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  #1  
Old 09-24-2017, 08:37 PM
Bradp Bradp is offline
 
Join Date: Apr 2016
Location: Pittsburgh PA
Posts: 2
Default How to minimize ground loops

Hi all-

I had a quick question about ground loops. I am going to be wiring a PMA 8000 series audio panel to an old KX-170B Nav/Com. The KX-170 used unshielded wiring and lacks pinouts for "audio low". I wanted to know which would be the proper method to wire the com output to a modern audio panel.


https://photos.app.goo.gl/m156OWCR4wGQzAVr2

The first option would have the audio low outputs for nav and com brought together to the current airframe ground at back of the KX-170B. The shield terminations would be grounded at the audio panel back shell with everything else.

The second option would have the low audio outputs for nav and com brought back to ground with the shield terminations at the back of the audio panel (all grounds shared at the back of the audio panel).

Seems like the second option would be the preferred method for minimizing ground loops, but I wanted to check with the group. I can't seem to find much in the way of printed guidance on these old - new interconnects.

Thanks and take care,

Brad
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  #2  
Old 09-24-2017, 08:49 PM
DennisRhodes DennisRhodes is offline
 
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Location: Taylorsville, Ga
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Keep the upwind wing low up to and in the touchdown and don t let it get that cross wind lift under it at least for a non A model
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  #3  
Old 09-24-2017, 09:10 PM
BobTurner BobTurner is offline
 
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Option 1. This will minimize ground loops. The audio low input is isolated from true ground.
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  #4  
Old 09-25-2017, 12:23 AM
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donaziza donaziza is offline
 
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Location: Atlanta
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Heck---And I thought this thread was going to be about "How to minimize ground looping"
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  #5  
Old 09-25-2017, 07:50 PM
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vlittle vlittle is offline
 
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Quote:
Originally Posted by Bradp View Post
Hi all-

I had a quick question about ground loops. I am going to be wiring a PMA 8000 series audio panel to an old KX-170B Nav/Com. The KX-170 used unshielded wiring and lacks pinouts for "audio low". I wanted to know which would be the proper method to wire the com output to a modern audio panel.


https://photos.app.goo.gl/m156OWCR4wGQzAVr2

The first option would have the audio low outputs for nav and com brought together to the current airframe ground at back of the KX-170B. The shield terminations would be grounded at the audio panel back shell with everything else.

The second option would have the low audio outputs for nav and com brought back to ground with the shield terminations at the back of the audio panel (all grounds shared at the back of the audio panel).

Seems like the second option would be the preferred method for minimizing ground loops, but I wanted to check with the group. I can't seem to find much in the way of printed guidance on these old - new interconnects.

Thanks and take care,

Brad
Ideally, option 1 with the shield grounded at either end (to the audio ground) would be the best. Your noise source will be the difference in ground potential between the comm and the audio panel, so they should each be connected to the same power ground.

By connecting both audio high and audio low this way, noise caused by the ground differences should be rejected by the audio panel. I don't have the audio panel schematic handy, but I it should have a fully differential input structure for this purpose.

Of course, once the engine is running, the noise won't matter....
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