RF noise from hydraulic system

[lancair360]

Hello all, need to tap into the collective knowledge here.

Finally got around to chasing some intermittent static on my radios (both). Mostly happens in the 122 MHz range, less when you go way up in frequency. Had the avionics shop here hook up an SWR meter to check all that and it's 100% good to go. Good power, good grounds (impressive on a composite bird), noise has to be being generated by something on board. Radios are new Trig radios from Dynon, all Dynon wiring harnesses and Rami antennae.

Flew around and started isolating systems. When I pull the HYD circuit breaker the static noise stops. The pump/motor is new, solenoids and flyback diodes all original. I do have an EngineBridge solid state controller for it all that broadcasts a wifi network but I cannot isolate the wifi and I don't think that's the problem either. The Dynon is broadcasting wifi as well and there's no issues there. The static noise happens even if the pump isn't running, so everything has power but isn't consuming so I don't know what could be generating RF noise. Electricity and electronics is above my pay grade no matter how hard I think. I wonder if maybe it's just the pump motor itself? That's a big piece of copper and magnets.

Appreciate any ideas chasing this down. Cheers

 

[Rhino]

You mention new and old equipment, but is the noise new, or was it always there?

Where are you getting the noise, via the radios or your audio system?

Induced noise is most often a wiring issue, though not necessarily so.

 

[lancair360]

Always been there. Finally around to tackling it, all the bigger bugs are squashed!

 

[Rhino]

Is the noise coming in over the radios, or via your audio system?

What EngineBridge controller do you have?

When you pull the hydraulics circuit breaker, what exactly is getting powered down? Is it your entire hydraulic system, just the motors, solenoids, or some combination of those?

You said the noise is there even when the hydraulics aren't being used. Does it change when the hydraulics are being used?

 

[lancair360]

Noise is over the radio, not intercom. It's breaking squelch on the comms. No difference whether pump running or not. And the breaking squelch on the comms is intermittent. You could almost dial it out with squelch control on the radio but then you'd never hear any transmissions. So turning the squelch down I guess you can say there is continuous noise, squelch filtering out some of it.

Gen 1, Landing gear pressure controller - wifi

Pulling the breaker cuts power to the whole hyd system, which is all through solenoids and diodes on the pump.

That's the curious thing, what exactly is powered up with the breaker in but pump not running? Is there a field on the pump motor like an alternator? It's all small gauge wires back to the solenoids. So power goes bus-breaker-gear switch-gear controller. Then there's a big line off the master solenoid through a 50a breaker to the pump (that fuse is not in the panel but in the pump area) Pressure transducers provide info to controller and controller based on switch position then powers up or down solenoids to energize pump. There's 12v to the controller at all times the hyd breaker is in. I emailed them to ask if there's a way to disable the wifi to take that out of play. Maybe I'll wrap the controller in AL foil and see what happens. Differential diagnosis.

One of the comm anntenae is in the pump area but the other is forward under my seat and I still get noise in both.

 

[Rhino]

I'm going to make the assumption this happens when you aren't flying, so we can do a few things on the ground to narrow the problem down.

First, disconnect pin 2 on the LGPC. That removes all power from it.

If that makes the noise go away, reconnect pin 2 and disconnect pins 5 and 7 in turn, to see if cutting power to the solenoids and relays does anything.

And to answer your question about what is powered up, the LGPC is. It transmits wifi signals constantly.

 

[Rhino]

Forgot some other questions. What kind of radio, antenna and antenna cable are you using?

Does any of the wiring for the LGPC run alongside the wiring for your radios or audio system? Is it shielded wiring?

Where are your radios grounded? Where is the hydraulic system grounded? And assuming you used shielded cabling, where is the shielding grounded?

 

[Rhino]

By the way, the foil idea may not be completely effective in blocking wifi signals, or in preventing them from being induced into your radio system. It probably works better keeping aliens from reading your mind.

 

[lancair360]

Thanks for the tips on isolating the controller. I doubt it’s the Wi-Fi causing the interference but you never know. Isn’t disconnecting pin 2 to remove power the same as pulling the circuit breaker? I know that takes away power and no Wi-Fi is transmitted from the controller.

Radios are brand new Trig sold by Dynon. Antennae are Rami and cables are the newest coax with TNC connectors (I forget the name of the coax). Antennae grounds are 24” metal bonding strap material, 4 per antenna in a cross with antenna mount in the middle.

There is aircraft wiring and antenna coax together in the belly/keel area running aft. But all the hyd system wiring is isolated in its area behind the baggage bulkhead. None of the wiring for the LGPC is close to any radio or audio systems. The radios themselves are not close to the hyd system wiring and would only share some space with the main wire run in the keel.

For grounds there are a few ground busses on the aircraft since it’s composite, everything eventually ends up back at the negative battery terminal. I’ve only done upgrades and maintenance, not initial build and install so every ground and shield termination I don’t know and will have to investigate. I am fairly confident that none of the wiring at the LGPC is shielded.

Thanks for the help, this gives me a few places to start to look at grounds and start to isolate a few things. Will visit the hangar tomorrow and report back.

 

[lancair360]

Update.

Spoke with my avionics guy. Likely is noise coming off the board itself. Because there is a power supply in there for the 12v to 5v input to output. It cannot be the solenoids or fly back diodes because those are open and it still makes noise. Can’t be a ground because it’s a composite plane and all the grounds end up together anyway. The grounds back in that area from the motor and board are a short run to a ground bus so the wires aren’t long enough to start acting like an antenna. Most likely source is the board power supply.

He suggested installing a noise filter on the 12v input to the landing gear board. Easy to do, just gotta get on the google box and find one.

 

[Rhino]

Disconnecting at pin 2 removes power just like the breaker does. But the difference is, it allows you to isolate the wiring itself as a possible source of the problem. The wire wouldn't be connected to the box, but with the breaker in, it would still have power, and, theoretically, could still couple noise into your radios if that wiring was the source of the noise. I was really more interested in pins 5 and 7. Plus, I wanted to eliminate the possibility of something else being on that breaker.

I'm not sure what you mean by a house filter, but go ahead and try that first if it’s easy to do. I'm all in favor of easy solutions.

 

[lancair360]

Typo. Noise filter. Install one on the 12v in

I did pull the wire at pin 2 and noise stopped so it’s not wiring running from panel to back of plane.

I didn’t pull pins 5 or 7 after talking with the shop and him saying the solenoid and diodes won’t make noise unless the solenoid was actually closed or chattering. Given there’s a power supply in the board just like a USB outlet (12v to 5v in this case) that’s likely the culprit.

You hear hoofbeats you think horses, not zebras. This will be easy to isolate and see if it’s a fix. Ordered this from spruce — NOISE FILTER

 

[Rhino]

Wow. A lot of money for a simple filter. But that's what happens when you get something FAA approved. Let us know how it goes.

 

[lancair360]

Yeah, I thought about getting one from Amazon but if it doesn’t work then I’d always wonder if it wasn’t good enough or just wasn’t the fix. Buy once cry once, can always return it. But I know it can do the job so..that’s what I’m going for.

 

[Rhino]

By the way, just to be clear, all that filter does is clean up the 12 volt input to the LGPC. If the power supply inside the LGPC is the original source of the noise, this won't eliminate it. That doesn't mean the filter can't be the fix. If the input voltage is noisy, it may work. But if it's the internal components of the LGPC generating the noise, and I suspect it is, this filter is unlikely to be the fix. Essentially, it's a shot in the dark, and unfortunately a somewhat expensive one. You also need to keep in mind, if your 12 volt input is noisy, you're jusy applying a band aid instead of fixing the actual problem.

 

[airguy]

If the power wires leading to the LGPC are serving as an antenna for the noise, then putting this filter as close as possible to the LGPC may do the trick. Does the LGPC have a metallic case to serve as a Faraday cage for internal noise? If not, the aluminum foil idea has some merit.

 

[lancair360]

By the way, just to be clear, all that filter does is clean up the 12 volt input to the LGPC. If the power supply inside the LGPC is the original source of the noise, this won't eliminate it. That doesn't mean the filter can't be the fix. If the input voltage is noisy, it may work. But if it's the internal components of the LGPC generating the noise, and I suspect it is, this filter is unlikely to be the fix. Essentially, it's a shot in the dark, and unfortunately a somewhat expensive one. You also need to keep in mind, if your 12 volt input is noisy, you're jusy applying a band aid instead of fixing the actual problem.

You know I asked my avionics guy that exact question. Will filter on the input clean up what’s inside and he said yes it will. Crusty old timer of an avionics guy who’s forgot more than we’ll ever know. See what happens.

The 12v input is not causing noise, the controller is. I pulled the 12v input and the noise stopped. So I know it’s not the wiring from the panel back to the controller. It’s internal to the controller.

I cannot fix the controller making noise, not without re-engineering it. If noise filter fixes it then that’s the fix.

 

[Rhino]

Sounds good. If the internal circuitry is getting the noise from the input voltage, your avionics guy is correct. The filter may indeed solve the problem. My point was, that if the noise is being generated from the internal circuitry instead, the input filter is unlikely to fix the problem. But it's not impossible.

As airguy noted, the foil idea may help alleviate noise generated by the internal circuitry, at least to some degree. But I would consider that to be a troubleshooting method rather than a fix. Obviously everyone has their own tolerance level as to the condition of their systems, but I would personally be reluctant to fly around in an airplane made operational by a few sheets of aluminum foil. I'd replace the controller. And if the filter fixes the problem, I'd be looking for a way to get the noise out of my power lines rather than adding another possible point of failure to my avionics system. But again, that's just me. You decide what's best for your situation.

 

[lancair360]

Installed the noise filter on the 12v in to the controller. There was no change. Removed the noise filter and wrapped the controller in foil tape and the RFI was through the roof, tons of noise. Removed that so now I'm back to where I started from. Talking with the controller manufacturer - I know there's a new version out, maybe an upgrade will fix it. I'm 100% confident the RFI is coming from the controller now.

 

[Rhino]

My guess is you're getting induced noise from the internal circuitry of the controller, that then propagates via your wiring. Wrapping foil around a box is sometimes effective in preventing outside noise from getting in, but it doesn't help with internally generated noise. In some instances, like yours, it makes the problem worse by reradiating the noise within the unit, offering it more opportunities to induce into your systems and wiring. A new controller is probably your best bet. And if you don't absolutely need it, I'd skip the wifi version too. It just offers another avenue to generate noise.