Portable AM Crystal Radio

Here's the portable version of my 'Series-tuned Crystal Radio'.

Portable AM Crystal Radio
The prototype was wired on a piece of perforated board.

Two 4.7 mH moulded inductors, connected in series at the feed point, resonate the 0.75 m long telescopic antenna at 612 kHz (frequency of the 200 kW AM station located 20 km away).

Portable AM Crystal Radio - Schematic
At first nothing was heard even on the shack roof. However, on moving around, a favourable spot was found, where the reception is indeed quite good. The spot is close to overhead CATV cables, which serve as passive radiators.

Encouraged by the results, the final version was built using the plastic front panel of a discarded radio. In this version OA79 diodes were used with equally good results.

Portable AM Crystal Radio - final version
This radio works well, unaided by passive radiators, up to 5 km away from the transmitter.