[Elecraft] Groundi loops

[Don Wilhelm]

  Jim,

You are correct, the term "ground loop" is not meaningful.

Eric, please excuse this post - I know you have ended the thread (and I 
changed the subject), but I fear many have become confused about my 
comments because private responses related them to the specifics of the 
Mac computers - my emphasis has nothing to do with the Mac, or any other 
computer - it encompasses everything in the ham station, or within reach 
of the operating position, be that a computer or a table lamp.

The real problem is the difference between the various grounds in the 
typical ham station.
One piece of equipment is grounded through the AC mains ground, and 
another piece of equipment is grounded to what the operator considers 
the "RF Ground" (it is usually not an effective RF Ground, but that is 
material for another discussion).  If that "RF Ground" is not connected 
to the AC Mains ground by a low impedance conductor to the Utility 
entrance ground, that may present a dangerous situation simply because 
there is resistance between the two grounds.  A surge event (lightning, 
rain, wind or rain static) can produce a substantial potential 
difference between the chassis of "supposedly grounded" pieces of 
equipment in the shack because the resistance between the grounds is 
finite - it will not be zero, and the surge currents can be very large 
(thousands of amperes).

The main consideration is to keep everything in the operating position 
at the same potential, and that depends on connecting everything that 
can be touched from the operating position together to a single point 
common.  That common point may be 1000 volts above something which we 
normally call "ground" during a surge event, but if it is all at the 
same potential, no problem exists (I exaggerated the voltage for the 
sake of clarity) - the operator will be safe.

BUT that includes everything within the "touch" region of the hamshack.  
Extend your arms out as far as possible from your operating position and 
think about what would happen if there was a potential difference 
between any two objects - include table lamps, telephones, radios, and 
anything else within reach.

The only way to make the operating position safe from a fault condition 
or a surge event is to have everything at the same potential, and that 
means connecting everything to a common ground point - that means 
everything, no exceptions (even the Mac computers).

As Jim Brown has pointed out numerous times, that also cures many hum 
and RFI problems too - but that is not my primary concern - the safety 
of each and every ham is my main concern.

Even though you may have not had any problems in the past, it has been 
said that the time you discover you have a problem, it may be too late.  
We do not need any unnecessary silent keys within the ham community, so 
be safe and bond things together, and most importantly, if you have 
ground rods that are not connected to the utility entry ground rod by a 
low impedance conductor (#4 or #6 copper wire), please correct that as 
soon as possible, you life may depend on it.

73,
Don W3FPR

On 4/12/2011 3:04 PM, Jim Brown wrote:
> On 4/12/2011 11:07 AM, Edward R. Cole wrote:
>> None of my computer chassis are grounded directly to my radio
>> grounds.  I made it especially that way to avoid audio ground
>> loops.
> That's why I abhor the phrase "ground loop"  -- it causes people to do
> exactly the WRONG thing, just as you have done. AC hum, buzz, and RFI
> are CAUSED by not bonding together equipment that is interconnected.
> Study the tutorials in the links I posted yesterday to understand why.
>
> And, as W3FPR has observed, this same lack of bonding that causes hum,
> buzz, and RFI also can cause severe damage in the case of a lightning
> strike or power line spike.
>
> Bottom line -- bonding equipment together, bonding it to your station
> ground, and bonding your station ground to all other grounds in your
> home, are critical both for lightning safety and for minimizing hum,
> buzz, and RFI.  Most important -- ERASE THE PHRASE "GROUND LOOP" FROM
> YOUR VOCABULARY!
>
> 73, Jim Brown K9YC
>
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