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Radio noise

Since the purchase of my cub this past spring, I too had been having extremely random radio static problems that didn't seem to correlate much with any one constant. Sometimes certain frequencies on my comms would be crystal clear, other days the same ground or tower frequency would be unbearable. Sometimes it would be a steady static noise, other days I would get pulses when the rear rotating (non-LED) beacon would pulse. Some days I could turn the beacon off temporarily and the noise would go away, other days turning that off wouldn't diminish the noise. Some days, I could turn the circuit breaker switch off for the electric turn and bank I have, and for a while that was the most consistent way to squash the noise, but then that seemed to have less of an effect. Didn't seem to be temp based or RPM based. Again, very very random and no constants that I could find to create the problem or solve it consistently. On the ground everything was crystal clear, after start up and flying things would get noisy.

As everyone says, check the grounds. I began doing that from tail to tip. First cleaning and ensuring the beacon ground was good.. Tracking wires forward. Check grounds and the wire situation under the wing root panels where my light switches are located, under the seat at my battery, grounded the engine block to the firewall stud as few suggest on here, etc.. Further following wires up to and behind the panel. Separated power wires and routed things further away from audio lines if I could. Outside of grounds we ensured that the VHF radio and antennae were working well enough, and that there was not a ground plane issue. The old Narco 810+ that was in my bird failed at the beginning of August (after take off transmit failed to work, but could receive.. a bench test proved transmit circuits were toast) and was replaced by a Icomm A220.. When having that installed I had hoped that perhaps the radio itself had some internal circuitry that was injecting some sort of interference, but no luck. The static was still there.

I knew it was something with the radio (not in the intercom), the turn and bank, and then one day discovered turning off the engine gauge also made static things silent.. And it turned out turning off the UMA 2 in 1 engine oil pressure and temp sensor gauge seemed to be the ticket. But unlike turning off the turn and bank, not too keen on flying without seeing what the engine oil is doing of course. I had a new connector put on the gauge as the soldering looked like it could have been suspect and also ran the oil temp/psi sender lines through a different hole in the firewall, away from power wires which they had been sharing another hole with. Both didn't solve anything.

So long story short, I finally called UMA. They asked when the gauge was purchased (jun 2016), and immediately suggested I send it to them so they could install a new or better radio frequency filter within the gauge itself. I paid shipping both ways, they installed the new RF filter at no cost, and sent it back to me the same day they received it. First flight with the new filter, no noise. I didn't want to get too excited here as I had had temporary success in the past. Second flight, no noise!!

Thanks to badmdcnman's posts above and comments made about the UMA gauge, they turned me towards the idea that the noise could be that gauge. Happy to have found a solution after 5 months. And if anyone else tells me to 'check the grounds' once more...
 
I have a KY97A that is also having intermittent static on some frequencies, some frequencies are all static and some clear. It changes throughout the flight. When I turn the alternator off, everything is static. Any idea what might cause that? Battery seems to charge fine.
 
With the radio making noise, pull the field AND output breakers and check for changes in noise. Also check for changes in noise with changes in RPM. Does anything change when going from both mags to left or right only?

Web
 
Doesn’t change with different rpm. I’ll have to try each mag. Didn’t think of doing that. Will also try pulling breakers. Come to think of it, the issue seemed to start after I replaced the master and starter solenoids.
 
..the issue seemed to start after I replaced the master and starter solenoids.

have had noise from bad master... to test turn master on, but then also jumper across it and see if sound goes away with jumper on.

the big lugs on a solenoid have square heads internally, and can rotate on installation some and be only making contact on one small corner of head instead of across the whole flat....
 
It’s quiet when engine not running and master on.
Will check the solenoid connections.
 
Checked everything above and it turned out to be the ground wire nut on the left mag was loose. Radio works like it is supposed to now. Thanks for all the input. You guys are great!��
 
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Checked everything above and it turned out to be the ground wire nut on the left mag was loose. Radio now works like it is supposed to now. Thanks for all the input. You guys are great!��

ummmmm.... ummmmm... that shouldn't be your problem, or let me rephrase that... if that solved your problem, then you have a bigger problem.... the P-lead ground should not be acting as an engine ground to your frame(it should NOT be connected to fuselage at key switch or toggle switch end ONLY to mag case.... EDIT: YES thats how Piper did it on newer cubs, but they should NOT HAVE... when you have a bad main ground and p lead shield serves as engine ground, the plead wires insulation melts and the engine gets shut off!! )

you have a bad ground between your engine and fuselage frame, add a 8 ga wire from an engine stud on back to one of the 3 #10 studs coming through your firewall from fuselage.... to original grounding on a cub is horrible going through mount bolts and tabs....
 
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mike, I think that he was talking about the P lead ground from the switch to the mag. Not the engine ground to the airframe.
 
I think the engine ground to frame is solid. You can just see the nut behind the oil temp ground wire.
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mike, I think that he was talking about the P lead ground from the switch to the mag. Not the engine ground to the airframe.

Exactly. And that should not be a noise factor since p lead ground was not connected to condenser when running. If plead ground was source of noise because of the loose nut that means it was acting as the BEST poor airframe ground at the time. Noise is just a variation the quality of a connection/flow. If that makes sense...


Sent from my iPhone using SuperCub.Org mobile app
 
Thanks for your input Mike and Wireweinie. I bought this Experimental so I am learning things as I go and electrical is not my strong suit. I checked the ground and the negative from the battery goes to the engine block. A similar sized cable then goes from the block to the frame at the motor mount. The connections have an oil film on them from a slight oil leak misting the area. Don’t know that that would effect grounding.
 
If the connections are tight, that oil film will not affect them.

Electrically it's good that the ground cable is attached directly to the crank case. The ground lead from the crank case to the engine mount should be moved from the mount to the air frame itself. The ground path has to many joints and seams to cross when attached to the mount. Also paint and powdercoat need to be removed from attach points.

Web
 
I’m having a similar issue. Not bad, but noticeable. All connections are tight, but left mag is making a snapping crackle in the radio. Brand new slicks. Key switch is fairly new too.

connected in the system is an electric tachometer too, signal from p leads at switch.

Since these wires are routed together, left and right leads, why is my left mag making noise?
 
Does the noise go away when you run on right mag only? Is the noise continuous or only present at certain RPM's?

Web
 
I’m having a similar issue. Not bad, but noticeable. All connections are tight, but left mag is making a snapping crackle in the radio. Brand new slicks. Key switch is fairly new too.

connected in the system is an electric tachometer too, signal from p leads at switch.

Since these wires are routed together, left and right leads, why is my left mag making noise?
Ignition harness new too? Could be a leak in the shielding of one spark plug wire.
Could be a leak in the P lead shielding of the other mag.
 
Ignition harness new too? Could be a leak in the shielding of one spark plug wire.
Could be a leak in the P lead shielding of the other mag.

When I select R on the key switch, all noise quits. I’m going to say it’s at all rpms, but definitely discovered during runup 1700 mag check. Hmm....Old plug wires, and they would not win a beauty contest. If I’m not mistaken, isn’t there a tool to check plug wires?
 
I assume that you mean the leakage checker. Similar to a megger. It's connected to the center conductor and shield. A high voltage is then placed on the center conductor to see if it will jump to the shield. It's purpose is to test the condition of the insulation.

In your case, I'd check for a loose connection in one of your plug wires. Connect an ohmmeter to each end of the center conductor of one plug wire. Then move the wire around and see if you lose continuity. Do this to each plug wire and don't be gentle. Any issues with testing or condition, just put on a new harness.

Also check the spark plugs. New plugs or old? Consistent plug gaps on each plug? Do they check consistently in a 'bomb tester'?

If everything checks good, you should have the mag bench checked as there is the possibility that you have bad points/capacitor.

Web
 
Just a thought; did you verify that the p-leads actually connect to the correct mag? Left p-lead to left mag to 'left' tabs on switch, etc?

Web
 
When I select R on the key switch, all noise quits. I’m going to say it’s at all rpms, but definitely discovered during runup 1700 mag check. Hmm....Old plug wires, and they would not win a beauty contest. If I’m not mistaken, isn’t there a tool to check plug wires?
Put a qualified person in the cockpit listening to the radio with the engine running on the noisy mag. Then carefully remove one spark plug wire at a time from the spark plugs on that mag. Does the noise go away with one of the wires removed? If so, that is the leaky wire.

The only time that there is current flow in the P lead wire is when that mag is turned off. If the shield on the P lead wire is the culprit, it will be the wire on the quiet mag.
 
Just a thought; did you verify that the p-leads actually connect to the correct mag? Left p-lead to left mag to 'left' tabs on switch, etc?

Web

Based on a previous problem with a plug, and use of engine monitor, yes.

Put a qualified person in the cockpit listening to the radio with the engine running on the noisy mag. Then carefully remove one spark plug wire at a time from the spark plugs on that mag. Does the noise go away with one of the wires removed? If so, that is the leaky wire.

The only time that there is current flow in the P lead wire is when that mag is turned off. If the shield on the P lead wire is the culprit, it will be the wire on the quiet mag.

Would selectively removing plug wires only identify a bad plug?

I have an electric tach that gets it’s info from the p leads, so not sure about no power through the p leads unless selected off.

Swap plugs from left mag to right etc. see if sound follows plugs


Sent from my iPhone using SuperCub.Org

Nothing on the backside of this cub is easy to get to. If the p leads are/were long enough, might see about having those swapped, but the plug thing is something easy that I can try.

Thanks for all the ideas and education.

It’s not bad/loud noise, but I plan to get to the bottom of this.
 
The power going through the p-leads is so small it's hard to measure. They only supply a signal to the tach, they do not power the it. And since the noise only occurs when the left mag is hot, it's not the tach/tach wiring.

Process of elimination. Go with the easier stuff first; wires and plugs.

Web
 
Based on a previous problem with a plug, and use of engine monitor, yes.

Would selectively removing plug wires only identify a bad plug?
That's the way we did it prior to the days of engine monitors. Rotating the plugs to the other mag would eliminate the plugs. If the wire isn't connected to the plug, the current flow isn't there producing the noise.
Does the noise sound like a continual noise or does it sound like just one wire/plug? Like tick, tick, tick with the time between tick following the rpm change.
 
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