13

I've seen many installations, particularly at field day and also in second-floor installations, where RF grounding is ignored entirely. What are the drawbacks to this and when is it absolutely essential to have RF grounding?

Bill - K5WL
  • 1,194
  • 1
  • 11
  • 18

2 Answers2

4

Two drawbacks to ignoring your grounding:

  1. You will have a poor(er) signal.
  2. You could become the ground and experience an RF burn first-hand.

That said, VHF antennas are often not grounded - handhelds and VHF radios in cars, for example.

Andrew Beals
  • 302
  • 3
  • 7
  • 1
    Is there a time when it is essential to have RF ground? Like when using a longwire maybe? – Bill - K5WL Oct 22 '13 at 21:09
  • Yes. What you have in a lot of situations where you don't have an exactly resonant antenna that's vertical to the Earth's surface is a situation where your ground situation is actively absorbing RF energy; think of it as the "pull" in a "push-pull" situation - your signal out the antenna is an action - the ground receives RF as a reaction. See my above comment about RF burns.

    Even when you're simply receiving, having a good ground can make all the difference in the world.

     – Andrew Beals Oct 22 '13 at 21:14
  • Saying that poor grounding causes poor signal is an oversimplification to the point of being misleading. There are situations in which this is true, and just as many where it is not. – Phil Frost - W8II Nov 11 '13 at 16:52
3

I think there might be confusion between RF ground, counterpoise, and electrical safety grounding. I am going to restrict my answer to RF ground (but, the word counterpoise is often used for the same thing).

In a perfectly balanced antenna, such as a Dipole at its resonant frequency, there is no need for an RF ground since no current would flow to the RF ground (like I said, in a perfect balanced antenna).

In a perfectly unbalanced antenna, such as a 1/4-wave vertical, an RF ground (aka counterpoise) is absolutely necessary to "complete" the antenna and make it whole. As they say, the ground image of your quarter wave antenna is the "other half" of the antenna and current will flow in this ground.

This is why a quarter wave antenna needs some sort of RF ground counterpoise made of conductors to make this current flow less lossy. Just relying on the ground itself results in a very lossy other half of your vertical and thus definitely not as efficient. In general, the more you can make the ground a good conductor (more radials, etc.) then the more efficient your antenna will be.

Given these two extremes, the need for an RF ground depends on all kinds of situations where the actual individual antenna geometry, height above ground, other nearby conductors, and so on come into play.

If your dipole antenna is not balanced for example, then common-mode current will flow down your feed line and radiate or enter into your shack and cause other problems. Making sure that your equipment is well grounded may help eliminate some of this RFI but it is best to eliminate the common-mode currents using an RF choke at the antenna feed point.

In summary, for good balanced antennas such as dipoles, Yagis, and similar geometries, RF grounding should not be necessary. If you have an unbalanced antenna like a vertical or a single long-wire antenna, or an inverted-L, or similar then a ground plane (RF ground) is required for efficient operating.

K7PEH
  • 2,998
  • 11
  • 14