INTRODUCTION

This telephone "bug" is simply a small, low-power FM transmitter that
transmits in the upper part of the FM broadcast band.  Power is taken 
from the phone line itself.  Any FM broadcast receiver can be used to 
receive the signal from the "bug".

The idea of this kit is to allow you to build a simple low-cost 
telephone transmitter for personal hobbyist use.  It is not intended 
for use as means of gathering evidence or for unauthorized 
eavesdropping.  It is similar to kits offered by a number of kit 
retailers.

The design uses surface mount technology (SMT) devices.  The PCB has 
been intentionally designed larger than necessary with oversize pads 
to ease assembly.  The kit includes extra SMT parts to allow for 
mistakes and some silver solder for soldering the components.  This kit 
provides an excellent way to get started with SMT.

OPERATION OF THIS DEVICE IS COVERED BY PART 15 OF THE FEDERAL 
COMMUNICATION COMMISSION'S RULES.  OPERATION MUST NOT INTERFERE WITH 
TV OR RADIO RECEPTION.

THE USER IS RESPONSIBLE FOR ALL ASPECTS OF THE USE OF THIS 
TRANSMITTER.


THEORY

This transmitter is a simple voltage controlled oscillator (VCO).  The
output frequency of a VCO at any instant depends on its input voltage. 
Telephone line voltage is applied to the oscillator through full-wave 
bridge formed by D1-4.  Small variations caused by audio cause the 
frequency of the VCO to vary, thereby frequency modulating the output.

The transmitter goes in series with either side of the phone line at 
any phone.  Only that phone will activate the transmitter when it is 
picked up.  Placing the transmitter at the incoming phone line will 
cause it to be activated when any phone is picked up.


ASSEMBLY

Use the parts layout diagram to place and solder the components on the
PCB.  Orientation is important only for the diodes D1-4 and the
transistor Q1.  Note that the capacitors are not marked and must be 
kept sorted until assembly.

Soldering SMT components is easier than you might think.  The key is 
to get one leg of the component tacked and then solder the other 
leg(s) well.  The return to the tacked leg and resolder it well. 
Components can be held in place with a toothpick or tweezers.  A trick
for picking up and initially placing components is to rub the end of a
toothpick on the sticky part of a "Post-It".  This sticky end can then
be used to pick up small components and place them until tacked.

The antenna can be any length of wire connected to the pad labelled 
ANT. Try 5-6" to start.  In general, the longer the antenna, the
farther the transmission.


HOOKUP

Hookup is trivial.  Simply place the transmitter in series with either
side of the telephone line at the LINE connections.  Place an FM radio
nearby and tune it to a "dead" spot in the upper third of the band. 
Take the phone off-hook and tune L2 with a tuning tool until a busy signal 
is heard throuh the radio.  Start with the tuning slug in the middle of the
coil.  It is preferable to use a non-metal tuning tool (Radio Shack has a 
3-piece kit for 99 cents - 64-2220).  You can use a metal Allen wrench, but 
the frequency my jump when you remove it.


TROUBLESHOOTING

Since this kit uses SMT devices, the output frequency isn't affected by
variation in lead lengths.  Other factors can, however, affect the output
frequency.  With the coil tuning slug in the middle and the phone off-hook,
tune your radio throughout the FM band listening for the busy signal.
Tuning can be touchy because the tuning tool and your hand holding the
transmitter cause variations in the frequency.  On the other hand, the bug
transmits a pretty broad signal that is easy to find.  Sometimes you will
hear the signal at different points along the FM band, simply pick the
strongest one.  The transmitter tends to drift as it warms up - usually the
output frequency drops slightly as warmup occurs.