Description
We have some other Radio Transmitter circuits of your interest;listed below:
The use of transmitters which have a more powerful output than the ‘flea-power’
are sometimes required when there are many obstacles in the path of
the surveillance transmitter and monitoring station receiver, or
the distance between them is too far so as to make a low powered
device feasible. Whereas a typical micro transmitter will produce an
RF power in the order of just a few milliwatts, i.e. a few thousandths
of a watt, the VHF-FM transmitter described has a power output of
between around a half and 2 watts, depending on the power source, which
may be anywhere between 6 volts and 30 volts d.c. The battery or
batteries should be of the alkaline high power type, since the current
drain will be found to be relatively higher when compared to
microtransmitter current drain. The power output of this device
is somewhat proportional to the current drain and so therefore both may
be decreased by altering the value of R6 to a higher resistance, or a
variable resistor with a value of around 1k may be introduced in series
with the existing R6, so as to give a variable power output. The variable resistormust
not be a wirewound device because this would act as an inductor which
will cause feedback problems.The audio input to the power oscillator,
which incidentally is formed by TR2 and associated components, is
derived from a piezoelectric microphone which drives the simple audio frequency amplifier
TR1. The input of the audio amplifier is controlled by the gain pot R1,
which selects the correct amount of voltage that is generated by the
piezoelectric microphone, then connects this signal to the base of audio
amplifier TR1 via C7. It may be found that there is insufficient
housing space for a bulky piezoelectric microphone, so with a slight
modification to the circuit, it is possible to employ an electret
microphone insert as shown. Since the RF field that is generated by this
transmitter is relatively large, the problem of RF feedback may very
well be encountered. This may be overcome by placing the transmitter inside a metal enclosure, keeping all internal wiring as short as possible and the aerial wire.
Component listing for 1 watt transmitter
Resistors Semiconductors R1 = 27k TR1 = BC547 R2 = 330k TR2 = 2N2219 fitted with heat sink R3 = 5k6 MIC = piezoelectric microphone R4, 5 = 10k R6 = 100R
L = 6 turns 22 gauge enameled wire wound on 3⁄16″ former
Capacitors
C1, 2, 3 = 330 pF C4 = 2–10 pF trimmer C5 = 4p7 C6 = 1 nF
C7,C8 = 40uF/25V Electrolytic
Circuit diagram for Long range FM Transmitter
We have some other Radio Transmitter circuits of your interest;listed below: