Shielded audio or not?

'Nother question. Has anyone used non-shielded wire for their headset/mic jacks? If so, did you experience any excessive noise; alternator, strobes, etc? I'd just as soon save the money for other goodies if the shielded cable is overkill, but I just as sure don't want to have to re-do it if it performs less than satisfactory. BTW, I'll be using Lightspeed ANC headsets and the intercom is a Flightcom 403(stereo). Thanx for any help.

Hawkeye7A said:

'Nother question. Has anyone used non-shielded wire for their headset/mic jacks? If so, did you experience any excessive noise; alternator, strobes, etc? I'd just as soon save the money for other goodies if the shielded cable is overkill, but I just as sure don't want to have to re-do it if it performs less than satisfactory. BTW, I'll be using Lightspeed ANC headsets and the intercom is a Flightcom 403(stereo). Thanx for any help.

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I used unshielded wire with no problems - but I was careful with routing. In the grand scheme of things wire is cheap though - get some two or three conductor shielded and you can use it both for the mic and stereo headset jacks.

hawk -

I agree with Kevin - if you gamble on unshileded wire and then find out you have a problem, you're really going to regret not buying the right wire! You don't need to buy aircraft shielded wire (IMHO) for this - check with the usual electronics suppliers and you'll be fine.

Paul

Thanx!

Yeah, I gotta admit, you guys are right. Better to overkill from the start than to have to re-do it later. Thanx!

You GOTTA use the shielded stuff. I fly a rented Decathlon and when you turn the transponder on, you get a noise. Then you turn on the strobe, another noise joins the chorus. I can't remember for sure, but I think even the boost pump chimes in. I vowed that I'd have no such nonsense on my RV. Spend the extra few dollars, cuz rewiring would be a royal pain.

The difference in cost at Stein Air is 32 cents a foot for 18Ga shouldn't make a huge cost difference if you did the whole plane shielded.

Shielded

I used some of Stein's shielded wire mainly for the convenience of having the individual wires nicely bundled. Noise reduction should be a nice side benefit!

One odd thing I noticed in the instructions on my PS Engineering intercom was you don't hook the shield up on both ends, only one end. I guess you can make matters worse grounding both ends of the shield wire.

Microphone wires need to be shielded

Your microphone wires need to be shielded because the input impedance is high and the signal level is lower than say your headset speaker. A shielded microphone wire will improve your signal to noise ratio, making it easier for ATC and other pilots to hear you. The reason you connect the shield to the airframe ground only on one side is to prevent any current from flowing down the shield itself. When noise is induced into the outside of a shield, it generally travels on the outside surface to the grounded end. As a "rule of thumb", shield wires that have low-signal levels or high-input resistance like microphone circuits, engine monitoring sensors, data runs or auto-pilot control signals should all be shielded.

John

Vans agrees

I talked with Ken Scott this a.m. about the shielding and he pretty much said the same thing, especially concerning the MIC circuits. He also highly recommended shielding on the PTT switch which I hadn't considered. Thanx to all for the inputs(No pun intended!).