[TenTec] A grounding question

[Dr. Gerald N. Johnson]

On Mon, 2007-01-08 at 06:25 -0600, Jim wrote:
> Mike,
> 
> The skin effect has nothing to do with the quality of the RF ground from the
> equipment to your central ground point.
> 
> Historically, amateurs have used either large conductor copper wire (AWG 8,
> 6, 4, or even 2) as well as 1 inch or 2 inch copper braid for connecting
> their equipment to their ground system. Many times even these measures are
> not the most effective especially if there is a longer run than about 6 or
> so feet to the ground point.
> 
> The key to a good RF ground for your equipment is to have the Lowest
> Inductance which means the lowest inductive reactance at RF frequencies. The
> best way to accomplish low inductance RF grounds from your equipment to the
> ground point is by using a wide solid copper strap (3 to 4 inches) wide from
> your equipment to your ground point, such as the ground rod field.
> 
> I have a solid copper bar going across the back of my equipment desk that
> bonds to a 4 inch wide solid copper strapping that I run from my equipment
> outside to the ground rod array.
> 
> The key is providing a LOW INDUCTANCE path to the ground field. This ground
> strap is the same kind of material that Polyphaser recommends with their
> solid copper grounding panel that can be mounted in the vicinity of the
> equipment.
> 
> Remember, the inductive reactance XL is equal to j omega L, and Omega is
> equal to 2 PI frequency, therefore, the XL increases with frequency, and you
> want the lowest XL possible at RF frequencies, so you need to keep the L
> very low. You do this with wide copper straps (solid) going from your
> equipment consolidation point to your ground field consolidation point, with
> the shortest run of strap possible.
> 
> Not many hams want to go to this extent, however, this is what it takes to
> make it truly effective.
> 
> PolyPhaser has some great technical articles about the need for Low
> Inductive paths at RF.
> 
> For DC grounds it does not matter, you only have to have a large enough
> conductor to handle the current load under a power surge or nearby lightning
> strike that provides either a large EMP on your ground field or via your
> power lines coming into your house.
> 
> Hope this helps.
> 
> Thanks,
> 
> Jim
> K4PV

No matter how broad (at least in practical widths under a couple feet) a
strap, when the electrical length gets to be a quarter wave or an odd
multiple of a quarter wave, at RF its an open circuit.

73, Jerry, K0CQ