Crystal Radios Of The 2006 Contest Entrants
1-AD 2006 Contest Report
It soon became obvious my new 957 acorn tube BFO was not working right. The BFO has double (or multiple) resonances a hundred or so Hz apart. When one resonance was zero-beat, the other(s) was squealing away -- and vice versa. Not good for hearing anything. Reception was much better on the plain crystal set with the BFO turned off -- but that's not the point of the contest.
After a half-day of frustration, I cast my lot with -- Ta-Daa! …
a BFO'ed Diode Doubly-Balanced Mixer (DBM) suggested by Brian Hawes. The Local Oscillator is last year's 1-FET Hartley BFO. The RF source is simply Antenna and Ground. IF Output (which is actually at audio frequency) goes directly to the Big Can Phones, with no matching transformer. In fact, no tuning or matching is done at any of the DBM ports. All tuning is done with the FET BFO.
I figured it would at least it will be an interesting
1-AD entry. Though it doesn't match last year's
1-FET BFO/MRL #39, performance has been very gratifying.
The complete Brianodyne rig is shown here.
Charles Pullen (Chuckster)
The spread sheet doesn't reflect the performance of the radio. The radio catches all the locals with excellent volume. I didn't try to track down spanish speaking stations, and I have several contacts in the log for stations that just didn't seem to want to ID themselves.
For the contest I did not use any impedance matching, only the Western Electric Type II Signal Corps headphones I refurbished with a home made cord, re-magnified the magnets, and cleaned up the head band. The quality of the audio from these phones is outstanding and the sensitivity the best of my 2k phones.
The circuit is the MPF 102 JFET circuit from Mr. Owens site, except I made it a double tuned set with a 360 VCAP in series with the ground. With this configuration I couldn't seem to resonate the antenna below ~ 800 khz. The solution would be to add another vcap in parallel with the antenna coil, but I really wanted to keep this radio simple.
The Det. Coil is 300 uH close wound (left over from previous experiments) and the space wound antenna coil at 270 uH is the second coil I wound for this radio in an attempt to get it to resonate the antenna below 800 khz with a single Vcap. Both coils are 26 guage on a 2.5 ups cardboard coil form. The tickler coil is 8 turns of scramble wound 16 guage plastic coated wire.
The set was constructed completely out of stuff I had on hand, went together in about three hours, minus the trip to radio shack for another JFET (I toasted the first one). I plan to make a shortwave version of this set, and I plan to redo this radio with a much higher Q factor for next year. This contest was a whooole lotta fun. Thanks yall.
Good job on the contest. This was the first time I had used this type of receiver and it was very enjoyable experience.
I am using a single tube regenerative kit from Mike Peebles. It uses a 1T4 tube with regeneration controlled by a variometer. The kit is stock except for using a larger knob on the VC for easier tuning. The sensitivity was good, and selectivity was more than adequate to separate stations 10 KHz apart. Headphones are WE-509's, antenna is 40'of wire laid on the roof with an 8' down lead. This is my crystal set / SWL antenna. This year we tried covering it with a foot of snow on the second evening of the contest. It did not help. (Actually it did not hurt either.) The set was run bare, without antenna tuners or traps. Spotting was done with a Grundig YB-400.
Thank you for sponsoring the contest, I look forward to next year with a scratch-built radio.