Intercom and Engine Nose

[ronpenrose]

I have been wrestling with my intercom and radio system for several months and not having any luck solving either engine noise through the mic during transmission or the (what I believe) magneto interference.

I purchased a 404SP FlightTech intercom. The intercom works great, masking the engine noise. However, when I key the mic, my voice in the headset is very loud and the engine noise comes through. Hte intercom has three pots that can adjust the engine noise, mic level but does not seem to have any effect when transmitting. Does anyone have any experience with this system?

I have engine interference that I suspect is magneto interference since the frequency of the sound varies with engine speed. I do have a generator but do not think that is the problem. I have 18 guage shielded wire for the p-leads. Both ground shields terminate at the switch end ground terminal. Each lead ground is grounded to the magneto's. Any ideas what else I can do to troubleshoot?

Thanks.
Ron

[M Lightsey]

Ron,
You might try disconnecting the shielding from ground on one end or the other. If it's connected to ground on both end, it creates a circuit and the wiring can induce a current into the shielding that can cause noise.
Mark

[Meadowlark]

I was having some trouble in my Husky. Aerotronics in Billings, Mt. put a leather cover on the headset mike and installed an Ameri-King noise filter (P/N AK950-FTR1) on the alternator. Problem went away.

J/C GTF

[JBMoore]

You list a couple of problems....
Intercom noise... I've not had any luck with my intercom either. I can cut the squelch back far enough so the engine noise (exhaust) goes away while the voice activated intercom conversations happen... with the exception of the front pit. No matter what I've tried the noise level is too great and the front headset picks up too much noise for me to be able to understand my passenger unless I throttle down considerably while they talk. I wound up putting a push to talk button up front so I could set the intercom controls at a comfortable level.
Engine noise... you don't say what the noise sounds like and I have found there are two different types and they come from two different sources. If it's mag noise, you usually hear a clicking sound in the head set. For us old timers, you'll remember when your neighbor drove his Ford past your house and your TV set made the same type of noise. Try Mark's suggestion of grounding only one end of the shield. I was taught to ground the end closest to the source of the noise. In this case the mag end. A generator/alternator noise is usually a whine that changes in pitch with changes in engine speed. In the auto world they hang capacitors and such on the citcuit to filter it out.

Jeff Moore