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.
_______________________________

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
_______________________________

Parallel-tuned Compact Loudspeaker Crystal Radio

Here are the schematics of two parallel-tuned versions of my 'Compact Loudspeaker Crystal Radio'.

Parallel - tuned Compact Loudspeaker
Crystal Radio - Schematic 1

Parallel - tuned Compact Loudspeaker
Crystal Radio - Schematic 2
The local 200 kW, 612 kHz AM broadcast station, just 20 km away, is heard quite well with either version on my 'Homebrew Horn Speaker'.

Related post: A Chance Crystal Radio Project
_______________________________

Tarnished Silver as a Crystal Radio Detector

A fully tarnished, shiny black silver artefact was tried out as a detector in place of the germanium transistor in my series-tuned, shunt-fed crystal radio.

Series-tuned Shunt-fed Crystal Radio - Schematic
Fortunately the presence of an untarnished spot facilitated the metal to metal connection.

A length of pencil 'lead' was used to probe the tarnished portion to locate the 'sweet spot'.

The local 612 kHz, 200 kW AM broadcast station, just 20 km away, was received quite well using a 60' wire antenna and balanced-armature phones. Headphone current, measured using a 1mA FSD 60 Ω meter, was 300 μA as compared to 750 μA with the germanium transistor and 50 μA with a razor blade as the detector. 

It was a confirmation of the shiny black tarnish being silver sulphide (a semiconductor).

A silver coin, stored in a plastic pouch and tarnished a dull grey, in its failure to detect, indicated that its tarnish was silver oxide (a good conductor of electricity).

Related post: Foxhole Radio Detector Variants
_______________________________