Eric,

I am a consultant for an AVL (automatic vehicle location system)
system used by the Southeastern counties of Michigan. The system is
used on winter maintenance vehicles and works on 900 MHz. The
vehicles are often stored overnight in metal buildings where it is
difficult to obtain transceiver communication from the AVL system. Is
there a low cost (possibly passive) way to port 900 MHz radio
transmissions into these buildings?


The most basic passive repeater is simply two antennas well-matched to
the lowest-possible-loss coax. Many years ago I experimented with such
repeaters optimized for specific VHF and UHF television channels and for
144 MHz amateur radio.

I'm assuming that your vehicle location system doesn't require a GPS on
the vehicle, since you didn't mention it -- which probably means that
your system requires the vehicle transponder to communicate with a
couple of base stations.

That means that the _outside_ antenna would have to be omnidirectional,
or, possibly, to provide some gain in the direction of the base
stations. It's possible that even if the outside antennas had to be
omnidirectional, they could be some form of stacked collinear array and
provide gain.

However, your _indoor_ antenna could probably be substantially more
directional -- pointing at the location where the vehicle is to be
parked-- and offer a substantial amount of gain.

If there is sufficient signal strength to and from the vehicle for the
system to function outside the metal building, making the system work
inside the building should be possible.

Northe
N6KO
Green Valley, AZ