Help Explain XM's Satellite Radio Wiring

Thread Starter

Schwarttzy

Joined Oct 28, 2017
4
I was hoping that someone could explain how XM Satellite radio wiring works a bit. Specifically XM's satellite radio box uses Ground, Audio Common, and Drain Wire is shown in the Connector Terminal Identification section of the manual. Ground has bunch of noise from the all the automotive electronics, making it seem like it would be impossible to get clean audio into the radio. Which leaves me to believe that the "Drain Wire" and "Audio Common" are used in some way to produce a clean audio signal.





Thanks for your time!
 

wayneh

Joined Sep 9, 2010
16,398
Well sort of. Some amplifier configurations, including those used in many cars, have a floating common that is not directly attached to ground of the power supply. So a speaker wire must connect to both output pins and you cannot instead ground one of the speaker wires. This could burn out the amp. I suspect the Drain (cable sheath) wire is probably grounded at one end but not necessarily. It's meant to drain off EM interference from the cable acting as an "antenna".
 

Thread Starter

Schwarttzy

Joined Oct 28, 2017
4
Well sort of. Some amplifier configurations, including those used in many cars, have a floating common that is not directly attached to ground of the power supply. So a speaker wire must connect to both output pins and you cannot instead ground one of the speaker wires. This could burn out the amp. I suspect the Drain (cable sheath) wire is probably grounded at one end but not necessarily. It's meant to drain off EM interference from the cable acting as an "antenna".
Pin 9 = Ground = Vehicle Ground with all of the vehicles noise
Pin 11 = Drain Wire = Probably used to drain EM interference
Pin 10 = Audio Common = (I don't have a clue...)

That leaves me with Pin 10. How could Audio Common (Pin 10) be used in a circuit to eliminate the noise in from Ground (Pin 9)?
 

nsaspook

Joined Aug 27, 2009
7,354
Pin 9 = Ground = Vehicle Ground with all of the vehicles noise
Pin 11 = Drain Wire = Probably used to drain EM interference
Pin 10 = Audio Common = (I don't have a clue...)

That leaves me with Pin 10. How could Audio Common (Pin 10) be used in a circuit to eliminate the noise in from Ground (Pin 9)?
The current path for the device (digital/power) electronics will loop into the Vehicle Ground while the current path for low level input signals will loop into the audio common. On some car audio systems there is a (PITA pioneer pico) fuse in the audio common to prevent the power ground current from using that path.

NSFW language


http://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html
 

Thread Starter

Schwarttzy

Joined Oct 28, 2017
4
The current path for the device (digital/power) electronics will loop into the Vehicle Ground while the current path for low level input signals will loop into the audio common. On some car audio systems there is a (PITA pioneer pico) fuse in the audio common to prevent the power ground current from using that path.
That sound in that YouTube video is exactly the problem I'm having in my circuit.

Let's see if I understand this then.

The "Audio Common" is ground, but it's just for the auido's ground. And the radio most likely has a PICO Fuse restricting non-audio-ground on the wire "Audio Common", which is why when I tried to power a RN52 off of "Audio Common" I would get nothing.

Is that right?

If I wanted to use the RN52 Bluetooth Chip to Hi-Jack the audio, should I only connect the RN52's AGND to the XM "Audio Common"?
 

nsaspook

Joined Aug 27, 2009
7,354
That sound in that YouTube video is exactly the problem I'm having in my circuit.

Let's see if I understand this then.

The "Audio Common" is ground, but it's just for the auido's ground. And the radio most likely has a PICO Fuse restricting non-audio-ground on the wire "Audio Common", which is why when I tried to power a RN52 off of "Audio Common" I would get nothing.

Is that right?

If I wanted to use the RN52 Bluetooth Chip to Hi-Jack the audio, should I only connect the RN52's AGND to the XM "Audio Common"?
That should work while the RN52's GND pin is connected to power ground.


When the Pico fuse is blown it's very common to get noise if the head unit is a Pioneer. For others exactly how the audio ground is connected to power ground depends on the circuit. Some are isolated so there is no direct DC current connection between audio common and 'Ground' while others are directly wired together at a common point inside the head unit. It's very likely the RN52 speaker level +- audio outputs are floating IRT audio or power ground. In this case it's common to use an audio transformer (like a cheap LOC) to isolate signals (break a possible ground loop to eliminate noise) and to provide the correct line level input signal.

https://www.amazon.com/PAC-SNI-35-Variable-Line-Converter/dp/B001EAWS3W
 

Thread Starter

Schwarttzy

Joined Oct 28, 2017
4
That should work while the RN52's GND pin is connected to power ground.


When the Pico fuse is blown it's very common to get noise if the head unit is a Pioneer. For others exactly how the audio ground is connected to power ground depends on the circuit. Some are isolated so there is no direct DC current connection between audio common and 'Ground' while others are directly wired together at a common point inside the head unit. It's very likely the RN52 speaker level +- audio outputs are floating IRT audio or power ground. In this case it's common to use an audio transformer (like a cheap LOC) to isolate signals (break a possible ground loop to eliminate noise) and to provide the correct line level input signal.
In the past I've made a quick 3.5mm headphone jack jumper that that used "Audio Common" as the ground and when a head phone jack is plugged in the audio was replaced and it had sound quality that is well within the limits of what I needed. So I would assume that this would work with the RN52 now that I understand the "Audio Common" better.
 
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