@database MTX.guide
@node Main "MTX Transmitter"
@{b}MTX Micro Transmitter@{b}

@{b}Information:@{ub}
Although this project is`nt Amiga related, I thought I`d include it on this
disk. It`s a bugging device which transmits to FM radio. However, @{b}it is an
offence to operate this transmitter in the UK.@{ub}  This @{"project" SYSTEM "PPSHOW MTX.iff"} is to show the
public how a transmitter works and is only for research purposes only. @{fg shine}It
is not to be build under any circumstances.@{ub} @{fg text}I will not take responsibility
for any member of the public breaking the law because of this article.  Now
we`ve got that out of the way, let's move on...


@{b}Circuit Description:@{ub}
The output from the mic is coupled to the base of a high gain
buffer/pre-amp formed around T1 with R1 providing negative feedback. T2
forms the oscillator section with the tuned circuit in the collector and
with a feedback capacitor across the emitter and collector to maintain
oscillation. FM modulation of the carrier is achieved by applying the
amplified audio signal to the base of the oscillator transistor.  The
output is coupled to a simple 1/4 wave length of flexible wire to act as
an antenna via C6.


@{b}Assembly Instructions:@{ub}
Although the MTX uses conventional assembly methods its very small size
calls for a certain amount of dexterity when soldering.  Be very careful to
avoid shorts between adjacent tracks and double check before applying
power.  Assemble resistors, capacitors and transistors as shown on the PCB
layout.

Carefully attach three short pieces of tinned copper wire, resistor
clippings are ideal, to the back of the microphone as shown.  Do not linger
with the soldering iron as the microphone can be easily damaged with heat.

Bend the wires so that they lie flat but do not short out on the metal case
of the mic.  Insert mic into board and solder quickly.  Only one leg of C6
goes through the board and this then lies flat to form the link across to
the collector track as shown.  The other leg of C6 is bent out at right
angles and forms the connection point for the antenna.  Fit the tuning coil
L1 without applying too much heat.

@{b}Setting Up Details:@{ub}
Attach a 70cm length of flexible wire to the remaining end of C6 to act as
an antenna.  Connect the battery clip noting the polarity.  Check the board
for bad joints and shorts.  When satisfied that all is Ok, connect a 9V
battery.  The current should measure about 5-8 mA at 9V.  Turn on a FM
radio and with the volume set to one quarter and the frequency set about
106 MHz place it about 2 metres away with the aerial pointing down.  Slowly
rotate the tuning coil until a clear feedback whistle is heard.

You will probably find about 2 positions which give feed back, but one will
give a more definite feedback, wide and clean sounding. It is now ready for
use.

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@endnode