Crystal Wireless
Like a lot of folks, I built a crystal radio many years ago (about 40) when I was in the Scouts. Since then I have had electronics as a hobby in one form or another including Amateur Radio. In the Ham hobby the last few years I have started to regress back to the things like QRP (Low Power) CW and wire antennas. Maybe it has something to do with getting older now, but I'm finding a renewed interest in the simpler life.
For Christmas my wife bought me the book "The Voice of the Crystal" by Peter Friedrichs, and that was all it took. That book, various web sights information, and a nice wood cigar box that was just looking for a project to be built around brought it all together. Actually, I found two boxes that look the same. The smaller one is a prefect size for the headphones and a coil of antenna wire.
My requirements were few. It had to have a nostalgic look, work reasonably well in a metro area, adhere to the K.I.S.S principal, and of course fit in the cigar box.
I decided to stick to the very basic dual tuned design. The antenna coupling coil is 147 turns of #24 wire on a 1.66 OD core (1-1/4" PVC) for a calculated 468uh with taps every 10 turns for the first 5 and 20 turns for the last 5. The 365pf variable cap is able to be connected to it in series, parallel, or not at all. The secondary coil for the tuner is 72 turns of #24 on the same coil form for a calculated 189uh with a tap at 50 turns for the detector. Because of the small size of the cigar box, I was not able to use variable coupling between the two coils and ended up with a fixed 1.0625 coupling space. The "Cats-Whisker" was made out of a brass fahnstock and brass rod due to the low profile required to close the box lid, and the crystal cup is a brass fixture cap. I added a extra set of clips for an auxiliary detector so I can use the 1N34A or try other detectors any time. The knob for the antenna load selector switch is a 1.5" hobby car wheel. I created the front panel in PhotoShop, and the headphones are Newcomb's that I bought from Scott Balderston.
How does it work? Not bad. Connected to my 4 wire 5 band ham dipole at 20' with the antenna tuning cap in series with the loading coil I have received stations from 690khz to 1500khz. When the 5kw station 1.6 miles away fires up during the day tho I can really appreciate the value of variable coupling (which my next radio will have). There is a station here (Mpls/St.Paul) that runs the old time radio shows from the 40's &50's at 10pm that I listen to. I'm going to send them over a signal report and photo of the Crystal Wireless thinking it might bring back some fond memories. "Who knows what Evil lurks in the Hearts of Men?.......... The Shadow Knows!!
George Pasek
WD0AKZ