Radio Static When Engine Runs

Other details:

- Switching the Mags .... no change
- Cutting out the Alternator ... no change
- Turning off various equipment ... no change

I did move ignition wires thru the insulators a bit to see if there
was any change. After doing this, the noise went away for the most
part. A test flight over central NJ for about 1 hour resulted in a
burst of static that lasted about 15 seconds about 20 minutes into
the flight. There are some occasional clicks here and there. It
seems to vary with engine speed, attitude, etc. I will continue
with the search.

Thanks all.

Ed Berberich

Aircraft ignition leads are shielded in a coaxial cable. To suppress
RFI which would otherwise be radiated off the HV leads, the shield must
be continuous (no breaks), and the shield must be electrically
connected at both ends, plug and mag tower. Might be necessary to
disconnect each lead (one at a time) at the plug end, and then use an
Ohmmeter to make sure you have continuity from each dangling gland nut
to the airframe.

Similarly, the P leads running from the mags to the rear of the mag
switch should be shielded to prevent RFI from being radiated. Their
shields should be unbroken, and grounded to the mag body, and to the
panel very close to where the mag switch is mounted.

You may have worn through and broken the shield braid where it passes
through a hold down clamp or the baffles. If so the shield may not
have full electrical conunity for the full length. Disconnect the
plug end of the wire and hook a ohm meter to the plug nut and the
other end to an engine ground. Now shake and pull the plug wire and
see of the reading changes. It should read less than 0.3 ohms. If
the shield is broken or worn through anywhere this leads to EM leakage
which you can hear in the radio.

On Thu, 03 Nov 2005 03:14:14 GMT, ECB wrote:


Other details:

- Switching the Mags .... no change
- Cutting out the Alternator ... no change
- Turning off various equipment ... no change

I did move ignition wires thru the insulators a bit to see if there
was any change. After doing this, the noise went away for the most
part. A test flight over central NJ for about 1 hour resulted in a
burst of static that lasted about 15 seconds about 20 minutes into
the flight. There are some occasional clicks here and there. It
seems to vary with engine speed, attitude, etc. I will continue
with the search.

Thanks all.

Ed Berberich