Re: Best Mobile HF?

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From: JCoote@aol.com
Date: Tue Sep 05 1995 - 17:30:30 EDT


My mobile setup is an Icom IC-735 and AH2 antenna tuner.

The AH2 is not one of those coax-only tuners used by lids to "forcefeed" 80
meters into a CB groundplane- It is designed for 3-30 MHz coverage with a
nine foot whip, or 1.8 - 30 MHz coverage with a fifty foot (or longer) wire.
 I use the AH2 tuner as intended, right at the base of a whip mount in my
full-sized '86 Ford van. I did not use the dorky looking Icom HF mobile
whip, and instead used Antenna Specialists mount, ball, spring and whip. The
tuner is on the inner wall of the van, right at the antenna feedpoint.

The AH2 works great at the base of center-loaded HF whips (like the Hustler
series) or with helical whips. It will not (for example) forcefeed a 20
meter whip on 80 meters and you will still have to change whips for each
band. I ran some tests with the AH2 tuner and did get better field strength
readings when I used Hustler KW whips (center loaded) or Mobile Mark
"Heliwhips" (fat helical antennas) compared to using the nine foot whip. Of
course center-loaded or helical whips are better than base-loading a short
whip.

When parked, I have used a combination of Hustler masts and my nine foot whip
to extend the whip beyond nine feet. This helped a little on 40 and 80.

Also when parked, I have attached a random length wire to the ball mount or
to the end of the whip. This provides 160 meter coverage and better coverage
on 80-40-30 than with any whip antenna. A 50' to 150' horizontal wire at 6'
to 25' above ground makes a good high-angle antenna for local contacts
(30-400 miles) on 160-80-40 without the skipzone problems found in vertical,
or other low-angle antennas. The military calls this NVIS.

How the system works: You dial in any frequency and press the tune button.
 In a second or two the tuner head gives you a green LED meaning OK to
transmit. No fumbling with SWR and tuner controls.

The tuner is admittedly expensive for some tastes, but the IC 735 alone may
be modified for QRP powers so that the RF power control (a slider) will cover
3-100 watts. The IC-735 QRP mod involves no component work, just tweak a
few pots inside the radio. Maybe you can locate a used IC-735 somewhere.

If you go mobile without the autotuner setup, there are several good
center-loaded and helical whip antennas on the market. Thick conductors in
antenna coils or windings indicate a good product.... some antennas use thin
wire, very lossy (mobile 50-ohm wirewound resistors) but better aerodynamics.

Forget about bumper mounts. Too many things to go wrong with connections,
especially ground and the antenna is too low. I recommend the Antenna
Specialists 3/8" ball mount with spring (not the lightweight CB toy
version). These are more rugged than Hustler and other brand X mounts. Get
the mount as high as possible. On my van, I have my HF and VHF-lowband ball
mounts as high as possible, just an inch down from the roof edge and
raingutters. (I have always doubled over in laughter at CB'ers and hams who
mount a whip at a low point of a truck or van, with the whip parallel to the
vehicle body... 2" away... and wonder why they "ain't getting out").

Finally, many vehicles have ignition systems, electric fuel pumps and other
gadgets which throw out hash on the HF bands. After installing the HF radio
with good #8 or #6 cables going direct to the battery positive and negative,
you may have to do some sniffing to find the sources of the RF noise. My
Ford E250 has *three* noisy fuel pumps (a dual tank system) and I still
haven't gotten around to trying ferrites or capacitors in their leads. Some
car manufacturers may have update sheets for mechanics on filtering AM or
other radio noise problems.

73, Jay
WB6AAM
WB6AAM@K6VE.#SOCA.CA.USA.NA


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