Here's the portable version of my
'Series-tuned Crystal Radio'.
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| Portable AM Crystal Radio |
The prototype was wired on a piece of perforated board.
M0UKD's
'Loaded Quarter Wave Antenna Inductance Calculator' gave a loading coil inductance of the order of 10 mH at 612 kHz (the frequency of the 200 kW AM station located 20 km away). Hence two 4.7 mH moulded inductors were connected in series at the feed point, to resonate the 0.75 m long telescopic antenna at that frequency.
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| 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 an overhead CATV cable working as a passive radiator. The cable runs exactly in the direction of the station like a Beverage antenna.
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.
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| Portable AM Crystal Radio - final version |
This radio works quite well, unaided by passive radiators, up to 5 km away from the transmitter.
Related post: A Tuned Passive Radiator
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