Hello. I am planning to build a crystal radio for the first time and i'm following a little book I found on the topic. The design comes in stages, and I think I understand everything until the "regenerator" circuit is added instead of the simple crystal set stage. so he is going from the top circuit to the bottom one (ignoring the amplifier stages that follow):
I have some questions about this if anyone could help me out?
1) In the top circuit i'm thinking of the antenna as a voltage source connected across the tuning circuit, so the resonant frequency is f = 1/(2pi√(LC)). In the bottom circuit you have the two extra capacitors coming off the top and bottom wires. I don't think these change the frequency equation much, but am I wrong?
2) It's difficult to see how the feedback is working. We want positive feedback right? So we need a 180° phase shift from collector to base (since the amplifier is inverting)? Just looking at the feedback through the 500pF capacitor I don't see how you can get this
3) Is the purpose of the RFC to allow the lower frequency modulating signal (the audio) and the bias voltages, whilst blocking the high frequency carrier?
I have a few more questions but maybe once I understand those three I'll be able to answer the rest myself.
Thanks for any help
I have some questions about this if anyone could help me out?
1) In the top circuit i'm thinking of the antenna as a voltage source connected across the tuning circuit, so the resonant frequency is f = 1/(2pi√(LC)). In the bottom circuit you have the two extra capacitors coming off the top and bottom wires. I don't think these change the frequency equation much, but am I wrong?
2) It's difficult to see how the feedback is working. We want positive feedback right? So we need a 180° phase shift from collector to base (since the amplifier is inverting)? Just looking at the feedback through the 500pF capacitor I don't see how you can get this
3) Is the purpose of the RFC to allow the lower frequency modulating signal (the audio) and the bias voltages, whilst blocking the high frequency carrier?
I have a few more questions but maybe once I understand those three I'll be able to answer the rest myself.
Thanks for any help