Crystal Radios Of The 2005 Contest Entrants
Charles Pullen (Chuckster)
Basic Double Tuned Set
The antenna coil is a 5.5 inch space wound with 16awg @ 240uh paralleled with a 20-340pf air variable, loosely coupled to a 5.5 inch space wound with 16awg @ 270uh paralleled with a 20-340pf air variable detector coil. The detector used was two 1ss98 schottky diodes in parallel. I Used the original ultimatch circuit by Steve Bringhurst for impedance matching. Used two Philmore xtal earbuds in parallel, connected to the ultimatch with a radio shack mono Y-adaptor.
The lone wave trap is a 4" x 3/8 inch ferrite rod wrapped with litz to obtain 270uH with a parallel 20-340pf air variable. This was arranged so it could be loosely coupled to the detector coil, suspended inside the center of the detector coil or outside the detector coil in axis with its center, or rotated 180 degrees out of the way. I found this particular style of wave trap to be extremely effective for even the strongest local.
The antenna was two separate wires, one 50 foot wire tacked to the ceiling running about 30 feet east-west the remaining twenty feet running north & south. The second antenna wire was a portable reel of 25 feet borrowed from my Grundig YB and attached to the set. This is in a second story apt. Ground was about 25 feet of speaker wire running to a CWP.
See complete description of Dave's radio at this link: Dave's #50 Set
Dual 660/46 litz coils and two tuning capacitors.
differential coupling capacitor
Schottky Diode Detector
Sound powered headphones
Antenna 40 meter wire up 3 - 4 meters running east to west.
33 inches (84 cm) per side. FO-215 Detector, Bogen transformer, Sound powered phones
See the details of this loop at Dave's Loops Page.
Bill Meacham (Exray)
This set is my third generation of a model based on Steve Bringhurst's TK-2 toroidial set. I went with an external detector coil on this one which offers the advantage of being able to close-couple an external trap (not shown) to the detector coil to notch out instances of interference when the coil itself is picking up local signals via the air.
The set is built on a Garolite front panel with custom-made decals and lacquered for durability and shine. All of the RF components are on standoffs to avoid any possible leakage path through the panel. Vintage tuning capacitors were used and they have been thoroughly cleaned and checked for rf integrity. Both are straightline tuning types to minimize crowding at the high end of the band.. The input tuner is of the "Tuggle" type and uses a toroidial inductor. The inline wavetrap also uses a toroid. The detector uses a nice Pilot Kilograd tuning cap and a coil of 165-strand litz wound on a Lexan former. Its Q is greater than 500 across most of the band. Detector is a germanium FO-215 and the set uses a Calrad output transformer with an adjustable AF impedance matching control (benny) for minimizing distortion on strong local stations. I have been using the set with sound powered phones and they match well.
Calibration on this set is very accurate and it's easily resettable to locate particular stations. I added a set of front panel terminal posts to allow for tinkering with other detector tank options. The coil mounting assembly on top is also configured in this fashion to allow experimentation with other coils. Ceramic standoffs and feedthru bushings were incorporated to assure minimal losses.
Cabinet is homemade, made with Baltic Birch and is stained and lacquered using clear and toned lacquer.
.. is the same 140 ft, base insulated, vertical I used last year. (picture is crooked, not the tower)
I made a few minor changes to this circuit. In place of the 1000 pf capacitor, I use 250 pf. The 82k resistor, I changed to 100k. I use a pair of ceramic earphones, wired in series.
The contest this year was a lot of fun. I put in many many hours of listening. The band was very up and down in Nebraska. Thursday and Friday nights were the only nights that I would call "normal". The unusual conditions on the other nights did however allow for the reception of a few stations that I had never heard before on my crystal radio. I probably heard at least 30 more Spanish speaking stations than I logged. I only logged the ones that were very strong or heard almost every night.
I heard many more stations this year than last year due to several improvements that I have made to my listening station. I used the same crystal radio as last year with the following improvements. My antenna is now higher and has been extended to about 240 feet in length. My ground system is improved. I was lucky enough last summer to acquire a pair of RCA "big can" headphones in very nice condition. They do help some. I finally built some filters that work very well to trap strong local stations. This allows me to now receive quite a few new stations on frequencies close to my local stations. The last improvement > is that every year I get "smarter".
Set: Same set as last year.
Headset: RCA Big Cans tuned and recharged by Steve Bringhurst.
Antennas: 88’ top loaded vertical up 50’ and 180’ inverted “U” up 50’.
Ground is the post 2004 DX contest ground described at the bottom of
I used the 2004 BCB Contest set again this year. We moved after the last contest, so the antennas, ground system, and location were different.
I used two antennas. There first was a top loaded vertical. The top section is about 110' long and is a 80M - 10M trap dipole. The antenna is up about 50' high. The coax feed line is used as the feeder.
The second antenna is an upside down U, roughly 40' vertical on each end, 260' horizontal. I feed it with ladderline in the horizontal section, about 20' from where one end goes vertical. This makes it about 60' from one end of the wire. The antenna was used in three different configurations:
1) Each bottom vertical run is grounded. This is the grounded loop configuration.
2) Only the end closest to the feedline is grounded. This is similar to an inverted L approach
3) No ends are grounded. This is similar to an off-center fed dipole. All changes were done manually (no switches or relays yet).