Radio noise

[tx_swordguy]

Hi guys, I bought glenn's red sonex 889AP last month and have been going through it, flying when the winds allow. I have an issue with radio noise. I thought is might be the antenna so I pulled the antenna off, cleaned all the paint off the top of the turtle deck, also cleaned the bottom of the antenna base as well as put star lock washers on the underside of the fuselage attachment screws in an effort to get as much ground plane surface connection as possible. It helped only very slightly. I have not been told by the tower there is any transmit issues but on recieve I can only get clear reception on aircraft within 5 miles and tower reception out to about 10 miles. The noise is static in sound, at cruise rpm a plane at 10+ miles is unreadable usually but I get full on static reception breaking the squelch. The tower is readable at 10 miles but far from clear. If I go to idle the static is not as abundant but still there at the same distances. It does NOT sound the same on rpm changes as an alternator whine. I originally thought that the jab 3300 was just loud and the same static at idle was there at cruise and the noise of the engine just made the radio traffic hard to hear. After re-attaching the antenna I am not so sure and think maybe I need to shield something but am unsure where to start. I kinda thought the aluminum cylinder covers for airflow would be enough to shield the spark plugs so haven't done them. Any ideas? distributor, spark plug wires? ??? Specs, sonex a model, jab 3300 1st gen, commit antenna approx 18" behind pilot up top with ELT antenna farther back but ELT not turned on. MGL radio. (have not had a passenger to talk to but just talking into the mic without transmitting I get no static through my side of intercom.) transponder ant on bottom of plane and cannot see a difference if transponder is turned off. The static is always there with engine running as the engine gets louder but hard to differentiate between increase engine noise level and if the static increases with it. I guess I could pull the plane out of the hanger and just turn the radio on without the engine to see if that is truly the issue. Not a super busy airport so may have to sit and wait a while :( When I flew yesterday after cleaning the antenna etc I was able to get a transmission from about 50 miles away which really surprised me, it was quite staticky but readable. I tried aiming the plane in different directions trying to see if reception might be dependant on direction of travel and could not get any definitive findings. Sorry for long post
Mark WHiddon

[Rick524]

Hi Mark, Cleaning the bottom of the antenna and making sure the antenna is grounded is a good start.
A check with a wattmeter for forward and reflected power would be a good check as well. You could also
swap the ELT antenna and the comm antenna cables for a test, either should work with the comm radio.
You didn't say if you have an efis or if the noise is on all frequencies or worse on some. If you have a portable
radio, with coaxial jumper cable you can temporarily connect the comm antenna to the portable and go
fly to see how it compares with the MGL radio. You can use the portable radio as a 'sniffer' and while on the
ground and engine not running, move it around the panel to see if the noise peaks up in certain areas. if
it gets really strong, take the antenna off and see if the noise still breaks squelch.

I'm sure you will pin down the source, good luck!

Rick
Sonex 524

[tx_swordguy]

Hi Rick,
I have the enigma efis . I do not have a portable radio but perhaps I could borrow one. I am curious about the antenna itself being suspect. My last plane (fabric avid flyer) I used a portable with a mounted antenna. The original mounted antenna I would get issues and feed back from certain areas while flying. I put in a flexible dipole antenna that was VASTLY superior in all aspects to the one originally on the airplane. Do people generally have issues with antennas in metal aircraft? All my time is in tube and fabric or gyros. As far as channels go, the tower freq of 120.575 is what I am having the most trouble with. The one time I got the readable but staticky transmission of 40-50 miles was on 123.000. Static was still there but the transmission was readable from a much greater distance. The transmissions of 5-7 miles on 123 were quite clear with only a little static but once you got beyond that it came back quickly

[lutorm]

If you get the same static with the engine running vs off on the ground, it's probably not the engine.

I noted that our enigma emits a fair amount of EMI, it's the first thing that breaks the squelch if it's set too low. Does the noise go away if you turn it off?

[Rick524]

Its important to have a good gound plane on a fabric airplane. The antenna should be about 22" long and the ground plane 5% larger. Sometimes its not possible to have the full ground plane but more is better and
there is no "too much". Generally antennas work better on metal airplanes. The best check of an antenna
is with a wattmeter. Mobile radio shops will have one rated for about 10 watts in the VHF band. You
should see about 6 watts going towards the antenna and 0 coming back. That would be perfect.

Enigma eh? I have an Enigma as well and its a noise generating machine. Open the squelch and Listen on 120.575 and cycle through the 9 different screens to check for changes in the noise. If it changes from screen to screen, you found the source. Mgl sell ferrite chokes to put on all the wires going to and from the Enigma.
I think I have around 10 on mine. I remember the GPS cable as being a bad one. I even bought some hobby store thin brass (.008) and shielded the top and sides of the plastic Enigma box. Got it down to a dull roar, but
it took some work. I also had problems with the altitude changing when I pressed the ptt. That problem
is mostly gone after the ferrite choke install.

Rick
Sonex 524

[tx_swordguy]

Thanks Rick, There are chokes in the wiring seen when the panel is opened, but don't know what wires specifically they are on.

[tx_swordguy]

lutorm, Sorry I missed your post. I have not gone that far into trouble shooting yet. I started with the antenna thinking that the paint etc was causing ground plane issues with reception. I will attempt more definitive testing as I have time. Unfortunately my plane is an hour away so can't just run over to work on it. Will try reception with engine off first and then fly gradually turning off individual items. I have turned off the transponder and all lights and strobes with no effect so far. I had seen a post somewhere , maybe not here, where someone wrapped a copper wire around the antenna and shrink wrapped it to improve reception. Might try that for giggles just to see what happens, I wouldn't think it would hurt anything but not expecting a lot.
Mark