Microair/static help please

Hi all, Hoping someone has seen this before
Did the first flight of my RV-3 today. With the egine running I'm getting a lot of static/crackling. The squelch, VOX and radio volume adjustments work normally but have no effect on the crackling. Interestingly, its the headset volume that lowers /raises the crackling volume ?
This crackling seems to be independant of the radio ? Can it have something to do with the headphone jack wiring ? I have used the shielded wiring. I've used plastic washers between the panel and the mic and phone jacks..should the body of the headphone jack be grouned ?
Switching mags off one at at time, alternator and boost pump off have no effect. The jacks are within 3-4 inches of the radio with the antenna mounted in the belly fwd of the spar. Coax is about 2 feet long.
Any help would be much appreciated.
Thanks
Mike

Here are a couple of ideas...

Try a different headset. My Lightspeed 15XL just began inserting all kinds of crackling and hissing into my radio - as soon as I changed headsets - the noise went away.

Are your headset jacks electrically isolated from the panel? Most radios today are designed to provide the headset jack ground via a separate ground wire from the radio. If you use the separate ground wire (and you should), the panel ground will create an electrical loop for power to flow and cause electrical interference. Headset jack isolation washers will prevent electrical loops. http://www.bandc.biz/insulatingwasherset1pair.aspx

I did everything I could to minimize or eliminate electrical noise in my plane.

For example, I added a 10,000uF capacitor http://www.bandc.biz/electrolyticfiltercapacitor.aspx directly between battery ground and battery positive to filter any alternator noise out. My alternator whine is non-existent!

I also added a filtered power supply https://matronics.com/aeroelectric/Catalog/AECcatalog.html for my LED Nav Lights. Before adding the filtered power supply, the electrical noise from the LED power supply was enough to give me a headache. After adding the filtered power supply - no electrical noise at all.

There are two other major sources of electrical noise - the Strobe power supply and the magneto. Fortunately, neither of those add any noise to my system, so I haven't had to do anything to mitigate them. However, Aircraft Spruce sells a magneto filter http://www.aircraftspruce.com/catalog/elpages/lsMagFilter.php which is simply bolted to the firewall and wired into the P-Lead of your magneto. If your strobe is creating noise, or other equipment such as autopilots or trim motors, you may want to install a power firewall http://www.aircraftspruce.com/catalog/elpages/smoothieFilter2.php which is essentially a very robust inductor/capacitor to remove any electrical equipment induced noise from getting into your electrical system.

At first glance, spending a little extra $$$ to eliminate noise may not appear to be "worth it", but having a whine-free headset will change your mind quickly!

Thanks for the info Scott
I have, the washers on the headphone/headset jacks, B&C capacitor in the alternator circuit, no lights or strobes.
I see Microair shows some ferrite supressors and I will check the grounds and maybe reroute the coax.
I'm open to any and all ideas at this point !
Mike

One step at a time

Mike,

the next steps would be a step by step isolation to find the source of the noise. If you have individual fuses or switches accessible in the cockpit, pull the fuses or turn off the equipment one at a time.

Have you tried flying with the alternator field turned off? You should have enough battery to fly long enough to test alternator whine.

Have you turned off one mag / ign and then the other mag / ign (preferably not both at the same time!) in flight? Could be noise induced by the high voltage P-leads.

Are you using a common ground? All of your grounds should originate at a single point, such as a ground bolt or ground tab. Your ground point should be connected to Battery ground with a robust ground strap or ground wire. Robust means #4 wire or bigger. BIG WIRE IS GOOD!!!

Is your engine grounded as well? Another #4 ground wire from your battery ground to an accessory stud/nut on your accessory case is vital to a good electrical system. Some people run a #4 or #2 wire for both 12V+ and GND to the starter. Good practice, but adds a little weight. I'm not so concerned about the starter, because the electrical noise generated during cranking doesn't matter to me.

You mentioned that the noise seemed to be affected by your headset, so I'll re-state what I said before. Try another headset. Try several other headsets! Try headsets on the co-pilot side instead of the pilot side to see if the issue is in the wiring to the headset plugs.

There's lots of things to try, but it really just involves isolating one system at a time, until the noise goes away.
Someone asked (offline) for a picture of my cap installation - here it is.

Thanks again Scott, really appreciate your input
I'll start the isolation process this weekend.
Mike

mvs163 said:

Hi all, Hoping someone has seen this before
Did the first flight of my RV-3 today. With the egine running I'm getting a lot of static/crackling. The squelch, VOX and radio volume adjustments work normally but have no effect on the crackling. Interestingly, its the headset volume that lowers /raises the crackling volume ?
This crackling seems to be independant of the radio ? Can it have something to do with the headphone jack wiring ? I have used the shielded wiring. I've used plastic washers between the panel and the mic and phone jacks..should the body of the headphone jack be grouned ?
Switching mags off one at at time, alternator and boost pump off have no effect. The jacks are within 3-4 inches of the radio with the antenna mounted in the belly fwd of the spar. Coax is about 2 feet long.
Any help would be much appreciated.
Thanks
Mike

Click to expand...

A few years ago I had the same exact issue (different radio.) I couldn't figure out for the life of me what the problem was until I started tugging at the ends of wires and it became obvious what the problem was...bad crimp on the power connection.

So it can be something as simple as that.

fixed it

Ran a seperate ground wire to the battey from the radio, cleaned all the ground connections and the static went away. Installed the suppressors from Microair (since I had them by the weekend) but probably didn't need them.
Radio check with ATC at 15 miles, 5 x 5.
Life is good again
Thanks to you guys for the help.
Mike