On 2024-01-16 12:13 p.m., David Knapp via groups.io wrote:
> For those hating to install radials for a counterpoise to their portable vertical or EFHW antenna, I have had good luck throwing two 48"x 84" aluminum window screens on the ground connected via two alligator jumpers. I am also testing a version that uses a Faraday cloth of similar dimensions, easier to fold into a bag and throw out quickly for a POTA activation. Since I hate to use more than one or two counterpoise radials during an activation, I was pleasantly surprised that the aluminum screens presented a much better VSWR bandwidth than 2 radials, depending on the ground conductivity.
SWR isn't everything. Antenna + ground system efficiency is more
important than SWR. You should measure the RESISTIVE component of your
antenna + counterpoise (or window screen) system, not just the SWR, with
each ground return system. (Reactance can be tuned out with whatever
antenna coupler you may be using.) An antenna analyzer will do this
measurement properly.
Suppose the antenna plus radial wire combination measures a lot less
than R = 50, and I suspect it will, with a short antenna. (To a first
approximation, the radiation resistance of a short monopole is
proportional to the square of its length, and it doesn't get up to 36
ohms or so until the length is a quarter wave.) And suppose the
resistance using a window screen measures closer to 50 ohms. The window
screen is going to give a better SWR. And the difference in resistances
is made up of ground losses, so your distant signal is going to be a lot
weaker with the window screen (provided your antenna coupling scheme
will tolerate the lower input impedance with the radials).
Another way to find out what is going on: have a friend measure your
signal strength, both ways. This should be done at a good distance, a
number of wavelengths away from the antenna so as to be out of the near
field, perhaps a few blocks away, but close enough that you are looking
at the ground wave to avoid normal ionospheric variation.
Maybe the window screen will do a good job up on 10 m, but at lower
frequencies I'll bet longer radials will win (unless your ground
conductivity is very high, as in a salt marsh).
David? VE7EZM and AF7BZ
David Knapp