WA8LMF Home Page | Main Ham Page |Updated 20 December 2009

 

 

WA8LMF 2006 Jetta TDI Mobile Installation

CLICK HERE for 2005 Prius Install Details

The photos below show the radio installation in my 2006 VW Jetta TDI sedan.  The hardware consists of a Kenwood D700 2M/UHF APRS transceiver, a Yaesu FT-857 HF/6/2/70CM transceiver, a Hi-Q Antennas Hi-Q-2.5/80 RT-S remotely tunable "screwdriver" HF antenna for HF + 6 meters controlled by a modified W4RT "Antenna Boss" (warning deep-links into framed web page), a Comet SB-14 6-2-70cm tribander antenna, a Panasonic Toughbook mobile computer running APRS and mapping software, and various other hardware. 

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Panoramic Interior View of VW Jetta Hamshack
Exterior View of Jetta TDI sedan showing the mobile antenna farm.
The Hi-Q "screwdriver" tunable HF antenna uses the typical 3/8'-24 HF mobile mount stud, but it is actually mounted to a super-heavy-duty reinforced NMO mount with a home-made NMO-to-3/8" stud adaptor.  In town, a 6M/2M/UHF antenna is mounted directly to the NMO mount. On out of town trips, the HF+6 screwdriver antenna takes it's place on the same mount.
 

Screwdriver-type antennas require that DC power to run the tuning motor (inside the lower part of the antenna) be supplied to the part of the antenna that is hot with RF. Note the ferrite choke and string of ferrite beads on the motor control leads of the antenna to prevent the power leads from shorting RF to ground.

The combination of two sets of ferrites ensures effective broadband RF choke action from 160 meters through 6 meters. The large core with several turns of wire through it is made of a ferrite mix optimized for maximum effectiveness on 1.5 through 15 MHz.  The string of small beads are effective over about 10MHz  to 100 MHz.  (The large core alone starts losing it's effectiveness as an RF choke above 10-15 MHz, as capacitive coupling between the turns of wire start bypassing the inductive effect of the wire windings.)

Mobile Office Table - Generation II
The table assembly that supports the laptop computer is a combination of a homebrew monopod mast assembly, a commercially-made swing-arm assembly from RAM Mounts, and a homebrew table-top cut from 3/16" aluminum plate.

RAM Mounts makes an almost infinite variety of ball-joint and swing-arm mounting systems to support practically anything (radios, laptops, GPS & satellite radio receivers, cell phones, etc) in any kind of vehicle. Some of the pages of individual parts that can be mixed and matched to build custom mounting systems are here.  A good mail-order retail source for RAM parts is GPScity.com .
Animated GIF image showing how the table is very adjustable.  The sequence starts showing the table parked over the center console so that a passenger can easily enter or exit. The next three frames show the table in it's customary position partly over the passenger's lap after they are seated. Note how the table top rotates to face either the driver or passenger. The last several frames show the swing arm extending to place the computer squarely in front of the passenger. WARNING:  This is a large (1400K) file.  Even on a fast broadband connection it will take time for all 8 frames of this animation to load. Once loaded, the 8 frames will loop endlessly IF you don't have ad-blocking software (such as Zone Alarm Pro or Adblock for Firefox) stopping animated (multi-frame) GIFs.
The mast supporting the swing-arm is made of 1" water pipe and pipe flanges bolted to a horizontal 1/8" steel bar sandwiched between the floor and the underside of the left-side passenger seat mounting rail. I drilled holes in the bar to line up exactly with the existing seat rail mounting bolt and tab. Amazingly, I got the holes in exactly the right place on the first try. Here are the pieces before assembly.
The lower part of the mast after installation. All I had to do was remove the seat rail mounting bolt, slip the bar under the rail, and then re-insert the bolt.  The bar is stiff enough that the table top only moves about 1 inch. The matte black plate in the lower left of the picture supports the Kenwood D700 under the passenger seat.
View of the entire mast assembly with Ram Mounts ball joint on top, before the swing arm and table top are installed,
Ram Mount swing arm assembly in place on top of the mast.  Note that this is installed upside down. Normally, the ball joint is at the top of the swing arm, under the table top.  My mast isn't perfectly vertical, due to the slope of the car's floor pan. I placed the ball joint at the bottom so that I can then adjust the axis of rotation of the double swing-arm to be perfectly vertical.
Home-made aluminum table top in place. I punched two 1-3/4" inch holes in the plate and mounted two small 12VDC fans from laptop computers underneath the holes to force cooling air against the underside of the laptop computer. A double-pole double-throw center-off toggle switch is wired to connect the two fans either in series or  parallel. In series, the 12-volt fans run on 6VDC each and draw a total of only70mA. They still move a surprising amount of air absolutely silently. In the parallel mode, they draw about 200mA, create quite a blast of air and are definitely audible. [This is the extreme climate mode for when the APRS gear is left running in a closed and locked car in Phoenix, Las Vegas, etc in the summer time.]

Other Interior Hardware
Mobile Mike Hangers.   A 1/16" thick aluminum plate with outdoor carpeting glued to it stuck in the pocket on the back of the passenger seat.  The back of the hand mike and the Kenwood VC-H1 handheld SSTV device are covered with Velcro hooks which stick very nicely to this carpeting.
View into passenger footwell area showing my homebrew system integrator console. This device provides switching to share a single hand mic, the Kenwood VC-H1 SSTV handheld SSTV device, and a TigerTronics Signalink sound card interface to any of three different radios. It also contains a video title generator for overlaying live SSTV images with text, and an opto-isolated serial port splitter to provide 4 separate isolated serial outputs from the Garmin GPS18 GPS. It also contains a Tigertronics TigerTrak configured for 300 baud 30M HF APRS, a 1200 baud TinyTrak for Mic-E bursts after SSTV LiveCAM transmissions, and several Astrodyne DC-DC power converters to provide ground-isolated DC to the VC-H1, the LiveCAM TV camera, the title generator and other hardware.

In two previous mobile installations, the "systegrator" box was wedged between the left side of the passenger seat and the center console with the knobs and switchs conveniently looking straight up and easily reached.  In this car, there is barely 1/4" clearance between the seat and the console; the box just wouldn't fit there.

Two amplified GE mobile speakers are Velcroed out of sight to the far forward carpeting.

The digital volt-amp-watthour meter in the foreground on the floor is a useful gadget available from PowerWerx.COM.  The meter is terminated with PowerPoles on each end. it can be plugged in from one end only to a PowerPole-equipped power distributor to monitor voltage.  Or it can be placed in series between a power source and a load (such as a radio) to monitor voltage, current drain, accumulated amp-hours and accumulated watt-hours.  All these quantities display alternately on the LCD screen on the device.  Called a "Watts Up" meter, the details are here. 
Audible SWR Meter. Located on the rear deck, this audio meter reader is based on the "Swailer" published in the January 1986 QST. This device was originally intended as a transmitter tuning aid for the blind.  I have it connected across the reflected power pickup in a Kenwood SWR bridge. It produces an audio tone proportional to the reflected power from the HF antenna. I can tune the Hi-Q screwdriver manually entirely by ear without watching the SWR meter.

You just flip the transmitter switch and push the up or down buttons (located on the homebrew remote control box next to the parking brake in the big picture above) until the tone drops to the lowest pitch. The reader is powered only in manual tune mode, so the rather raucous tone doesn't come on during normal operating or while in autotuning mode. 

Trunk Area Installation
View looking into the Jetta's trunk.  The radio and power distribution hardware is mounted to aluminum plates which are then stuck to the fuzzy trunk carpeting on the back of the rear seats with the hook half of heavy duty "Velco Extreme" fasteners. The aluminum flashing at the very top center of the picture is the ground strap from the HF antenna mount in the center of the trunk lid.
Closer up view of the two mounting panels. The black box at the left top is the main chassis of the Yaesu FT-100 (since replaced by the similar-sized FT-857) transceiver. The zinc box below it is my repackaged W4RT "Antenna Boss" screwdriver controller.
DC Power Distribution.   The zinc box at the top right contains a 12VDC-to-5VDC isolated switching-mode power converter that powers the Garmin GPS-18. The net current draw of the GPS at 12 VDC is only about 40mA -- normally I leave it on 24/7 so it's always in lock and ready to go.

The "Chargeguard" is a programmable timer-controlled switch that senses engine-off voltage drops. It allows my thermoelectric ice chest to continue to run for two hours after parking, and then shut off before the batteries are drained. This is more than enough time to keep the cooler running during rest stops, lunch breaks etc. but will turn it off if I forget about it overnight.  

The blue box is a Tripplite 375 watt DC-to-110VAC inverter, handy for running a soldering iron or computer printer in the field.

The black finned box at the bottom of the stack is a Hellroaring Technology power FET battery isolator. When the engine is running, it connects a second 12VDC battery to the car's charging system with less than .05 VDC drop.  When the engine is shut off and the battery voltage drops below 13VDC, the FET switch automatically opens and disconnects all the radio and computer gear from the main (starting) battery. A panic switch can force the isolator to turn back on if the main battery needs a boost for starting.
Although the car is a sedan, the rear seat backs fold down like a station wagon or hatch back. This makes it very easy to work on the hardware without having to reach all the way to the front of the huge trunk from the rear opening. 

With the seat backs up, the center armrest folds down to open a hole from the trunk through the center of the rear seat back. VW intended this for carrying skis, but it's very handy for base station whips, mast sections, pieces of PVC pipe, etc. You can fit full 10' sections of masting through here from the trunk up to the dashboard if needed.
Battery and Charger Assembly.   The second battery is an Optima SpiraCell Yellowtop deep cycle barely visible under the plate holding a 110VAC to 13.6VDC 25A switching power supply. The supply provides "shore power" to allow the computer and radio gear to run indefinitely while parked. The cord reel originally had 25 feet (~7M) of 14-3 orange heavy-duty cable in it.  I repacked it with 75 feet (~22M) of 16-2 zipcord which is more than enough to handle the 300 watts max that the power supply draws at full load.  It is also long enough to reach into motel rooms, mountain top radio site shelters, or to a generator far enough away to keep the acoustic noise down.
Underside of trunk lid, showing the ground strap and an EMI filter used to prevent RF from the HF antenna from following the screwdriver's DC motor power leads into the trunk interior.  Note reflection of antenna with capacity hat in rear window glass.