Crystal Radios Of The 2004 Contest Entrants
N4AHJ 2004 CONTEST CRYSTAL RADIO and OTHER INFOANTENNAS:
(1) End-fed inverted V long wire, 135 feet with apex at 40 feet, two 135 feet counterpoises under the antenna.
(2) Vertical, 48’ tall Tee; top-loading consisted of two parallel wire spaced 38’ and run 90’ to Southwest and 40’ to Northeast; 10 radials with lengths from 40’ to 100’; series fed at base with single wire feed. Vertical core consisted of a cage of four parallel wires spaced 12" and two wires from each of the top-loading legs dropped down, spaced 4" from core center, and connected to base to provide broader bandwidth.
(3) Sloper, 118’ with far end at 50’ and station end at 8’, oriented toward East-Northeast.
(4) Sloper, 130’ with far end at 50’ and station end at 8’, oriented toward West-Northwest
Ground system: Ham station ground - six ground rods interconnected and connected to shack with two quarter-inch copper straps; supplemented by one 8’ ground rod directly under Vertical antenna and 2-4’ ground rods under the wires dropped from the top-loading legs, all inter-connected with copper wire; both ground systems connected with two runs of copper braid salvaged from old RG-8 coax. Radials were 17-ga aluminum wire (used for electric fences).
(1) Tunable(1) - 2-section variable, sections in parallel, 240pF total; Rook coil with 18 gauge wire, 5.25 inches effective diameter, 47 turns; air-coupled to the Detector coil.
(2) Tunable (2) (located in Antenna Matching Unit) - both use 14 gauge enamel wire on FT-114A-61 cores and dual-section variables with both sections in parallel.
(3) Fixed (9) (located in Antenna Matching Unit) - 14 gauge to 22 gauge enamel wire on FT-114A-61 cores, silver mica fixed capacitors, and plated ceramic trimmers (one trap for each of the local "powerhouses"). Each link-coupled to the antenna feed to the set.
ANTENNA MATCHING UNIT (AMU):
One 4-section variable capacitor, four fixed capacitors (500pF, 1000pF, 2200pF, and 5000pF), and two coils (42 turns 14 gauge enamel on a FT-240-61 and 26 turns 16 gauge enamel on a FT-114A-61). All components switched to provide four matching arrangements: series LC, parallel LC, inductance only, and capacitance only. Both inductors tapped to provide 23 settings. An antenna switch is provided for switching between up to five antennas.
Capacitor - 520pF variable, 4 sections, 2 used in Tuggle arrangement, vernier is a surplus right-angle unit with a 25:1 ratio.
Coil - Two Rook coils with 16 gauge enamel wire, 5.25 inches effective diameter, 15 turns each, 30 turns total; bandswitched to provide either series or parallel coupling to provide Low band and High band tuning, a la Ben Tongue’s arrangement; air-coupled to the Detector coil.
Capacitor - 420pF variable with home-made vernier with a 32:1 ratio (vernier constructed from gears salvaged from a VCR and a TV tuner).
Coil - Two Rook coils with 16 gauge enamel wire, 5.25 inches effective diameter, 20 turns and 21 turns, 41 turns total; bandswitched to provide either series or parallel coupling to provide Low band and High band tuning, a la Ben Tongue’s arrangement; switchable taps (High Band: 100%, 75%, 50%, 25% and Low Band: 100%, 87.5%, 67.5%, 50%, 25% ) on coils to provide matching to diodes.
Diodes - Three 1N34A Radio Shack equivalents, paralleled and matched for Forward and Reverse resistances.
Matching - Reproduction of Steve Bringhurst’s Ulti-Match circuit.
Headphones - Two Automatic Electric GH-66919 elements (manufactured 1942) out of a military handset.
The basic set is the same as my 2003 contest set. I moved the fixed traps from the Tuggle Tuner to the AMU and complemented them with two tunable traps. There were a number of times when I used all three tunable traps and one, or more, fixed traps!
I determined optimum AMU settings across the AM BCB for each antenna prior to the contest.
Notice the spotter set and audio matching unit on the bottom shelf.
View from right side
View from the left side
This is the Crystal Radio to End all Crystal Radios. Hello there. Can't you just feel the tension rising? With this new radio I shift gears again. Large litz wire, high quality variable capacitors, schottky diodes. It won't get much better than this. Last night I am proud to announce that I heard KMOX in St. Louis on this radio. That is my furthest DX ever. I am sure that the ionosphere was hot and the wind was blowing my way, but a heard station is a heard station. Enough bragging and on with the show.
This radio is built in modular form. Mike Peebles gave me the idea when he had his modular crystal set published in the Crystal Set Society newsletter. The first part built is the detector. This consists of the main tuned circuit with my 660/46 Überlitz Coil. This is of my own design. I am a big fan of litz spider coils, and this is a big litz spider coil. I believe I hit crystal set heaven with this coil. The detector unit also has a selectivity / sensitivity control using a differential capacitor. Besides all of this there is, of course, the detector diode itself. I made a board with a three position link switch and places for three diodes to be connected. This allows me to easily compare 3 diodes in the same set. After the diodes is an audio output transformer and RC network. The 27 mh choke provides a DC return path for the diode circuit.
The variable capacitor is an old one made by National Radio. I made a wheel and fashioned a vernier tuning system with a grommet and a dowel rod. I get nice, slow and smooth tuning with this system. You can use a vernier dial instead if you don't have one of these capacitors in your junkbox.
The selectivity and sensitivity are handled by a differential capacitor and a piston trimmer. This system was first used in the Hobbydyne II circuit by Jim Frederick. The piston trimmer is for tracking adjustment. You adjust the piston trimmer until the main tuning needs no touch up after turning the differential capacitor. This is a breakthrough in weak signal reception on a crystal set.
The audio transformer matches the very high (100 k ohm +) detector circuit with the much lower impedance headphones. I am using a 100k to 1.5k ohm transformer. If you can find a high quality transformer, go for it.
This covers the detector section of my high performance radio. Next comes the antenna input circuit and maybe a wavetrap.
My tuning unit is now complete. The coil is made from 660/46 litz. The hub diameter of the coil is 3 inches. The coil form made from 1/16 inch styrene sheet is 6-1/2 inches wide and 7-1/2 inches tall. There are 33 turns on it for an inductance of 150 µH. The variable capacitor has 600 pf per section. Smaller ones can be used, however the low end of the band might not tune. You could probably get away with a 500 pf per section capacitor. This antenna tuner is wired as a "Tuggle Tuner".
Earlier I had used a 150 micro henry coil made from 40/44 litz wire. This worked quite well. One night very late, I scanned the dial and with this set up I heard 40 stations. Not bad for a September night.
The two units are placed next to each other. The coil distance for good overall operation are about 15 inches apart. Careful adjustment of the antenna tuner and detector tuning are required. The Q of these types of coils have been measured at over 1000! This ain't your grand pappy's crystal set.
If you build one of these, let me know how it plays for you. Happy crystal set dx. Dave, N2DS