[time-nuts] Best phase detector / mixer for 100MHz?

[Bob Camp]

Hi

Would be nice to use something like the ADS1278. 

http://www.ti.com/product/ads1278

Lots of channels to cross correlate, and very little flicker noise.

Bob


On Nov 28, 2012, at 9:29 AM, Support HpW-Works.com <support at hpw-works.com> wrote:

> Hi Bruce,
> 
>>> The equivalent phase noise (measured in dBc/Hz) is essentially independent of
>>> the sample size.
> 
> The dBc/Hz normalization is based on this (also the sample rate). While the sample
> rate & sample size = FFT Bin size (resolution or filter band width) is used to get
> the required correction factor of the spectrum to get the dBc / (1Hz) Y scaling
> back.
> 
>>> So increasing the sample size isnt particularly useful for reducing the phase
>>> noise floor.
> 
> By theory, yes... but we use a sound card with a lot of flicker noise on the lower
> end, also we have the 10...20Hz low freq. cutoff due the usage of a servo / single
> 5V power. Also the raising noise below 100Hz (ADC serve & noise on the ADC power /
> input circuit) limits the performance.
> 
> In my simple test increase of the sample size reduced the noise floor in better way
> than just using sample size with 1-2K and large averaging cycles.
> 
> Keep in mind, Bin resolution is sample rate / sample size:
> 
> Example: 
> 
> - 32khz / 32678 = about 1Hz
> - 32khz / 1024  = about 31 Hz
> 
> 
>>> However with a sound card plus a mixer a somewhat lower number of samples
>>> should suffice since there is no carrier.
> 
> 
> Ideally the input circuit & ADC of the 3562A would be nice but with much larger RAM
> buffer and ASIO interface O:)
> 
> Hanspeter
> 
>>> -----Original Message-----
>>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf
>>> Of Bruce Griffiths
>>> Sent: Dienstag, 27. November 2012 12:31
>>> To: Discussion of precise time and frequency measurement
>>> Subject: Re: [time-nuts] Best phase detector / mixer for 100MHz?
>>> 
>>> Support HpW-Works.com wrote:
>>>> Bruce,
>>>> 
>>>> 
>>>>>> There's no evidence of a cross power spectrum function in this suite.
>>>>>> One needs to be able to average at least 10,000 cross power spectra
>>>>>> for some applications.
>>>>>> 
>>>> In the PSD (power density)&  PSP (power spectrum) there are cross
>>>> power and cross power complex average implemented (selectable using the
>>> spectrum channel mixer)!
>>>> Additional to this you may apply / add averaging of the resulting
>>>> spectrum or use additional peak hold.
>>>> 
>>>> Average of 10'000 cross points is a large count and often seen on 1-4k
>>> sample size.
>>>> Better in my opinion is to use a higher sample size 32k-64k and then
>>>> less averaging is required.
>>>> 
>>> The equivalent phase noise (measured in dBc/Hz) is essentially independent of
>>> the sample size.
>>> So increasing the sample size isnt particularly useful for reducing the phase
>>> noise floor.
>>> The increased frequency resolution achieved by increasing the sample size is
>>> only useful for measuring spurs.
>>> In the direct digital method of measuring phase noise a few terasamples (a few
>>> gigasamples at baseband) need to be processed to achieve a sufficiently low
>>> instrument noise floor.
>>> However with a sound card plus a mixer a somewhat lower number of samples
>>> should suffice since there is no carrier.
>>>> Just download the evaluation version with fully feature set.
>>>> 
>>>> HpW
>>>> 
>>>> 
>>>> 
>>> Bruce
>>> 
>>> 
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> 
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