Crystal Radio with a ferrite loopstick antenna

The local 200 kW, 612 kHz AM broadcast station, located 20 km away as the crow flies, is quite readable on this simple crystal radio employing a ferrite loopstick antenna (with its broadside oriented in the direction of  the station) and balanced-armature phones.

Ferrite loopstick antenna

The loopstick comprises 12 pieces of 4" long, 3/8" diameter ferrite rods stacked inside a 1½" diameter paper former.

Crystal radio with a ferrite
loopstick antenna - Schematic

The coil is 33 turns of PVC insulated copper wire (wire overall diameter 1/12"). It is tuned using a 500 + 500 pf variable capacitor with its sections connected in parallel.

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Another Loop Antenna Crystal Radio

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.

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.

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.  

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. 

Related post: Loop Antenna Crystal Radio
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