UHF Crystal Radio

A crystal radio was wired up to check for reception of VHF/UHF signals in the vicinity of the shack.

VHF / UHF Crystal Radio - Schematic

Using a gold bonded Germanium diode 1N65, a 500 mm whip antenna and balanced-armature phones, no signals were audible either in the shack or on the shack roof.

However, using a 250 mm whip, a weak digital signal was detected while moving on the shack roof. Position on the roof and direction in which the whip was pointed were quite critical.

It was presumed that the signals were from a nearby cellphone tower.

A 3 Element Yagi Beam for 33 cm was made using a broken snare drum stick for the boom and 20 SWG bare copper wire for the elements.

UHF Yagi Beam Crystal Radio  - Schematic

The coil was wound integral with the driven element. 

UHF Yagi Beam Crystal Radio

With this setup a higher signal strength was obtained.

A second Yagi Beam was then rigged up, with another diode providing the return path for the audio, instead of the coil.

UHF Yagi Beam Crystal Radio
with additional diode - Schematic

The signal strength was not as good. During trials, a chance shorting of  the first diode gave a considerable increase in signal strength.

Single-diode UHF Yagi Beam
Crystal Radio - Schematic

The diode and capacitor were hence discarded. Performance of this single-diode UHF crystal radio is quite good.

Single-diode UHF Yagi Beam Crystal Radio

A folded dipole version, mounted on a terminal block, followed.

UHF Folded Dipole Crystal Radio - Schematic

It obviated the need for a coil / additional diode and worked quite well too.

UHF Folded Dipole Crystal Radio

The terminal block arrangement made it convenient to replace the folded dipole with a full wave loop.

UHF Full Wave Loop Crystal Radio

Likewise with an AWX antenna.

UHF AWX Antenna Crystal Radio

Results were as good as with the folded dipole.

Related post: Minimalist UHF Crystal Radio
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