Re: [time-nuts] PN on internal/external references and Cross correlation

[John Miles]

> Thanks for clarifying this issue! I may use references with close-in PN
> (1Hz-1kHz) 10 dB noisier than the DUT, however as you said it may
> require an overnight run for 1 Hz offset, which isn't the nice part... I
> assume then that speeding up the measurement process can only be
> obtained using references sources at least quieter than the DUT.

A 10-dB deficit may not be too bad, since the performance improvement isn't 
linear with time.  If your instrument takes 8 hours to drop the measurement 
floor by 20 dB, for instance, it will only take 4 hours to achieve 18.5 dB of 
improvement, or 2 hours for 17 dB.   So if each of the references is 10 dB 
noisier than the DUT, their effect will be mostly gone after 2 hours.

-- john, KE5FX
Miles Design LLC


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Re: [time-nuts] PN on internal/external references and Cross correlation

[Vasco Soares]

Thanks for clarifying this issue! I may use references with close-in PN 
(1Hz-1kHz) 10 dB noisier than the DUT, however as you said it may 
require an overnight run for 1 Hz offset, which isn't the nice part... I 
assume then that speeding up the measurement process can only be 
obtained using references sources at least quieter than the DUT.


Em 2017-09-28 23:29, John Miles escreveu:
In a PN measurement system with a dual channel cross correlation is 
there a

simple rule of thumb for how low should be the PN of the (external)
references compared to the DUT? (even with a 20 dB noise floor
improvement with 1 cross correlations)


If you have two references, then it's OK for them to be somewhat
noisier than the DUT.  Their contribution will average out of the
cross spectrum over time just like the rest of the instrument noise.
There is no penalty in accuracy, only in measurement time.

Given a choice, you're better off using references with good close-in
noise performance rather than good broadband performance, since it
takes longer for those FFT segments to converge.  You can achieve 20
dB of noise floor improvement at offsets >10 kHz within a few minutes,
but a 20-dB improvement at 1 Hz might require running overnight or
even longer.


In the case of the references
have an equal noise contribution compared to the DUT will the results 
suffer

from loss of accuracy?


With two references it's not a problem.  If you have only one
reference source -- or if your measurement setup doesn't do cross
correlation at all -- then the reference needs to be at least 10 dB
quieter than the expected DUT performance to keep its contribution
below 0.5 dB.

-- john, KE5FX
Miles Design LLC


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Re: [time-nuts] PN on internal/external references and Cross correlation

[John Miles]

> In a PN measurement system with a dual channel cross correlation is there a
> simple rule of thumb for how low should be the PN of the (external)
> references compared to the DUT? (even with a 20 dB noise floor
> improvement with 1 cross correlations)

If you have two references, then it's OK for them to be somewhat noisier than 
the DUT.  Their contribution will average out of the cross spectrum over time 
just like the rest of the instrument noise.  There is no penalty in accuracy, 
only in measurement time.

Given a choice, you're better off using references with good close-in noise 
performance rather than good broadband performance, since it takes longer for 
those FFT segments to converge.  You can achieve 20 dB of noise floor 
improvement at offsets >10 kHz within a few minutes, but a 20-dB improvement at 
1 Hz might require running overnight or even longer.

> In the case of the references
> have an equal noise contribution compared to the DUT will the results suffer
> from loss of accuracy?

With two references it's not a problem.  If you have only one reference source 
-- or if your measurement setup doesn't do cross correlation at all -- then the 
reference needs to be at least 10 dB quieter than the expected DUT performance 
to keep its contribution below 0.5 dB.  

-- john, KE5FX
Miles Design LLC


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[time-nuts] PN on internal/external references and Cross correlation

[Vasco Soares]

Hi All,

 

In a PN measurement system with a dual channel cross correlation is there a 
simple rule of thumb for how low should be the PN of the (external) references 
compared to the DUT? (even with a 20 dB noise floor improvement with 1 
cross correlations). In the case of the references have an equal noise 
contribution compared to the DUT will the results suffer from loss of accuracy?



Thanks!

 

Regards,

VS
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[time-nuts] Weird GPSDO behavior

[Skip Withrow]

Hello Time-Nuts,

I have a NTGS50AA GPSDO (close cousin to the NTBW50AA and Thunderbolt)
with the OCXO removed and a SRS PRS-10 rubidium oscillator in its
place.  I have been running Lady Heather 5.0 and have changed the
damping, gain, and time constant to give me a 20,000 second time
constant with a damping of .6.  I have attached a Lady Heather screen
shot of the weird behavior.  You can see that my GPS antenna is in a
very none ideal location (window on the west side of the building).

Once per day (about 8am) something disturbs the system.  So, the GPSDO
spends much of its time recovering and never gives me anywhere near
the performance that this system is capable of.  I would think that it
is not the PRS-10 as it has no knowledge of time.  I would also think
that it is not the GPS system or receiver, since the GPS constellation
repeats twice per day.

Kind of the two things that I am left with are a glitch by the power
company every morning (there is some large industrial machinery across
the street (but then I would kind of expect glitches at 8am and 5pm),
and perhaps Lady Heather doing something funny.  This system has been
running for quite some time, I have not tried restarting Lady Heather
yet.

Anybody seen anything like this, or have any good ideas?

Thanks in advance,
Skip Withrow


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Re: [time-nuts] Better GPS coming to phones

[Peter Monta]

>
>
> Also the new iphones now support Galileo in addition to GPS and Glonass.
>

Any word on whether iOS will support raw observables, as Android has for a
little while now?  I gather the APIs need to support continuous tracking
better so that phase observables are meaningful across epochs.

Will the phones put back the headphone jack, not for audio but instead
repurposed for PPS?  :-)

Cheers,
Peter
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Re: [time-nuts] Better GPS coming to phones

[Chris Caudle]

On Wed, September 27, 2017 9:38 pm, Bill Hawkins wrote:
> Sadly, it is not the phone users who will benefit. It is the advertisers
> who use your location to send targeted ads.

I doubt that knowing which side of the parking lot you are in will be of
much interest to advertisers.  It will help navigation apps with things
like determining whether you are on the access road or already on the
highway, or which of two parallel roads you are on.

In a timing context, I would hope that having a more consistent solution
to the position/time equation would reduce the PPS jitter.  It would be
really nice to see one of these low power, high precision receiver devices
used in a Thunderbolt style design that locks the chipset clock to the
derived clock to avoid hanging bridges to see if the 10x better precision
in location solution could result in 10x lower PPS jitter.

-- 
Chris Caudle


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Re: [time-nuts] HP-103AR frequency beyond adjustment

[Charles Steinmetz]

Jeremy wrote:


The only thing I've not adjusted is the oven temperature.
I know there's been discussion of this subject here in the
past but my searches come up empty—I must be using the wrong keywords.
The 103AR is just a toy for me so no harm is done if the frequency can't be
raised to 1 MHz but if it's possible I'd like to try. Have I missed something
somewhere?


To adjust the frequency trim range, replace selected capacitor C103 
inside the oven (nominally 18pF).  Use a C0G/NP0 ceramic.  Note that HP 
indicates this "Component [is] not separately replaceable."  But at this 
point (nearly 60 years on), opening sealed oven assemblies has become 
routine for those who maintain old HP standards.


The procedure for adjusting the oven temperature is described in 
paragraph 8-11 of the operating and service manual 01037-2 (printed Jan 
1962).  Be advised it is somewhat tedious.


If you do not have the manual, you can download it here:



Best regards,

Charles


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Re: [time-nuts] Better GPS coming to phones

[Attila Kinali]

On Wed, 27 Sep 2017 11:54:11 +
Mark Sims  wrote:

> http://www.theregister.co.uk/2017/09/27/centimetre_accurate_gnss_chipset_tested/

Sadly, the IEEE Spectrum article, which they reference, is so full
of mistakes. One would think that the largest electrical engineering
association would have someone to proof read what they publish.


Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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[time-nuts] HP-103AR frequency beyond adjustment

[Jeremy Nichols]

My HP-103AR has drifted beyond the ability of the "coarse" and "fine"
frequency adjustment capacitors. The 1 MHz output measures 0.999 9992 MHz
and will not go higher. The only thing I've not adjusted is the oven
temperature. I know there's been discussion of this subject here in the
past but my searches come up empty—I must be using the wrong keywords. The
103AR is just a toy for me so no harm is done if the frequency can't be
raised to 1 MHz but if it's possible I'd like to try. Have I missed
something somewhere?

Jeremy

-- 
Sent from my iPad 4.
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