One Transistor Radio


Here is a simple circuit
for a one transistor Audion type radio powered by a 1.5 V battery. It
employs a set of standard low-impedance headphones with the headphone
socket wired so that the two sides are connected in series thus giving
an impedance of 64 Ω. The supply to the circuit also passes through the
headphones so that unplugging the headphones turns off the supply. Using
an Audion configuration means that the single transistor performs both
demodulation and amplification of the signal.

The sensitivity of this receiver is such that a 2 m length of wire
is all that is needed as an antenna. The tap on the antenna coil is at
1/5th of the total winding on the ferrite rod. For details of the
antenna coil see the article Diode Radio for Low Impedance Headphones.
This circuit is suitable for reception of all AM transmissions from
long-wave through to shortwave.


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