Crystal Radios Of The 2006 Contest Entrants
The rig for the 2006 contest is a Jim Frederick design, the Hobby Dyne 2. I added crystal switching and use a reduction on the tune side capacitor.
The headphones are sound powered made from SP mike elements. A bogen transformer handles the output transformation.
The antenna is a 100 foot wire bent to fit the lot! A cold water pipe handles the ground.
The unit at the left rear is the antenna tuner. The coil is 33 turns of #22 magnet wire. The cap. is a dual 365pf variable purchased from the XSS.
The unit at the center rear is the detector tank. Its coil is 40 turns of #24 magnet wire. The front cap. is a dual section variable salvaged from a junked radio. The smaller front section is not used. The rear cap. is used for band spread.
The unit at the right rear is the inductive trap. The coil is 40 turns of # 24 magnet wire. The cap. is a single gang 365pf purchased from the XSS.
At the right front is the detector stand mounted on a salvaged trophy plinth. The mass of the wood and marble lowers the detector stand's sensitivity to vibration. All logged stations were heard with the cat whisker and galena crystal. At the start of each listening session, I would tune in a weak local station using a germanium diode and then disconnect it and match the signal's strength and clarity to a hot spot on the galena crystal. The whole process took less than a minute. The crystal was purchased from the XSS.
The unit at the right front is my version of Steve Bringhurst's UltiMatch 2. I used a pair of RCA "Big Cans" connected to the Red tap of the Bogen transformer.
..Note that the audio impedance matching unit is a copy of Steve Bringhurst's UltiMatch 2 … only the Bogen T725 transformer was used, and the Benny was bypassed …
My interest in crystal radios was less than a month old when I found out about the DX contest. The result is my entry which, for reasons that will become obvious, I have dubbed the Comedyne. If you find any of this humorous rest assured that you are laughing with me and not at me.
I entered the formula for calculating coils into a spreadsheet. Later on I modified the formula so that I could enter the diameter instead of the radius and promptly forgot that I had done so. The coil form I used was 4 inch PVC that I turned down and threaded at 22 TPI. When I went to calculate the length I entered a 2 instead of 4 and came up with a length of 5 inches. This resulted in a coil of 800 uH instead of the 280 to 300 uH that I wanted. I was too green to recognize that this was not right and of course the coil was all soldered up before I found my mistake.
The one thing that went right on the coil was the winding and tapping. I had tried various methods of making taps on a coil with little success. Seems I don’t have the patience, eyesight and requisite number of arms to do a decent job of it so I came up with a new (at least to me) idea. I drilled line of small holes at every 5th thread. I placed the coil form in the freezer for a while to shrink it and then quickly wound the coil. Then I scraped the enamel off each wire that passed over a hole with a sharp pointed hobby knife. I bent a small hook in the end of each tap wire passed it through the hole, turned it 90 deg and "hooked" the winding. I placed a tiny dab of flux on the wire and then folded the tag end of the hook down tight on the coil. A dab of solder finished the job. The result was a nice tight, neat (if slightly over-wound) coil. I bridged all the taps together with a loom to help take the stress off of the solder joints.
The only caps I had were some I ordered from Antique Electronics to play with because they were cheap. They are 4 section totaling 240pf and 540 deg. rotation. I found out why they are so cheap. Nobody in his right mind would want a VC designed for PC board mounting. I finally figured out a way to mount them and only destroyed one in the process. I didn’t have time to order a shaft extension so I machined one out of some plastic rod.
When selecting a diode from two dozen 34As two of them accidentally touched together and the sound level really jumped up. I called them a pair and mated them forever. My antenna is an almost 300 foot wire running due north/south. It ranges from 15 to 20 feet off the ground. The ground is a piece of ½ inch black pipe driven 6 feet into the ground.
I used 12 pos. rotary switches from Antique Electronics for the antenna and tuner taps. For the other switches I used the slide type strictly for looks. (Certainly not for the "ease" of mounting!) The tuning knob and slide switches are from Radio Shack.
Four of the slide switches are for the capacity. 200pf, 30pf, and 85pf on the variable and a 150pf fixed cap. The other switches the ground to switch out half the coil. My grand plan was to be able to do some short wave tuning. (I did manage to do some.)
I’m an admirer of Art Deco and Arts and Crafts design so I set out to make a case for the radio that would look at home in a room designed by Frank Loyd Wright. I also wanted it to look like it had been around for 50 or 60 years. The sides are the very last scraps of some birch plywood from a project I did over 6 years ago. The remainder is solid oak and some oak trim that I modified. An artfully sloppy stain job (left dark in cracks and crevi and lighter on the corners and edges) with Minwax English Chestnut stain gives the look of age. It is finished with three coats of Deft semi-gloss. I am more or less pleased with the result. The trim above the faceplate is a little too wide and I’m not crazy about the flat top. I may do something about the top.
The faceplate is 1/8 in plastic that I found laying around the engineering shop at work. I made a milling template on Autocad and adhered it to the plate. After milling I soaked it off with some WD-40. I then modified the Cad drawing for the graphics and printed it out on some parchment looking card stock that I found at Hobby Lobby. Adhering the graphic onto the faceplate in proper alignment was another comedy of errors. Needless to say there are come creases and wrinkles that worked out perfectly in my plan for the "aged" look. Two coats of spray poly were applied to protect the paper.
The back plate is a 97-cent clipboard from Wal-Mart. I cut it to fit and shot it with some cheap black spray paint. It has the perfect cheap-black-fiberboard-radio-back appearance. Maybe because that’s what it is.
The set tuned very broadly. That may have to do with the huge coil. A local was smeared all over the dial in the daytime and half of it at night. A hastily constructed trap was used to block the local until they signed off at 11PM. Then I would reconnect the antenna directly to my set. Even switching out half of the coil had little effect on the selectivity. Strong stations like WHO and WWL covered a lot of my tuning range. Using the trap as an antenna tuner may have helped but I wanted to stay within the hobby class regulations.
Still I think I did pretty well. I managed to get about 35 stations for a score of just over 55,000 points. The furthest was CBC in Vancouver BC. I will wind a proper coil for the set when time allows.
...Turned out to be quite a contest. Conditions were very flat until the second Friday (20 Jan.); then propagation really picked up. Area T-storms produced a moderate static level Sat. & yesterday, but good prop. seemed to persist.
Same set as last year's event, except I did put a lead telluride rockstand on the stronger local stations. (This was the same detector I heard KRVN 880 Nebraska on several contests back. But that was on the Lyonodyne 17 set.)
Two of the stations heard were new: KXTK 1280 never heard before on any set; CFAC 960 first heard in last year's 1-AD contest.
Mercifully a clandestine neighborhood super noise source held off during prime listening hours …