[time-nuts] Input filter for data logger

Vlad time at patoka.org
Sun Nov 19 16:10:54 EST 2017

> The MV89 is a beast of an OCXO and uses more power at warm-up than any 
> other
> I know of. But it is spec'ed ~1W for steady state. Which means the
> outside of the OCXO should be about hand-warm. If it's too hot, then
> the heater circuit is probably broken and running at full-throttle.

If so, I think something is not OK with my MV89. It is probably 110 
degrees or so.

> Can you show us what _your_ circuit looks like instead of some bad
> (literal) screenshot?

Here is my schematic:


I did some simple tests for this. In it seems it was OK up to 10Mhz.

> But guessing from what you showed, I would say that your amplifier
> circuit isn't stable and has some gain peaking at around 10MHz.
> There are two ways to proceed: Either optimize your circuit or
> simplify it using modern components to the input signal you expect.

The main purpose for this circuit is to protect the MCU input and make 
some sine to square conversion.

> If you only want to time-stamp input pulses and you can ensure
> that those pulses are between 0 and 5V, then I'd use a 74LVC1G34
> or 74LVC1G04, depending on whether you want inversion or not
> (do not use the 74LVC1G14 as the hysteresis will increase the noise 
> level)

I was using 74AC04 just because it was readily available in my junk box. 



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