Hey guys!
I'm very interested in learning more about RF electronics (I'm more of a "digital guy"). I've seen a circuit on a magazine I bought the other day, it is a wideband regenerative receiver. They explained the circuit but they were not very clear in some parts so can you guys check if I got it right?
- They say that the input cap shorts the audio signals in the input to ground via the coil... Now lets take a 200Hz signal at the input. Its a 10uF cap so we have a reactance of 79ohms, so the signal that arrives to the base of the transistor is attenuated. On the other hand if we take a 500KHz RF signal at the input, the reactance we get is around 0.031 ohms, so it arrives at the base of the transistor with almost no attenuation to be amplified, correct?
- Now, at the collector of the transistor, we got the amplified signals, with a mix of both RF high frequency signals, and also the demodulated audio, so we wanna short out the high frequencies to ground, and wanna keep the audio frequencies as an output... They use that 10n cap to short out the RF component... They use a 10nF and not a 10uF, so that the audio is not shorted out too, because at 10nF capacitance an audio 200Hz signal would get 79577 ohms and at 10uF it would be 79ohms. But then they use that 10uF cap, I guess its only to block DC?
- And what about the 10k resistor and the 1M negative feedback resistor, how does one pick those values?
Thank you guys, happy new year!
Miguel
I'm very interested in learning more about RF electronics (I'm more of a "digital guy"). I've seen a circuit on a magazine I bought the other day, it is a wideband regenerative receiver. They explained the circuit but they were not very clear in some parts so can you guys check if I got it right?
- They say that the input cap shorts the audio signals in the input to ground via the coil... Now lets take a 200Hz signal at the input. Its a 10uF cap so we have a reactance of 79ohms, so the signal that arrives to the base of the transistor is attenuated. On the other hand if we take a 500KHz RF signal at the input, the reactance we get is around 0.031 ohms, so it arrives at the base of the transistor with almost no attenuation to be amplified, correct?
- Now, at the collector of the transistor, we got the amplified signals, with a mix of both RF high frequency signals, and also the demodulated audio, so we wanna short out the high frequencies to ground, and wanna keep the audio frequencies as an output... They use that 10n cap to short out the RF component... They use a 10nF and not a 10uF, so that the audio is not shorted out too, because at 10nF capacitance an audio 200Hz signal would get 79577 ohms and at 10uF it would be 79ohms. But then they use that 10uF cap, I guess its only to block DC?
- And what about the 10k resistor and the 1M negative feedback resistor, how does one pick those values?
Thank you guys, happy new year!
Miguel
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