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Radio interference to instruments

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nuckollsr(at)cox.net
Guest

Posted: Sun Mar 04, 2007 8:37 pm Post subject: Radio interference to instruments

 	  Quote: 	
		  Comments/Questions: When I push my PTT switch to transmit on my radio I 

get an increase in manifold pressure and either a large increase or 

decrease in ammeter reading.  This is intermittent and happens about 80% 

of the time.  All works great with the radio off.


	


Sounds like these instruments were not designed to live

in the real world of airplanes. They seem to suffer from

radio frequency interference.



Check your coax cables from transceiver to antenna. If the

shield ground comes loose at either end, the coax can radiate

very strongly into airframe wiring.



You might try putting a ferrite cable-choke-core over the

bundles going into the back of these instruments. See:



http://tinyurl.com/28bdgm



        Bob . . .



        ----------------------------------------

        ( IF one wishes to be "world class" at )

        ( anything, what ever you do must be   )

        ( exercised EVERY day . . .            )

        (                  R. L. Nuckolls III  )

        ----------------------------------------

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Randy.McFarland(at)novell
Guest

Posted: Mon Mar 05, 2007 8:26 am Post subject: Radio interference to instruments

Thx for the question.

I have the same problem. I have a SD8 and Denso 60amp being monitored by a

EIS 4000 engine monitor. The alarm goes off almost every time I key the Mic

PTT due to one or both Amp readings going out of limits (typically decrease)

Doesn't seem to matter whether I am transmiting using Garmin 430 or KX125.

I'll check my coax cabling and shields.

Randy



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Bill Denton

Joined: 10 Jan 2006
Posts: 97
Location: Chicago, IL USA

Posted: Mon Mar 05, 2007 9:07 am Post subject: Radio interference to instruments

May or may not be relevant...



Keep in mind that your power consumption goes up quite a bit when you key

the mic. Your transponder also has pulsed of higher power consumption.



I've heard of guys who set their alarms based on the airplane running with

everything turned on. But when they key their mic, especially when the

transponder is also transmitting, they get an alarm.



As I said, maybe not relevant to your situation, but you might consider

it...





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N6030X(at)DaveMorris.com
Guest

Posted: Mon Mar 05, 2007 10:10 am Post subject: Radio interference to instruments

Whenever I hear of RF producing a DC voltage effect somewhere, I 

immediately think "corrosion".  Dissimilar metals, moisture, 

corrosion, rectification.  I've seen bad splices wipe out an entire 

manufacturing plant's data network, but only when it rains.  Check 

your connectors for white powder and the back of your panel for moisture.



Dave Morris



At 11:06 AM 3/5/2007, you wrote:

[quote]



May or may not be relevant...



Keep in mind that your power consumption goes up quite a bit when you key

the mic. Your transponder also has pulsed of higher power consumption.



I've heard of guys who set their alarms based on the airplane running with

everything turned on. But when they key their mic, especially when the

transponder is also transmitting, they get an alarm.



As I said, maybe not relevant to your situation, but you might consider

it...





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