I think that no one can say anything on that setup. Anyway, try this: run
the GPSDO 10MHz into the radio and take the measurements. Then run your
signal and let us know the difference. Usually running the reference
against itself (if possible) gives the noise floor of the measurement
setup... if you can't see any difference then maybe the noise is too high.

On Wed, Jul 4, 2012 at 10:23 PM, Bill Dailey docdailey@gmail.com wrote:

Hi Bill,

On 07/04/2012 10:23 PM, Bill Dailey wrote:

At this point you should have 1 kHz sampling rate, and the FFT window
will be 32,768 s long. So far my only question is what your radio is
dialled into, as it will give the beat frequency on the audio side and
also the scaling factor for the phase-deviations.

How do you do that? If you have a 32,7 s long FFT window, you only get
results at that rate. Are they interleaved? 32 interleaved will give you
measures every 1,024 s.

If you taking the readings out of the top bin on your spectrum plot,
then the FFT window time will scale the "instruments" hardware
bandwidth, as to be expected from the Nyquist theorem. This has proven
not to be all the truth, as there will be a droop (bias error) for the
short-tau ADEV measures, which wears off and is essentially gone after a
decade or so. Hence, using long FFT windows will reduce the rate of
samples and cause short tau measure of interest to be biased and untrusted.

The recommended practice is to use a higher sampling rate, and in your
case shorter FFT window, maybe skip the decimation, such that you can
afford to remove low tau0 multiples such that what you see is what you
can trust.

Please have a look at the Allan Deviation wikipedia page, I think you
will find some useful stuff there. I'd happy to adjust it if needed.

It's a fair question to ask. It's also a good question to ask.

It would be good if you could calibrate your setup by using known
sources with known phase-noises. While I like the tool I have, I will
sure that I do my calibrations one way or another.

Cheers,
Magnus

Yes, I'm also interested in how-to. At the moment I think it is a hack:
there is no sound card AFAIK that accepts a reference input. I have
recently bought an Acqiris/Agilent DP105/U1067A 150MHz 500Ms/s digitizer
PCI card that accepts an external 10MHz as a reference for the sampling
process.

On Fri, Jul 6, 2012 at 4:43 PM, Stewart Bryant stewart@g3ysx.org.uk wrote:

I think a number of higher-end sound cards accept a "word clock" or
"world clock" (I've seen it both ways) that's intended to allow syncing
to an external source.  The challenge I've seen is that the frequency
(either in the 12 or 24 MHz range) is one that's not simple to
synthesize precisely (i.e., zero offset from nominal) and with low
jitter/phase noise from a 5 or 10 MHz reference.

I think it would be a great project to come up with a synthesizer block
that could do that.  It's been on my list for a long time, but hasn't
yet risen near the top.

John

On 7/6/2012 10:51 AM, Azelio Boriani wrote:

On 7/6/12 7:51 AM, Azelio Boriani wrote:

while there are no "sound cards" (in the sense that they physically plug
into the PC bus) with external clock inputs, there are quite a few sound
interfaces that take a sample clock input (e.g. at 44.1, 48,96, 192) of
some sort.

A lot of them use 1394/Firewire (for historical reasons)

what you're looking for is "word clock in"  or similar things

On 7/6/12 7:51 AM, Azelio Boriani wrote:

oops I was wrong.. there ARE people making PCI multichannel audio
interfaces with external clock.. RME in Germany makes more than one.

OK, found it: the RME HDSPe RayDAT PCIe audio card has this reference but
with the optional extension card (of course). It is $950 for the card + the
expansion card for the world clock...

On Fri, Jul 6, 2012 at 5:09 PM, Jim Lux jimlux@earthlink.net wrote:

Word clock generators appear to exist that will accept standard external reference frequencies.  One of the vendors also sells a stand alone 10 MHz rubidium reference for driving their word clock generator.

Sent from my iPod

On 2012-07-06, at 8:09 AM, Jim Lux jimlux@earthlink.net wrote:

I don't know if they've been discontinued, but a number of the M-Audio
cards had word clock inputs as well.  They are/were pretty widely
available on eBay.

John

On 7/6/2012 11:24 AM, Azelio Boriani wrote:

A few cards accept a reference clock in the MHz range (usually under the term "Superclock"), but most wordclock inputs are made for the wordclock frequency itself, for example 48 kHz. An internal PLL (of varying quality) multiplies that up to a multiple of it for driving the converter and shift clocks.

Those PLLs often have a rather wide lock range, so you'd be able to feed 50 kHz (or 100 kHz or 200 kHz) into it, which can be divided down from 10 MHz quite easily.

Not sure whether that's what you want, however.

Cheers
Stefan

Removed the oscillator and send it the required freq (24.576MHz) that is disciplined to 10MHz.  Put an sma connector next to the card in the little cover on the pci slot.  Currently using my ds345 but am getting a Valon Synthesizer board with a divider.  Tried ve1alq but the dividers aren't right and can't seem to fix that.  Have a vcxo but no way to discipline it.  Just going to break down and go the Valon route.  Will also use it for 125MHz for my qs1r.

Have done this setup with 2 sound cards.  One is a SB xfi surround USB and the other is fata1ity extreme gamer.  Works like a charm for both.  20uHz plus minus through my radio (with 10MHz signal)  Should be much better with audio but can test because my ds345 is tied up.  I would bet I will have substantially sub-uHz precision is the audio only domain.

Doc
KX0O

Sent from my iPhone

On Jul 6, 2012, at 9:43 AM, Stewart Bryant stewart@g3ysx.org.uk wrote:

OK, I'll take a look at my cheap audio cards searching for the oscillator.

On Fri, Jul 6, 2012 at 5:59 PM, Bill Dailey docdailey@gmail.com wrote:

On 07/06/2012 04:58 PM, John Ackermann N8UR wrote:

A correct word clock should run at sample rate, i.e. 48 kHz or 96 kHz,
which isn't stellar in synthesis difficulty.

For description of Word Clock, please see Appex B in AES 11.

There are system clocks also being used, typically x128 of the sampling
rate, so 6.144 MHz, 12.288 MHz and 24.576 MHz hence is popular. Again
not stellar to lock.

Cheers,
Magnus

On 07/06/2012 05:09 PM, Jim Lux wrote:

digital audio => need to lock clocks.

Long ago existed audio boards which sample rate converted (badly)
digital audio, this proved to be a killer for pro apps. With digital
audio you need to control your clocking and have things tied to a
master, especially when having multiple sampling boxes. etc.

The analogue world was so much easier in this regard...

Cheers,
Magnus