Nice Treat

[flyguy]

Out flying over the hills this morning and went to check Left mag while cruising along at about 2100 RPM; was inbound to airport with the radio on, doing it's little snap crackle pop in the background. Switch to left mag and the radio goes dead quiet, like nothing. Back to both, noise. Over to Right, noise. Back to left, dead silence and then this guy from about 80 miles away comes through like he was in the seat next to me. Clear as a bell.
Nearly fell out of the seat.
The mags have had some work done on them lately, but were still noisy afterwards. Better, with both new harnessed installed, but still had noise.
But later I had removed the "P" lead connector on that mag to get it out of the way of the tach fitting or something, and while I had it off had redone the shielding at the mag connection.
Wow, now I know that it is possible to get these mags to be really quiet, and I now have a pretty good idea where the noise is coming from on the remaining noisy mag.
Nice way to start the day. Was an enjoyable flight too.
Darryl

[astjp2]

Re: Nice Treat

Which mags? I was running the SF-4's and went to Slicks and still get some noise but only on reception, it never transmitted any. Tim

[flyguy]

Re: Nice Treat

Oops sorry, I thought everyone knew about my noisy Eisemanns from previous threads on magnetos.
They are old LA-4's with some "new" parts in them.

I had previous thought that perhaps being an older design that they had some fault in that design that made them inherently noisy. Now I know that is not so. I am tickled pink because the cases are really beautifully designed and they are built like a tank compared to some others. Once they have new bearings in them they appear to be pretty much bullet-proof. Eventually there will be bigger problems with getting parts, but good precise quality repair is still possible at this time.
DC
Edit: As I understand the functioning of magnetos it is not likely that they will produce transmitter noise because the noise they produce is in microvolts and it takes the sensitive receiver front end to pick up those small signals. The transmitter doesn't have an equivalent circuit to my knowledge.

[VictorBravo]

Re: Nice Treat

My ship has old but recently rebuilt Eisemanns and I get perfect radio performance too.

[astjp2]

Re: Nice Treat

If you have noise on older shielded mags, its usually the Capicator or the points being worn. You can get them tested and repaired for a reasonable price. Tim

[flyguy]

Re: Nice Treat

In case I didn't state it clearly enough it is about 100 percent certain that all of the noise I was getting on that mag was being radiated by the P lead. When I cleaned up the shield connection on the P lead the problem went COMPLETELY away.
Someone here had suggested that the P leads might be the problem a while back when we were discussing magnetos. Good call guy, whoever you are.

Strangely enough the Sacto Sky Ranch book on magnetos specifically states that the P leads only radiate "low frequency noise." So much for that bit of expertise.

Not to step on anyone's toes but my understanding of the mag circuit suggest that new points and new internal capacitors are actually likely to increase the noise, not dampen it. Reason being that they will produce a more powerful and faster rise time ignition pulse. The fast rising leading edge on the pulse along with the spark plug arc is what generates the radio frequency noise. More powerful and sharper edged pulses equals more RF noise. To suppress it you have to either damp it with resistance as in automotive leads and resistive plugs, or shield it completely as we try to do on our planes.
Darryl