Crystal Radios Of The 2009 Contest Entrants
Dan McGillis, SW Class (regen set)
Thanks again for letting me enter my SW regen (with it's Radio Shack amplified speaker) in the '09 Sprint contest.
The contest gave me the needed nudge to really exercise the receiver and learn about it's strengths and weaknesses. I only tuned a lower CW portion of 40m (7.025 - 7.070 MHz) but there were hundreds of stations that could have been copied over the weekend period. Turns out there was a PA QSO party and a FISTS contest part of the weekend also. So there were weak and also extremely strong signals everywhere.
But I wasn't in the contest to score lots of points. I wanted to evaluate the receiver on weak & strong signals, so I restricted my station search to those calling CQ, especially the weak ones next to strong signals.
Click here for a link to Dave Schmarder's RadioBoard with a schematic and discussion of the radio.
Dave Schmarder, BCB Class (crystal set)
Here is the link to my contest entry. I just put up the Google map, so the page is now ready. I received 73 stations in the contest on my #76 crystal set. I had fun using my band pass radio. The outcome was better than I had expected.
Glen Yarbro, BCB Class (crystal set)
Dave's crystal radio #44
Headphones: Navy 4k
Antenna: 300 ft long wire
Gary Nichols, BCB Class (regen)
I was using a single J310 regen with a B+ of 4.5V. My tuning range was a bit below and above 680 and 1320. I forgot to measure it and I've already taken some of the set apart in preparation for mods.
The restricted tuning range was due to the 30-145 pF ARC 5 variable that I like to use because of the really slow and precise worm drive. The set was a bit of a last minute effort, so I gave up on extending the range. I had plenty of stations to listen to anyway. My problem was that it seemed more difficult than usual to ID stations based on the info broadcast. There were a lot of games on over the weekend evenings and also the usual "sports talk" stations which are as bad as Radio Disney to identify, it seems.
I also forgot to listen for my area stations during the day! Ooops!
The antenna was about 50 ft of wire sloping to the ground from a 2nd floor window (10 ft of it inside). I sloped it south-westerly for possilbe best performance from my location here in the northeast near Syracuse, NY. My ground was the nearby 2 draw metal filing cabinet. One time I sat down to listen and noticed more than the usual hand capacity. I quick check and I realized I hadn't hooked up the filing cabinet!
I used a "Bringhurst String" (5.6, 10, 22, 47 pF) of "clip selectible" fixed series caps between the antenna and top of the L/C to control signal strength and "pull" the tuning a bit up and down band.
James Kearman, BCB Class (regen)
My receiver was a homebrew solid-state regen, the one shown here. I used a homebrew air-core loop, 14-foot circumference.
Sean Whiteacre, BCB Class (crystal)
The diode is a FT-205 Type. I used Dynalec Headphones and RCA Large Can Sound Power headphones.
Jack Bryant, Two-way Shortwave Class (regen)
I participated just a bit in the contest. I started Sunday night and made a two contacts and then one more early in the morning. The set you see was "rescued" from the Shelby, NC hamfest a few years ago. It was beautifully made with a plexi-glass case and painted front. It was sold as a non-working unit. I hated to see this fine construction job go to waste. The rig had a two tube crystal controlled transmitter and a two tube receiver, all in one package.
The receiver did work but covered about a 3 MHz tuning range. The vernier was a tiny one. I swapped it out for a NOS Velvet Vernier. The tuning range was narrowed down considerably, now covering roughly 3.500-3.508 MHz. I changed the top coupled detector antenna cap to 1.5 pf. The plate voltage on the regen detector was reduced from about 130 volts to 22 volts. The power cord was changed to a three prong cord.
The change in receiver performance is dramatic. The receiver is now very usable. I wanted some additional selectivity, so I put a .005 uF cap across the primary of the audio output transformer. I fed the audio output into my PC and used the Spectrogram program to check out the bandwidth. The audio peak is between 400 and 800 Hz, just right for my ear. The tube lineup is a 6CY5 detector and a 12AX7 two-stage audio amp.
The transmitter initially did have some output, but it was acting strangely. It turned out that the pi-network output of the transmitter had to be redesigned. It worked, but with an output at 40 meters instead of 80 meters! Some turns were removed from the coil and new fixed capacitors were installed. The output variable cap had to be changed as well. I had to fabricate a mounting plate so the existing front panel hole could be utilized.
Now the transmitter puts out 10 watts (plus or minus). It is sensitive to the type of crystal used. For the contest I used a small surplus 3.547 MHz crystal installed in an old FT-243 case. It worked great. The transmitter uses a 6C4 oscillator and a 5763 power amp.
This rig looks a Novice station project, perhaps from an old ARRL publication; however, I have not found a schematic for it yet. The station does work well. It drives either phones or a small external speaker.
Go to 2009 page 6.