Hi If odd “almost 10 MHz OCXO’s were more common, you could indeed have a bit more freedom on the offset. DDS is sometimes used. DDS spurs (which can be *very* close in) can be both hard to predict and hard to spot in the data. An OCXO is a much better bet unless you have a lot of time on your hands or a really good spectrum analyzer.
Much easier to get a $20 Trimble OCXO at auction and ground the EFC pin…. Bob On Oct 12, 2014, at 8:25 PM, Magnus Danielson <mag...@rubidium.dyndns.org> wrote: > Bob, > > I know, and I know you know. Just let others see how things connect up. > > Still have some 10.000110 MHz OCXOs lying around. > > Cheers, > Magnus > > On 10/13/2014 02:15 AM, Bob Camp wrote: >> Hi >> >> The 1/F noise vs beat note “amplification” tradeoff is what pushes me up to >> 10 Hz rather than staying down around 1 Hz with most setups. It’s also a >> rational offset to achieve at 10 MHz with common OCXO’s. Once you get past >> about 20 Hz, your OCXO choices diminish. >> >> Bob >> >> On Oct 12, 2014, at 7:57 PM, Magnus Danielson <mag...@rubidium.dyndns.org> >> wrote: >> >>> Increasing the beat frequency to find a balance between 1/f noise and >>> f/delta-f amplification may be worth doing and have been seen done to find >>> "optimum" performance. If you use hard limiters or audio channels to >>> achieve it is however a little detail. >>> >>> The benefit of audio channels is that the A/B channels does not disperse >>> out in time, such that you loose cross-correlation of transfer oscillator >>> noise. >>> >>> Some AD inputs may need to be modified to remove DC-blocking cap. Not all >>> ADCs is happy with this. Some boards already have that and do DC-removal in >>> digital filters. >>> >>> Cheers, >>> Magnus >>> >>> On 10/12/2014 11:09 PM, Bob Camp wrote: >>>> HI >>>> >>>> A little more information: >>>> >>>> If you are doing the ADC thing, you still need to estimate zero crossings. >>>> In all likelihood you would be doing bandpass filtering first (say 8 Hz to >>>> 12 Hz) on your 10 Hz note. Next you would do some sort of estimator to get >>>> the zero cross. A curve fit is one sort of estimator, there are others. A >>>> simple straight line fit over 4 or so points might do it. A higher order >>>> fit over a few more points is possible. Why does that matter? The fit >>>> improves your accuracy quite a bit. It also reduces your vulnerability to >>>> odd single sample issues like popcorn noise. Since you are running at a >>>> very low frequency 1/f noise can be an issue. >>>> >>>> Bob >>>> >>>> On Oct 12, 2014, at 2:37 PM, Hal Murray <hmur...@megapathdsl.net> wrote: >>>> >>>>> >>>>> anders.e.e.wal...@gmail.com said: >>>>>> Does it matter that the ADC in the sound-card is probably clocked by a >>>>>> crystal clock that is 50ppm off and has bad ADEV? >>>>> >>>>> You can calibrate the clock on the ADC. >>>>> >>>>> One way is to feed a known reference frequency in on the other channel. >>>>> (That's assuming you have a stereo setup and don't need the second channel >>>>> for something else.) >>>>> >>>>> Another way is to compare the sample rate with the PC clock. That will >>>>> correct for any long term drift but may not track shorter transients. >>>>> >>>>> -- >>>>> These are my opinions. I hate spam. >>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- time-nuts@febo.com >>>>> To unsubscribe, go to >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.