[time-nuts] Help with TCXO

[Michael Malloy]

On Mon, Nov 28, 2011 at 7:14 PM, Michael Malloy <mechano at gmail.com> wrote:
> yeah it is squaring up, but not great I have already designed the
> circuit boards, hmm
> maybe if i replace the 74HC04 with a 74HC14 (schmitt trigger input)
> which I do not have
> I did make a surface mount single gate schmitt trig after the 74HC04
> as I knew that
> this squares things up much better, however after the 74HC04 it goes to
> a 74HC4040 divide by 12 counter and from that input it goes to another
> 74HC04 into the processor
> I am worried that the fact that the counter and the processor are 90
> degrees out of phase clock cycle
> if I put the single gate schmitt trig in it will bring both in phase
> I may need to make software adjustments if this happens??
>
> and no I did not test the unit without any load, I had a hombrew TCXO
> in the original
> circuit but its performance was only +- 10PPM and caused problems with the codec
> its a very sensitive design to jitter, TXCO was cheapest option but if
> I had the money would have put an OCXO
> in but they are not cheap in small runs, I am getting off track
> I will take a picture of my oscilloscope and post it
>
> let me see if the 74HC14 is pin for pin compatible with 74HC04 maybe I
> will replace with this.
> but I do not think I have any here
>
> On Mon, Nov 28, 2011 at 6:36 PM, Attila Kinali <attila at kinali.ch> wrote:
>> 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
>>
>> --
>> Why does it take years to find the answers to
>> the questions one should have asked long ago?
>>
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>
>
>
> --
> #include <sig.h>
> /* ================ */
> Michael
> /*How crazy does it get on the moon, when theres a full Earth?*/
>



-- 
#include <sig.h>
/* ================ */
Michael
/*How crazy does it get on the moon, when theres a full Earth?*/