[Motorola] Installation Tips

[Eric Lemmon]

Dennis,

If you mount the radio units in the toolbox and the antennas on the cab
roof, you must run the coax back through the pass-through and somehow up
through the trim and headliner to the roof.  This can be a lot of extra
effort.   You also should use double-shielded coax for these runs where the
cables are close together for a significant distance.

I have done a number of installations using both locations, and have found
no difference in coverage.  However, I always use gain antennas which have a
least half of the whip above the level of the roof.  Since most gain antenna
designs radiate primarily from the upper half of the whip, there is
relatively little shielding effect from the cab.  I know that this statement
is not universally accepted as fact.  However, I think most radio system
designers will agree that in those cases where the cab shielding of a
tool-box-mounted antenna actually impairs the coverage, such a system is
poorly designed and has an inadequate link margin.  Several commercial
mobile antenna manufacturers make "elevated feed" antennas for just this
situation.  Alternatively, you can install an "antrenna bridge" at roof
level that is supported by tubes insterted into the front stake pockets or
welded directly to the tool box.

The local PD  has motorcycles with low-profile, "hockey-puck" antennas
mounted on the lid of the center equipment box, and they exhibit practically
no directionality- even though the officer's body completely blocks the
radiation to the front.

I still view box-mounted antennas as the "most practical" location.  In my
case,  a gain antenna on the cab roof would exceed the clearance under the
garage door.  However, if you plan to use high-power radios AND are
concerned about EMF safety, the roof location offers the least RF exposure
to vehicle occupants.  Choose wisely.

73, Eric Lemmon WB6FLY

"Dennis L. Wade" wrote:

> I am curious, though, about mounting antennas on the lid.  What do you
> suppose the disadvantage (or advantage) compared to the cab roof would be?