Crystal Radios Of The 2008 Contest Entrants
Click here to see Evan's set that he also used in the January 2008 Crystal Set DX Contest.
Ralf 'Brösel' Siemieniec
My crystal radio tunes the mediumwave (broadcast) band as well as the shortwave band, both are split into two subbands, and the longwave band. To keep the receiver small, I was using closed ferrite cores from Epcos, P18-11-M33 for the MW & LW bands and RM5-K1 for the SW bands. The coils are all done using litz wires 80 x 0.02 mm (two wires in parallel for MW and SW1) and two paralled litz wires of silver-plated copper strands for SW2. Actually, this is the same wire as I used for the wiring, the insulation of the silver-plated litz wire is made of Teflon, which should not cause too much losses (as I hope). The antenna and detector coils are each wound on a separate core which were later stacked together.
The radio has two tuned circuits and a variable antenna coupling and can be switched between single- and double-tuned mode. Additionally, there is an attenuator in case of need, the variable antenna coupling capacitor is a two-ganged type and can be switched in series or parallel. The antenna and detector tuning caps are both silver-plated devices. Rectification is done using two paralleled 5082-2835 for the BC band and again two paralleled BAT15-03W for the SW band. The matching section consists of two transformers - a 53.49 by Reinhöfer Röhrentechnik in Germany (input impedance 240k) switched together with a Bogen T-725. I managed to get a pair of Baldwin Type C headphones which are much more sensitive than all of my modern but more comfortable types.
All is mounted at a polypropylene sheet for proper insulation. The most distant station received so far was 1419 km away in Tunesia. Could probably be more if I had another antenna than the metal made balustrade of my balcony - I live in a multi-party house, thus there is not much chance for long antenna wires.
Lem used an updated version of this set that was used in the last several Crystal Set DX and Sprint Contests.
Same loop as in the photos for last winter's contest. However, I was not using the STM, only the T3/AM20 100:100k transformer and the single 107 nA Schottky. Also, I was not attaching the ground to the variable's frame and using a RFC for diode DC continuity through the variable.
The ground of the detector/audio went to the center of the loop winding > instead. I found that there was much less interference from a local FM station this way.Click here to see more about this set that Garry also used in the January 2008 Crystal Set DX Contest.
The infamous Lyonodyne-17, double-tuned, 12101 3RT detector, two wave traps, RCA Big Cans.
Click here to see Jack's set that he also used in the January 2008 Crystal Set DX Contest.
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