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johnzybourne
Jan 31, 2023
In Solid State Radios
Hi all, Recently I've been playing around with JFET transistors, something new for me if I must be honest. Originally I was intending to build a grid (or gate in this case) leak detector using a JFET in place of a tube, but I found that I couldn't get it to work. So after looking at schematics online I instead decided to try using the JFET as an RF amplifier and then feed the output into a crystal detector. That worked surprisingly well, once I figured out how to bias the thing properly! Of course I had to use a piezo earphone to hear anything, but it was much louder than the unamplified crystal sets I had built previously. I then decided to build an audio amp so I could use low impedance headphones in place of the piezo buzzer. The RF amplifier is a 2N5457 JFET and the AF amp is a 2N3906 PNP. I used a 1N34A for the detector diode. Performance wise it works alright, I'm able to pick up three local stations during the day, including one I can't really hear with an unamplified crystal radio. This is still experimental so I'm using a loopstick I bought at a hamfest (so I'm not really sure what it was originally intended for) with a 200 pF varicap for the tank circut. As a result the band coverage is limited. Now that I know it works though I'm going to make a better tapped coil and use a different varicap with a higher value. Unfortunately my antenna situation is terrible (patch cords hooked up to the metal vent hood over the stove in my apartment) so my reception is limited anyway. Anyway, I know it's not much, but it's the first amplified radio I've gotten to work well so I'm proud of it. If anyone has any suggestions for improved performance please let me know. Cheers, JZ PS, Here is the schematic:
An amplified crystal set content media
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johnzybourne
Jan 25, 2023
In Crystal Radios
Hi all, I'm fooling around with crystal sets again, well amplified crystal sets. I'm slowly working my way up to proper reflex and regenerative receivers. I was wondering if anyone had a favorite coil type they liked to use with crystal hookups. What is a good ratio of turns between an antenna load coil and a tank coil? Cheers, JZ
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johnzybourne
Jun 18, 2022
In Crystal Radios
Whoops! I originally posted about this in the wrong subforum! Anyway, I recently built an Australian crystal mystery set and an external LM386 based amp so it could run a speaker. The set has decent performance, given that I live in a smaller apartment and only have a ~1 m long wire clipped to my stove's vent hood as an antenna and a pipe connected to a radiator as my ground. I'm able to pull the local AM stations and a few from further afield. I figure if I had a larger antenna and a better ground my sensitivity would be greatly improved. Has anyone else built one of these? I came across these experimental variants for the short wave bands that I'm going to experiment with over the next few weeks. https://www.qsl.net/kc4iwt/xtal/SWMystery.htm Cheers, JZ
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johnzybourne
Jun 17, 2022
In Welcome to the Forum
Hi all, I was a long time lurker and occasional poster on the old Radio Board forum. I look forward to talk about homebrewing with all of you. Also, does anyone know what happened to the old forum? One day it was just gone. Cheers JZ
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