Tune Up Tune In
workshop
TEACHERS’ GUIDE
REMEMBER
Handle the components gently.
Push them into the board using the plugs.
Never pull a component out by its wires.
Some components MUST be put in one way round only.
Tune Up Tune In
workshop
TEACHERS’ GUIDE
TUNING
Tuning means selecting
one signal to hear.
Aerial
The aerial is a long piece of copper wire
covered in plastic.
There are lots of different radio waves
travelling through the air all the time.
Radio waves travelling through the air
cause an electric current to flow in the
radio’s aerial.
This is picked up by the electrical circuit in
the radio set.
The tuning part of the circuit is needed so
that just one signal is selected.
Variable
capacitor
The dial is the visible bit of the tuning circuit.
The tuning circuit in this radio is made of
a variable capacitor and an inductor. The
inductor and capacitor work together to tune
the radio set.
When the dial is turned, the tuning circuit
is made to ‘resonate’ with different radio
frequencies. When the circuit resonates
strongly, the radio is in tune with a particular
frequency of radio wave.
AMPLIFICATION
The weak input signal needs
to be amplified so the output
signal can be heard.
Transistor
The transistor is an important component
in the amplification part of the circuit.
The transistor has three pins: one where
power enters, one where the original
signal enters and one that outputs the
amplified signal.
In the circuit here, this means that the audio
signal entering the transistor is ‘boosted’
when it exits the transistor. This amplifies
the signal, making it stronger and louder.
Transistors can also act like an electronic
‘switch’. Modern microchips have millions
of tiny transistors on them, arranged to form
tiny logic gates that carry out instructions
from computer programs.
Batteries
These AA batteries provide 3 volts of
electricity to the circuit.
Early radio sets called crystal radios did not
need a separate source of power, as they got
all of the energy they needed from the radio
waves sent by the transmitter.
Electrolytic
capacitor
Like a battery, the electrolytic capacitor
needs to be plugged in the right way round
for it to work. The ridge on the left shows the
positive end of the capacitor.
The electrolytic capacitor does the same
job as a capacitor, but at a much higher
capacitance. The electrolytic material inside
the capacitor makes this possible.
DEMODULATION
Capacitor
The capacitor works with the resistor and
the diode to demodulate the signal.
Capacitors store charge between two plates
separated by an insulator.
Demodulation means
separating the audio signal
from the carrier wave.
Capacitors can hold charge and discharge it.
This can affect the signals in a circuit.
In this case the capacitor ‘smoothes’
the signal. This is part of the process of
removing the carrier wave.
Resistor
The resistor works with the diode and
capacitor to demodulate the signal.
Resistors get their name because they
resist the flow of current in a circuit.
In this circuit the resistor works with the
capacitor to smooth the signal. They work
in parallel.
Diode
In this circuit, the diode forces the electricity
to flow in one direction only.
The diode works with the resistor and
capacitor to demodulate the signal.
The diode takes a signal that is swinging
between positive and negative and chops
it in half. This means only the positive
part remains.
WARNING!
The diode MUST be connected red plug
to red terminal and black plug to black
terminal, otherwise it won’t work.
Your circuit should now look like this...