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SBEC noise

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I am using the SBEC voltage converter from FirmTronics to step down from 12V to 5 volts on my pan/tilt/video Tx rig. The noise from the SBEC totally scrambles the

video signal whenever I toggle the servos. No noise when servos are idling.

I have tried repositioning the SBEC without any improvement. I have not tried the ferrite ring trick as yet.

When I switch to a separate 4.8V battery there is no noise, so I'm certain that the SBEC is the culprit. I really want to use just one battery on the P/T.

Any suggestions?

Thanks!

Tom

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I just checked the Kool Bec site, and indeed, they advertise "Absolutely no noise" . They go on to say,

"Most importantly, any "noise" that radiates from the UBEC is not relevant to the bands within our radio systems."

I'm using a 2.4Mhz Tx (Part 15 compliant). Obviously, this is not a "relevant band" as referred to above. Is the 2.4Mhz band more susceptible to noise from a device such as a BEC?

Tom

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Is the 2.4Mhz band more susceptible to noise from a device such as a BEC?

No. The lower VHF and UHF frequencies would be more likely victims.

If your video clears up when it is run from an isolated battery, and the SBEC is still powering the servos, then the problem is not radiated RF. It would then appear to be conducted RF or excessive supply ripple. Ferrite donuts and low ESR caps rated for switching supply applications might help reduce the noise for the first issue, and bulk capacitive filtering might help the latter (big value, low ESR caps).

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I agree that the noise is probably conducted, not radiated, as the video signal is rock steady with the SBEC as the power source. The noise only occurs when the servos are actually in motion. It goes away as soon as the servos settle back to idle.

No noise at all with a separate battery (SBEC disconnected). I tried attaching a ground wire from the video board to the aluminum chassis of the P/T.....no improvement.

Being somewhat electronically challenged, I was hoping for a simple fix.

Where would you recommend placing the ferrite donuts?

I appreciate all the responses!

Thanks,

Tom

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Where would you recommend placing the ferrite donuts?

Not enough is known about the nature of the problem to know that bit. So, you will have to experiment. Do your best to get several turns of wire around them.

Are you sure this isn't just a simple voltage ripple issue due to the servos' current? If you have access to an o-scope then poke around and look for the simple things first. If it really is conducted EMI/RFI that is affecting the 2.4Ghz system, then you won't see anything with a typical scope (which is a clue in itself). But if it is ripple, it will be easy to see.

There might not be a single cure for this issue. It may take other efforts too. Like revisting your grounding scheme (use a star ground system, not daisy chain), changes to the wiring (length & routing), and installation of additional decoupling or filter caps. Or, it could be a bad SBEC, or a battery supply that is not capable of handling the peak currents.

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I'll play with it for a while and see if I can figure it out. I think I'll go ahead and get one of the Kool Bec units and give it a try. In the meantime I'll use the two battery approach. Since it a surface use system, weight is not a concern.

Thanks for your help!

Tom

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