[aprssig] APRS HF Mobile Antenna Suggestions

Sun Oct 5 23:50:26 EDT 2025

On 10/5/2025 8:37 AM, Arte Booten wrote:
> Hi all,
>
> I'm retiring next year and will be living in a Class A Motorhome - roughly 
> the size of a bus. I already have a Yaesu FT-991A 160M-70CM principally for 
> HF & C4FM and two 2M/70CM FM antennas.
>
> Ideally, I'd like an all-HF-bands antenna rather than have to climb the 
> ladder to change hamsticks though I don't intend to operate HF SSB while 
> driving - too many potential distractions.
>
> What's worked for you. Equally pertinent - what didn't? 73
>
[On the road in Grand Junction, Colorado, returning to Michigan after a week in 
Los Angeles.]

Assuming you are going to use the FT-991, I think the "no-brainer" choice 
(assuming you don't need 60 and 80 meters) is the Yaesu ATAS-100 or ATAS-120 
mini-screwdriver mobile antenna. The FT-991, like the FT-857 and FT-891, can 
completely automatically control the ATAS.   Just select the band/frequency 
40M-through-70cm and hit the TUNE button on the radio.  No separate control 
cable for the screwdriver motor is required -- the motor control voltage is 
sent up the coax to the antenna.

When the ATAS is hard-mounted on a substantial sheet metal mass like the roof 
of a vehicle (not on a crappy gutter clip or trunk-lip mount) it works 
amazingly well, even on 40 meters. It tunes onto 30 meters very well for HF 
APRS operation too.  (I have mine in the center of my Jetta TDI's trunk lid.)  
It's no taller than a common 2M 5/8ths wave - about 56-60 inches depending on 
what band it is tuned to.  (Gets longest on 40 meters; shorter on the higher 
bands.)   You might need one of the motorized tilt-over mounts to lay it flat 
while enroute if mounted on the roof of a Class A.

The ATAS base is a PL-259 connector; you will need a mount with an SO-239 
socket; not an NMO.   I have multiple heavy-duty Larsen NMO mounts (that are 
made of stainless steel-not the usual brass) on my car.  I then use the Tram 
NMO-to-SO239 adapter.  Note that the Tram is the only such adapter that is 
cylindrical (not tapered) and fully supports the entire base of the ATAS which 
is almost 2" diameter around the recessed PL-259 connector.  (There are a lot 
of other NMO-to-SO239 adapters out there but they all taper to a smaller size 
at the SO239 end only suitable for supporting lightweight VHF/UHF whips with 
PL-259 bases.)

As for the other post about using the SGC-230 Smartuner:

Normally the Smartuner is used with at least a quarter-wave of wire at the 
lowest frequency of interest, like the back-stay of a boat.   It WILL tune into 
a 9' solid CB whip even on 75M, but will be hideously inefficient on the lower 
bands (40-60-80 meters). The tuner's internal L-network has to configure to 
such an extreme matching ratio with such a short radiator that most of the TX 
power is dissipated in the tuner - not delivered to the whip. SGC used to offer 
a 9' fiberglass whip with two concentric copper-tape helical windings that was 
far more "tuner-friendly" than a simple 9' solid stainless whip.  It was 
dramatically more efficient on the lower HF bands.  Alas, SGC no longer exists.

For any kind of a end-fed whip to work efficiently, you MUST have an effective 
ground.  This means connecting the ground terminal of the SGC or similar tuner 
to a substantial metallic mass.  At least the vehicle body.   If you are only 
operating in camp (not mobile), consider the LOG (loop-on-ground) ground.  
Instead of just stretching a straight wire outward from the ground terminal of 
the tuner, you stretch 40-50-70 feet of wire outward from the tuner ground 
terminal, form a roughly circular or elliptical loop on the ground and bring 
the far end of the wire back to the tuner ground terminal. This DRASTICALLY 
increases the coupling to earth ground compared to a straight wire without 
having to drive ground stakes into the ground.

One final comment:    I considered the FT-991 for my "Studio B" radio trailer 
setup.  It looked appealing due to it's "DC-to-light" band coverage, it's 
built-in sound card, the continuously-variable DSP IF filters (nice for 
digi-modes including my HF APRS-over-VARA operation), and it's ability to 
directly control the ATAS screwdriver antenna.  My radio trailer is intended to 
be powered by batteries and solar power.

I rejected the '991 because of it's rather high power consumption on receive:  
nearly 3 amps while most HF rigs (FT-857, FT-891, IC-706, etc) consume only 
about 1 amp on receive.  If you are boondocking on battery-power-only, this is 
a major issue.  The ultimate power conservation setup would be an FT-818 
"porta-luggie", with an external 5-watt-to-100-watt amplifier.  If you can 
tolerate the tiny front panel of the FT-818, it draws less than 300mA on 
receive. It's actually essentially an FT-857 minus the 100-watt-output PA.  It 
has the same 160-thru-UHF coverage as the FT-857 and looks essentially like an 
FT-857 to CAT control software. However the '818 lacks the auto control for the 
ATAS screwdriver -- the FT-857/897 and the FT-891 do have the ATAS control 
capability.

-------------------------------------------------------------------------------

Stephen H. Smith    wa8lmf (at) aol.com
MS Teams::        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page: http://wa8lmf.net

Live APRS Mapping on HF & VHF
<http://WA8LMF.net/map>

"Studio B" Ham Shack on Wheels
<http://WA8LMF.net/Aliner>

-- APRS over VARA  --
<http://wa8lmf.net/VARA/APRSoverVARA>

----   Sent from my Panasonic Toughbook mobile laptop

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