Varactor Crystal Set
It probably doesn't qualify as a real crystal set since 9 volt power is applied to the varactors but here is a quick set that I lashed up:
Here is a scope pic of WDBC 680 kHz Escanaba:
WDBC is about the only AM station I can get during the day on a crystal set. Using a 40 meter dipole lying on the ground as an antenna and the ground connection was made to the power strip ground. I will have to re-try it tonight and see what else can be heard.
I didn't get a chance to try the Mikrowave1 design:
https://wb9kzy.blogspot.com/2024/07/varactor-crystal-set-video.html
Just used a 260 uH coil wound on an old large pill bottle. A Radio Shack 1n34 was then hooked to a tap on the coil. No primary winding was used but I did add a 113 pF cap between the LC and the antenna which seems to help with sharpening up the response of the LC circuit. Two 1SV149 varactors are used in series and they are controlled through a 100k ohm resistor by a 10 turn, 10k ohm pot connected to the 9.2V power supply.
It works !
Here is a circuit used to try out the series varactors:
Basically just added a 2.2 megohm resistor to ground to provide a leakage DC path for the top varactor. The capacitance varies from 13 pF at 8 volts to 200 pF at 1 volt.
Here is a chart of resonant LC frequency for the crystal set:
Here is a scope pic of WDBC 680 kHz Escanaba:
WDBC is about the only AM station I can get during the day on a crystal set. Using a 40 meter dipole lying on the ground as an antenna and the ground connection was made to the power strip ground. I will have to re-try it tonight and see what else can be heard.
I didn't get a chance to try the Mikrowave1 design:
https://wb9kzy.blogspot.com/2024/07/varactor-crystal-set-video.html
Just used a 260 uH coil wound on an old large pill bottle. A Radio Shack 1n34 was then hooked to a tap on the coil. No primary winding was used but I did add a 113 pF cap between the LC and the antenna which seems to help with sharpening up the response of the LC circuit. Two 1SV149 varactors are used in series and they are controlled through a 100k ohm resistor by a 10 turn, 10k ohm pot connected to the 9.2V power supply.
It works !
Here is a circuit used to try out the series varactors:
Basically just added a 2.2 megohm resistor to ground to provide a leakage DC path for the top varactor. The capacitance varies from 13 pF at 8 volts to 200 pF at 1 volt.
Here is a chart of resonant LC frequency for the crystal set:
 |
| not quite linear but decent |
It's too hot and sticky to try and finish this crystal set, it will be left for another day.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
