Please assist TS..Headache has limited his effort

Can not understand image ..The calculation, why correct?

Thank you

 

That calculation is confusing since they don't show the power voltage to the op amp, and, since that voltage affects the op amp output voltage, it also affects the hysteresis value.

 

That calculation is confusing since they don't show the power voltage to the op amp, and, since that voltage affects the op amp output voltage, it also affects the hysteresis value.

my fault..did not say

+-15 and finally assumed output voltage is 10V which is used in the calculation

 

What about the calculation do you not understand?
The hysteresis is the difference between the high and low output voltage reduced by the voltage divider action of R1 and Rf.

 

Vut (upper threshold) is the voltage at the + pin when output is 10V ?

so in the calculation shouldn't it be 7V* and not 10V*

 

Yes, you are correct Zeeus. The voltage across Ra will be the difference between the op amp saturated output and the reference voltage, divided by the resistor ratio. Then add the ref.

So in the figure you posted, the output of the op amp has to be assumed to be + 13 volts for the equations to be correct. Alternately, if the output of the op amp is +10, then the formula should be 7 * [18/(18+91)] + 3.

 

Yes, you are correct Zeeus. The voltage across Ra will be the difference between the op amp saturated output and the reference voltage, divided by the resistor ratio. Then add the ref.

So in the figure you posted, the output of the op amp has to be assumed to be + 13 volts for the equations to be correct. Alternately, if the output of the op amp is +10, then the formula should be 7 * [18/(18+91)] + 3.

Please explain this circuit..."Start of a beginner's transmitter...." will learn it later but just want to understand a little

Thanks

 

Please explain this circuit..

That's a Colpitts transistor crystal oscillator.
A Google search will turn up much info on that.

 

That's a Colpitts transistor crystal oscillator.
A Google search will turn up much info on that.

Yes it will turn up much info..Just need summary of that information now as will surely read on it later in book

Is the crystal itself not an oscillator? why then add the transistor and capacitor etc

 

Is the crystal itself not an oscillator?

No.
The crystal is just a mechanical resonator with a very accurate resonant frequency.
The crystal is piezoelectric so the mechanical resonance creates a small electrical signal, but it can't resonante by itself.
So an amplifier is needed to feed a signal back to it and keep it resonating.
This is provided by the transistor, with the capacitors to generate the proper phase for the feedback signal.
Such oscillators can be finicky, and if the circuit isn't turn just right to generate the proper feedback to the crystal, it can refuse to oscillate.