GSK-715
FM Radio Kit
User Manual
INTRODUCTION
This circuit is an economical FM radio mini-receiver with a built in amplifier.
ASSEMBLY INSTRUCTIONS
Please follow the printed silkscreen on the PCB for
component placement. It is best to add the lowest
height components to the board first: the low
resistant components first and then the higher. It is
important to note the direction of polarity of the
diodes, capacitors, and transistors. Please arrange
them carefully according to polarity before mounting
them on board. Care must be taken when bending
any of the leads. Hold the leads in needle nose
pliers when you bend the leads. Do not bend them
against the case by pushing them over with your
fingers as this can easily break the case.
CIRCUIT DESCRIPTION
This is a very simple circuit built with just a few
components. The integrated circuit (IC) serves as
the core of the functionality for the FM radio
receiver. This allows for a minimal, compact tuner.
The IC is composed of a local oscillator, IF
amplification, quadrature detector, and muting. The
radio frequency (RF) signal from the antenna
passes through C3 into L1 at pin 11 and pin 12. C1
and C2 couple the signal, while C3-C9 and C16-C17
act as a filter of the amplification and demodulator
circuit. Pin 14 of IC1 is connected to the negative
current and pin 4 to the positive. Pin 2 is the output
leg of R2 while C12 de-emphasizes the volume
through C21 to pin 7 of IC2. IC2 amplifies the input
signal and sends it out to the speaker.
R1
0
Ω
TR1
=
=
-
-
-
-
-
-
-
-
-
-
-
-
=
=
=
IC1
=
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TESTING
Turn the variable resistor (VR1) to MIN position.
Connect a 6 VDC power supply to the circuit.
Turn VR1 clockwise to slowly turn up the volume
of the amplifying unit that is connected to it. You
should hear sound from the speaker. Test by
moving the variable capacitor position to where
you hear back-to-back sounds from the radio
stations. Compare with a radio at maximum
modulation to start. If the tuner is idle, test by
adjusting the trimmer until it can catch the
sounds of the maximum frequency modulation
(FM) station.
INSTALLING THE COMPONENTS
+
K
A
K
K
A
A
Watch the polarity
K
A
1
Watch the position
of the notch
2
3
SCHEMATIC
ANTENNA
VARIABLE
ANT
CIRCUIT DIAGRAM
+
L
POWER
A
K
+
1
+
- 6 VDC
Trimmer
L
+
+
MIN VOL MAX
VARIABLE
SPEAKER
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