Conrad Course material 10090 14 years and over 10090 Manual De Usuario
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10090
The Integrated Circuit
Now the most important component of this radio is built, an integrated circuit (IC) type TA7642. The
IC has a plastic housing like the transistor and also three connections. Observe the other direction
when installing. The flat, labelled side points to the board's minus side.
The function of the radio IC can be imagined simplified as amplifier, similar to a transistor. In fact,
the IC contains many transistors, resistors and capacitators, however. The central connection is the
amplifier input.
Another resistor at 100 k
Ω (brown, black, yellow) services to let a small input current flow, similar to
the base resistor of the transistor. This current then can be amplified and reduced by low radio
signals. The changes are amplified and made audible.
Touch the input with your finger. You will probably hear a hum, buzz or prattle. Operation of a light
switch in the room should be audible as a cracking sound. The circuit therefore is already a simple
high-frequency receiver that is able to take up radio interferences.
signals. The changes are amplified and made audible.
Touch the input with your finger. You will probably hear a hum, buzz or prattle. Operation of a light
switch in the room should be audible as a cracking sound. The circuit therefore is already a simple
high-frequency receiver that is able to take up radio interferences.
A LF Low Pass
Install a ceramics disc capacitator with 100 nF (print 104). This capacitator has no polarity and may
be used in any direction. It is now installed as low-pass filter and leads to high-frequency signals (HF)
at the output of the receiver IC being suppressed and signals in the audible range (LF, low frequency)
being retained. Demodulation inside the receiver IC delivers the NF signal that was modulated onto
the HF signal of a transmitter. Although the device is far from being done, you may already listen to
the radio now with a little luck. If there is a strong station nearby, its signal will likely be enough to
be received. Your body serves as aerial. A long wire works just as well. Put the speaker on the sound
opening of the casing so that it can serve as speaker box.
The sound becomes louder and fuller. Later, the board should be installed in the casing. At the
moment, however, open experiments on the table are more comfortable.
The Receiver Coil
The small coil with 220 micro henry (µH; black sleeve) has thin copper wire that is coiled onto a coil
box of ferrite and connected to the two connection wires. The coil is covered with a plastic sleeve.
Install this coil at the receiver input. It short-circuits LF signals so that only HF signals get to the input.
Reception interferences are suppressed. The coil acts as a filter. Another capacitator with 100 nF is
used as coupling capacitator and lets HF signals get to the input without discharging the input direct
current. Again, a touch of your finger may replace the aerial. Your local medium wave station will be
received even more clearly now.