Radios Of The 2010 First Final Farewell DX Contest
O. T. Anderson, Open Class Entry
This the same crystal set I used last year with a few revisions. I had 66 stations last year and my goal was to double it. The Mexican stations come in good in Oklahoma.
This crystal set is the same as last year with 3-4 updates.. The extra coils are wave traps for knocking out that KFAQ, 50,000 watts, in sight of our house. Also another 50K across the town. Up high is a new wave trap with silver caps. It will tune any local station. The pictures also shows a "Drug Store" spotter and a Knight Sig Generator. The two dials show the freqs and also spots several local stations. The right dial has another calibration, one is the 1700 to 530 freqs, the other calibrations is the high end freqs when using only the 140 mmfd condenser, about 1750kcs to 1000 kcs. Lots of band spread.
The other picture is the RF section with a silver cap at the far end. It tunes the antenna. The small var cap with the nearest blue wire connects the 2 nearest caps for all the freq 1700 to 540, normal use. With the blue wire not connected we use only the 140 mmfd cap, tuning about 1750 to 1000. This gives good band spread at the high end. The blue and yellow wires connect a 15 mmfd var cap, helps to "rock" in a distant station. If I good get rid of that terrible KFAQ signal things would be a lot better.
Jack Bryant, Open Class Entry
I only worked the last week of the contest, focusing on the broadcast band. I used essentially the same set for that I used in years past.
I have used a Realistic DX-398 for several previous contests, and I used it for this one, too. I used a PC for logging along with paper copy backup. I used a four foot table from Lowe's as my listening post.
Garry Nichols, Loop Entry
(Note from Jack: don't you just love the back of the envelope schematic! A wise sage at work use to say that if a detailed study didn't agree with the broadbrush, back of the envelope calculations, then the detailed study was probably wrong!)
A few changes for my loop this year:
1) Turns spreaders at the midpoints of the frame tightened things up and stopped rattling wire. Don't know why I didn't do this sooner!
2) I seriously reduced my troublesome FM interference with a simple trick. Somehow I noticed that a few pF across some of the loop turns seemed to reduce it. So I experimented first with a tiny variable (which turned out to have too many pF even fully open) and then with a small length of thin teflon insulated wire. The best positioning was from the exact center of the total winding across a few turns to a position one turn in from the end of the winding opposite the diode. I put it there to possibly help balance the loop because I use the other half of the winding for the detector. A few turns of the wire around each winding did the trick.
The upper half of the BCB used to be plagued by FM. It was difficult to tell if I was hearing a weak AM station or FM interference unless I spent some time listening. A real pain! My mod suppressed interference on the upper half and I can only hear FM if I tune above 1700. A lucky break after on and off problems for years!
3) I tried Ben's diode bias circuit this year along with my favorite 107 nA Schottky diode. I had to bias the diode, so that it appeared to have a higher saturation current. A bit more, lower in the BCB, and a bit less near the top. Fits theory pretty well! I used only the T3/AM20 transformer on my RCA mic elements to avoid possible problems with the Select-To-Match circuit and the bias circuit not getting along. How best to hook the two up left some doubt. For my setup, I could never decide if the STM was better than the T3/AM20 alone anyway.
Dan McGillis, Open Class Entry and Active Device Entry
I used two radios in the 1/15/10 contest.
For the BCB Crystal radio section, I used a simple double tuned Mystery set made with dual-gang capacitors from Leeds Radio and ferrite rods wound with 165/46 litz. It's described here.
It was a very good daytime performer, but only a fair night time DX catcher. The bandwidth was just a bit too wide for all the strong DX stations and the digital hash which now seems to be everywhere at night. Still, it's a nice loud little radio.
For the active device section, I used a 2-JFET Regen plus an op-amp audio amplifier with an active bandpass filter. My primary goal was to be able to copy Morse code (CW) in the 40 meter ham band (7 MHz). The radio is described here.
The performance of this simple set-up really surprised me. It's an excellent CW receiver -- stable, quiet, sensitive, and selective. Excellent for SSB and AM too. A real keeper. I even managed to make some 2-way contacts on 40m using this receiver and about 3 watts of transmitting power. That was a lot of fun.
Jerry Walker, Open Class Entry
-The crystal set used was double tuned.
-The antenna was a 75 ft long wire.