Pocket-size crystal radio

Living in a big city is very unconvinient for crystal-set listening, so i decided to construct a set which could enable me to go somewhere outside the QRM -field. Antenna (30m of thin PVC insullated wire) and a small crystal-plug earphone, as well as an earth-connection, are portable too.

The set has two tuned circuits, two ant.connections and output transformer for different phone impedances. I named it "Minidyne". And, it works just fine!

Best regards,

Dejan

• minidyne (27 KB)
• minidyne, inside view (63 KB)
• minidyne-circuit diagram copy (87 KB)

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I would like to ad some more information about my set:

It was made with two tuned circuits to improove its selectivity. L-1 was wound at an ferrite-rod with litz wire. to get higher Q. Also, the load is minimized using only 3 turns at 5cm distance to link it with the tank - coil. Detector diode is connected to the top, to get the highest RF voltage. Impedance - matching transformer minimize the load (primary imp: 200kOhms), and its secondary has taps for different phone-impedances.It was wound at an ferrite core. The capacitors are dual-gang, air isolated, with 6:1 reduction. Smaller section of the first is used to automatically adjust the antenna-coupling along the BCB.By the second, both sections are connected parallel, so less turns of L-4 were needed to cover the band. Diode - current is adjusted by rheostat to avoid distorsion at very strong signalsThe content of the portable package is shown at attached picture.

During day-time, I can hear 3 local Belgrade

-programs, TX at 10-25 km, Budapest (Hungary) at 400km and 2 Rumanian: Temisoara at 150km and Bucarest at 500km. After sunset, (19-22h), more than 15 stations.

Have fun!

Dejan

• completed set (180 KB)

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Dear Dejan
When I type "Pocket-size crystal radio" to Google (not mentioning us), I get your wonderful crystal detector as first result right away.

I hope you like this - and this shows how important we are and how interesting it is to publish here for a great community of readers. :-)

PS:
I just see now that before this you published a Cigar-box Crystal Radio. And I saw your Contest-grade double-tuned crystal radio set.

I'm still very much impressed by your practical work for "Rewindiung the DLR-5 to "Hibaphone", a High-Impedance-Balanced-Armatur Phone). The set has an AC Impedance at 1 kHz of  83,5  kOhms instead of the 758 Ohms from before.
I'm glad that Ralph Oppelt is using it now for some experiments and I will ask him to publish a plot for it.

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Dear Ernst,

You are right about the importance of Radiomuseum!  Also, when I type "Contest Grade Crystal Radio" at Google, my set comes as the first result.

PS: after Rewinding the DLR-5, I have posted two more articles about those phones. Did you see them too?

Greetings,

Dejan

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