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alros_100

900mhz video transmitter and FMA copilot II interference

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Hi folks

I wonder if anyone can offer me some advice. I am trying to set up a FPV stryker with on board stabilization using the new copilot II from FMA, and OSD and return to home using eagle tree system. A full explanation of my issues and tests/video are located on post 640 here on the FMA RC group site.

Essentially, 910 mhz range video type transmitters cause the copilot II to induce a left or right banked orientation as well as servo jittering. This banked orientation is also seen on the roll indicator of the FMA programmer readout and can be repeatedly reproduced by moving the transmitter closer and farther away from the plane/copilot II. A transmitter distance of 2.5 feet or greater is needed to not cause this interference. FMA suggested adding 1000 picoF capacitors on the servo leads, but this didn't help. In fact the roll changes occur with the servo leads disconnected altogether suggesting the transmitter interference may be entering by way of the copilot II sensors, their leads, the copilot II computer itself, or the in servo leads entering the copilot II from the RC receiver/ eagle tree OSD. I also bought this 900mhz low pass filter and accompanying antenna from DPCAV but unfortunately it didn't help. Interestingly I borrowed a friends old copilot version (CPD4) and it did not have any interference issues even with vid transmitter right on it.

Any ideas of how I could isolate the copilot II from my transmitter (other than putting the transmitter on a 2.5 foot stick trailing the stryker) ? Or is it a lost cause and I should sell the copilot II.

thanks

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Why not just trade with your friend? Or is he FPVing also...

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To devise a plan of action you need to determine if the interference's major contribution is from conducted or radiated pathways. The easiest way to do that is to run the 900MHz Tx and camera completely isolated from the R/C system and FMA co-pilot. Do not have any electrical connections between them, even indirect wiring, and do not share power. Create two separate and working entities. When you do this, do your see dramatically better noise immunity?

If you do see things get much better, then how close can you get to the FMA now before it gets weird? Where is the most sensitive spot? The little details matter, so be very diligent in your testing.

900Mhz Tx's are very popular in the USA and are not going away. Good RFI solutions begin with the design stage and field fixes are usually second best. So I would think that FMA would want to solve this using their engineers. Have you had a nice heart-to-heart chat with them? But if they don't want to cure this then I suppose customers like you must take on the challenge.

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To devise a plan of action you need to determine if the interference's major contribution is from conducted or radiated pathways. The easiest way to do that is to run the 900MHz Tx and camera completely isolated from the R/C system and FMA co-pilot. Do not have any electrical connections between them, even indirect wiring, and do not share power. Create two separate and working entities. When you do this, do your see dramatically better noise immunity?

If you do see things get much better, then how close can you get to the FMA now before it gets weird? Where is the most sensitive spot? The little details matter, so be very diligent in your testing.

900Mhz Tx's are very popular in the USA and are not going away. Good RFI solutions begin with the design stage and field fixes are usually second best. So I would think that FMA would want to solve this using their engineers. Have you had a nice heart-to-heart chat with them? But if they don't want to cure this then I suppose customers like you must take on the challenge.

Mr. RC-Cam

Thanks. The transmitter was completely separate for all tests with its own battery and no physical video connection. My original link above shows a nice video of what I am seeing + more detailed description. So it has to be radiated interference. At a distance of 2.5 feet or greater, the interference diminishes to where the two can be used together. the closer to the copilot II computer the worse the servo deflection to a "banked orientation". On my larger plane, I have the two separated by just under 2.5 feet, and the copilot seems to work ok even with the video leads connected, and I have been able to fly this plane FPV. But on the smaller stryker, I cannot get the transmitter far enough away from the copilot computer. The effect on the computer is to induce a bank orientation of the aileron servos, and loss of sensitivity of the copilot to changes in plane attitude. ALso I noted that the interference was slightly less with the dpcav black dipole antenna and worse with the stock whip positioned straight without a bend - but not sure 100%. Unfortunately I don't have access to a spectrum analyser.

I have posted extensively on this in the FMA RCgroups site, and also emailed them. They did advise me to put 1000pico F capacitors on the servo leads but Have not yet heard back from them after I posted that their suggestion didn't work and I also posted a new video of the problem. I am committed to working this out with them, but I am looking for anything I could do to the transmitter to reduce this interference. That is why I was hoping the 900mhz low pass filter might help thinking it was a harmonic, but it didn't help. Does this mean that it is the actual 910mhz frequency that is messing with the copilot computer?

Thanks

Al

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That is why I was hoping the 900mhz low pass filter might help thinking it was a harmonic, but it didn't help. Does this mean that it is the actual 910mhz frequency that is messing with the copilot computer?

That is what it is telling me too. My guess is that the co-pilot is unfortunately sensitive to common RF sources. The main carrier from the video Tx (910Mhz) is the strongest source, so in this case eliminating the harmonics and spurious noise would not offer an obvious improvement.

I've never seen the actual Co-Pilot II. But looking at their catalog page, I see that the new thermopile sensing head is a three wire affair. Since it needs power and ground, that means that the XY thermopile signals are mux'd into the third wire. So, my gut feeling tells me that the data is sent digitally to the main board, whereas the old version sent it analog on two wires.

So, assuming I guessed correctly on how they implemented this, I would say you need to improve the noise immunity of the sensor itself. That is because once the signal is digital, there is little reason to expect it can be harmed by the 900MHz Video Tx. We only care about the analog domain at this time.

The first thing on the list is to install a quality Toroid core at both ends of the sensor cable. This will keep EMI/RFI from being conducted INTO the sensor. Use something like dpcav's TOR-001 and get at least ten (more is better) turns of tightly wound cable through it. Do not cheat -- get a lot of turns on it. Do NOT use a split core Toroid. One Toroid should be on the cable end next to the sensor, the other Toroid on the end next to the controller.

Next, completely cover the sensor head with copper tape, leaving small holes for the thermopile windows. This tape must be soldered together to unify it, then bonded to the PCB's ground with wide diameter wire. Solderwick or coax braid works good -- Since this is an RF problem, a small diameter ground to the copper tape will not be effective. The goal is to Faraday cage the sensor so it is shielded from radiated RF.

Also add a Toroid to the 4-wire A/V cable that enters the video Tx. It should have 10+ wire turns on it and be placed on the cable about 1-2 inches from the video Tx. Do NOT omit this.

You should see a dramatic improvement. If you don't then post photos of your work and maybe we can see where things went wrong. Beyond this, I suspect the solution will become much more involved and require the help of the Co-Pilot II designers.

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You should see a dramatic improvement. If you don't then post photos of your work and maybe we can see where things went wrong. Beyond this, I suspect the solution will become much more involved and require the help of the Co-Pilot II designers.

Ok I'll give this a try. Regarding the ground for the copper tape. does it have to be on the board's ground or can I ground to the ground wire.

Thanks for your suggestions

Al

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I recommend using the board's PCB ground layer (with shortest possible wire length to copper tape). If that is not practical then try using the external ground. Keep all leads short.

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I recommend using the board's PCB ground layer (with shortest possible wire length to copper tape). If that is not practical then try using the external ground. Keep all leads short.

Mr. RC-Cam

Possible success!! I didn't have copper tape at home, so I tried a partial job until I could get some. I put toroids on the sensor side and on the computer side. and I wrapped the sensor in tin foil (no grounding) - this significantly reduced the interference. I was able to now bring the transmitter within a few inches of the copilot before interference occurred. This got me thinking. I had previously tried toroids in the past without success - but clearly I made a major mistake. Previously I put the toroid in the middle of the lead with quite a bit of free wire to the sensor and the computer, not right up to the sensor as you suggest. So I tried removing the tin foil - but keeping the toroids - still good. Then I removed the toroid on the sensor side - this put us back to major interference. I put the toroid on sensor side back on and removed the computer side toroid - minimal interference. I am kicking myself for previously placing the toroids in the middle of the leads. I think you nailed this - next step is to a do real world flight test and see if the reduced sensor sensitivity is also gone. if not I'll make the copper shield and report back

Thank you very much!!

Al

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Glad to hear you are seeing improvements with the Toroids. The copper tape would probably be wise to add (to ensure additional noise immunity). Don't forget to add a Toroid to the Video Tx's cable (near the Tx's end).

My experience has shown that a good number of wireless video related interference issues are mostly common mode noise, even when it appears it is only from radiated sources. However, I hear from a lot of folks who say they tried Toroids (ideal choices in resolving common mode noise) and they report that Toroids didn't help their particular RFI/EMI issue. But I typically find they did not use them optimally. With some coaching they find the Toriods really do solve a lot of problems.

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they report that Toroids didn't help their particular RFI/EMI issue. But I typically find they did not use them optimally. With some coaching they find the Toriods really do solve a lot of problems.

I am a good example of the above, I didnt know how to use them and assumed incorrectly that they did not work!!

I'll pick up the copper tape and order several more toroids

Thank you !

Al

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Greeting,

I was wondering, does it (co-pilot II) interfere with gas engine??

I have a GASSER Helicopter powered by Zinoah 260.

Thanks,

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It won't cause any problems with the engine. It's more likely the engines spark ignition would interfere with the co-pilot and all other eledctronics.

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It won't cause any problems with the engine. It's more likely the engines spark ignition would interfere with the co-pilot and all other eledctronics.

Thanks RON,

Ok, what is the safe distance to move the co-pilot computer unit from the ignition system? to stop the interference!

Or, do I need to install a magnet(ferrite) rings to reduce the RF?

Cheers,

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Thank you for the post!

I also purchased Co-pilot 11, and later saw something posted about Eagle Tree not recommending Co-Pilot 11, but using the old version, Co-Pilot 4.

Apparently over the problems you discovered.

I just ordered the old version - still available, and much cheaper.

Comforting to see you found a solution, and I can use either.

Many Thanks -

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