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NAV audio hum - simple question

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mitch(at)skybound.com
Guest

Posted: Tue Feb 13, 2007 1:18 pm Post subject: NAV audio hum - simple question

I've verified the hum coming out of the Garmin 430's NAV 1 audio hi pin 

(on connector  4006), it has peaks at 500 and 1500 Hz, and is 60 

millivolts when measured with an oscilloscope.  Many people won't care 

about this because they have audio panels and the NAV audio is typically 

turned off all the time unless you're identifying a VOR.  I care, 

because I don't have an audio panel and my NAV 1 audio is always present 

(mixed by Bob's Iso Amp with COM audio, marker beacon, and traffic 

warnings).  I can knock down the level of the hum a little bit with a 

T-Pass filter of sorts: two 500 ohm resisters with a 100 pF cap going to 

ground in the middle.  I have hi-buck Bose-X noise canceling headphones 

and stereo music, and here is the million dollar question:



Will a 60 millivolt hum into an intercom be audible when the engine is 

running?



If so, my choices are

1) return the unit to Garmin for testing/fixing (hopefully), might have 

a bad capacitor on board or something, or it might be considered 

"normal" by them, in which case I've just wasted two weeks.

2) put the nav 1 audio on an on/off switch on the instrument panel, 

which I would like to avoid.



Thanks for any educated responses!

Mitch Faatz  RV-6A  Never Ending Finish Kit   Auburn, CA

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Bill Denton

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

Posted: Tue Feb 13, 2007 1:29 pm Post subject: NAV audio hum - simple question

As a short-term solution, why not just turn off NAV audio by pushing the

VLOC volume knob? Or you can just turn down the volume with the same knob.



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mitch(at)skybound.com
Guest

Posted: Tue Feb 13, 2007 2:09 pm Post subject: NAV audio hum - simple question

The hum is present with the NAV audio all the way down.

Bill Denton wrote:

[quote] 



 As a short-term solution, why not just turn off NAV audio by pushing the

 VLOC volume knob? Or you can just turn down the volume with the same knob.



 --

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john(at)ballofshame.com
Guest

Posted: Tue Feb 13, 2007 2:23 pm Post subject: NAV audio hum - simple question

Maybe I'm not envisioning this right (my mind is fried trying to get

through a bug at work) but the filter you described sounds like a low pass

filter.  I think you would want a high pass filter assuming that you don't

ultimately track this down to some other problem somewhere else.



Like I said, I could just be thinking about it all wrong due to not enough

coffee and too much thinking today 



-John

www.ballofshame.com



 	  Quote: 	
		   

 <mitch(at)skybound.com>



 I've verified the hum coming out of the Garmin 430's NAV 1 audio hi pin

 (on connector  4006), it has peaks at 500 and 1500 Hz, and is 60

 millivolts when measured with an oscilloscope.  Many people won't care

 about this because they have audio panels and the NAV audio is typically

 turned off all the time unless you're identifying a VOR.  I care,

 because I don't have an audio panel and my NAV 1 audio is always present

 (mixed by Bob's Iso Amp with COM audio, marker beacon, and traffic

 warnings).  I can knock down the level of the hum a little bit with a

 T-Pass filter of sorts: two 500 ohm resisters with a 100 pF cap going to

 ground in the middle.  I have hi-buck Bose-X noise canceling headphones

 and stereo music, and here is the million dollar question:



 Will a 60 millivolt hum into an intercom be audible when the engine is

 running?



 If so, my choices are

 1) return the unit to Garmin for testing/fixing (hopefully), might have

 a bad capacitor on board or something, or it might be considered

 "normal" by them, in which case I've just wasted two weeks.

 2) put the nav 1 audio on an on/off switch on the instrument panel,

 which I would like to avoid.



 Thanks for any educated responses!

 Mitch Faatz  RV-6A  Never Ending Finish Kit   Auburn, CA

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Bill Denton

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

Posted: Tue Feb 13, 2007 2:28 pm Post subject: NAV audio hum - simple question

If you are not getting any "nav audio" with the volume knob turned all of

the way down, one would suspect that the problem lies outside of the

radio...

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john(at)ballofshame.com
Guest

Posted: Tue Feb 13, 2007 2:51 pm Post subject: NAV audio hum - simple question

Never mind.  You definately don't want to get rid of 500hz and 1500hz. 

LOL...divide by 10 problem on my end.



Where's my coffee?....



-John

www.ballofshame.com



 	  Quote: 	
		   



 Maybe I'm not envisioning this right (my mind is fried trying to get

 through a bug at work) but the filter you described sounds like a low pass

 filter.  I think you would want a high pass filter assuming that you don't

 ultimately track this down to some other problem somewhere else.



 Like I said, I could just be thinking about it all wrong due to not enough

 coffee and too much thinking today 



 -John

 www.ballofshame.com



> 

> <mitch(at)skybound.com>

>

> I've verified the hum coming out of the Garmin 430's NAV 1 audio hi pin

> (on connector  4006), it has peaks at 500 and 1500 Hz, and is 60

> millivolts when measured with an oscilloscope.  Many people won't care

> about this because they have audio panels and the NAV audio is typically

> turned off all the time unless you're identifying a VOR.  I care,

> because I don't have an audio panel and my NAV 1 audio is always present

> (mixed by Bob's Iso Amp with COM audio, marker beacon, and traffic

> warnings).  I can knock down the level of the hum a little bit with a

> T-Pass filter of sorts: two 500 ohm resisters with a 100 pF cap going to

> ground in the middle.  I have hi-buck Bose-X noise canceling headphones

> and stereo music, and here is the million dollar question:

>

> Will a 60 millivolt hum into an intercom be audible when the engine is

> running?

>

> If so, my choices are

> 1) return the unit to Garmin for testing/fixing (hopefully), might have

> a bad capacitor on board or something, or it might be considered

> "normal" by them, in which case I've just wasted two weeks.

> 2) put the nav 1 audio on an on/off switch on the instrument panel,

> which I would like to avoid.

>

> Thanks for any educated responses!

> Mitch Faatz  RV-6A  Never Ending Finish Kit   Auburn, CA

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nuckollsr(at)cox.net
Guest

Posted: Tue Feb 13, 2007 4:21 pm Post subject: NAV audio hum - simple question

At 01:16 PM 2/13/2007 -0800, you wrote:



 	  Quote: 	
		  



I've verified the hum coming out of the Garmin 430's NAV 1 audio hi pin 

(on connector  4006), it has peaks at 500 and 1500 Hz, and is 60 

millivolts when measured with an oscilloscope.  Many people won't care 

about this because they have audio panels and the NAV audio is typically 

turned off all the time unless you're identifying a VOR.  I care, because 

I don't have an audio panel and my NAV 1 audio is always present (mixed by 

Bob's Iso Amp with COM audio, marker beacon, and traffic warnings).  I can 

knock down the level of the hum a little bit with a T-Pass filter of 

sorts: two 500 ohm resisters with a 100 pF cap going to ground in the 

middle.  I have hi-buck Bose-X noise canceling headphones and stereo 

music, and here is the million dollar question:



Will a 60 millivolt hum into an intercom be audible when the engine is 

running?



If so, my choices are

1) return the unit to Garmin for testing/fixing (hopefully), might have a 

bad capacitor on board or something, or it might be considered "normal" by 

them, in which case I've just wasted two weeks.

2) put the nav 1 audio on an on/off switch on the instrument panel, which 

I would like to avoid.


	


    Hmmmm . . . you may well be experiencing one of those

    unforeseen consequences of quantum technology jumps.

    For years, I've been able to sit in cockpits of some

    REALLY expensive airplanes and hear things in the phones

    that (to my way of thinking at least) shouldn't be audible.



    Indeed, once the engines are running and you've got wind

    noise blowing over the the fuselage, the ambient noises

    overpowered the offending noises.



    More than one customer has complained about hearing

    things they'd never heard before after installing a

    good noise cancelling headset system. It may be that

    Garmin will readily admit to the "noise" being

    present but still well within any published signal

    to noise ratio specifications. Those frequencies sound

    like they might be associated with the "AC" voltages

    needed to drive LCD screens.



    If push comes to the hard place, it may take a couple

    of notch filters to attenuate them to acceptable if

    not inaudible levels. I'll have to remember to ask

    the customer support techs if they've had any cases

    of unacceptable noise level complaints resulting from

    the installation of super headsets!



    Bob  . . .



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

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

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

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