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                           Glasair-List Digest Archive
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                     Total Messages Posted Thu 06/19/08: 1
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Today's Message Index:
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     1. 03:40 PM - More RFI tricks  (MPPalmer@aol.com)
 
 
 
________________________________  Message 1  _____________________________________


Time: 03:40:57 PM PST US
From: MPPalmer@aol.com
Subject: Glasair-List: More RFI tricks

As I mentioned before, I've been in a fog lately. (Literally as well as 
figuratively. I heard a report that dementia has been correlated with poor vision.

I can verify that!)  As I think about it more, I remember now that, on that 
intercom RFI problem from years ago, the solution wasn't to go with triax but 
rather with 100% shielded wire. That is, foil wrapped audio cables.

The numbers vary, but IIRC, the shield on ordinary braided coax is only about 
60%. So a lot of energy leaks out. (This is why new house TV cable installers 
recommend "quad shielded coax.") That doesn't sound like Tom's problem, 
since, when he tried the dummy load, most of his RFI went away. (Sounds like he

must have some good coax (or triax) in his installation.) But for others, the 
usual trick to identify the culprit is to wrap a continuos piece of aluminum foil

along the coax (or any other suspected wire). Then take a bare wire and 
spiral wrap that (about a turn per half foot is fine) along the length of your

foil. That's called a "drain wire." Ground that at one end or the other (usually

near your common ground point) and see if that reduces your problem. It's a 
little hokey, but it works.

In our Glasair, I made the mistake of ordering the shorter of the two ADF 
antenna cables that King offered. The original plan was to have all receiver 
cables go down the pilot side of the fuselage and all transmit cables go down the

center. (Strobe wiring to the tail and potential autopilot altitude servo on 
the right side.) But, due to the shortness of the wire, I had to run the ADF 
cable near the transponder cable down the center. Wrapping both in aluminum foil

and doing the drain ground reduced the "rrapp pop" sound from the transponder 
in the ADF to the point that it doesn't interfere with ADF operation. (ADF? 
What's that?)

Hope this helps,

Mike Palmer <><<BR><BR><BR>**************<BR>Gas prices getting you down? Search
AOL Autos 
for fuel-efficient used cars.<BR>      
(http://autos.aol.com/used?ncid=aolaut00050000000007)

 

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