Hiss in the headphones in a Rotax-powered airplane

slsaowner · Post by **slsaowner** » Mon Mar 16, 2009 4:00 pm

I have recently noticed an annoying hiss in the headphones installed in my Rotax-powered plane. It is equally loud on both radios, but loudness seems to be rpm-dependent. and non-existent at idle power. There's no change in the "frequency" of the sound when RPM changes, only the volume. Anybody have any idea what's going on?

rfane · Post by **rfane** » Tue Mar 17, 2009 7:32 am

If this came up without adding any additional equipment, I would look for a loose ground connection.

rsteele · Post by **rsteele** » Tue Mar 17, 2009 1:22 pm

I agree, a bad ground is the usual cause, but it can also be a ground loop, where both ends of a shield ground are connected to ground when it should be just one end. I fly behind a Rotax and have never had a problem.

A side node/example. I just bought a new pickup. It has a jack to listen to my IPod, which is great, but when I set my IPod on the charger (in the cigarette lighter) there is a very annoying hiss. I'm sure it's a ground loop and this in a 2009, brand new vehicle. Without being in the charger it works great.

Ron

slsaowner · Post by **slsaowner** » Fri Apr 10, 2009 8:59 am

I think what I'm hearing is noise picked up by the mike - a David Clark electret - because when I wrap my hand around it the "hiss" goes away. It's as though the mike is picking up the sound of air rushing by the cockpit, a combination of propwash and slipstream air.

CharlieTango · Post by **CharlieTango** » Fri Apr 10, 2009 10:34 am

maybe your intercom squelch?

slsaowner · Post by **slsaowner** » Sat Apr 11, 2009 7:39 am

Yeah, I've been thinking the very same thing. I'll check it out next time I fly.

flyboy2007 · Post by **flyboy2007** » Sat Apr 11, 2009 8:45 am

(a David Clark electret ) Just in my opinion this is a lot of your problem. I have had david clarks and every set I have had were JUNK! I got a nice set of avcomm and they work excellent and are about half the price. Just My oppinion.

slsaowner · Post by **slsaowner** » Thu Jun 11, 2009 8:21 am

It was the squelch - squelch knob was turned all the way down.