[Icom] Mobile antenna considerations

Al Waschka [email protected]
Thu, 27 Feb 2003 20:32:06 -0500


I have used  (1) Icom AH-2 with a whip and (2) Hustlers.  The Hustlers win
hands down.  The Icom tuner with an 8' whip is virtually useless below 20m and
it ain't great on 20.  The AH-2 works !GREAT! with a 50' long wire and would
probably work well on a sailboat backstay, but simply does not work with a
whip.  I did some comparative groundwave tests and the AH-2/whip combo was
15-20 dB below the Hustler on 40 and 75. There are really two problems.  The
Hustlers (and the sticks) are center-loaded antennas.  It takes less inductance
to resonate an antenna if the loading is at the center. The efficiency of an
antenna is the ratio of the radiation resistance to the loss resistance (Q
effects plus ground resistance).   "Q" is the ratio of resistive loss to
inductance (and you get it by the cubic inch.) The more inductance, the more
resistance for a given Q so the base-loaded whip takes more inductance and (for
a given Q) has more losses than a center-loaded whip.  For a given
installation, the ground losses are the same.  So you want to minimize the
required inductance and you want to maximize the Q.  If you look at the inside
of the tuner, you can see why the losses are high.  The inductors are lumped
circuit potted elements about 1/4" x 1/4" x 1".  The Q of these inductors is
very low, so the losses are high.

You can make the same comparison between the Screwdriver and the Hustler or the
Hamsticks.  Look at the diameter of the loading inductors.  Remember what I
said about Q coming by the cubic inch.  I have never owned a screwdriver-type
antenna but I can easily understand why they beat Hustlers and Hamsticks in
head-to-head shootouts.

That being said, I only have experience with the AH-2 which is the tuner for
the IC-735, so I can't speak for the later (706-compatible) tuners but the
basic mobile tuner was derived from the marine tuner which was designed to tune
a 50' or so backstay on a sailboat, not an 8' whip.

If you can afford it, go for the screwdriver.  If not, get the Hustler or the
"sticks".

73,

Al K5TAN


Jack Hartley wrote:

> I'm getting ready to mount my 706MKIIG in my pick-up.
> In looking at antennas and have a question:
>
> There are 3 considerations-
> A: 'sticks'  for each band.  Which I'm using now and this system, while not
> convenient, works very well
> B: Screwdriver antenna
> C: Whip & tuner
>
> The questions is asked to those of you that have had at least two of the
> configurations and like one or the other.
> Does either of these 3 choices have a proven performance advantage?  Has
> anyone done a comparison?
>
> Price wise the screwdriver types can run up into the $500+ range once you
> include the heavy duty mounts required.
> ICOM's combination, which includes a very expensive whip is about the same
> cost.
>
> Jack Hartley
> K4WSB
> ARRL - QCWA - OOTC
> http://www.ultimatehat.com
> 10% discount to fellow Hams
> Put your call on the order
>
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