[SOLVED] Output of regenerative circuit contains both audio and RF?

[neazoi]

Hello,
I consider the output of a single stage regenerative receiver circuit. Is it just audio or also amplified RF ?

If it includes amplified RF too, can I demodulate this RF at a later stage, i.e. not using the regenerative circuit as detector?

 

[chuckey]

Regenerative circuit has got a small amount of positive feed back so as to increase the effective Q of tuned circuits and hence the voltage gain of that stage. Super regenerative receiver allows the RF stage to go into oscillations at very high Audio frequencies ("super sonic") and quelch the oscillations automatically, this stabilizes (to some extent) the positive feed back and the overall stability of the circuit these always demodulate the RF as well i.e. they provide audio.
Frank

 

[neazoi]

So the regenerative in some extent amplifies RF at a selectable tunable frequency, whereas the super-regenerative demodulates it too?

I am a bit confused, I consider this weird but working circuit KR1S VXO Regenerative Receiver, Page 2
He sais that it is a regenerative circuit and also he mentions:

"Instead of direct-to-audio conversion, I'm using an infinite-impedance detector by Felix, VK4FUQ, from the Elliott Sound Products site, "AM Radio - Approaches to high fidelity AM broadcast band reception."

He has used a separate detector, so has he re-detected the audio?
It seems so confusing, as many authors call regenerative circuits super-regenerative and vice versa

 

[FvM]

If it includes amplified RF too, can I demodulate this RF at a later stage

To answer the question more directly: Yes, the RF will be always available at the output for later demodulation, unless you filter it somehow. The shown VK4FUQ circuit does in fact the opposite, filtering the audio by using an inductor load.

 

[neazoi]

To answer the question more directly: Yes, the RF will be always available at the output for later demodulation, unless you filter it somehow. The shown VK4FUQ circuit does in fact the opposite, filtering the audio by using an inductor load.

That is more clear to me now. Let me summarize:

The regenerative circuit output contains both AF and single frequency amplified RF. Then the audio is filtered on the VK4FUQ circuit and the RF is demodulated by the diode.

Am I getting it right?

 

[betwixt]

I would guess the VXO works in a slightly different way, not quite regenerative and not quite super-regenerative. I think it works as a simple XTAL oscillator which under normal circumstances would stabilize t's own output level and operating conditions. When a signal is injected close to the oscillation frequency, I think it may pre-empt the start of each oscillation cycle and make the operating conditions change in sympathy with the signal. The change in conditions will cause a demodulated image of the signal to appear at the output.

Such a receiver would have a very narrow bandwidth and would probably work well for CW signals but be poor with AM and FM signals. It would probably only have a tuning range of a few KHz.

Brian.

 

[neazoi]

So, in a sense, he has achieved very good selectivity combined with the amplification advantages of the regens?

 

[betwixt]

Possibly - again, I'm guesing but I would imagine the amount of signal recovered ( it's efficiency ) would depend largely on how strong the oscillation was. A weak oscillator would be more prone to influence from a weak signal. Maybe a gain control to set the circuit just at the point of oscillation would help. It would be essential to add a pre-amplifer stage too, otherwise the oscillation would simply be coupled to the input and if that was an antenna it would radiate interference.

Brian.

 

[neazoi]

Maybe a gain control to set the circuit just at the point of oscillation would help.

The variable 0-3V VCC wouldn't set this point??

 

[betwixt]

Obviously it wouldn't work without a supply at all and at some supply voltage it woud have enough gain to start oscillating. It may be that the threshold voltage is not optimum for best reception though, it might work better with a higher supply voltage but a load resistor in the drain circuit for example. It would be interesting to test it's performance but it would require a matching signal source and crystal to evaluate it.

I've been considering a design for a receiver using a very low or even zero frequency IF and an op-amp with RC filters to give it selectivity. As the VXO will act as a mixer at frequencies very close to it's center frequency, it would make a nice experimental project.

Brian.

 

[neazoi]

Re: ??? Are you talking about cell phone jammers?

What are you talking about, a audio jammer? not clear, introduce you a excellent place, maybe you can go there to find what you want.Cell Phone Jammer Kit - Mobile Phone Jammers - Cell Phone Blockers

No, not at all. Just a common regenerative receiver.