ????

    RF module pins (ground-black,PPM-orange,Power-red) looks the same on my Spektrum DX7se as picture show on DX7 in this manual.

    greetings ALL FPV-fans from Slovakia-midle Europe
    Slavo

  8. Ian Davidson says:

    I imagine mod’ing the DX7se will be the same as mod’ing the DX7, although having never seen the inside of a DX7se, it’s impossible for me to be 100% sure.

    Just pop the back off your DX7se and if you see the same 3 wires going to the 2.4GHz RF module, then just give it ago, it’ll probably be fine!

  9. Malcr001 says:

    Ok I have done this mod and everything should be fine. Only trouble I’m having now is finding an s-video to 3.5 jack cable. I thougtht I would be able to solder one together instead but the wires on these audio cables are super thin and soldering them just doesnt work.

    Where can I find the adapter shown in the last image?

  10. Tokaz says:

    very good mod. Im planning to test a chain link on my dx7. I have bought the switched 3.5mm stereo jack but i have to bought one 3.5mm jack male to. Do you have a pickture how to solder the cabble from the chainlink to the 3.5mm jack plugg. Best reggards Fredde

    • Ian Davidson says:

      As detailed in the main guide. Wire a stereo plug to the DragonLink (or ChainLink) 3-wire lead. GND to the top band, POWER to the middle and PPM to the tip.

  11. Phreak Out says:

    I believe I received all the items to convert my DX7 – this is a gigantic help!

    Mega-thanks!
    :)

  12. Tokaz says:

    Tonight I made the mod. Very simple. Now I just have to decide which long range to buy. Suggestion?
    Anybody know if is possible to do a similar mod on a jr dsx9?
    Many thanks from sweden Fredde

  13. easymoney99 says:

    Guys check out this Youtube video:
    More FPV: Chainlink UHF has arrived and works with Spektrum DX8 PPM. FY-21AP BEVRC 1.3GHZ

    http://www.youtube.com/watch?v=SJIdvUemP3E

  14. hockeymonkeymark says:

    I did the mod today, rechecked and rechecked all pinouts for my EZUHF and DX7. I am not getting power from this mod. Does this also power the EZUHF transmitter? Or do I still need an external Lipo to power the UHF transmitter? I followed it exactly but I guess I’ve missed something. red and yellow from the lower DX7 board to the outer pins. Red and yellow from the 2.4 module to the inner pins. Black (ground) to the same charge ground. Tip is PPM, middle is power, bottom is ground for the cable. My voltmeter is getting nothing. Any thoughts? Thanks guys…

  15. hockeymonkeymark says:

    Wow, thanks for all the replies. I did exactly what was done above and somehow fried my effin DX7 for the 2nd time. I was proud of my clean and tidy work too. I should learn my lesson for hacking into expensive electronics. This will be the last attempt to amplify my RC signal. Tried a 2.4 booster and fried my transmitter, now an attempt to power my EZUHF internally has fried it again. I will keep it short range. I have no FPV buddies any where around me and am very frustrated for information from time to time. This would definitely be one of those times. Thanks for letting me rant. Ahhh this hobby…..

  16. Ian Davidson says:

    Are you sure you’ve blown up your DX7 and not just blown the replaceable fuse in the DX7?

    • hockeymonkeymark says:

      Yeah. I checked it. Its the transmitter board right on top of it. It is not receiving power now. I put it back the way it was. Carefully resoldered the two wired that I spliced. Checked everything with a voltmeter. All is well but not receiving power up there. Something pooped on me. Gotta send it back to Horizon for another 80$ repair. I should just quit tinkering and go fly.

  17. Pingback: DragonLink eller EZUHF?

  18. PeeBee says:

    Thanks for this helpful blog. However, I have a DX7s, and it does not have a three wire connector to the RF board. The RF board looks like it may be the same as a DX8 (It has DEX8 in the part number). Can you help? (I have photos)

    Also, can you comment on the option of using the trainer port weak PPM signal, feeding it into a logic level shifter (e.g. 2N7000 plus pullup) to bring it up to 5v, then feeding that into the LRTX?

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