E
F
GH
Fig. E: Drill holes through the spine for the microphones.
Fig. F: Mics and rubber dampers in place.
Glue the cardboard floor to the bottom of the
compartment and give the walls 3 coats of a 50/50
solution of white glue and water. I dried each coat
for about 12 hours, with waxed paper on the top cut
sheet to prevent it from gluing shut, and the whole
thing under weights to keep the pages flat.
Clamp the book between 2 boards using
drywall screws or handscrew clamps. For each
microphone and its surrounding rubber sound
damper, drill a ½" hole through the spine, clear
into the compartment (Figure E). Clean away the
shredded paper and paint the tunnels with the
50/50 glue solution.
HOOK UP, STRAP IN, TURN ON
I used velcro tape to mount the components to the
compartment floor, and before sticking them in,
I slid the microphones with their dampers into their
holes in the spine. Inset the mics about
1" so they
won’t touch the dust jacket (Figure F).
Tidy the wires so that they’re all well within the
chamber and the book can be closed (Figure G).
Test the rig again, put the dust cover on, and you’re
ready to save the free world!
Fig. G: Electronics all tucked neatly inside the book.
Fig. H: Some books are not to be trusted!
Another cool use for this setup is as a covert
2-way communication system. Assemble 2 of
these systems, then you and your fellow agent
can conduct a whispered conversation in a noisy
environment — listening on one another’s frequency
— without sitting together.
LIMITATIONS
The problem with these in-car FM transmitters is
that their range is only about 15'– 20'. The listener
can be in an adjacent room or the room above or
below if there’s no metal blocking the signal.
Sorry about that, Max — you probably can’t tune in
from a car parked at the curb of the subject’s building. For that, you might consider modifying a wireless
lapel mic system, like the ones used by presenters.
David Simpson also wrote “G-Meter and Altimeter” in this
volume of MAKE, as well as “Hydraulic Flight Simulator” in
Volume 12 and “Explosion Engine” in Volume 13.
Make: 91
