Crystal Radios Of The 2006 Contest Entrants
Charles Pullen (Chuckster)
Station count was a little better than last year. I modified the metro to have a tuggle tuned antenna, added vernier drives for the antenna and detector capacitors and installed an old 5 gang fm tuner to give the detector circuit a selectable bandspread cap.
The antenna is a sixty foot inverted L approximately thirty feet up, and the ground is two four foot copper clad grounding rods tied together. I slapped to inline wave traps together to help tame the bandmasters. I used my copy of Steve B.'s ultimatch for impedance matching, and my head set was two philmore xtal earplugs connected to the ultimatch with a radio shack mono y adaptor.
My coils were severly mismatched and pretty beat up as seen in the photo of the "improved metro", but just ran out of time before the contest began to conjure up a new set of coils. I plan to replace the coils with toroids next year ala the TK2 circuit. Experiments with the toroids look really good but again didn't get them ready in time for the contest.
I'm pleased with the results I got considering the shape my coils were
in and the really warm weather conditions we've had …
...I used my #63 set with the crystal detector on the antenna tuning unit board...The other coil is a wave trap circuit.
The receiver is a loop receiver with sides of 26x38 cm (10x15 inch). The wire is 660x0.04 mm litz wire (660/46).
Number of turns: 16
The two transformers have a total primary impedance of 300 k.Ohm. The headphone is a modern 2x32 Ohm type (Sennheiser HD202).
The radio I used is a double tuned set with the coils space wound on a 5” form. (3 liter soda bottle). I built a variation of Owen Pooles’ “Project Radio” on his website.
The antenna coil is 35 turns of space wound solid 18ga hookup wire. I used a combination parallel/series Tuggle tuner with separate 365pf vcaps with the series vcap in the ground path instead of between the antenna and primary tank. This gives me kind of a band spread.
The secondary or main tank vcap was pulled from an old battery set and has a 6:1 vernier built in. The main tank is 47 turns of space wound 18ga solid hookup wire on a 5” form. Only the antenna circuit is grounded to a cold water pipe.
The detector coil is solid 18ga wire wound on a 4” ferrite rod and fastened on the inside of the main tank. The detector itself is a 1N34A diode connected through a 39K ohm resistor bypassed with a .1 mylar capacitor connected to the white lead of a Bogen T725 transformer.
The headphones I used were the elements pulled from a discarded hearing impaired telephone series wired into a set of shooters muffs. These sound elements are much more sensitive that regular telephone elements. They work the best on the 375ohm tap off the Bogen. Much better than my 2000 ohm Newcomb magnetic headset.
The antenna itself is 12ga stranded wire 50’ high and 100’ long on the horizontal part oriented east to west. The far end is the west end …
I've made a few minor changes to the schematic …
(1) The fixed value cap is 250 pf instead of 1000 pf.
(2) The fixed resistor is 100 k instead of 82 k.
(3) I used an audio transformer plus a set of "big cans"...instead of the Xtal earpiece. (my skull is still distorted from those big cans) I think it'll still work without the fixed capacitor and resistor if I go back to using the Xtal earpiece. This would leave me with a set made from just four parts. I may try running it, in that fashion, next year.
73, Ed NN2E
I decided to get serious about the 2006 crystal radio contest and make the maximum commitment to do my best. I knew that I could do better than what I did in the 2005 contest. I wanted to see what a maximum commitment would produce. I started the day after the 2005 contest ended. The following is commited, devoted, crazy, or whatever you want to call it. The following documents over 400 hours spent toward this goal. After all, I'm retired and have plenty of time. What better way to spend it?
First thing was to build a new and better crystal radio that had the maximum efficiency that I could possibly put into it. The design would use the same basic circuit as I had been using. The coils had to have the highest Q possible. I needed a test instrument to measure Q. Thank you Ebay for allowing me to purchase one. Now to get some good wire to use. I purchased some different guages of stranded silver teflon wire. Thank you Ebay again. I wound many many coils. I found the proper size for maximum Q at the frequencies to be received. No larger or smaller wire size is better. No larger or smaller coil diameter is better. No more or less turns of wire is better. Maximum Q is found. Now, one pair of coils in the receiver will not maintain maximum Q all the way across the broadcast band. I use two different sets of coils. One set for 530-1100 kc. One set for 1100-1700 kc. Now I have maximum Q across the whole broadcast band! These coils are the basket weave type held together with hot glue. They are air core coils using 22 guage stranded silver teflon wire. The two sets of coils can be swapped on the radio in less than 60 seconds.
Both of the variable capacitors that I use have porcelain insulation for the stator plates. The range of tuning must cover as much of the 180 degree range of the variable capacitors as possible. This must be done for both sets of coils with no critical lossy switches or taps on the coils. This was accomplished by using dual section capacitors and a couple trimming or padding fixed silver mica capacitors as necessary. The only tap on either coil is one on the secondary coil for the detector crystal. The position of that tap was determined by actual on the air listening for maximum selectivity and sensitivity in that order. The support for all RF parts is white 1/4 inch thick plastic. All wiring in the radio is made using stranded silver teflon wire.
Now I had to have calibrated dials to quickly and accurately go to any frequency. Each of the two tuning shafts pass through the two panels. Each has a six to one vernier attached to the panel. So, each shaft has a 36 to 1 tuning reduction! On each shaft between the two verniers is an insulated flexible coupler. This isolates the tuning knobs from the RF circuits of the receiver to eliminate hand effect capacitance to the receiver. On the front of the rear vernier I placed a four inch diameter plastic disc. This disc is directly fixed to the shaft of the variable capacitor. On this disc I have paper dials calibrated for both coil sets. Each coil set uses a different colored ink. They are held on by double sided tape for easy removal. Thus, I can remove and make a new one in about a half an hour.
The detector is two parallel 1N34 diodes. They were selected for maximum sensitivity to a weak signal by on the air testing. I have a 50 microampere meter in series with the diode detector. A signal of less than 1 microampere is 100% readable. I am about 700 km from Chicago and Denver. It is not unusual for KOA or WBBM to come in at a full scale reading of 50 microamperes.
The headphones that I use are unique. I started with two USI balanced armature low impedance elements taken from an old sound powered handset. I first took them apart. I removed the coils. I took all of the wire off of the coils. I rewound them using super hair fine wire from a 6000 ohm sensitive relay coil. Each headset coil now measures well over 2000 ohms dc resistance. They were installed into a cheap, but nicely padded, headset that I already had. They are very sensitive. I also like the frequency responce of them as they reproduce higher audio frequencies better than the lows. The lows tend to be "muddled" on crowded frequencies.
Last summer was antenna experimenting time. I put up, tested, and took down more different sizes, lengths, heights, and orientations of wire than I can remember. Needless to say, considerable time was spent on this aspect of my endeavor. What I wound up with was a wire about 200 feet long that generally runs east and west. It is up 40 feet at the east end, 60 feet up at a point 120 foot west of that, and then sontinues 80 feet southwest of that ending up 25 feet above ground. The down lead comes off at a point close to the 60 foot support. All wire in the antenna is 18 guage stranded silver teflon wire. I have a ten millihenry choke to ground at the listening bench. Before I put that on, I saw 3/4 inch sparks from the antenna.
Designing filters to kill local stations became a must. I have a one kilowatt station only two kilometers from me. The Q meter came into use again. I ordered a number of each of three different sizes of torroids from Amidon. The coils for the traps are designed for maximum Q at the operating frequencies. I needed five for the top of the band and only one for the bottom of the band. They are wound using 22 guage stranded silver teflon wire. Each has a small 365 pf capacitor in parallel with it. There is a small winding on each for coupling. These small coupling windings can be put in or out of series with the antenna with a flip of a switch. Any number of traps can or can not be used at any time. They are all mounted on plastic to preserve their Q. These traps work very well and tune very sharp. This filter unit is a separate unit from the crystal radio. Also on this unit is a variable capacitor with poreclain insulation and silver plated plates. It is used to trim the antenna when needed.
By now, I was getting a good start on my quest. Next up was getting familiar with the broadcast band. This means lots of time spent listening. I listened almost every evening and night from the middle of August until the contest started in January. I estimate that I spend at least 300 hours listening and gathering information. I systematically monitored every frequency at all times of the day and night and carefully documented which stations could be heard at what time and on what frequency. The more times that I heard an individual station, I knew that on any given day there was a good chance of my hearing it. All of this information was used in the contest for maximum efficiency of the time available. This is critical because many stations can be heard only during a small window at sunset. Last year in the contest I didn't even listen at this time of day figuring that all of these signals were too weak to be heard. Wow, was I missing the boat or what? This is the best time to listen. I added almost 150 stations this fall to my all time heard list by listening during this period of the day. The information I then had for possible reception of stations was put to use in the 2006 contest. It worked well. 144 stations logged on the first day! The broadcast band conditions on that first night were the best that I have experienced in the past two years. They were nothing short of amazing. I put in 14 hours of listening and logging on that day alone. On every day of the contest I was by the radio for a couple of hours around sunrise, off and on during the day, and from 4 PM until about 11 PM. A person just can't miss that one more station logged. I put in at least eight hours of listening and record keeping for the contest for each of the nine remaining days of the contest. Almost 100 hours during contest week.
Total time spent for construction, preparation, and contesting turned into somewhere near 400 hours of fun. Every day listening is different. That's what makes it so interesting and fun. The band conditions were very good almost every day of the contest. Some nights produced longer distance reception and some nights shorter reception. That allows for reception of many many stations. Of course there were a fair number of frustrating times that a station faded away and caused it not to be logged. I didn't log every one of those because one never knows if the next night it may be heard again and identified. I did log 265 stations. 246 of which were identified. My list of stations heard and identified over the last two years is now at 334 stations. Wow. Still room for improvement in the contest. On to next year.
Evan Haydon Lincoln, Nebraska