[time-nuts] ADEV vs MDEV - DMTD sound card

Bob Camp lists at cq.nu
Sun Feb 7 08:36:09 EST 2010


That was actually talking about a heterodyne system.

Indeed a good digitizer could be used with a DMTD. One thing I have not looked into is the DC accuracy required if you go that way. Some of these approaches have odd little gotcha's. By analogy with a heterodyne setup it might not. That's not always the best way to analyze things ....


On Feb 7, 2010, at 3:50 AM, Magnus Danielson wrote:

> Bob Camp wrote:
>> Hi
>> I believe the statement:
>> "Both systems are equally limited by the reference oscillator"  was part of the same paragraph as the comment on 10811 short term stability.
>> Neither system, no matter how well set up will get below the stability of the reference oscillator.
> For DMTD systems the transfer oscillator noise can be partially cancelled. You do have two inputs, but you then play three-cornered hat tricks. However, for a DMTD system to be able to cancel noise, good time-correlation between channels is needed to make the noise-integration time-periods of both channels to match up. The more they are apart, the bigger difference in noise it is between the channels and thus it will fail to cancel. Thus, phase-alignment prior to ZCDs could be a treatment. Using the audio channel approach avoids the issue as the full-wave signal is being used and time correlation between samples is high, an approach not available when DMTD was developed.
> Cheers,
> Magnus - while visiting fellow time-nut
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