Question about counterpoise

[OkieBoyKJ5JFG]

I've noticed when testing antennas on my truck, if I touch the radiating element, SWR usually improves, sometimes quite a bit. I assume my body is acting as a counterpoise. Why doesn't the same thing happen when I run a wire from the antenna to a grounding screw on the truck?

 

[mmckenna]

I've noticed when testing antennas on my truck, if I touch the radiating element, SWR usually improves, sometimes quite a bit. I assume my body is acting as a counterpoise. Why doesn't the same thing happen when I run a wire from the antenna to a grounding screw on the truck?

It's not a counterpoise, your body is coupling with the radiating element and becoming part of it, changing the resonance.

A counterpoise can be a substitute for an earth ground. Depending on the antenna type, it'll be looking for a flat plane under the antenna base.
Simply running a wire from the base of the antenna to some random ground point doesn't satisfy that need. It might provide a DC ground, but not a good RF ground/counterpoise/ground plane.

 

[OkieBoyKJ5JFG]

It's not a counterpoise, your body is coupling with the radiating element and becoming part of it, changing the resonance.

A counterpoise can be a substitute for an earth ground. Depending on the antenna type, it'll be looking for a flat plane under the antenna base.
Simply running a wire from the base of the antenna to some random ground point doesn't satisfy that need. It might provide a DC ground, but not a good RF ground/counterpoise/ground plane.

That's interesting. So far, I've never seen it make the SWR worse, or if it did, I didn't notice it. I would think changing the resonance would make it worse about as often as it makes it better.

 

[EAFrizzle]

Human bodies add capacitance to antennas, as well as coupling with the elements. That was the reason you kept having kids in the 50s and 60s, to have voice-controlled TV antenna tuners!

 

[OkieBoyKJ5JFG]

Human bodies add capacitance to antennas, as well as coupling with the elements. That was the reason you kept having kids in the 50s and 60s, to have voice-controlled TV antenna tuners!

I was one of those.

 

[EAFrizzle]

I was one of those.

As were many of us.

Heck, I remember being grown at deer camp out of Crockett and hanging foil, wire, grabbing the antenna,  anything to get a football game out of Lufkin to come in.