Set 3

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This receiver uses a loop antenna, which is a large coil.
The coil picks up energy from the transmitter, so there is no need for any external antenna or ground connection.
The coil is 88x60 cm and has 8 turns.

The receiver has a calibrated frequency dial. In receivers with a external antenna this is not possible, because de length of the antenna influences the tuning frequency.

On the coil there are several taps for connecting the diode. I got the best results with the tap in the middle of the coil.

An audio transformer transforms the impedance from 16 kΩ primary to 16 Ω secondary.
As a speaker we can use a modern headphone, with both 32
Ω speakers connected in parallel.

I received 33 different stations with this radio.
The loop antenna is directional, so sometimes we must turn the receiver for better reception.

The coil is made of litzwire 40x0.07.  This wire has 40 individually insulated 0.07 mm strands.
With this wire we can make coils of high quality.

The unloaded Q factor of the LC circuit is as follows:

Q factor
600 128
900 146
1200 144
1500 124

Circuit diagram of receiver "set 3"

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