mstechca said:This is the closest match on the web to my design. Also a transistorized ultra-audion oscillator I found in a book is the closest match as well. What I am ultimately seeking is a way to adjust several dozen Mhz using only one trimmer capacitor not two, AND be able to pick up CHTV (channel 11) at a decent amplitude.
My previous design worked, but the problem is that I had to adjust two capacitors, every time I want to change the frequency.
These capacitors are the positive feedback one, and the one in the emitter tank.
Is there a way I can do it?
mstechca said:If I add that coupling capacitor from emitter to collector again, then the frequency will change, and more math will come into play. If someone could explain the math (even if I decide to add the capacitor in the future), I would be happy.
I think it has to do with neutralization, but I am not sure.
I am taking that into consideration. I have C2 grounded, because the circuit I looked at also has it grounded. The problem is if I make C2 the feedback like you suggest, and I have no capacitor from collector to ground, the circuit won't work well for me.audioguru said:MStechca,
A common-base oscillator works by C2 coupling a positive feedback signal from the transistor's collector to its emitter. Your circuit doesn't.
Let's ignore the varactor then. That will happen in the future.The varactor diode's capacitance connects to the high internal resistance of the battery and not to the tuning coil because your circuit doesn't have a
ceramic disc supply bypass capacitor.
mstechca said:what I have been asking for for the longest time is an E-Q-U-A-T-I-O-N.
You know, some math!
Something that allows me to determine the correct frequency based on the components.
It isn't as simple as 1/(2 * pi * sqr(LC)) because I have to somehow mix in the feedback capacitor into the equation!
I guess no one here knows that answer. oh well
Which is probably behaving like an inductor at that frequency.I changed the capacitor from base to ground to a ridiculously large value (22uF).
Nigel Goodwin said:the formula above is the one you need - BUT you can't use it effectively because you've no way of determining the values of L and C - there's also NO NEED TO CALCULATE THE TUNING FREQUENCY.
Note though that you would have a far better chance with a correctly designed circuit, with a random collection of components you can't calculate anything!.
Of course. The inductor at the collector is the tank coil with some stray capacitance across it.mstechca said:I discovered something. When I tie a small value capacitor to the pull-up resistor, the frequency changes.
Why? An LC tank is at a transistor oscillator's collector, not at its emitter.I'll take the LC circuit in the emitter as is.
audioguru said:Of course. The inductor at the collector is the tank coil with some stray capacitance across it.
Thats different. When I went to:
**broken link removed**
and looked at his circuit, he states:
Q1's emitter has a 6 turn RF choke connected to it; below that choke are a 10k resistor to ground and a .001uf cap across that resistor. These 3 components form a subcircuit that makes the superregen unique: the Quench Oscillator. (The 10k resistor is also the emitter load across which we take audio which is sent to the second transistor, Q2, for amplification).
...
The .001uF cap across the 10K resistor forms an RC time-constant circuit that sets the "quenching frequency".
He is agreeing with me.
I think it is just two components (resistor and capacitor), and you are saying it is the capacitor and inductor.
My resistor capacitor and inductor are connected together the same way. except the other end of the inductor is connected to collector and the resistor and capacitor are pull-ups instead.
and I have another question. When the emitter inductor is at 0.1uH I hear more "hum". When I replaced it with a 1uH inductor, I hear more stations. I want a low value instead, because I want to enter the aircraft and TV frequencies.
I wonder if the breadboard is causing difficulties, because I'm doing alot of my testing on a breadboard.
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