FM Band Monaural Transmitter

A high quality monaura FM transmitter is quite useful in a variety of applications. The
audio from a TV or entertainment system may be transmitted for remote or portable
listening and for wireless earphone listening. The audio from an AM receiver placed near
a window can be retransmitted within a metal building where AM reception is not
possible. Two transmitters will convert two portable FM receivers into cordless stereo
speakers for outdoor events. A keyboard may be played through the stereo without wires
simply by tuning in the transmitter. A child wil love an operational, miniature FM station
complete with transmit "on the air" light. Simply connect the stereo's monaural output to
the transmitter and transmit CDs, tapes, microphones, and other audio sources. Connect
the transmitter to the computer's sound card and have big speaker sound. Even silence
may be transmitted. Tune the transmitter to your favorite station and when the annoying
commercial starts, simply flip on the power and... silence (or the audio of your choice).

Ideas:
1) Use ground plane construction. Solder the ground connections directly to the copper circuit board material and keep the RF
leads short.
2) Add a 680 ohm resistor in series with an LED to make an "on the air" light.
3) Leave the transmitter on when not in use to eliminate warm-up drift. Use a jack for the antenna so that it may be unplugged
when not transmitting.
4) A lower voltage regulator may be used to regulate a lower voltage molded supply.
5) Bypass the 100 ohm resistor in the 2N4401's emitter with a 470 uF capacitor for greatly increased audio gain. Also remove
the 33 ohm resistor and use a 100k pot for increased sensitivity. The entire audio stage may be replaced by an op-amp biased for
V/2 volts on the output.

4 Transistors Tracking Transmitter

DESCRIPTION:

This tracker works with your regular AM/FM radio or car stereo. Car stereo would be best because it is designed to perform optimum in all conditions.

Real distance is unknown at this time because I never measured it accurately but guess about 300 feet (100 meters). The reception of the signal also depends on the surroundings like tall buildings etc. Most likely the best performance is optained with line-of-sight.

If you can somehow use a longer antenna and beef up the supply voltage to 12V, the performance will be a lot better, just make sure the electrolytic capacitors have the correct working voltage (25V) 1/8" (" = inch) is approximately 3.5mm. 22 ga (USA gauge) is approximately 1.5mm. Antenna: 10 - 12" is approximately 25 to 30cm. A "Non-conductive" core means: wooden dowel, plastic, paper, etc.

47K means 47,000 ohms. The 'K' stands for '1000'. C2/C5: .001uF is the same as 0.001uF or 10nF (nanoFarad). A 'trimmer' capacitor (C3) is an adjustable air capacitor (available everywhere).

The 'ground' symbol shown at the end of Q2's emitter (e) is the negative side of the battery supply.

This circuit belonged to the collection of Art Swan's "Circuit Land".