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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Shortwave Crystal Radio

It was my first attempt at building a shortwave crystal radio.

Shortwave Crystal Radio
It's single-tuned and uses a 1N270 to drive vintage sound-powered phones.

The circuit was 'breadboarded' on an old fan regulator baseplate with the coil wound on a white plastic pill bottle.
Shortwave Crystal Radio - Schematic
A 2-section variable capacitor, with slow motion drive, was used for tuning. The 2 sections were connected in series for an effective maximum capacitance of 180 pF.

Using a 60' wire antenna and earth resulted in 'local strong medium wave station breakthrough' and hum.

With earth disconnected, the breakthrough and hum reduced considerably and it was possible to tune-in to a faint shortwave broadcast. It was from AIR Chennai, on 7380 kHz, located 270 km away.

Tuning further up, a weaker Oriental station was heard.

Severe fading was experienced with both the signals.

Similar results were obtained using a 1.5 m long telescopic antenna and earth.

On a later occasion the same stations came in louder, with no breakthrough and hum, using a 20 m inverted 'V' antenna.
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