[TowerTalk] There's 'ground', and then there's 'ground'

[Jim Jarvis]

1)  I think you'll find that all unibody constructed cars
have serious anti-corrosion coatings applied, after welding.
Bolted-on components are almost never electrically connected,
unless there is a reason for it, as it represents both extra
work, and a breach of the corrosion protection.
    As the owner of two Passat's which had an ic706-2 installed,
I was careful to attach to the unibody when installing the
antenna.  Cutting holes is painful, though...as was the bodyshop
repair when I sold the vehicles.
    
2)  Most contemporary transceivers do not have a single point 
ground.  There is a logic ground, an RF ground, an audio
ground, and a chassis ground.  They exist in different areas of 
the radio, on different boards, and may be deliberately 
separated from the chassis, for purposes of noise reduction.
    Yes, chassis ground shows up on the back panel.  And yes,
I would expect RF ground shows up at that point, too.  But 
the logic and audio circuits reside internal.
    I think you'll find the mic 'ground' isn't the cable shield.  
You'll also find that the 'shield' side of the mic audio connects to 
chassis ground, on the PCB, via a resistor of 10 ohms or so. 
There is usually a 'single point ground' for audio, which references
that circuit to chassis, and prevents ground loops. The mic element
itself is usually floating within the housing.  
    
3) External audio processing equipment requires particular care
not to create ground loops.  As someone observed, pro-audio folks
put real effort into that, in their equipment.  

4) One could write a volume on proper grounding and shielding in
the mixed signal environment presented by a hamshack.  And I won't.
At least not here.  Just one sentence:

	SAFETY GROUND SHOULD BE TESTED.  SPEND 10 BUCKS ON A 'PLUG CHECKER',
AND TEST ALL OUTLETS THROUGHOUT YOUR HOME.  YOU MAY BE SURPRISED, 
PARTICULARLY IF YOUR HOME WAS BUILT IN THE 60'S, OR HAS ALUMINUM WIRING.
          

n2ea
jimjarvis at ieee.org