[kwlug-disc] Grounding for antenna

[John Johnson]

On 2014-06-16 10:02, Paul Gallaway wrote:
> In theory your two grounds (the antenna rod and hour house ground) are
> suppose to be bonded (a wire between the two). Apparently with a
> differential grounds you can get ground-loop hums, or voltage
> travelling between the two if you ever have a situation with
> differential voltage of the two grounds is great enough (e.g. it would
> travel across your tuner). There is no easy way for me to do this
> based on where my antenna is installed (I would have to run a wire
> through the foundation and don't have the tooling to do this) so I
> haven't bonded my antenna ground to my house ground yet. So far no
> issues but YMMV. Maybe John has more information on the reasons for
> doing this and the likelihood of problems?
>    
Ref: http://en.wikipedia.org/wiki/Stray_voltage

AFAI - almost - K: I doubt if widely spaced earth grounds in a 
residential lot will have a potential difference.
And bonding, as described, should be safe.

If there is a potential difference, it may be caused by nearby 
transmission lines or other high voltage systems in the area.
And if there is a potential difference, it is caused by current and 
resistance; remember Ohms Law applies.
And in this case, bonding may exacerbate the situation by providing a 
low resistance path for the source of the current.

On this part, I will stop here as it has been about 5 years since I 
worked for an equipment supplier in the area of electrical safety.
And, at the time, I was barely aware of the phenomenon of stray voltages.

I have experienced the "hum" Paul mentioned. And, in my case, it was 
caused by potential differences in the neutrals in interior wiring. Or 
failing equipment. These potential differences would case AC currents in 
the grounds between audio* equipment, where shielded wire was 
incorrectly wired with shields connected at both ends. The AC currents 
would inductively couple into the signal wires feeding the amplifiers, 
with the resulting 60 Hz hum.

* TV can be affected too. In the "old" days, AC hum would appear in the 
video as slowly vertically rolling black lines while the picture was stable.
This "rolling"  is the difference between the 60 Hz "hum" and the NTSC 
Vertical frequency of 59.94 Hz.

jsquared


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