A heavy 2 m x 2 m floor-standing wooden showcase in the shack appeared to be suitable as a frame for a crystal radio loop antenna. As luck would have it, the lone 20 km distant 612 kHz, 200 kW AM broadcast station being in the end-on position by default, there would be no need to move the unit. The counter top would make it quite convenient to sit down and carry out the testing.
The 5 turn loop was easily wound using about 42 m of ordinary hook-up wire.
The shack is relatively quite small to get a photo of the actual unit.
Here's a representation of the same.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEib9TxLB71XoWoXXMHvjkuYvdu-vLTH0HdKls-irk2aLgy2yz0eOSwueZZieeQaAE2aLMXOUC3NGR0vc0AxIn0u_1DKbJeWwo9b5Eth75GqZ93nlQedwPfl6ebeJnKFA_LXGr21w9rv9Bk/s200/Loop+Antenna.jpg) |
Makeshift 2 m x 2 m Square Loop Antenna |
The shunt-fed circuit was wired first, using a 500 pF variable capacitor and a MBR 1060 Schottky rectifier found in the the junk box.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgye3XZosLrxOkcX3J8cIDkGkUJgE3zZu6Q_xKkJdvR0Qx8xhAhX9zGVGrXm0evaH5gVUZtPBlmWZkvPF30uwisy2_cyRCD8SRB57TnELP9oO7rkuKT7gi0bMXzToinPW7xd3qROtQsVYs/s200/456.JPG) |
Shunt-fed Loop Antenna Crystal Radio - Schematic |
The local station came in real loud through the balanced-armature phones. Headphone current, measured using a 1mA FSD 60 Ω meter, was
200 μA.
Next the series-fed circuit was tried out.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiVRrMijVguFloXXKfnwntakEtGi3afoP647ysiHqshCQmqT-z5Z2O61vObX50jUiho2x-o6WvftmDSrINvQEef_xrB1gwlHPaF9Pm779esk3tPgnivPjxPnmNos5yRhqeOXqsSMK0vmBA/s200/123.JPG) |
Series-fed Loop Antenna Crystal Radio - Schematic |
Reception was quite good, with the OA 79 diode delivering a headphone current of 100 μA.
A 14 turn 0.75 m x 0.75m loop antenna, wound with the same hook-up wire, yielded a headphone current of 100 μA when shunt-fed and 50 μA when series-fed.