Radio noise in flight

[jetjr]

Hi, In y J200 with 3300 engine Ive had a radio noise issue and a power supply problem for a while. Recently tracked down a loose BUS bar connection which fixed up power, now to seriously attack "clatter" noise when in flight. This problem has developed, ie wasnt always there.

 

Can anyone help with places to start?

 

Its a Microair 760N, recently upgraded and adjusted and working well.

 

Cant hear it when radio VOX is "off", but whenever mic is open its very noisy.

 

It is rev dependant but is always there, much louder when @ higher revs ie. 2800rpm

 

Doesnt depend on radio volume, always there

 

I know this has been spoken alot about but rarely does anyone get back as to what fixed the problem.

 

JR

 

 

[frank marriott]

Do you have a transponder and if so does it go away with transponder turned off.

 

Frank

 

 

[Guest Maj Millard]

Frank, sounds like your 'mic gain' needs to be adjusted. Download the 760 ops book from the Microair website or give me a call. It covers the adjustment in the manual.

 

If that don't work you may need a noise filter in your charging circut somewhere.

 

 

[jetjr]

No transponder fitted

 

Could be mic gain - Ill look into this

 

What about noise from loose spark plug wire? Can someone explain how this can do it?

 

JR

 

 

[Ross]

When there is any kind of loose electrical connection that results in a spark of any size it produces an electromagnetic wave transmission - in other words a radio signal.

 

Examples you might be familiar with would be the click noise you might hear in a radio when an electrical switch is turned on or off or when there is a lightening strike.

 

The spark produced by the spark plug also produces a radio transmission but usually has a bit of trouble escaping from inside the engine where it could then be detected but a damaged plug lead might result in a spark inside a plug lead or where it connects to the distributor or the spark plug thus producing interference.

 

 

[motzartmerv]

Have you ruled out the headset??

 

 

[BigPete]

....and that would be both headsets.....

 

regards

 

 

[frank marriott]

Ross

 

I don't have the problem now. My case was obviously different, it was transponder interference which I fixed by replaceing the coax lead from the tranponder to the aerial.

 

John had similar problem - fixed by seperating transponder lead which was cable tied to radio aerial lead. Suspect poor shielding on the original coax.

 

I tried this on mine too but successfully transferred the noise from Com 1 to Com2. Problem fixed by fitting commercial grade coax.

 

Frank

 

 

[Guest Maj Millard]

Roger that, The Microair installation manual list the coaxes to be used, and there is a suitable length required. Andrew Hicks explained it all, but it was all gobbly gook to me, something about so many times the length of the antennae.

 

Fitted mine as it came, as it was already out of another aircraft and it is fine. Got lucky again I guess !..........................................................................

 

 

[jetjr]

There are 2 sets of head sets, noise was there with only one plugged in, these had no noise when used in a handheld in flight, so yep Ive ruled them out

 

Im betting on plug lead being loose but wouldnt this show up as a miss on mag checks?

 

JR

 

 

[jetjr]

If the noise was spark generated RF wouldnt it only be there when recieving or transmitting? or does it come through radio wiring all the time

 

This is there whenever the VOX circuit is open, even when talking on intercom?

 

JR

 

 

[Guest brentc]

The leads should be good for 1,000 hours +. In theory it would be very easy to find if that was the problem by disconnecting 1 set for starters and then trying the others.

 

 

[Guest Maj Millard]

It's always a good idea to 'Hide" the antenae from the engine if you can . I mean line of sight type of thing................................................................................

 

 

[zodiac3813]

I had a terrible "scratchy" noise on high rev settings (there all the time) in the ol '55.

 

It turned out to be a relay behind the panel that had to be kept free from any vibration. Some idiot (me) had velcro'd it to the firewall to "tidy it up". I set it free wrapped in 1/2" foam, and no more noise!

 

I don't think later Jabs have the relay, but it might pay to check.... Jamie at Jabiru alerted me to it.

 

Cheers, Jim.