Crystal Radios Of The 2008 Contest Entrants
Set: Double tuned torroid, with Tuggle front end, using FO215 and Schottky diodes. 100k to 1 k Hammond matching transformer, and sound powered phones. Coupling is accomplished with a third torroid, primary has 3 turns inseries with ground lead, secondary has 3 turns in series with main detector coil.
The set uses a Tuggle Tuner, a Schottly diode detector with three diodes in parallel, and a UTC A27 matching transformer.
My antenna was a 135 dipole fed in the center with 45 feet of 450 ohm open wire line. I connected the feed line wires together at the set and worked the antenna as a T against ground.
Again the contest was fun. I did better than last year, copying 100 stations. Conditions may have been better or it could be due to my new set and more sensitive headphones.
This radio is big improvement over the radio that I entered in the 2001 Crystal Radio building contest. I started tinkering in early January 2008 and finally decided on a design on 17 January 2008, and built the radio that afternoon … ready to use the next day.
My coils are wound on 4.5” PVC pipe with 80 turns #18 wire space wound the width of the wire with nylon masonery cord. The coils actually have too much inductance, however I did not have time to change them. The variable capacitors have ¼” dowel wooden extensions to avoid the effect of hand capacitance. To provide smooth operation and stability a ¼” washer is glued to the front panel.
My antenna is about 200 feet of wire strung through the trees in the backyard about 20 feet up. In operation, the right side is tuned to where you want to be, then the left side is tuned for the strongest signal, the coils are moved in/out as needed for signal strength and selectivity. I have had real good results with this design.
At my location in Winston Salem, NC we have a real strong station at 830 KHz and I can routinely hear 840 KHz WHAS in Louisville, KY in the clear. Two small stations were heard during the 2008 contest: (1) WMAC 940 KHz in Macon, GA (2) CKNX 920 KHz in Wingham, Canada. A total of 35 stations were copied. A simple piezo earphone was used. I plan to tinker with this design to optimize reception.