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2001 Mitsubishi Galant ES with DK3 Screwdriver HF Antenna
Early HF mobiling
Prior
to attending college in 1978, I had a Heathkit HW-101 that I had used
as a Novice and then as General class. When I decided to trek off to
college, I wanted to keep operating on HF but living in an apartment
left little chance of actually operating fixed at home since there was
no place for an antenna in the first place I had. As most of the old
timers know, radios back then weren't just tap in 12VDC and away you
go. Between college workload, after school part time job and homework
to be completed left very little time for operating so it was a bit
before I hit on the idea of operating mobile. By that time I was
working at the Heathkit store on Ross Avenue in Dallas, Texas, close to
where I lived. With a nice employee discount, I eventually owned (and
still do) many fine Heathkit amateur products, one of them being the
HP-13 DC-DC converter for the HW-101 radio. Combining the HW-101, HP-13
and a Hustler mobile setup with a few monoband coils, I was up and
mobiling away. This was really nice since this was many years before
cellphones and with a somewhat limited income from a part-time job,
being able to communicate on 40M with my parents who lived 225 miles
away for free was great (yes I know I had to buy the gear).
I have used to following HF mobile setups in different vehicles over the last 25 years or so:
HW-101 w/ Hustler monobanders
SB-1400 (FT-767GX clone) w/ Hustlers
SB-1400 w/ Spider 4 bander
TS-440S/AT w/ Spider 4 bander
FT-100D w/ ATAS-100
FT-100D w/ DK3 fullsize screwdriver antenna
Current HF mobile setup
I was a bit disappointed in the results
I was seeing with the poor band conditions of late and using the Yaesu
ATAS-100 mini screwdriver antenna on my Mitsubishi Galant. I decided I
wanted to get a full size screwdriver antenna but there just isn't too
many places to mount such a large antenna on a Japanese mini car.
I
did some
analysis and exploring of the frame structure (or should I say the
unibody structure - not much of a frame). I found that there were two
large bolts on either side of the car backend holding on the rear
bumber
assembly. As luck would have it, since the desired side to mount the
antenna was the drivers side to help avoid street side low limbs, etc.,
and of course
being an import, the exhaust was also on the drivers side. That
forced me to look at the passenger side to mount the antenna.
Not being sure what sort of ground
I could get there, I decided to just use the point as a physical
mounting spot and run short 1/2" braid to the actual ground points. I
designed and welded up a simple but effective mount to attach at the
bumper bolts and extend out past the bumper enough to allow an antenna
support to be installed on the mounting arm. Since I wanted to get the
antenna as high as possible but not extend the top tip too high as to
be illegal (13.5' is DOT legal max height), I needed to raise the
attachment point up from the mounting arm. I used the trick described
in the Don Johnson, W6AAQ "40+5 Years of HF Mobileering" book and used
3/4" Type M copper pipe with 1/2" to 1/8" MIP adapter sweated
(soldered) onto each end. The 1/8" MIP threads closely match the
standardized 3/8x24 antenna mounting studs. This put the base of chosen
screwdriver antenna at 21" above the road, which should provide decent
ground losses to an effective antenna system. Here are some photo links to the mounting I made and used.
PHOTO1 - shows mounting under trunk lip to stabilize lower tube body
PHOTO2 - shows the same mounting with trunk lid shut. I used a small hinge to allow quick disconnection of mount
PHOTO3 - shows the 12" copper tube riser pipe under the lower antenna body and wiring closeup
PHOTO4 - shows full antenna mounted from rear of car
PHOTO5 - shows full antenna from right rear side of car
PHOTO6 - shows full antenna from left side of car closeup
If
you haven't read Don
Johnson's trio of HF mobileering conpendiums, I highly recommend them.
Lots of facts and ideas to play with. Two of Don's three works are
contained on the "WorldRadio 2000 Archive CD" which is available at
this writing for $24.95 from WorldRadio magazine. For the active or future HF Mobileer, this could well be the best money you'll ever spend.
While conceiving a mount for the
Mitsubishi Galant (why don't car manufacturers hire any hams for their
design teams?!?!?!?!), I started looking at different screwdriver
antennas on the market. Needless to say the sky is the proverbial
limit. I found units from a couple of hundred bucks to upwards of $1K
for all the trimmings. Being a ham who likes to 'roll my own' or at
least as much as possible, I found the DK3 screwdriver antenna from Don
Johnson W6AAQ (incidently Don designed and built the original
screwdriver antenna in 1991 - almost all other units on the market are
a direct pirated copy or a enhanced redesign of the original). At this writing, the DK3
is marketed for Don by Doug Huston KC6FRY at STARFIRE TEC
for $175 plus shipping. Don/Doug refer to this antenna as a 'ready to
install Heathkit' meaning the antenna portion you buy is completed
ready to install, but it is only the central portion of a 'Heathkit'
style antenna. You must supply the mount, wiring, motor control
switching method for
tuning and a top whip (66 inch is recommended for 3-30Mhz coverage
although with 66" I could only get as high as 25Mhz. I may need to lop
off a
couple of inches to get to 10M. Not too much as or you'll never get to
80M. Kind of a compromise between the ends. With 66" top whip, I have
about 2" of coil travel left for 75M phone band. Probably would need
about 75"-80" for full 75M/80M coverage but then maybe no 10/12M???
Anyway I didn't have a problem
with designing, building and installing the reset of the system from
scratch. If you aren't handy with tools maybe you should reconsider HF
mobileering with a screwdriver antenna. I recommend that you at least
take a serious look at screwdriver antennas if you plan on operating HF
mobile regardless of the actual antenna you may eventually build or buy.
To control the antenna movement, 12 V is
switched to the screwdriver motor inside the antenna. One polarity
raises, the other lowers it. Myself, not being one for simplistic when
gold plated is better - isn't it?, decided to make a few tweaks to the
basic center loaded momentairy switch idea. I added your basic ON/OFF,
a speed control (NORM/SLOW) with Normal mode applying the full 12V and
Slow mode adding in a 3 ohm 25W ballast resistor to limit the current
therefore slowing the motor to appx 60-70% of Normal speed for
finetuning the SWR. And of course I had to have the customary LED
indicators for speed and direction. Click here for control panel layout. Here is the schematic of my controller box (In JPEG format)
Tuning is realtively easy - maybe not as
easy as the ATAS-100 tuning - it's not single pushbutton but close.
Raise or lower antenna listening to RX audio.At peak, stop tuning,
switch the FT-100D meter to SWR and inject an AM carrier. Check SWR and
in SLOW mode, tweak antenna for low SWR (3 or less bars on FT-100
meter). Done!!!
I have noticed that the signal levels I am hearing (on the
average) are about 2 S-units better than the ATAS-100 I had on the car
before.
Final Touchups
Finally
got a tube of Penetrox (conductive grease) and pulled all ground
connections. Cleaned each one and made doubley sure all paint and dirt
was cleaned away to bare metal. Applied a good coating of Penetrox and
retightened all grounds secure.
While
the antenna was removed from the mount, I touched up the paint job on
the lower mast that had gotten chipped and marred during the trial
fittings of the upper support arm. The final paint dried and the
antenna was reinstalled and the cabling was reattached and redressed.
The fiberglas whip in the original photos was replaced by a surplus 67"
stainless steel whip like those used by the CHP a few years back for
lowband VHF communication and a Hustler QD-2 Quick Disconnect.
I
wanted to keep the ability to quickly disconnect and remove the antenna
for storage. If you look closely at the photos, you will notice that
all thats required to do this is: Disconnect coax connection
Disconnect motor control cable
Disconnect ground braid connections
Lift antenna off mount
Here are some pictures of the final installation.
PHOTO7 - Rearview of car with final install and steel whip
PHOTO8 - Side view closeup of mounting
PHOTO9 - Close up of reworked cabling and RF ferrite cores to reduce screwdriver motor hash
Dimensions of my installation:
Ground Level to Bottom of Lower Antenna Mast = 22"
Length of Lower Antenna Mast = 36"
Length of QD2 = 2.75"
Length of Upper Mast = 67"
Short Length (no coil extension) = 22" + 36" + 2.75" + 67" = 127.75" = 10.65 ft.
Full Length (16" coil extension) = 127.75" + 16" = 143.75" = 11.97 ft
If you have any questions about my installation or the performance of the DK3 antenna I use, feel free to email me
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