photo 1
On the radio opposite, there is no variable tuning capacitor, so the
most powerful station wins. Be careful, a good antenna
(>20 m) and a good ground are needed to pick up a distant station. The absence of a tuning capacitor must have made it
an entry-level radio. That said, there were probably fewer stations than today
fig.1
fig.1 
fig.2
A block diagram (fig.2) gives an idea of how the radio is used.
Reception is sought by «tickling» the tip of the spring on
the piece of galena clamped by a tightening screw. The Mikado capacitor of
0.2/1000th of µF (0.2nF), filters the "high frequency" residue
favoring the audible signal. One of the two coils is mobile. When
it is moved away from the fixed coil, selectivity is increased: transmitters that are too close are better separated.
A look at the signals
The devices are shown below. To make the signals visible, the radio is driven not
by an antenna but by an RF generator set to 370KHZ and modulated at 1100Hz. To better simulate the real behavior, a dipole called
In the last figure, detection has taken place. The HF residue will be filtered by the capacitor in parallel with the headphones.
dummy antennais placed between the generator and the antenna input of the crystal radio.
In the last figure, detection has taken place. The HF residue will be filtered by the capacitor in parallel with the headphones.
The characteristic detection of galena is observed. It is the asymmetry of the Voltage/Current function that makes this possible.
The galena crystal and
the point can be assimilated to the following
diode/resistors circuit:
Amazing detectors
Since a strong asymmetry of the U/I curve is sufficient,
rather bizarre detector setups have been experimented with: here a razor blade
and a safety pin as a point.
