First of all, the subject grounding is controversial. Some say it's a need in your shack, some say the mains earth is good enough for safety. Since I use a safety transformer in the mains to supply 230V to my shack a mains safety earth is not working. So I made a separate earthrod outside the shack and connected it to the connectorpanel just behind the outside wall. Now this is just for safety, it's not a HF earth. However I am an experimenter and would like to test a HF earth, if it doesn't work I can simply disconnect and nothing is lost.
I wrote about this subject before:
The RF surpression ground system myth
Making a second floor shack ground
Now in my case a problem with a earthloop was rising between the connectorpanel and the earthpoint in the shack which is best bonded to the last item in the coax chain, the antennatuner. Since the coax is earthed to the chassis of the panel a extra groundstrip would led to a groundloop. But I have the connectorpanel for safety, when the coax to the shack is unplugged the antennas and outside coax cables are grounded through the panel and I hope I'll not get dangerous high voltages on my equipment chassis when a lightning storm is nearby. So I made a two-way knife switch to choose between the shack earth and the panel. That way I will not create a earth loop. I don't really know if it is all worth the trouble, but at least it gives me a trusty feeling when the counterpoise is grounded for safety.
Now some of you will think....why a counterpoise? That's only working when you have some sort of impedance problem with a unbalanced antenna. A simple balun grounded near or on the antenna works ten times better. Oh, yes indeed that's true. But actually my RFI is related to my balanced 84 Mtr horizontal loop fed by a 450Ohm ladderline which I have only up in the winter and is used on all HF bands through a Palstar antennatuner. Actually I don't need a counterpoise with 1/4 wave length wires, but that's what still had from previous experiments. The goal actually is to bond as much metal in the shack to the common grounding point to get a equal potential on all equipment when transmitting. More information about this can be found on the website of W8JI. Best would be a conductive grid on the floor below the carpet or so, I will make that in the future.
Just for the record, normally you don't need this. Most shacks don't need a HF earth at all. A safety earth is more then enough. However if you have a antenna very close to the shack it could help against RFI. In my case I do have the horizontal loop in winter very close to my operating position (2 meters distance) and have som RFI into the the headset, deskmike and computerscreen when operating on 17m and 15m. Very annoying and I hope this will partly solve the problem. Only time will tell.
|Left to right: Knife switch in relation to the panel, Knife switch in shack position,|
Common grounding point, large grounding strip.