"Irv Finkleman" wrote in message
...


In an article on portable vertical antennas someone mentioned that a
Portable Laundry Reel,
readily available at most camping goods stores, made an excellent windup
counterpoise. It will easily
hold about 80ft of 18 insulated wire, which when measured and marked can
easily be reeled out
to a desired length, and later quickly reeled up again. They are
manufactured by Coghlans and
very reasonably priced (I paid $3.98 CDN). The reel opens easily (it
twists apart). The unreeled
portion does not seem to affect the RF length. To me, it seems like a
very handy item to
have for my apartment antennas.which require counterpoises.

I have also devised a portable counterpoise, albeit not an adjustable one as
you describe, so I see room for improvement. Thus far, I have made two, one
each for 40 and 20. For each, I took a flimsy, disposable aluminum baking
pan and bolted two quarter-wave wires to it. I then use a 3/8-24 mag-mount
base to pin the baking pan down onto any available heavy steel object. From
there, a Hustler (or other) short, single-band whip threads into the 3/8-24
base. Unless it's really lopsided, the antenna stands up nicely.

My AA-54 analyzer showed an in-band VSWR minimum of 1.5:1. I worked a 20m
mobile in Wyoming yesterday from San Diego at "Operating Day" in the Fry's
parking lot. S-5 noise from nearby power lines prevented multiple other
QSOs, guys I could hear buried in the noise.

Irv, if I get four such laundry reels I can dispense with my flimsy baking
pans. I have enough wire to implement your idea with another set of my
surplus chassis slides.

Request for comments and wisdom: Is it accurate to say that say a vertical
needs at least four radials but will not benefit greatly from more than
eight?

Graphs like http://www.wc7i.com/radial%20efficiency.GIF

inspired this question. (The shape of the curve suggests radials added in
the beginning produce big improvement but not so much, later.) From the
graph, going from 50% efficiency toward 70% is certainly less than a
doubling, under half an S-unit, but it takes 20 more radials to get there,
impractical for portable ops. This graph appears to start at four
radials -- It doesn't consider two radials to be worthy of graphing.
Hm-m-m-m ... I know more today than yesterday.

Thanks,
"Sal"
KD6VKW