[Icom] Mobile antenna considerations

Fri, 28 Feb 2003 21:48:55 -0600

Al
I suspect that your problem may be that the whip is too close to the body of
the vehicle and too low - I know it is very difficult to have the whip mount
on the roof , but the proximity to the body detunes the antenna. The whip
worked well for me once I got it up and away from the body of the car.
Another problem may be the location of the tuner itself - it is best when it
is at the base of the antenna and having a radiating wire running through or
near the body adversely affects the output - And the tuner does work much
better on the higher bands just because the whip is a much greater portion
of a wave length and has a higher resistance than the lower bands. I would
be interest in how you had the tuner and antenna mounted -
73
George
W4LT
----- Original Message -----
From: "Al Waschka" <[email protected]>
To: <[email protected]>
Sent: Thursday, February 27, 2003 7:32 PM
Subject: Re: [Icom] Mobile antenna considerations


> 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
> >
> > ----
> > Your Moderator: Dick Flanagan W6OLD, [email protected]
> > Icom Users Net: Sundays, 1700Z, 14.315 MHz
> > Icom FAQ: http://www.qsl.net/icom/
>
> ----
> Your Moderator: Dick Flanagan W6OLD, [email protected]
> Icom Users Net: Sundays, 1700Z, 14.315 MHz
> Icom FAQ: http://www.qsl.net/icom/
>