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LED comm noise

Electrogunner

Well Known Member
Yes, another LED noise thread. I?ve spent the last couple of hours reading threads about the issue and still couldn?t find the smoking gun. I have MR16 LED taxi lights, aeroled sunray+ landing and fly leds nav/strobe in each wing. The squelch break only comes in with all of them turned on. When I turn any one of them off it stops. I ran shielded wire to the taxi and landing and followed the fly led instructions for those. I did ground the taxi and landing local though. I?m going to run a temp ground from the FOT to the wingtip for the taxi and landing and see if that does anything to help. I checked for Rf with a handheld and didn?t get anything. Any ideas would be appreciated.
 
Shield

I grounded the shields at the power source. I think I might try disconnecting that and see if there is a change.
 
shield ground

I grounded the shields at the power source. I think I might try disconnecting that and see if there is a change.
You probably know this, but the aeroelectric book recommends that shields are only grounded on one end. Might be something to check if not already done.
 
These long distance attempts are often just swinging blindfolded, since we have limited info. But a couple of thoughts.

Assuming you're talking about breaking radio squelch, and not intercom squelch (check to be sure which is happening), don't ignore the radio's coax (both ends) & antenna ground integrity.

Charlie
 
Antennas

These long distance attempts are often just swinging blindfolded, since we have limited info. But a couple of thoughts.

Assuming you're talking about breaking radio squelch, and not intercom squelch (check to be sure which is happening), don't ignore the radio's coax (both ends) & antenna ground integrity.

Charlie

Thanks, I will double check antennas ground as well with my meter. Swinging blindfolded is ok as long as there is no one standing in the way ;) .
 
SNIP... I did ground the taxi and landing local though. I’m going to run a temp ground from the FOT to the wingtip for the taxi and landing and see if that does anything to help..... SNIP .

Old school Cessna airframe ground practice works well for old school incandescent bulbs, but not for potential RFI sources like MR16 and other LEDs.

You may also want to look at RFI being coupled to other wiring if you have wires bundled.

For the MR16LEDs consider an aluminum backing plate for the lamp, the lamp ground going to the backing plate with as a short of lead as possible, then the lamp ship ground connecting on the same point. The objective it to limit the RFI “antenna” coming off the LED. The backing plate need only be 3” diameter or whatever fits.

Carl
 
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Is your airplane painted or vinyl wrapped? My wrap job totally changed the plane?s impedence, requiring a different approach to the LED grounding scheme.
 
Grounds

Old school Cessna airframe ground practice works well for old school incandescent bulbs, but not for potential RFI sources like MR16 and other LEDs.

You may also want to look at RFI being coupled to other wiring if you have wires bundled.

For the MR16LEDs consider an aluminum backing plate for the lamp, the lamp ground going to the backing plate with as a short of lead as possible, then the lamp ship ground connecting on the same point. The objective it to limit the RFI ?antenna? coming off the LED. The backing plate need only be 3? diameter or whatever fits.

Carl

Thanks Carl,
I will play around with the bundles and the grounds this week. Glad I left all of the interior access panels off for now.
 
Paint

Is your airplane painted or vinyl wrapped? My wrap job totally changed the plane?s impedence, requiring a different approach to the LED grounding scheme.

It's painted. I wish I would have fired up the audio panel before it was painted to give me another data point though.
 
As mentioned above, ground the shielding at one end. The grounded end should be near the source of the noise - in this case, the lights.
 
Grounding

As mentioned above, ground the shielding at one end. The grounded end should be near the source of the noise - in this case, the lights.

Hmmm, I grounded the shields at the supply end and not at the light end. That would an easy one to mock up and try as well. I may try that before a run a seperate ground out to the wing tips. I must have been mistaken, I thought you ground the shields at the power supply end. Thanks for the info. One good thing is the comms are clear on the receive before I turn on all of the lighting loads.
 
I’m going to run a temp ground from the FOT to the wingtip for the taxi and landing and see if that does anything to help.

That's not likely to help. Where the ground terminates has no impact on radiated EMI. Running the hot and ground together, though, can help. The radiated magenetic fields of the positive and negative wires tend to offset themselves when located next to one another. Twisting the two wires together additionally breaks up the magnetic field. In my experience, twisting pairs is far more effective than shielding for EMI. Sadly our aviation wire is not twisted pair. All wires are twisted together and therefore don't provide the same EMI benefit that twisted pair does.

Unfortunately, most of the "noise" with high frequency switching technology is generated on the circuit boards and carried through the wire and not from the power transmission itself. This makes it very difficult to tame with wiring solutions. Unfortunately managing this noise is something of an art and many EE's / board designers are not that good at it.

Just ask anyone that tried a cheap USB power port. As soon as you connect a device to it via the shielded USB cable, you start breaking squelch. Running shielded wire from the bus to the power port provides no relief.

Larry
 
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EMI/RF

That's not likely to help. Where the ground terminates has no impact on radiated EMI. Running the hot and ground together, though, can help. The radiated magenetic fields of the positive and negative wires tend to offset themselves when located next to one another. Twisting the two wires together additionally breaks up the magnetic field. In my experience, twisting pairs is far more effective than shielding for EMI. Sadly our aviation wire is not twisted pair. All wires are twisted together and therefore don't provide the same EMI benefit that twisted pair does.

Unfortunately, most of the "noise" with high frequency switching technology is generated on the circuit boards and carried through the wire and not from the power transmission itself. This makes it very difficult to tame with wiring solutions. Unfortunately managing this noise is something of an art and many EE's / board designers are not that good at it.

Just ask anyone that tried a cheap USB power port. As soon as you connect a device to it via the shielded USB cable, you start breaking squelch. Running shielded wire from the bus to the power port provides no relief.

Larry

Larry, please correct me if I'm wrong, but if it's a radiating problem wouldn't I be able to pick that up with a handheld? I'm not getting any squelch break on my handheld. Much like I do from the radiating of the adsb and transponder antenna while I'm in a closed hangar.
 
There are different forms of radiation. RF noise can be picked up by a handheld. There is also magnetic noise from an expanding and contracting magnetic field around a wire that induces electrical current in an adjacent wire. Think transformer. Category 5 and 6 Ethernet cable contains twisted pairs of wire to reduce interference between pairs. Use twisted pairs of wire for both antagonists and victims. Keep single conductors as short as possible.
 
Larry, please correct me if I'm wrong, but if it's a radiating problem wouldn't I be able to pick that up with a handheld? I'm not getting any squelch break on my handheld. Much like I do from the radiating of the adsb and transponder antenna while I'm in a closed hangar.

If your radio is breaking squelch, it is picking up "something" from it's antenna circuit (which include the ground plane and any noise introduced into it). Therefore something is radiating. As I said, I don't believe it is from magnetic fields generated by power transmission on wire. I believe it is high frequency noise coming from the three devices mentioned. I don't know if this noise is being carried by the wires or not. It likely is and therefore your installed radio is more sensitive to it, as it and it's antenna share the power system/ground with the noise generating devices nad you handheld does not.

I would be looking for more specific solutions to the problem, like chokes, etc. I don't believe your problem will be addressed with a dedicated ground wire.

Larry
 
If your radio is breaking squelch, it is picking up "something" from it's antenna circuit (which include the ground plane and any noise introduced into it). Therefore something is radiating. As I said, I don't believe it is from magnetic fields generated by power transmission on wire. I believe it is high frequency noise coming from the three devices mentioned. I don't know if this noise is being carried by the wires or not. It likely is and therefore your installed radio is more sensitive to it, as it and it's antenna share the power system/ground with the noise generating devices nad you handheld does not.

I would be looking for more specific solutions to the problem, like chokes, etc. I don't believe your problem will be addressed with a dedicated ground wire.

Larry

Thanks Larry. Seems I have some experimenting to do. Oh so close to the finish line.
 
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