Re: LOOKING FOR INFORMED OPINION ON STATION GROUNDING PROCEDURE(S)
Don Wilhelm <w3fpr@...>
Dr. Don,toggle quoted messageShow quoted text
I disagree that any ground rod and connection to it via any wire or copper strap will be an effective RF Ground.
I think of 3 things that are considered "ground" - the first is AC safety ground (follow the NEC rules for compliance), and the next is Lightning Protection Ground, which is more complex than the AC ground - one can find good information on that subject on the Polyphaser website. Ron Block had a 3 part series in QST some time back and I consider that a good resource.
Then comes "RF GROUND" - that is a nefarious term and is very often misunderstood.
No "ground wire" will provide an RF Ground if there is any length of wire or copper strap required to connect to Mother Earth. Consider a good driven ground rod system outside the shack, then connect it to the shack with an 8 foot long wire or copper strap.
Now -- remember that RF flowing on a wire follows the same rules as for antennas and transmission lines - the impedance is low at the ground point, but is high 1/4 wavelength from that point.
On 10 meters, that 8 foot wire is about 1/4 wavelength long - so it has a low impedance at the connection with the ground rod, but at the end of that 1/4 wavelength wire, the impedance is quite high -- hardly a good ground for RF.
My view is that RF Ground is more of a concept than any physical thing. It exists at the point(s) where the RF voltage is zero. That occurs midway between the transmission line connection to a dipole, and midway between the transmission line connections to a vertical monopole and the ground plane. It also occurs at several other places in the antenna field and transmission line system. Creating an RF Ground in the hamshack at all frequencies we operate is an insurmountable task.
The solution is to keep the RF from getting back into the shack. That is what baluns and current mode chokes on the transmission line are for. Jim Brown K9YC has an excellent tutorial on handling RFI in the hamshack - see http://www.audiosystemsgroup.com/RFI-Ham.pdf -- his common mode chokes are good (he does not like the term 'balun') and quite effective.
In other words, keep the RF out of the shack and there is no need for an "RF Ground" in the shack - in fact, it is impossible to construct an RF ground in the shack at all frequencies.
On 1/8/2015 6:01 PM, Don Sanders w4bws1@... [4sqrp] wrote: