Pseudo FM Crystal Radio

After several failed attempts to build an FM Crystal Radio with a diode detector, a dual-gate mosfet version was tried out but also in vain.

The mosfet used was a 3N187 from the junk box.

FM Crystal Radio - Schematic

Now at a dead end, powering it up with a rundown 1.5 V button cell was the only way out. And it sprang to life!

Pseudo FM Crystal Radio - Schematic

A number of local stations were received.

Pseudo FM Crystal Radio

Notwithstanding the problems of hand effects and oscillations, it was music to my ears.

Pseudo FM Crystal Radio - Final schematic

The 330 μH moulded inductor was a later addition that solved the oscillation problem.

Pseudo FM Crystal Radio - Inside view

The factors contributing to my failure in building a real FM Crystal Radio could be the distance of the transmitters (6 km away as the crow flies) and their low power rating (1 to 10 kW).

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A Tuned Passive Radiator

The problem with my 'Portable AM Crystal Radio' is that it works well only when close to an overhead CATV cable working as a passive radiator.

Hence it was decided to create a tuned passive radiator to further improve its performance.

One half of my 40 m inverted 'V' dipole antenna was chosen as the passive radiator. The series-tuned circuit was connected to the core of the coax at the shack end and earthed as shown.

Series-tuned Passive Radiator - Schematic

This setup enabled faint reception of the local 612 kHz 200 kW AM station on the portable crystal radio inside the shack.

After tuning the passive radiator to resonance, performance of the portable crystal radio was found to be quite good across the shack roof.

Identical performance was obtained when a parallel-tuned circuit was used.

Parallel-tuned Passive Radiator - Schematic

Related post: Portable AM Crystal Radio
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