[TowerTalk] folded radials

[Jim Lux]

At 02:53 AM 6/21/2005, Tom Rauch wrote:
> > >An old AM broadcast engineer I know is also a ham and I
>
> > I would imagine that chap had good soil conductivity,
>especially some
> > distance away.
>
>You can hear all kinds of things presented as fact, even
>when they aren't.
>
>Unless he lives in a saltwater pond the plate doesn't do
>much over a handful of short radials the same length and
>would never be high efficiency except perhaps on 6 or 10
>meters.
>
>My F series large pickup trucks are in the area of 15-20
>ohms of ground loss resistance on 80 meters, and they are a
>heck of a lot larger than 4ft by 4ft.
>
>73 Tom
I tend to agree with Tom here, although, the plate is a LOT closer to the 
ground than Tom's truck (unless it's one of those nifty dual use 
planter/antenna base types without wheels<grin>)

Just ballparking the capacitive coupling.. 4x4ft, 1/2" away... call it 1.5 
m2, 0.01 m spacing, about 1300 pF.  At 4 MHz, about 30 ohms reactance

Comparing the car, say 6x12 ft, 6" away, about 394 pF., at 4MHz, about 120 
ohms reactance.

The flat plate on the ground has a low enough impedance to the ground that 
it's going to couple pretty strongly, compared to the truck.

Neither is going to be particularly wonderful, of course.