[TowerTalk] Screwdriver Antennas?

[Jim Lux]

----- Original Message -----
From: "Michael Tope" <W4EF at dellroy.com>
To: "TowerTalk" <towertalk at contesting.com>
Sent: Tuesday, September 28, 2004 10:29 PM
Subject: [TowerTalk] Screwdriver Antennas?


> I was thinking of getting a screwdriver antenna for my pickup
> truck and was wondering if anyone out there has any experience
> with the various models of the N9JMX Predator or the Tarheel
> line of screwdrivers. I would like something that will tune 160 - 10M,
> be as reasonably efficient as one can expect from a mobile
> antenna, and handle at least 500 watts (preferably 1500W).
>
> The Tarheel 200 advertises 1500Watts power handling,
> but doesn't cover 160meters. Their model 300 covers 160
> but is advertised as only handling 400 watts. Or am I barking
> up the wrong tree trying to get an all-in-one 160 -10 meter
> mobile antenna (e.g. would it be better to get two antennas, 1
> for lowbands, and 1 for highbands)?

It's probably impossible to tune one whip over the entire range. However, on
mine, when it's all the way out at the 80 m position, I can get a SWR dip on
10.

The screwdrivers are incredibly narrow band on 75/80.  QSY of 2 or 3 kHz and
you'll need to retune, and it's tough to "bump it in" exactly.

You might do better with some sort of relay switched tuning networks for
bandswitching and an auto tuner for within band match.  There is someone
selling the relay switched scheme (http://www.bandhopper.com/, I think).
This seems to be a better strategy, esp for QRO.  If I could figure out a
decent way to switch center loading coils (a'la bug catcher) remotely, I'd
build something like that.

SGC's multiband whip is an interesting take on how to solve the "need two
different length whips in one widget" for wide band coverage (they put the
autotuner at the base).  Their whip has two wires in it.  One is straight up
the middle of the form, the other is helically wound up the outside.  I
haven't been able to look at one closely, but some early modeling seems to
show it would work.  I also modeled a scheme where you just hook two
verticals of different (electrical) lengths in parallel.  One straight whip,
one helically loaded, about 6" apart.

FWIW the SGC rig that handles QRO is about $1100-1300.


There's some other screwdriver links on
http://home.earthlink.net/~w6rmk/antenna/screwdriver.htm

I would be exceedingly skeptical of power ratings... They're sort of like
"peak music power" for car stereos.
>
> Thanks,
>
> Mike, W4EF............................................................
>
>
Jim, W6RMK