[time-nuts] Input filter for data logger
kb8tq at n1k.org
Sun Nov 19 14:57:11 EST 2017
Based on what I’ve seen off of eBay, a properly working surplus MV89A is a rare beast. The
ones that are “ouch” to the touch do indeed have malfunctioning oven circuits. Out of a few
dozen purchased I don’t think I found one that fully met the specs that it did when shipped.
That easily could have been a function of only buying from the cheapest sellers …..
> On Nov 19, 2017, at 11:40 AM, Vlad <time at patoka.org> wrote:
> I am doing another fun project. It is data logger at this time. The "heart" is MV89A OCXO and the "brain" is STM32.
> "The box" has 1PPS input to control DAC which will control OCXO. BTW, this M89A is pretty hot to touch. My other OCXO's not that much warmed. Is it normal for this Morion model ?
> I woul ask an advise regarding following issue. I have signal generator which produce the square wave. The freq. is 192Hz.
> However, the logger measure it TWICE ! I think its because of that signal form. Here is the output (in microseconds):
> In average delta is .0026041 s, which is almost equal to 384 Hz (192x2)
> For the input I am using the schema similar as HP was using in one of their counters:
> I tried another source (DDS sine generator, referenced from GPSDO) and that beast produce exact number of events:
> However, it is some "spikes" in the data flow (see above the number "26.23559295", which suppose to be something as "26.58..."). I can't understand the reason for that.
> The "delta" is .0052 s, which is almost equal to 192 Hz. But data flow is not that "smooth" though.
> In square wave mode, "school grade" Wavetek generator produced exact 192 events with no issues. (Except its output frequency is not that stable)
> However, if I switch Wavetek to sine, my logger detected twice number of event (384)
> I would assume, some improvement needs to be done for the data logger input. I am using 2N5485 and 74AC04 elements there. Any advises will be appreciated ! Thanks !
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