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Video TX interfering with RC RX... how do I fix?

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My second video system seems to be going the way of my first… that is, not working. I have got a 600 mw system from BWAV on a GWS SS and I am getting terrible interference (glitching servos) whenever it is on. I have tried both my FMA M5 and my Berg G6 3 but cannot get more than 200-300 feet before I find myself sprinting across the field to close distance with my airplane so I can regain control. As soon as I turn off the video TX I don’t have any problems anymore. The video TX and RC RX are not co-located and the RC RX antenna runs out along the length of the wing so as to keep it away from the aluminum fuselage. Any ideas or have the RPV gods shafted me again?

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Some things that may be helpful for others to know:

- How is the Video Tx powered? Does it share the R/C battery?

- How long are the Tx's battery leads?

- What R/C freq band are you on (35Mhz, 40Mhz, 50Mhz, or 72Mhz)?

- Can you post a photo that shows your installaton in detail?

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- I have tried powering the video TX with both a battery common to the RC RX and separate with both resulting in terrible range.

- The video TX leads are approximately 4 inches long.

- 72

post-5-1089257452_thumb.jpg

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The installation looks fine. Here are some things to consider:

(1) Do not share the R/C pack until you fully resolve the problem. A shared pack is tough to get to work well so you do not need that headache at this point.

(2) The LM2940's output cap looks like a common electrolytic rather than a low ESR tantalum, but it is hard to tell. Regardless of what you are using, does its ESR spec satisfy the strict requirements discussed on the Vreg's data sheet? Do not skimp here.

(3) I cannot see in input cap on the LM2940. What are you using?

(4) Slip some small ferrite rings over the servo cables. They look like they are prime suspects for RF interference since they are closely coupled to the Tx.

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2 - It probably is a common electrolytic cap... I know nothing about electronics but I do know I was supposed to use a 22uF... so, like, I have no idea what part I would order... something like this?

3 - I am not using an input cap since it was not indicated as necessary... should I use one? Should it be some sort of specialty cap or will any old .47uF one do?

4 - I will rework the mount so that the video TX is mounted off the right side by about 6 inches

http://cache.national.com/ds/LM/LM2940.pdf

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It does not need to be SMT. For Vreg stability (so it won't oscillate) the cap just needs to be low ESR, like the type used in switching supplies. You will find that the ESR improves as the uF increases, so keep that in mind. Digi-Key has many to choose from (just compare the ESR specs and pick a low value offering).

The input cap is needed since your battery is located away from the Vreg. The data sheet will help you out in picking something.

Adding/changing these parts may not fix your problem, but then again they might help a bit. You have to chip away at these sort of problems until you find the magic recipe. Suspect everything.

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That cap is 4.7uF. A 22uF is minimum, but in your case larger would be better.

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Maybe the servos themselves could be harmed by the proximity of th TX antenna.. I would try to switch on the R/C TX, put it far away where you notice the problem, and then try to move the video components to see if it gets better. Just a suggestion...

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Maybe the servos themselves could be harmed by the proximity of th TX antenna..

I agree. On my SlowStick I mounted the Video Tx under the landing gear. This kept it away from the R/C electronics.

If the Tx must remain near the servos, then some ferrite beads on the servo leads may help. But, distance is your best friend in these sort of situations.

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I’ll guess something totally different.

I wouldn't use that mounting style for the 600mW system.

I mount the ones I have by silicone gluing the TX base to a piece of light-ply and then securing the light ply mount to the plane. You don’t want any pressure on the top cover.

There is a trimmer pot on the circuit board that is flush with the top cover, some stick above the top cover. My first 600 was soldered off enough that the top cover wouldn’t even snap in place if the board was flexed up to meet the solder joint.

The tie-wraps your using may be causing a problem.

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The other test I would include, just to rule this out, is to fire up the tx without the camera attached and see if that affects your range. This will eliminate possible radiated noise from your camera cable.

Bill

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I’ll guess something totally different.

I wouldn't use that mounting style for the 600mW system.

I mount the ones I have by silicone gluing the TX base to a piece of light-ply and then securing the light ply mount to the plane. You don’t want any pressure on the top cover.

There is a trimmer pot on the circuit board that is flush with the top cover, some stick above the top cover. My first 600 was soldered off enough that the top cover wouldn’t even snap in place if the board was flexed up to meet the solder joint.

The tie-wraps your using may be causing a problem.

The zip-ties are very loose since they are there simply as a backup incase the servo tape would fail as a result of the video TX getting warm. In addition, I have since disattached the unit with no noticable improvement in the situation.

The other test I would include, just to rule this out, is to fire up the tx without the camera attached and see if that affects your range.  This will eliminate possible radiated noise from your camera cable.

Bill

Camera or no camera, range is seriously effected either way.

Ok, I basically have figured out that proximity of the video TX to ANY of the RC components is causing the interference. I think I am going to create a pylon mount out about 1 foot on the wing since distance seems to really be the only solution at this point. What I would love to know is how everyone but me seems to be achieving wonderful result with all of their equipment in relatively close proximity to the video TX. Oh well, just another one of life’s curious insults...

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That is strange,

I’ve never had a problem with interference or reduced range with my 600 or 1-watt BWAV systems.

My 600mW is probably about 1.5 inches from the (Futaba Dual conversion) receiver, and even with the R/C transmitter off I can switch the video system on and off with out even a slight servo twitch.

Good luck and let us know what you find.

Jim

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The same for me, I've been flying with a R/C RX, servos, video TX and TL100 less than 2cm away from each other without any problems. I also had 4 cams with cable length up to 1m that time.

Really strange, although I've noticed that some receivers are much more sensitive than others (especially cheap or small ones). I have a 4 channel micro receiver that I can't use if someone is transmitting 2-3 channels next to me or I have awful interference even at 1m.... Not selective enough.

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I have tried both an FMA M5 and a Berg G6 3... both excellent RXers. I wish I could post a video of the video TXs influence over the servos, I can actually control the servos position by moving the video TX into different positions relative to the servo itself...

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Well.... as my wallet will soon testify the solution of moving the video TX about 8 inches away from everything didn't work. I have a SS and a brand-new AXI brushless sitting in the trash. I am going to give this one more go before I give up. How is it that I am the only one who seems to be having problems??? I just don't get what I could possibly be doing wrong... the latest incident happened about 150 feet out, I had Nikko brand RC cars from Walmart that went further than that when I was 12...

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Now that is interesting....

I have seen exactly the same thing once before, but it was when I move the video tx in close proximity to a small piezo gyro.

Do you have a gyro on the aircraft, or perhaps a co-pilot?

The direct correlation of servo position to tx proximity makes me think that the microwaves are hitting a diode or transistor in your setup and generating a dc bias that is being interpreted as a change to the adjustment pot of the gyro, or the IR light hitting the copilot sensor.

The analog-sounding nature of the reaction just does not sound like interference in the digital/pwm link from tx to rx to servo.

Bill

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Well, today I found out that the video TX has nothing to do with my loss of range and control as I was losing control of my aircraft today at similar ranges without the video TX even being on... So now I at least have my problems narrowed down to my 9C or my berg, I am betting on the 9C being the cause of the problem. Anyway, I assumed the problem was the video TX and I was wrong. I guess the lesson here is to never assume...

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I've experienced a similar incompatiblity with my berg 5 and 9c, so you are not alone.

Glad to hear it wasn't the video, but still sorry you are having problems :(

Bill

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I've experienced a similar incompatiblity with my berg 5 and 9c, so you are not alone.

Hi Bill, the mic is working nicely :D, could you elaborate on your above quote since it might save me from having to send in my berg g3 and my 9C for checkups?

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I read somewhere that the futaba puts out a non-standard pulse-train... not sure what exactly that means, but it was the reason given for the incompatiblity of the Berg receivers with Futaba.

A recent visit to www.aircraft-world.com turned up a bunch of 'new' Berg receivers that are supposed to work with ANY radio, so I might have to give them a try. I definitely like the very small form factor of the berg units.

Glad the mic is working ;)

Bill

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