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Radio noise



Airplane on ground not running- radio is clear. Airplane on ground engine running- radio is clear. Aircraft in air static starts immediately after take off and and continues to increase the longer I am in the air until the radio is completely unreadable. After touch down- radio is clear. What is going on here?
From your description it seems like airframe static is building up and interfering with the radio. Could it be that the antenna is mounted to a surface which has become ungrounded? Is this something that just cropped up, or has it been ongoing?
Trouble shoot it. When it acts up, turn off alternator field then turn back on. turn off one mag off and on then other (mag drop test). Turn off the radio. Turn off the intercom. Pull each breaker, one at a time, then push it in. Note any changes and when they occur. Also, fly with another headset. Do all these simple things first. You might be able to fix the problem yourself, if not, your avionics guy will appreciate the info.

Just the way you describe the issue, I'd guess problems with either the radio or intercom. What models are you using?

We had a problem like this after having a new mgl v6 installed in our cub, and it was really annoying. After adjusting mic and squelch settings, it is fine except when we get near a FM radio tower in the vicinity.
It was never perfect, but the last ten hours it has gotten to the point were the radio is unusable in flight
run new ground wire direct from engine to firewall small stud thats welded to tube(there's 3 of them) 8GA works..... too much slop in original engine mounts to be a good ground system over time
Thanks Mike. Will the size of the wire matte Red? Also I would like to understand what is going on. It makes sense that the airframe is building up a static charge, what I need to know is is that static charge back beating through the ground the power side or both into the radio? If that's the case will a filter on one of those wires also reduce the noise?
Do your troubleshooting. Until you know the source of the noise you're just 'shotgunning' and hoping something fixes it. Filters are a great example. It just covers up the noise. Find the source and deal with it appropriately. I never install filters when I install avionics. Unless there is an internal issue in a component, proper wiring and routing always eliminates noise. You still haven't told us the model radio and/or intercom you are running. It makes a big difference if you are running something like a NAT intercom with shielded wires or an old Sigtronics with the jacks grounded to the airframe.

Is it Transmitting when this happens. I had a similar situation this spring. I thought some one in the area had a hot mic. Found out it was me when I noticed my TX light flickering on and off. Ended up finding the rear push to talk switch had a broken wire. But same thing only in the air would it vibrate to make it cause problems.
It is a Becker radio and pm1000 intercom. I did a radio check and I seem to transmit fine so it appears to be only on receiving end. I am at the airport now. Installed a new engine to airframe ground and heading up to try this. Will also check alternator while I am up,
Okay, you eliminated your alternator and loose engine ground as cause. Did you shut down the radio and the intercom to see if the noise goes away with one or the other? Did you pull each circuit breaker and check for changes in noise?

Let me give you an example: You pull the intercom circuit breaker and no change in noise. Reset it and pull the com circuit breaker and the noise goes away. That would tell you that the source of the noise is in that particular com system.

You will need to narrow this search down to a particular system in order to meaningful repairs as the source of this noise could, literally, be in any electrical system on the aircraft.

You did adjust the squelch in the Becker? It has a range of 0-200, and we have found that it takes 175 or so to get it to work. I prefer squelch knobs, but the modern way is to pre-program it.
Yes I did adjust the squelch in the air to no avail. Just pulled the trim off at the antenna and no ground between and antenna and airframe so going to add one. Looking at the wiring diagram it appears they wired a single power source and ground for the PM 1000 and the becker. If I pulled the DB plug off the back of the PM1000 would that isolate the radio? It also shows an optional ground on the side of the case but it is not grounded on the radio, would this make a difference?
Yes I did adjust the squelch in the air to no avail. Just pulled the trim off at the antenna and no ground between and antenna and airframe so going to add one. Looking at the wiring diagram it appears they wired a single power source and ground for the PM 1000 and the becker. If I pulled the DB plug off the back of the PM1000 would that isolate the radio? It also shows an optional ground on the side of the case but it is not grounded on the radio, would this make a difference?

How/where is your antenna mounted? Don't worry about the case ground on the Becker unless some one got 'creative' on the wiring. Are you saying that the Becker and PM 1000 use a single power wire and single ground wire? If so, removing the connector plug from the PM1000 will isolate it but, unless you have emergency jacks wired directly to the com, you will not be able to use your head phones.

Check you PM messages

Yes there are emergency jakes. The antenna is mounted on the wing root trim. No ground from antenna base to air frame. Wondering if vibration of trim would cause problem. Just about finished with this ground and will see if it helps.
I'm not a big fan of mounting the antenna on that fairing but there are about four bazillion of them mounted that way with no noise problems. The only way that the fairing being loose would cause a problem is if the shield braid on the coax cable was not connected and the fairing was not making contact with the airframe through, either physical contact or the mounting screws.

If you fly again, disconnect the intercom and plug into your emergency jacks. This will tell you if the intercom is the source of the noise or something else.

A friend has a squeal in his radio. Disconnect the intercom and squeal goes away. There you are......it's the intercom! Have you changed the battery? Don't need a battery........it's wired in. So did you check the battery? I told you it don't need a battery, it's wired into the radio! Just satisfy my curiosity and open it up, please. Well look at that....there is a battery in there. What's hanging on the wires? Is that corrosion? Well, yah, sorta. It's the connector ends off the 9V battery. You mean the battery fell apart? Well, yah. So how old is that battery that wasn't in there? Ugh, it says 1999 on it. So now the long dead battery is out and the squeal is still there from the intercom. I'd guess the ooze and corrosion from the dead battery fubared the intercom. He's gonna try another intercom, maybe. jrh
Similar problem with new panel installation by self with new Becker, electronic gauges etc etc. First problem (no volume control) a result of my soldering job (and cold solder joint) on the miserably tiny pins supplied with the radio. Resolved by having an Avionics shop build me a new harness and installing myself. Still static and ultimately determined the static was being generated by the new UMA oil temp/pressure gauge and could be eliminated completely by pulling the breaker( by the method suggested above).

I assumed it was my solder job on that instrument as well and took to my Avionics shop to have them replace in the plane rather than remove all the sending units for the gauge. Wire harness was redone professionally. Static did not go away. The avionics shop called the company (UMA) and they were well aware of the problem. I returned the gauge to them and they warrantied a new power supply and subsequent installation produced a perfectly clear static free radio.

I am not an avionics expert by any means but have a little experience in electronics in the past as well as present so was not intimidated by doing the install myself. However I found out from my Avionics shop that they throw the solder type terminals away and install crimp type terminals instead of the supplied terminals. The pins with the terminals supplied are 20-22 gauge pins, yet the wires supplied with and specified for some of the circuits are 16-18 gauge. The harness supplied by my Avionics Shop (Park Rapids Avionics) in Park Rapids MN was really impressive. They also manufacture the Hub system which is another slick wiring system for installing and cleaning up an avionics installation.

Hope my experience offers some help to either you or others.. Good Luck.........Rod
Most of us that chase wires will use the crimp pins over the solder type any time it's possible. It actually saves the customer money as the harness assembles more quickly than soldering wires. As for 18 gauge wire in a 20 gauge pin, there are a couple of specialty pins out there that adapt the big wire to a small pin.

I've found that a lot of guys are willing (and able) to install harnesses in the aircraft but want nothing to do with the fabrication of the harness itself. I love it because I can sit at the table and fab the harnesses and let someone else stand on their head for the installation, lol.

Was the UMA power supply one of the AC types? If so, make sure to never bundle the AC wires with or near any audio lines. They put out a buzzing type noise that just wont go away unless physically separated. Treat them like P-leads.


The power supply was internal to the gauge. However the light bezels had an independent power supply invertor that required separation from audio lines. I agree it would be better to sit at the kitchen table working on these things than crammed upside down underneath the panel working in tight spots needing 3 hands when you only have two to fix something.

One thing my avionics guys suggested and I followed through on was to make my I-Pad mini Air Gizmo dock removable with four screws on the front of the panel. It provided a huge access to the back of the panel which greatly simplified removal of the UMA gauge when I needed to return.........Rod
Update! Installed a ground wire from the antenna direct to the frame and all noise disappeared. I took it for an hour flight this morning and the radio was clear as a bell. One of the great things about Supercub.org is the experience and knowledge base of the members. Wire Winnie thanks for taking the time to help, Mike thanks for your input. The only problem with the site is the fact I never get to meet the guys that are so much help and thank them in person.
Yeah - these guys have helped me immensely over the years too.

So tell me - your antenna was grounded to the upper wing-to-fuselage fairing, but now you have a wire to the steel in the fuselage - those sheet metal screws were not enough to ground it? Did I understand it correctly?
Glad to hear it worked out. You might want to plan on getting a new coax fabricated for the antenna when you have it apart. Something to work in with an annual.