I don't understand how you would go about giving an RF ground to your antenna. Would it not become an additional radial and affect the signal?
What is the proper way to ground your station's antenna?
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$\begingroup$ What kind of antenna? $\endgroup$– Phil Frost - W8IICommented Oct 29, 2013 at 22:24
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3 Answers
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To answer your first question, yes, it will affect the signal, but it's a good thing.
What you do to (RF) ground your antenna(s) depends on what type of antenna you are using. For instance, dipoles do not require a ground. Typical vertical antennas do require a graound though some types such as the GAP Challenger use 3 wires insulated from ground (in this application they are referred to as a counterpoise).
In a typical vertical antenna installation, your radiator is λ/4 tall (electrically at least, it might be physically shorter through the use of coils or whatever). This is referred to as a monopole and is half of a good antenna. You make the ground be the other half of the antenna but creating a ground plane with radials. This creates a virtual image antenna that completes the overall antenna effect. These radials are usually buried just below the surface or stapled down to the ground and grass is allowed to grow through them to hold them down.
That's your RF ground. In addition, it's usually desirable to have an electrical ground for lightning and static electricity protection. This is achieved by making a lower impedence path to ground than you feedline presents. Usually one or more 8' copper-clad rods are pounded into the ground at the base of the antenna and bound to it. The area of effect of this is below the ground plane and doesn't detract from the signal.
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1$\begingroup$ There's a lot more to effective lightning protection than pounding a couple rods in near the antenna (and in fact, this is likely to make things worse if this is all you do). See How can I protect equipment against a lightning strike? $\endgroup$ Commented Jun 20, 2014 at 14:29
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If you are looking for the safety ground, as lighting protection, it's mostly done by inserting a copper rod in the ground, and when you are not using the sation, the anthena should be connected to that rod, so if a lighting hits it, there is no significant damage.
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$\begingroup$ The question is about RF-grounding, not DC-grounding. $\endgroup$– on4aaCommented Nov 1, 2013 at 2:15
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1$\begingroup$ It was not clear to me it was about RF-grounding and not DC-grounding. Thx for your explanation. $\endgroup$ Commented Nov 27, 2013 at 15:35
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2$\begingroup$ That's also likely to do very little to protect you against a strike. What you are missing in your diagram is the power cord for the transceiver, which is connected through your home's wiring to another ground rod. No matter how great your lightning rod is, it looks like a pretty high impedance, while your home's wiring is a low impedance to another path to ground. The thousands of amps of current from the strike will want to go to both grounds, leaving about half of it to go through your transceiver to get to the other ground. $\endgroup$ Commented Jun 20, 2014 at 14:32
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The following comments might be of interest to those using base-fed, vertical monopoles:
Medium-wave AM broadcast stations typically use an r-f ground path through a set of 120 x 1/4-wavelength, uninsulated, copper conductors buried radially in the earth, with their common point located directly below the base of their radiators. They also use a series-connected arc gap between the tower base and one or more ground rods buried near the tower base. The gap spacing is set to flash over when the radiator base voltage exceeds the normal value for the modulated peak power at the feedpoint, by a given amount. Also the tower base is connected directly to the ground rod(s) through an r-f choke at the operating frequency, to avoid d-c (static) buildup voltages on the tower.
Even though their vertical radiators can approach heights of 1,000 feet AGL, such AM broadcast stations continue to operate during nearby lightning events without component damage(s), and without loss of service except for the very short (x-millisecond) intervals when the arc gap flashes over, because protection circuits in their transmitter sense the arc event and kill their r-f output for that time interval.
