NOISY intercom

[senior]

Re: NOISY intercom

Bendix , Slick, Case , I know that Case gear fits Slick not sure about anything else. I have them all in the shop will check.

Thanks
Thats good to know.
Gives me options if I run across a set of used mags

[flyguy]

Re: NOISY intercom

I haven't checked the manual yet, but I did think of one thing. You will probably not want to tolerate the main problem that you get with the shielded Eisemanns. One has to pull the engine to remove the mags with a short mount. It really is a pain. (Just ask me how many times I had to do it.)

Because Eisemanns are really well crafted and rugged, I have found ways to correct most of their problems, and they produce one heck of a powerful spark, I am willing to put up with the difficulty of removing them.

DC

[senior]

Re: NOISY intercom

Here's a suggestion from *#@%^*

Any opinions on whether this would work.
Remember I'm not in Certified catagory!


I'm an electronics guy (since I was 14). Technically the problem with "partial" shielding such as you mention is that the ends become little antennas.

Secondly, and probably most important is the noise is due to the fast changing voltage part of the ignition pulse. If you put some resistance in the circuit (plugs or cable) the fast part gets damped like an electronic shock absorber and the noise (at radio frequency) never gets developed. It works better to kill it that way than to hide it after the fact.
Resistive wire is not used in aircraft normally because the older stuff would fail with long use or abuse.

Replace your plug leads on one mag ONLY with resistive automotive wires. I think it could be done. Then you just switch on to that mag when you want to communicate. If you could put in adapters and switch to resistive auto plugs that would help too.

The spark plug adapters for resistive auto plugs are widely used by the experimental guys, particularly when they put in electronic ignition systems, and are available from aircraft suppliers for experimental aircraft.

[Forrest Barber]

Re: NOISY intercom

and I repeat from many moons ago that "noise rejection" was very high on some older hand held radios the "Comm-Spec " was one that worked real well
I had a Radio shack antenna with ground plane on bottom way back in fuselage of BC12D. non-shielded mags and it was fine . Squelch took out noise and reception was about 30-50 miles... The old operate on one mag worked good too! bye brrrrr. Off for Cold Beer & Liver & Onions tonight

[robbie]

Re: NOISY intercom

Way back when, I had case mags. I needed new wiring so i picked up resistance wire and put on the ends.You might ask how did you solder the ends too the wires since its not a copper wire.Well I solder a copper brad nail to the fittings and pushed them into the wire.
It did reduce the noise by 2/3. I ran that way till the case mags gave out.
Legal NO, but ran it for about 7 or 8 years and 200 hours.

[flyguy]

Re: NOISY intercom

Forrest, you just gave me an idea.

I wondered how they would do that in a radio as I have heard from several sources over the years that some radios are very good at suppressing ignition noise. Never thought about it much before.

As the noise tends to be fast-rise-time higher-frequency "snaps" I would think that a low-pass filter might do the job.

Second thought. How about a passive (simple, no-power-required) low-pass filter that would plug in between the audio output of the receiver (phone jack) and the headphones. Hmmm, low impedance circuit, might be a problem.

That would be a fun project. Radio Shack/Frys Electronics, standby for a parts run by yours truly. LOL

DC

[flyguy]

Re: NOISY intercom

Nah, it will not work with passive parts only, I had forgotten that you get a broad cut off with passive filters. Would mess up the audio.
But...pretty good stuff can be done with an active filter with an IC in it.
Lot more components. Worth the trouble?

Maybe I'll look at the noise signature with a scope to see what we have; how much voltage, frequency etc. Put it on my list LOL.
DC