[RFI] grounding your ham equipment

Ian White GM3SEK gm3sek at ifwtech.co.uk
Sun Jul 30 08:35:59 EDT 2006

Tom Rauch wrote:
>Personally, I'd never run a separate ground lead from each piece of 
>gear to the outside entrance panel ground.

Neither would I. Any advice to use that technique is impractical because 
it ignores the realities of station layout, and forgets what the 
in-shack 'grounding' is trying to achieve.

We would like to keep all the equipment inside the shack at the same RF 
potential, but that is fundamentally impossible because the equipment is 
physically spread out. In a large station, the layout can extend into an 
L-shape or a U-shape.

Also, the 'separate ground leads' advice ignores the fact that equipment 
is very much interconnected. Adding separate individual ground leads 
will often be *creating* continuous ground loops that enclose a large 
physical area, making them very vulnerable to magnetic induction.

The best that can practically be done is to install 'table ground bus' 
of very low inductance along all the operating tables, and then pick a 
single point to bond this bus back to the entrance panel ground. All the 
equipment can then be bonded to the table ground bus by very short 
connecting straps.

There are several good reasons for recommending a wide strip rather than 
a pipe for the table ground bus. The first is that you can make a strip 
much wider than a pipe of equivalent performance, without breaking the 
bank. The second is that a strip is easier to install and doesn't get in 
the way - just lay it down at the rear of the table-top, and place the 
equipment on it. The strip doesn't have to be thick (if very large RF or 
lightning currents have gotten inside the shack, there was something 
badly wrong with your outside grounding system, and a thick busbar won't 
save your equipment); but the strip does have to be wide, to minimize 
its inductance. The width of a roll of flashing seems just about right 

Then clip all the interconnecting cables down onto the bus strip. This 
minimizes the enclosed area of any ground loops, and at the same time 
maximizes the effectiveness of the ground bus to short out any induced 
voltages along its length. The same principle should apply to the common 
ground strap running back to the entry panel: all cables should be 
routed along this strap, to minimize the open areas of the ground loops.

Compared with this approach based on good engineering principles, 
"separate ground leads" looks very much like a token gesture.

73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)

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