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IC SUPERHETERODYNE AM RADIO SK-232A
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It belongs to the Popular Science
Series and is tailor-made for electronic science beginners
in junior secondary classes. Through making the radio
you will grasp the basic knowledge of radio theory and
the electric components, and you may also learn soldering.
IC
SUPERHETERODYNE AM RADIO SK-232A You can listen to the
medium wave programs (535KHZ to 1605KHZ) through this
radio. High quality integrated circuit board is used
to enhance excellent sensitivity and tone quality. Such
good performance is maintained by this special high
performance IC, with low power consumption (three no.5
batteries) ensures long battery life. It is suitable
for junior secondary students or above to construct.
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Know more about Radio
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The
device used for information reception is called receiver,
commonly known as radio. Nowadays such device, besides
for commercial radio signal reception, is also used
for receiving visual images and digital data (as in
televisions and telegraphs). Here we would like to
talk about the evolution of radio. Since human beings
discovered that electromagnetic wave can be used for
conveying information, and thus communication, we
strive to advance the communication technology by
improving its reliability, increasing the conveying
distance, making the devices handier and smaller,
and more energy-saving.
The earliest radio is called crystal
radio. Crystal radio cannot perform signal amplification,
its reception sensitivity depends only on the height
and length of the antenna and a good connection to
the ground. The greater the height and longer of the
antenna, the better is the reception, and vice versa.
To improve the sensitivity of radio,
radio frequency (RF) amplification radio is invented
shortly afterwards. It amplifies the RF signals received
before the detection (as in crystal radios) and so
the detected audio signals are much stronger than
the crystal radio, and such reception method greatly
increases the distance of reception that a crystal
radio can perform.
Super Heterodyne Radio
receives the external
signals through the antenna and mixes them with the
internal oscillator signals to produce a new frequency
called the intermediate frequency (IF), and this (IF)
frequency is further amplified and later be detected.
The detected signals will then undergo audio power
amplification before driving the speaker.
Because the super heterodyne circuit
gain its sensitivity by amplifying the intermediate
frequency (IF) which is much easier then the radio
frequency (RF), so the performance is much more stable
and sensitive.
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Circuit description diagram
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Key: Voltage of different terminals
in integrated circuit ULN 2204A:
1:
10V 2: 1.0V 3:
0V 4: 4.5V 5:
4.4V
6:
1.0V 7: 1.0V 8:
1.4V 9: 0V 10:
1.1V
11:
0V 12: 1.9V 13:
4.4V 14: 4.4V 15: 4.4V
Note: The voltage listed above is taken with respect to
ground and
measured by a 20K¦¸/v DC meter.
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ULN 2204A Block diagran
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 The
integrated circuit (ULN2204A) used in the radio is an
AM/ FM radio integrated circuit, in which amplifying
devices, resistors and other components are included.
To produce a hi-tech radio with excellent performance,
what you need is to add some tuning capacitors and a
coil for station tuning.
Operation Description:
The antenna
tune circuit consists of ferrite bar antenna (L1) and
the variable capacitor (VC1B), resonates with the radio
station to be picked up, provides the selectivity for
radio stations. Suppose the frequency of a radio station
being F1, and it connects to pins no. 6 and 7 of IC1.
Coil T1, capacitor VC1A and pin 5 of IC1 form an oscillator,
which generates frequency F2 (the local oscillator frequency).
The signals of F1 and F2 are mixed internally and two
new frequencies (F1+F2 and F1-F2) are then generated,
in which F1-F2 is the intermediate frequency that we
use (455KHZ), and intermediate frequency transformer
T2 resonates at such frequency. The chosen intermediate
frequency is then connected to the amplifiers in IC1
for further amplifications; and then passes through
T3 to the detectors inside IC1 for detection, then is
out from pin 8 of IC1. This audio frequency signals
are very weak and must be further amplified by the audio
amplifier in IC1 after being selected by the potentiometer
VR1, and further amplify to drive the 8¦¸ speaker.
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