[time-nuts] Help with TCXO

ehydra ehydra at arcor.de
Mon Nov 28 02:58:01 EST 2011


Maybe the HC04 oscillates but the experimenter doesn't see it. Or 
misunderstood that ICs have to be seen from top, not bottom like 
transistors.

It is better to use an HCU04. Even a 4069UB should work at 8MHz at 5V. I 
would prefer 100K feedback and several stages AC-coupled.

The 5V is nominal, so use 5V not 4,9V. But it is not important for your 
problem.

- Henry


Attila Kinali schrieb:
> On Mon, 28 Nov 2011 16:15:37 +1100
> Michael Malloy <mechano at gmail.com> wrote:
> 
>> Hi all I ordered a 8.192MHZ TCXO 1.0PPM
>> Now it was supposed to have a clipped sine wave output? however it
>> looks more like a saw tooth, I assumed a clipped sine would be a sine
>> wave with the peaks clipped, I am running this through
>> a 150pF cap and then using a inverter amplifier i.e. 74HC04 with a 1M
>> resistor from input to output.
>>
>> am I over loading or loading down the the oscillator, or should I be
>> changing the buffer capacitor?
>> I mean the circuit is working but its not 45/55 duty cycle
>> the out put looks like the first 0 -90 degrees of a sine wave then
>> drops to zero stays there for about 20% of the duty cycle then ramps
>> back up?
> 
> Do you measure the TCXO raw, w/o any circuitry attached?
> Because this sounds rather like that the 74ZHC04 is messing
> with the signal. Maybe the 1M resistor isnt really 1M?
> 
> Other than that, i would feed the output directly to
> a 74HC14 (schmitt trigger input) to square it. If you
> want to have precise or adjustable duty cycle, you can also
> use a comparator (but make sure to include enough hysteresis,
> otherwise the comparator might oscillate)
> 
> 
> 			Attila Kinali
> 

-- 
ehydra.dyndns.info




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