[time-nuts] Help with TCXO

Michael Malloy mechano at gmail.com
Mon Nov 28 03:30:36 EST 2011


its a shame i cannot post the picture i took is there any way to be
able to send my oscilloscope picture its 800k thats the problem

On Mon, Nov 28, 2011 at 7:29 PM, Michael Malloy <mechano at gmail.com> wrote:
> 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?*/
>



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




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