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[SOLVED] One transistor radio, can somebody help me please

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michael 1978

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hello

can somebody explain me, how does work capacitor between emitter and collector? and all circuit if its possible

6coFaTR.png

[from imgur. com/a /fcJ5w]
 
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It looks like a super regenerative receiver:
https://www.youtube.com/watch?v=qvpvn6T5PBQ&t=143s

Without the capacitor the circuit wouldn't oscillate. If you put the correct capacitor between the collector and emitter it will create a negative AC resistance on the collector.
With noise and negative resistance the LC tank will resonate, and the amplitude of the oscillation will increase.

In super regenerative receivers there is an other oscillation which is called "quenching". Quenching is when a slower circuit or the RF oscillator itself stops its own RF oscillation from time to time.
It creates a very good sensitivity for the receiver, because at the building up of a new RF oscillation period the received signal is added to the noise of the RF oscillator, and the building up is exponential!

So, for example if the received signal is an AM signal, and the momentary amplitude of this wave is a bit higher, the oscillation will build up much faster, and reaches higher power before the next stop.

It works with wideband FM signals too, in that case it works like a slope detector which is regenerative.

About how the quenching works you can read more from this paper, page 3:
https://www.smarterworld.de/fileadmin/media/whitepaper/files/MCA481wp_Low_costembedded_receiver.pdf
 
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one transistor radio, can somebody help me please

hello

can somebody explain me, how does work capacitor between emitter and collector? and all circuit if its possible
 

Attachments

  • single-transistor-FM-radio-circuit-1.rar
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Re: one transistor radio, can somebody help me please

You are asking about this simple circuit from India on many websites forums, aren't you?
I can't open a RAR file, why not post an ordinary PNG or GIF file instead?
 

Re: one transistor radio, can somebody help me please

hey man, where did you find me here? ;-), this the same one transistor radio, but is it tru that capacitor between collector and emitter act as voltage divider
 

OOh man thank you very much, but still i dont understand, capacitor betwen collector and emitter act like voltage divider? the capacitor he makes me very complicated circuits

- - - Updated - - -

It looks like a super regenerative receiver:
https://www.youtube.com/watch?v=qvpvn6T5PBQ&t=143s

Without the capacitor the circuit wouldn't oscillate. If you put the correct capacitor between the collector and emitter it will create a negative AC resistance on the collector.
With noise and negative resistance the LC tank will resonate, and the amplitude of the oscillation will increase.

In super regenerative receivers there is an other oscillation which is called "quenching". Quenching is when a slower circuit or the RF oscillator itself stops its own RF oscillation from time to time.
It creates a very good sensitivity for the receiver, because at the building up of a new RF oscillation period the received signal is added to the noise of the RF oscillator, and the building up is exponential!

So, for example if the received signal is an AM signal, and the momentary amplitude of this wave is a bit higher, the oscillation will build up much faster, and reaches higher power before the next stop.

It works with wideband FM signals too, in that case it works like a slope detector which is regenerative.

About how the quenching works you can read more from this paper, page 3:
https://www.smarterworld.de/fileadmin/media/whitepaper/files/MCA481wp_Low_costembedded_receiver.pdf[/QUOTE

OOh man thank you very much, but still i dont understand, capacitor betwen collector and emitter act like voltage divider? the capacitor he makes me very complicated circuits

- - - Updated - - -

I agree that it is a super regen crappy FM tuner. It is too simple to be a real FM tuner.

where did you find me here man;-; rely this capacitor make me very complicated circuits, help me
 

Re: one transistor radio, can somebody help me please

No, it is not the same radio because on the other websites you posted two radio tuners (not radios that have power amplifiers), a lousy AM crystal radio tuner and a lousy "FM" super-regen radio tuner.
The AM crystal radio tuner had a capacitor from the collector to ground (also the emitter was at ground) so the capacitor did not make a voltage divider, instead it made a lowpass filter. The super-regen radio tuner had an emitter resistor and inductor so that the capacitor from emitter to collector also did not make a voltage divider, instead it caused the transistor to oscillate.

- - - Updated - - -

On the other forum you posted the schematic of an "FM" super-regen radio tuner and received a reply about it that had a video that explained how it works. Here is the schematic from India that you posted:
 

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  • super-regen FM tuner.png
    super-regen FM tuner.png
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Re: one transistor radio, can somebody help me please

but i think this work also without capacitor between collector and emitter, i simulate
 

Re: one transistor radio, can somebody help me please

but i think this work also without capacitor between collector and emitter, i simulate
"work" means what particularly?

There isn't even an antenna input shown. How do you check correct operation?

The common base circuit might oscillate without external feedback by the working of parasitic Cce or other feedback effects, but probably it doesn't.

My question is, do you understand common base circuit, positive feedback, oscillators, LC tank circuits, super-regenerative receivers?
 

Re: one transistor radio, can somebody help me please

this i dont understand super-regenerative receivers
but i put ac van 200mv between c1 - +
 

Re: one transistor radio, can somebody help me please

The antenna input of the simple super-regen tuner is not C1. C1 is a capacitor to ground the base of the transistor to radio signals so that it operates as a common-base oscillator. My old schematic is VERY similar to yours and shows the antenna connected to the EMITTER of the transistor:

- - - Updated - - -

The problems are that Michael 1978 does not understand the basics of electronics and his simulation program knows nothing about a stupid simple super-regen tuner.
 

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  • super-regen FM tuner.png
    super-regen FM tuner.png
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OOh man thank you very much, but still i dont understand, capacitor betwen collector and emitter act like voltage divider? the capacitor he makes me very complicated circuits

yes, it acts like a voltage divider. the Cce and Cbe capacitances are the parts of the divider. Cbe usually higher, so to maintain good division ratio, people add extra Cce capacitor sometimes. the capacitive divider and the transconductance of the transistor create the negative AC resistance at the collecor then.
 
I disagree, a capacitive voltage divider does not matter. The capacitor between the collector and emitter simply provides positive feedback so that oscillation can happen.
Also, the transistor collector does not have "negative resistance".
 

Positive amplifier feedback and creating a negative impedance are complementary views on electronic oscillators. Both are valid explanations.
 
i read one articul over super regenarative oscillator, but i dont know wich value of capacitor c1 and c5 to put
 

i read one articul over super regenarative oscillator, but i dont know wich value of capacitor c1 and c5 to put

The value of C1 determines its ability to "ground" the base of the transistor at radio frequencies.
The value of C5 determines the squegging frequency. For an FM tuner you do not want the squegging frequency too low to beat with the 19kHz pilot tone or beat with the 23kHz to 53kHz stereo sidebands or with the 67kHz storecast music sidebands. But you want the value of C5 to bypass R3 at the radio frequency.
 
The value of C1 determines its ability to "ground" the base of the transistor at radio frequencies.
The value of C5 determines the squegging frequency. For an FM tuner you do not want the squegging frequency too low to beat with the 19kHz pilot tone or beat with the 23kHz to 53kHz stereo sidebands or with the 67kHz storecast music sidebands. But you want the value of C5 to bypass R3 at the radio frequency.

so wich value to chose for c1 standard value are? yes i want for radio frquence, but sorry i forget to ask about value of c4
 

Are you making a tuner for the FM broadcast band at around 100MHz?
Did you try it with the capacitor values shown on the schematic you found and the similar schematic I found?
 

Are you making a tuner for the FM broadcast band at around 100MHz?
Did you try it with the capacitor values shown on the schematic you found and the similar schematic I found?

Yes the values on schematic
 

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