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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".
C4 smooths radio frequency variations on the supply voltage for the oscillating transistor but its value is not high enough to affect audio frequencies.
Wikipedia shows a voltage divider with two capacitors at the emitter but this circuit has only the feedback capacitor from the collector to the emitter. Stray wiring capacitance will add a small amount of voltage divider action that does not matter.
Wikipedia discusses the negative resistance of a different Colpitts oscillator with feedback from the emitter to the base.
Wikipedia shows a voltage divider with two capacitors at the emitter but this circuit has only the feedback capacitor from the collector to the emitter. Stray wiring capacitance will add a small amount of voltage divider action that does not matter.
Wikipedia discusses the negative resistance of a different Colpitts oscillator with feedback from the emitter to the base.
"One method of oscillator analysis is to determine the input impedance of an input port neglecting any reactive components. If the impedance yields a negative resistance term, oscillation is possible."
This is the first row of the theory. Doesn't matter the circuit. At the collector if you take an analysis you will also get a negative resistance part for the impedance. The LC tank can't see the circuit, it just needs a negative resistance to compensate its own dissipation. We use positive feedback to create this negative resistance. Same thing as FvM mentioned.
And you forgot about the above circuit's Cbe capacitance. The base is AC grounded by C1 capacitor, so Cbe represents the second capacitor which is on the Wikipedia. Cbe is not negligible.
The above circuit? No. Any other colpitts and supreg receiver? Yes. But I don't see too much difference. And I also did the analysis of the grounded base oscillator of the wikipedia page. The impedance at the collector:
The imaginary part of Z(jω) are the capacitors of the LC tank (C1×C2), and the real part is the frequency dependent negative resistance.
rd is the differential resistance of the transistor in the operation point, it is Ut/Ie0, where Ut is the thermal voltage (≈26mV on room temperature), Ie0 is the DC operating emitter current.
If the absolute value of the resistive part in the complex Z(jω) is higher than the losses of the LC tank, it can oscillate. Sorry for repeating.
At least 1 million, rather a hundred. Or 10, maybe 12. It depends on the frequency you want, the total capacitance at the collector, the cross-section, permeability, diameter of the carrier material, the diameter of the wire. You are a beginner at electronics, aren't you? Altough it uses one transistor, supreg is a complicated thing for beginners.
Your schematic of the super-regen FM tuner is marked "Swagatam Innovations" which is a hobby site in India. Didn't you see the project that I could not find there? Didn't the project have instructions about how to make the coil?
I looked at FM Super Regen in Google and most circuits use a coil of 5 or 6 turns around a 1/8" to 1/4" former (3 to 6mm) and the turns have a small spacing so they do not touch each other. Then turn the variable capacitor to tune in FM radio stations.
Try using a 40cm wire as the antenna connected to the emitter of the transistor as shown in the similar super-regen FM tuner I posted.
Since FM radio is at a very high Frequency then the way the parts are connected together is important. A pcb is usually used but I use a compact stripboard layout for my circuits. It will not work if you build it on a solderless breadboard because there is too much capacitance between the strips of contacts and wires.
Your schematic of the super-regen FM tuner is marked "Swagatam Innovations" which is a hobby site in India. Didn't you see the project that I could not find there? Didn't the project have instructions about how to make the coil?
I looked at FM Super Regen in Google and most circuits use a coil of 5 or 6 turns around a 1/8" to 1/4" former (3 to 6mm) and the turns have a small spacing so they do not touch each other. Then turn the variable capacitor to tune in FM radio stations.
Try using a 40cm wire as the antenna connected to the emitter of the transistor as shown in the similar super-regen FM tuner I posted.
Since FM radio is at a very high Frequency then the way the parts are connected together is important. A pcb is usually used but I use a compact stripboard layout for my circuits. It will not work if you build it on a solderless breadboard because there is too much capacitance between the strips of contacts and wires.
Do you need an FM radio that works well, or are you simply learning how to solder parts together?
This circuit is so simple that it has some serious problems if you can fiddle with it to make it do anything:
1) It is overloaded by strong local radio stations.
2) It has poor sensitivity so it will not pick up weak distant stations.
3) It has poor selectivity so more than one local station might be heard at the same time as another local station.
4) Since it does not have a proper FM detector it picks up all kinds of AM pops, clicks and buzzing interference.
5) Since it does not have a proper FM detector then it produces pretty bad distortion, depending how you tune it.
6) Its tuned radio frequency and amount of distortion will change as the battery voltage runs down and if the temperature changes.
Maybe you should make a kit FM tuner instead. Many years ago my first electronic projects were a kit power amplifier and a kit FM tuner. The kits came with all the parts and a pcb. They were designed properly, worked perfectly and performed very well.
Supreg receiver doesn't like FM at all. The most reliable receivers are working in the aircraft band or airband, where the quenching can be at higher frequency and the modulation can be AM. As I know.
Do you need an FM radio that works well, or are you simply learning how to solder parts together?
This circuit is so simple that it has some serious problems if you can fiddle with it to make it do anything:
1) It is overloaded by strong local radio stations.
2) It has poor sensitivity so it will not pick up weak distant stations.
3) It has poor selectivity so more than one local station might be heard at the same time as another local station.
4) Since it does not have a proper FM detector it picks up all kinds of AM pops, clicks and buzzing interference.
5) Since it does not have a proper FM detector then it produces pretty bad distortion, depending how you tune it.
6) Its tuned radio frequency and amount of distortion will change as the battery voltage runs down and if the temperature changes.
Maybe you should make a kit FM tuner instead. Many years ago my first electronic projects were a kit power amplifier and a kit FM tuner. The kits came with all the parts and a pcb. They were designed properly, worked perfectly and performed very well.
i have a chip TDA7000, but problem is that i want to understand the procedures, how work radio, modulation amplififer, lowpass highpass etc,
in that kit fm tunner do they explain something? of only how to connect, because i buy crystal radio kit, they dont explain nothing, just how to connected.
can i use for oscillator , i dont see good i think bc547, and for amplifier two stage 2N5551
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i dont know, wat to say, maybe to try te get a little experience
The TDA7000 radio IC is obsolete and had poor performance. It was replaced by the TDA7088 that also had poor performance. A "radio" with a TDA7088 can be purchased at The Dollar Store for only one dollar. I have two of these awful "radios".
The "radio" comes with a battery and earphones so the actual "radio" is free. The TDA7088 scans for the next radio station but frequently misses a few.
Why aren't you learning about electronics in school?? You need to learn about a real radio circuit that is used in almost every radio, not this extremely simple super-regen or a crystal radio.
Why do you want an oscillator? Why make an amplifier with high voltage, low current 2N5551 transistors? A speaker needs high current not high voltage.
The TDA7000 radio IC is obsolete and had poor performance. It was replaced by the TDA7088 that also had poor performance. A "radio" with a TDA7088 can be purchased at The Dollar Store for only one dollar. I have two of these awful "radios".
The "radio" comes with a battery and earphones so the actual "radio" is free. The TDA7088 scans for the next radio station but frequently misses a few.
Why aren't you learning about electronics in school?? You need to learn about a real radio circuit that is used in almost every radio, not this extremely simple super-regen or a crystal radio.
Why do you want an oscillator? Why make an amplifier with high voltage, low current 2N5551 transistors? A speaker needs high current not high voltage.
ohh man i am working, i dont have time so much for that, if i have a time i will go cursus for electronics ,i need money so i have to work,
and also td7000 i buy a chip, i have to connect all other components, do you know any good book aboud radio???????electronics??????
in 2006 i start one course basic electronics, that called elektronika is niet moelijk deel 1 and deel 3 digital, but for me now is not so difficult, i most to stop to NTI
i dont know so much about transistor, wich one you prefer to take for high current
thnx
A low power audio amplifier has at least 3 transistors. A voltage amplifying driver transistor and a complementary pair of emitter-follower power transistors. If I tell you which transistors that I use then you will probably say they are not available in your country on the other side of the world. Here is a very simple low power amplifier:
Because you found an OLD super-regen radio tuner and an OLD TDA7000 obsolete IC. Then it seems that modern things are not available where you are. Can you buy TIP31 and TIP32 transistors that are made by Texas Instruments? Where are you living?
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