Re: [TenTec] RF Ground

["Bob McGraw - K4TAX" <RMcGraw@Blomand.net>]

Jim and I occasionally agree and then there's times that we don't see 
eye-to-eye on a topic.  Agreed, his tutorial is very good.  I suggest that 
all should read it.
One very common item that I've found and observed with the "pin 1" issue it 
the fact that folks do not acknowledge the difference between ground and 
shield and the application of each.  The rule I've always followed is shield 
should never be positioned as a current carrying conductor.  Thus in audio, 
shield must not be connected at both ends but one end only.   In a balanced 
audio line there should then be 3 conductors surrounded by a shield.   Many 
use 2 conductors plus a shield and connect the shield incorrectly at both 
ends so that it does serve as a current carrying conductor.  The shield 
should be connected to ground at one end only.  Thus the convention is; 
audio HI, audio LO, ground, and shield.  Now, this system can be operated as 
a balanced system or as an unbalanced system without concern for ground 
loops.
As to coax radiating, if it does then it will also receive.  If it is in the 
area within the station then the noise generated by computers and switching 
supplies near or on the desk will likely be received as well.
73
Bob, K4TAX




----- Original Message ----- 
From: "Jim Brown" <k9yc@audiosystemsgroup.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Sunday, April 05, 2009 2:01 PM
Subject: Re: [TenTec] RF Ground


> Gary Hoffman wrote:
> > My point is different.
> >
> > I don't care if the coax radiates.  In fact I accept that it will in
> > virtually all cases, at least to a degree.
> I do, for three reasons. RF in the shack, RF in my living room and my
> neighbor's living room, and, VERY important, noise coupled from
> reception on the coax to the antenna to the RX.
> > I was referring to the effect at the input to the radio.
> IF the coax is connected to the CHASSIS of the radio, no shield current
> (common mode) enters the radio. If, however, the shield is connected to
> some point INSIDE the radio (by definition, a pin 1 problem), shield
> current (common mode current) WILL enter the radio.
> > If we shunt the current away from the radio....to ground... at that 
> > point,
> > then it will not flow into the radio.
> This doesn't matter if there's no pin 1 problem (that is, if the shield
> goes straight to the chassis).
> > I was trying to keep noise out of the radio, for the purposes of 
> > addressing
> > the original "buzz" problem.
> >
> > Of course many posters here don't agree that ground has anything to do 
> > with
> > it, and some focus on "pin 1" and others have their pet causes.  I was
> > addressing one item that had a theoretical solution.
> I'm simply cutting straight to the physics of what's happening. As EMC
> guru Henry Ott says, we must keep track of where the current is flowing.
> Henry talks about the hidden schematic concealed behind the "ground"
> symbol. As Bob, K4TAX, observes, those points labeled "ground" are not a
> single point, they are wires with inductance and resistance. If current
> flows on them, they will radiate. Any radio wave that hits it will
> induce voltage and current. And any current will produce an IZ drop.
>
> If you guys went to study my tutorials on the pin 1 problem, you
> wouldn't be arguing with me!  :)
>
> 73,
> Jim Brown K9YC
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