"Not necessarily. Many oscillator circuits do not deliver a good sine wave to begin with"
This is very true. However if it is worse than -30dB harmonic sinewave back stream then the oscillator is probably extremely high in phase noise anyway. Since the threshold is off center, the phase noise of the 20% duty cycle squarewave will have additional amounts from the AM noise on the signal adding in from that threshold offset. The reason we want 50% is to get the cleanest signal possible with what we have to work with. :) Jerry N9XR. On Jul 25, 2015 3:17 PM, "Alexander Pummer" <[email protected]> wrote: > it is relative easy to make a perfect 50% square wave from almost any > input wave form > > U1 could be any-- fast enough for the desired frequency--comparator or a > transistor pair similar to Charles Wenzel's circuit, R1 C1 is a long time > integrator,[ RxC >> 1/f of the incoming frequency] the voltage at "A" is > proportional with the duty cycle, U 2 is some high gain low noise, low > input offset voltage high input impedance amplifier, the duty-cycle is set > by R4/R5, fine tuning with R6, C2v removes the noise Vr is well stabilized > reference voltage, > To set up the circuit the output should be connected -- with DC decoupling > -- to a spectrum analyzer's input for watching the second harmonic [a > perfect 50% duty cycle square wave lacks of even harmonics ..] of the input > frequency, which has to be adjusted to minimum with R6, using the same > stile resistors for ±0,1%, R4 and R5, with value 100 times of R6 a very > good temperature stability could be achieved. for better short time > stability R2 's top could bealso connected to Vr, > If the drive capability of U1 is not enough for the load non-inverting > buffers could be inserted to U1's output, of course that circuit wil > contribute some phase noise/ jitter too. > 73 > KJ6UHN > Alex > > > On 7/25/2015 1:34 AM, [email protected] wrote: > >> >> bypassing the inverter you will improve phase noise. Yuo will probably >>> need a sine buffer at 10MHz to drive 50 ohms. >>> >> This separator con be the solution: >> http://www.timeok.it/files/hp5065AoptH10v200.pdf >> high input impedance, output 50Ohm, high power handling and low additive >> phase noise. >> >> But before measure using an oscilloscope the output of the GPS OCXO >> directly on the output pin to verify if there is a sine-wave or square >> >> Luciano >> timeok >> Message sent via Atmail Open - http://atmail.org/ >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
