Topband: 160 Meter Mobile Operations

[zborg]

Hello Top Banders,

I usually just lurk here, but thought I'd share a little info on my 
approach to operating 160 M mobile.

I built a multi-band HF station in a 2006 Toyota Tacoma truck that has 
served me well since 2006 on the top band.  Primary use has been in the 
WA State Salmon Run contest.  The station was built as follows:

I ripped out the plastic storage compartments behind the rear seat of a 
double cab Tacoma and installed a 1/4" Al plate to vertically mount the 
main radio, amplifier and power distribution components.  A second 
glass-mat type deep cycle battery was also installed behind the rear 
seat and linked to the front battery with 00 gage welding cable and a 
200 amp smart solenoid.  The positive run is 200 amp fused on each end.  
A manual engagement switch allows the second battery to be available to 
start the engine or run a winch when needed.  The body was bonded to the 
frame with many braided, tinned 1" flat cables.  This included body 
sub-components and the engine and exhaust system.  The coil-over-plug 
ignition coils were flame-sprayed with a 95/5 Al/Zn at an aerospace 
flame-spray house in San Diego.  Type 31 ferrite suppressors were placed 
on critical electrical systems such as the air bag, active restraint, 
fuel injectors, throttle body servo and computer systems. 

I selected a Hi-Q 5-160RT antenna for 160-10 meters use.  I built and 
potted a remote-controlled vacuum latching relay (Kilovac K43R) to 
select from two different output taps of a W2FMI UNUN (18 and 32 ohms).  
I built an antenna mount for the Hi-Q antenna which is made of two 
layers of 1/2"x2" 304 SS mounted into the rear transfer bar for the 
heavy duty trailer hitch assembly.  There is a turnbuckle between the 
frame and the antenna mount to support the cantilever beam design and 
dampen vibration.  The Hi-Q antenna has a lengthened lower mast section 
and fiberglass struts to provide support for lateral thrust.  The 
antenna uses a Hi-Q quick disconnect mount and military-grade electrical 
quick disconnects for the motor and selsen lines inside the antenna.  
There is also a six inch air-core choke wrapped with about 30 turns of 
RG-213 feedline.  N-connectors were used for all exterior unions to 
provide better weather resistance.  The control line from the antenna is 
suppressed with more type 31 ferrite chokes internally and external to 
the antenna.

The antenna is fed about 600 watts from a Metron MA1000b SS amplifier.  
VSWR is monitored at the amplifier output with a Comet remote sensing 
meter.  The amp is excited with an early vintage Icom 7000 with two 
external small muffin fans mounted on the radio body top to keep the 
class A driver stage cool.  Radio control head is mounted immediately 
behind the stick shift.  Inside the center arm rest, controls are 
located for transformer impedance tap selection, the antenna contactor 
position (a modified Ameritron SDR 100) and the Metron amp.  It is 
relatively quick to change bands and tune manually.

I use a two foot extension above the antenna's five inch coil to a large 
two-dimensional top hat with a three foot whip above the hat for the 160 
meter band.  Overall antenna length is about 11 1/2' long.  The system 
matches perfectly on all bands 160 to 15 meters, with a slight bump on 
ten meters with the Hi-Q.  The 18 ohm impedance tap from the W2FMI 
factory potted transformer (CWS Bytemark Corp.) is only needed for 
operation on 160 meters. 

Many times people have had trouble believing my 160 meter signal was 
mobile (when propagation on the band is good).  Having 600 watts 
available for this band is a BIG help.  The tuning is critical and only 
about 3 kHz wide at resonance for 160 meters mobile with the five inch 
coil Hi-Q antenna.   The VSWR ratio is quite stable when in motion with 
this set-up, as long as you don't transmit under overpasses or next to 
other large metal structures.  The system has been in operation now for 
about four years now without any mishaps.  It is relatively quiet RFI 
wise while in motion (S3 noisefloor typical) and the 7000's noise 
blanker and noise reduction circuitry is most helpful as well.

I hope this description is of some use to the mobile community on top band.

73

Paul WN7T