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There are times when a good RF ground is impossible to achieve at many ham station locations. A good RF ground is difficult to attain. If you use a standard 8' copper ground rod, with a good solid connection, even that has a few ohms of contact resistance, even more in some cases with poor soil conditions. In many, many cases shorter ground rods are used because of the difficulty in getting them driven into even good soft soil. In most cases, practical ground installations require many feet of ground wire between the station equipment location and the actual ground point, usually outside the staion. With stations that are located on second and third floors of a home, the ground wire itself can becomes a radiator of RF energy and becomes part of the problem it was ment to help solve.
A long ground wire can be several wavelengths especially at VHF frequencies. It actually becomes a "long wire" antenna. Keep in mind that a good station ground will cure some transmitter (RFI) problems, by - 1.) Placing the chassis of the transmitter or piece of equipment at a low-impedance reference point. - 2.) By changing the problem location "hot spot" as it is called and placing it further away from the suscepatble piece equipment!
Keep in mind that grounding is NOT a cure-all for ever type of (RFI) problem that can come along. I have found in most cases the shorter the ground system, usually the better off you may be. ( Joe Dozpat WA3UVP )
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Joe, this is very helpful. We are currently in the process of installing a new tower and the subjectg is very much in our planning. I have two questions that don't seem to be answered anywhere I have looked or written:
ReplyDelete1. What is the best way to ground a tower. Our new TX455 has 3 legs. We bought a bar from ICE that clamps across two legs and has connection points for multiple #6 wires. I ran 3 wires to ground copper claded steel rods at each corner leg. That implies that the installation is not symmetrical, since the connection is not to the leg directly. One cable, about 3-4 ft long runs to the back leg, the other two are much shorter. Is this OK or is another method preferable? Is symmetry necessary?
2. I read a lot about making sure there is a central ground for the house and the equipment and the antennas. My station is in the 3rd floor attic. I run a 1" steel strap through the eves, down the side of the house to 2 ground rods in series. A lightening arrestor for the coax from the tower runs by and is connected to these ground rods also. But how do I connect the house? The electric box is in the center of the basement and would require 10-15 ft of wire to cross the eves and out the opening where the dryer vent is to connect to the same ground rods. The electical box is connected to the cold water pipes. But I don't think it connects to ground, as they used a rubber tubing to go through the concrete foundation. What to do?
Hi Fred,
ReplyDeleteThanks for stopping by the Blog Site, and I am glad you found the post, "What About Grounds" somewhat helpful, and thanks for your comments.
From what you had in your post, it sounds like you are at least on the right track with your tower install and grounding method. Keep in mind, whatever you do for grounding for the most part, is better than not doing anything at all!
Much like your grounding method, I did something somwhat the same, with some minor changes. My tower is a steel 30' Amerite 18" face tower with a tilt over base. The base section is a 4' three leg support for the rest of the tower. Once I had the hole dug for the base section and had the base supported. I installed three 6' ground rods, one at each base leg of the tower support. Each of the copper clad ground rods were connected to the one leg of the support and then all three tied together with a #8 copper wire. Then before filling the hole with concrete, I ran three #8 copper wires, one from each leg of the base to a 8' ground rod outside the concrete base. One 8' rod for each tower leg. Each of those #8 copper wires were approximately 6' in length and connected to the 8' ground rods. In the case of my tower installation, I used what I had on hand as far as copper wire and 1/2" ground rods. My tower has been up for 4 years with good results as we have frequent summer lighting storms here in N.E.PA.
As far as your grounding for your station, again, it sounds like you are doing what you feel needs to be done given your station and location in your home. I fine that most electrical services usally carry a seperate ground to a ground rod outside the residence, at least that's the way my service is. I also have a 12KW Generac emergency generate with an automatic transfer panel as part of my electrical service.
I carry a #8 copper wire from a seperate ground at the rear of my residence to just outside the shack. Then I interface it to a 2" wide copper strap into the station for all station. grounding.