W5TOM Invisible, Top Down,

2 Meter 440 Installation.

How to have a VHF UHF rig installed in a car that is always parked with the top down.

Here is the completed installation.  Nothing to steal here.


    Anyone can install a 2 meter/440 rig in a car, lock it up and be reasonably sure that it won't be stolen.  The challenge was to have an installation that won't be stolen when the car is parked with the top down.  It had to be invisible.  In a Miata, it had to be hidden under the seat, there is no other place.  Since the steering wheel makes it very difficult to reach under the seat with the door closed, and the alarm goes off when the door is opened, the only place is pretty safe.  Also thieves generally don't steal things they can't see.  The small quarter wave antenna is the only give-a-way.  Today CBers don't steal antennas anymore, and with cell phones and the like, weird antennas are pretty much ignored.  I leave the cover on the cigarette plug open so the intelligent thief (oxymoron) will think that the radio is in the trunk.

This is what's under the seat.  It is all tywrapped together.  Just attach the antenna and power.  A handie talkie was used because a speaker/mic was needed, and the conventional mobile rigs can't use one. Initially I was using the speaker/mic, but the road noise made it hard to hear and shift gears.  I then added an ear bud that plugged into the mic.  I could hear well and the mic didn't pick up much of the ambient noise.  The best was an "earbone" mic with a finger PTT.  I bought one from MFJ for $35 and it worked great for the set up, but the TX audio was lousy.  After returning it, I purchased a professional "earbone" set up that should be here soon and make the installation complete.


The power cable has a quarter with a hole (cheaper than a brass washer) for the ground connection and a .005 shim for the fuse box.. The "washer" chassis ground was bolted under the seat rail mount.


The shim is attached to the fused side of the auxiliary (cig plug) fuse.  When the ignition is turned on, it becomes hot.  The amp and the rig draw 6 amps in high power.  The .005 brass shim is connected to one side of one leg of the mini blade fuse.  I was concerned that it might get hot with the 6 amp current.  Testing revealed no heating whatsoever.  I was also concerned that the initial surge of voltage, or an inductive spike might harm the rig.  Well, modern cars full of electronics worry about the same thing, so a relay disconnects the auxiliary circuit when starting.  No problem here. 


This is the schematic of the installation


Here you can see the 3 1/2 inch mag mount with the thin wire home made 1/4 wave antenna.   The path from the mag mount to the amp was difficult.  I had to weave the coax around the top mechanism and then behind the seat.  The coax was attached to the underside edge of the top well with heat glue.  I hope the ideas used in this project will be of some help, and maybe result in an installation you might not have before considered.  There is always a solution.  Please note my great wax job.