[TowerTalk] [RFI] Back of desk grounding buss

[n8de at thepoint.net]

I've been following this thread for a while and wonder why no one has  
mentioned that a 'ground bar' is NOT a single-point ground.

Think of the 'ground bar' as a series-string of very low value RESISTORS.

Now ... think of your equipment as being connected to the 'nodes'  
between each of those resistors ... rig A at one end, then rig B at  
the first 'node' ... rig C at the second 'node' ... etc.

During a lightning strike, the huge voltage of the strike MIGHT appear  
across that 'string' of resistors, causing each 'rig' to be at a  
DIFFERENT potential.

POOF !!

I suggest that each piece of equipment have its own 'ground wire' and  
those all be connected to a SINGLE point, perhaps at a point closest  
to the ground rod.  (Mine are all connected to a #0 wire going through  
the wall to the ground rod about 7' from the 'single point'.

Good luck.
Don
N8DE


Quoting Jim Lux <jimlux at earthlink.net>:

> On 3/20/14 10:34 PM, Jim Brown wrote:
>> All of the replies I've seen here are obsessing on the wrong topic. By
>> all means DO take care to avoid oxidation and dissimilar metals
>> problems. But that ground bar, whatever it is, is NOT an important
>> element of what you're doing, which is primarily LIGHTNING SUPPRESSION,
>> but also minimizing hum, buzz, and RFI.
>>
>> What matters is that EVERY CHASSIS in your shack be bonded together by
>> short fat copper, and that combination of chassis bonded to everything
>> in your house by short fat copper.
>
> I agree on bonding, but not on fat.  At RF frequencies, the inductance
> (1 uH/meter) will  dominate over the AC resistance.  At 1 MHz
> (lightning frequencies) 1 meter of AWG 16 copper wire has a AC
> resistance of about 0.07 ohms.  It has an inductive impedance of 6.3
> ohms.
>
>
> That includes antenna entry, every
>> ground rod, the power system ground, the telco ground, the CATV ground,
>> the satellite ground, structrural steel ground (if any), and, if your
>> tower is close to the house, the tower ground.
>>
>> You are also forgetting that bonding between equipment should also be
>> short, fat copper. When you run wires from each piece of gear to a bar
>> at the back of he desk, that usually makes the connection more than
>> twice as long. That means double the resistance and double the
>> inductance. NOT a good thing.
>>
>> The BEST bonding method in the shack is short, fat copper from chassis
>> to chassis of every piece of gear in the shack, then a bond from one of
>> those chassis (preferably the rig) to those other grounds in your home.
>> Chassis to chassis bonding minimizes hum, buzz, and RFI. Bonding all the
>> grounds together and to earth provides lightning safety.
>
>
> I'd rather have someone use smaller easier to manipulate wire that is
> short, than big fat stiff bars or wires that wind up being long.
>
> And, of course, avoiding loops which can intercept the magnetic field
> from a transient flowing in another conductor.
>
>
>
>
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