I am having problems with an Xbee900 system where the Tx is interfering with the servos, HK 12G Digital.

The interference is constant and stops if I unplug the Xbee from the APM or if I touch the Tx antenna.

This is on a small plane (X5 ) and so I would prefer an "electronic" solution rather than moving the Xbee out to the end of the wing.  i..e. a choke or orther device. any ideas that work would be appreciated. Can the servo lead be screened, if so how do I do that?

2nd question .. how long can the APM -Xbee cable be made? just in case I have to move it.



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Hi Guys

Any electronics gurus have any idea on an easy whay to fix this?, Thanks

Yeah.  Plug the Xbee into at least 4S Lipo directly.  After the smoke stops, order a 3DR Radio. ;)


Seriously though, this is a big problem, and I struggled with it for a long time.  There's a lot of info in a huge Heli thread somewhere.  But going by memory...  Choke on the ground line for the Xbee.  Shielded wire for the servo signal wire.  Cap on positive/negative right at the servo.  Make sure the servo is grounded directly to the APM.  Actually, that was a huge one for me.  I had made a servo breakout board where the power and ground were direct to Lipo, and only the signal came from the APM.  The APM was attached to the same exact battery as the Servos, same ground, but no matter.  It was really really bad like this.  Really bad.  When I moved the servo ground to be on the APM, the problem was 90% reduced.

Uh...  don't aim the little wire antenna at the servo.  That's a big one too.

Some servos are susceptible, some are not. 

IIRC, the issue was something like, the Xbee that uses that stupid little wire antenna has no ground plane, and uses the entire negative side of the power supply as a ground plane.  (I'm no EE).  I had seen somebody say that if you use the Xbee with a real antenna, there would be no problem.  So if you HAVE to use an Xbee, get one with the SMA connector, and a little antenna.  

I really like these little antennas more than rubber duck antennas for airborn side.


Thanks for the info,  There were times last year when I was trying to get the xbee system to work that I considered exterminating it with a large hammer. I finally got it all working with some help by people on this site and especailly Dany from Canada drones. It has worked flawlessly in my old plane since then. my old plane retired and everything got put into the X5. The new setup is the same wiring and connections all to the APM and the power is from a UBec at 5 volt. this leads me to conclude that the xbee is too close to the APM and i need to move it away. can I extend the power/comms connector and how much?


I will try to finf the heli thread you mention.

Do the 3DR radios cause less interference then, ? Thats could be interesting as well .

I've never had a problem with the 3DR.  I think it may be because they use a proper antenna with a ground plane?  I dunno for sure.

But note, they don't have IC approval.  Not a big deal probably if you're just "some dude".  But if you use them in a professional application, could be a problem.

Oh, now I remember what I had done!  If you look at your Xbee, you'll see that there are pads to solder on a standard SMA connector.  That is what I did.  I converted it to a real antenna.  

I can't remember whether or not I tested it on a servo or not after that.  But you could try.  It's low risk and cheap.



If it doesn't help, you'll have done no harm, and probably increased range anyway.

I am using for telemetry XRF modules (from Ciseco) which are similar with Xbee.

To avoid interference usually I am using ferrite ring on servos wire.Same thing on FPV camera wires.

Also I am twisting the APM telemetry cable and this help to avoid interference.

Try to twist also your servos wires.

Let us know about progress.


Still trying to get rid of the problem, I tried extending the cables and moving the Xbee all over the plane but on an X5 there is not much real estate to choose from!. All my srvos are grounded at the APM as R_L, Twisted all the cables added chokes, ferrites are next.

In the process of this I managed to disconnect/ reconnect the Xbee when I moved the cable to far and it promptly fought back by "bricking" itself. Grrrr. Its now working again but another evening was lost fighting with it.

I think the time has come to order the 3DR.

More news later.


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