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RF detector can oscillate?

neazoi

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Hi, I would like to know, if I increase the gain of this RF detector by the P1 (and possibly alter R2) can this circuit be used as an oscillator?
 

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vfone

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    neazoi

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neazoi

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I would like to avoid super regeneration. Is there any way I can do it in this simple circuit?
I thought that in any oscillator if I increase the gain very much, it will break into oscillation. Obviously I am wrong.
 

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A Colpitts oscillator should not super-regenerate, it should just oscillate, they are slightly different processes.

Beware that if you add positive feedback to make it oscillate the meter will almost certainly be damaged. You need to add a series resistor. As a field strength meter it will only see a few mV of signal but as an oscillator it could be more that the battery voltage.

Brian.
 

    neazoi

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neazoi

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A Colpitts oscillator should not super-regenerate, it should just oscillate, they are slightly different processes.

Beware that if you add positive feedback to make it oscillate the meter will almost certainly be damaged. You need to add a series resistor. As a field strength meter it will only see a few mV of signal but as an oscillator it could be more that the battery voltage.

Brian.
I thought I could make this oscillate easily to double as a signal generator too. I thought so too about the meter. Ok so the answer is no, in this configuration it won't oscillate?
--- Updated ---

see also this https://translate.google.com/translate?sl=auto&tl=en&u=https://www.robkalmeijer.nl/techniek/electronica/electronicabladen/elektuur/2003/11/page68/index.html
Isn't this circuit the same as mine? With the LC connected to the gate and to the ground?
 
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betwixt

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No,it isn't an amplifier or oscillator, its a mixer.

Your original schematic is a tuned amplifier and rectifier (detector) to indicate RF is present at the frequency it s tuned to.
The second schematic (vfone) is an externally quenched superregenerative receiver. It needs a second oscillator to 'pulse' the main one.
The schematic in post #5 is a mixer. It takes a signal from a DDS and mixes it with a known AM radio station so you can adjust the DDS reference for zero beat.

Using a local example, a 5KW BBC transmitter is located about 10Km from here so it is a strong signal. It radiates on 880KHz so if a DDS was programmed to produce 880KHz and it was fed to the mixer, any difference in the frequencies would leave the mixer as an alternating level. The DDS reference oscillator could then be adjusted for zero beat and it would mean that DDS was then accurate at other frequencies.

Brian.
 

neazoi

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You are right! I have missed a connection.
Is there any simple way to make this thing oscillate so that it can be useful as a "generator" too?
 

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You could try removing C2. The reason a dual-gate FET is used is they have less signal conduction between G1 and D, the 'top' FET provides isolation. With C2 removed it opens the chance of internal capacitance causing feedback. How well it works and whether it oscillates over the whole range will depend on the individual components and construction. A well designed oscillator will have a controlled feedback path rather than relying on stray coupling.

Brian.
 

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