[time-nuts] Help with TCXO

[Michael Malloy]

I was pretty sure that the 4000 CMOS range was only really good sub
1Mhz I am wrong here? please correct me
thats why I chose the 74HC series as its high speed CMOS??

On Mon, Nov 28, 2011 at 6:58 PM, ehydra <ehydra at arcor.de> wrote:
> 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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Michael
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