[time-nuts] Square to sine wave symmetrical conversion (part 2)

[jerry shirᴀr]

"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" <alexpcs at ieee.org> 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, timeok at timeok.it 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 -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>