Re: [time-nuts] three cornered comparison tools
Hi Tom,
Clear as crystal thanks. I'll post some results.
I just reread Bill Riley's notes on this, and they now also make perfect
sense.
Thanks.
david
Folks,
I asked about 3 cornered comparisons some time ago, and now have plenty
of data to start exploring, and way more than the 3 oscillators I had
when I asked six months ago.
Apart from Stable32, which I do not have access to, are there any free
tools which will allow me to perform 3 cornered comparisons between my
oscillators?
Thanks,
david
I use Excel on the { tau, ADEV } pairs when I want to get fancy, or just a
calculator for something quick. You can sometimes simply eyeball it on a
composite log-log adev plot.
I'll give the formula is below, but to understand, first consider this
backwards example:
Suppose for some tau the ADEV of three oscillators is 6e-12, 8e-12, and 10e-12,
respectively. But -- you don't know that yet -- because all you have is
pairwise measurements. The assumption is that noise is rms additive. Let's do
the numbers:
When you measure A vs. B you should get 1.00e-11, since that is sqrt( 6e-12 ^ 2
+ 8e-12 ^ 2 ).
When you measure B vs. C you should get 1.28e-11, since that is sqrt( 8e-12 ^ 2
+ 10e-12 ^ 2 ).
When you measure C vs. A you should get 1.17e-11, since that is sqrt( 10e-12 ^
2 + 6e-12 ^ 2 ).
So given your three ADEV measurement pairs (AB=1.00e-11, BC=1.28e-11,
AC=1.17e-11) you just work backwards to compute ADEV for A, B, and C, as in:
A = 0.707 * sqrt(+ AB*AB - BC*BC + AC*AC)
B = 0.707 * sqrt(+ AB*AB + BC*BC - AC*AC)
C = 0.707 * sqrt(- AB*AB + BC*BC + AC*AC)
Depending on how clean your measurement system is, and how well-behaved and
modestly different the oscillators are, the 3-hat technique can work pretty
well.
/tvb
___
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] three cornered comparison tools
Folks, I asked about 3 cornered comparisons some time ago, and now have plenty of data to start exploring, and way more than the 3 oscillators I had when I asked six months ago. Apart from Stable32, which I do not have access to, are there any free tools which will allow me to perform 3 cornered comparisons between my oscillators? Thanks, david ___ 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.
Re: [time-nuts] three cornered comparison tools
It seems that a free tool is not available but from the relations found here http://www.ke5fx.com/timelab/readme.htm I can write a simple processor to implement the extraction of the desired data from the couples Sab, Sac, Sbc On Wed, May 1, 2013 at 2:36 PM, David Hooke dho...@gmail.com wrote: Folks, I asked about 3 cornered comparisons some time ago, and now have plenty of data to start exploring, and way more than the 3 oscillators I had when I asked six months ago. Apart from Stable32, which I do not have access to, are there any free tools which will allow me to perform 3 cornered comparisons between my oscillators? Thanks, david __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://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.
Re: [time-nuts] three cornered comparison tools
Folks,
I asked about 3 cornered comparisons some time ago, and now have plenty
of data to start exploring, and way more than the 3 oscillators I had
when I asked six months ago.
Apart from Stable32, which I do not have access to, are there any free
tools which will allow me to perform 3 cornered comparisons between my
oscillators?
Thanks,
david
I use Excel on the { tau, ADEV } pairs when I want to get fancy, or just a
calculator for something quick. You can sometimes simply eyeball it on a
composite log-log adev plot.
I'll give the formula is below, but to understand, first consider this
backwards example:
Suppose for some tau the ADEV of three oscillators is 6e-12, 8e-12, and 10e-12,
respectively. But -- you don't know that yet -- because all you have is
pairwise measurements. The assumption is that noise is rms additive. Let's do
the numbers:
When you measure A vs. B you should get 1.00e-11, since that is sqrt( 6e-12 ^ 2
+ 8e-12 ^ 2 ).
When you measure B vs. C you should get 1.28e-11, since that is sqrt( 8e-12 ^ 2
+ 10e-12 ^ 2 ).
When you measure C vs. A you should get 1.17e-11, since that is sqrt( 10e-12 ^
2 + 6e-12 ^ 2 ).
So given your three ADEV measurement pairs (AB=1.00e-11, BC=1.28e-11,
AC=1.17e-11) you just work backwards to compute ADEV for A, B, and C, as in:
A = 0.707 * sqrt(+ AB*AB - BC*BC + AC*AC)
B = 0.707 * sqrt(+ AB*AB + BC*BC - AC*AC)
C = 0.707 * sqrt(- AB*AB + BC*BC + AC*AC)
Depending on how clean your measurement system is, and how well-behaved and
modestly different the oscillators are, the 3-hat technique can work pretty
well.
/tvb
___
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.
Re: [time-nuts] three cornered comparison tools
I recently made some measurements between 3 oscillators. It wasn't a
true 'Three-Cornered Hat' measurement because the measurements were made
sequentially. When I do the three-cornered hat calculation for the
hopefully 'better' oscillator, I end up trying to take the square root
of a negative number. Is that a red flag that the data is invalid? If
I ignore the minus sign, the results seem reasonable and I can
successfully calculate from the result for each oscillator back to the
measured results.
Ed
On 5/1/2013 12:08 PM, Tom Van Baak wrote:
Folks,
I asked about 3 cornered comparisons some time ago, and now have plenty
of data to start exploring, and way more than the 3 oscillators I had
when I asked six months ago.
Apart from Stable32, which I do not have access to, are there any free
tools which will allow me to perform 3 cornered comparisons between my
oscillators?
Thanks,
david
I use Excel on the { tau, ADEV } pairs when I want to get fancy, or just a
calculator for something quick. You can sometimes simply eyeball it on a
composite log-log adev plot.
I'll give the formula is below, but to understand, first consider this
backwards example:
Suppose for some tau the ADEV of three oscillators is 6e-12, 8e-12, and 10e-12,
respectively. But -- you don't know that yet -- because all you have is
pairwise measurements. The assumption is that noise is rms additive. Let's do
the numbers:
When you measure A vs. B you should get 1.00e-11, since that is sqrt( 6e-12 ^ 2
+ 8e-12 ^ 2 ).
When you measure B vs. C you should get 1.28e-11, since that is sqrt( 8e-12 ^ 2
+ 10e-12 ^ 2 ).
When you measure C vs. A you should get 1.17e-11, since that is sqrt( 10e-12 ^
2 + 6e-12 ^ 2 ).
So given your three ADEV measurement pairs (AB=1.00e-11, BC=1.28e-11,
AC=1.17e-11) you just work backwards to compute ADEV for A, B, and C, as in:
A = 0.707 * sqrt(+ AB*AB - BC*BC + AC*AC)
B = 0.707 * sqrt(+ AB*AB + BC*BC - AC*AC)
C = 0.707 * sqrt(- AB*AB + BC*BC + AC*AC)
Depending on how clean your measurement system is, and how well-behaved and
modestly different the oscillators are, the 3-hat technique can work pretty
well.
/tvb
___
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.
Re: [time-nuts] three cornered comparison tools
On 05/01/2013 10:09 PM, Ed Palmer wrote: I recently made some measurements between 3 oscillators. It wasn't a true 'Three-Cornered Hat' measurement because the measurements were made sequentially. When I do the three-cornered hat calculation for the hopefully 'better' oscillator, I end up trying to take the square root of a negative number. Is that a red flag that the data is invalid? If I ignore the minus sign, the results seem reasonable and I can successfully calculate from the result for each oscillator back to the measured results. Doing sequential measurements could give you that result. sqrt(abs()) isn't the ideal, but understandable. I've asked our favourite tool maker to include three-cornered hat, but he has not done it so far. Look forward to take it on a test-spin. Cheers, Magnus ___ 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.
Re: [time-nuts] three cornered comparison tools
Ed, I make sequential measurements as well and create the 3-hat from the calculated ADEV values. It's ok to do it that way. I have heard that even using simultaneous measurements you can get negatives, but I have not verified this. It usually means it's too close to call or you data runs are not as clean as they could be. Make sure to look carefully at your phase and frequency plots before you blindly compute ADEV. Or do multiple runs each and pick a set that's well behaved. Or cross your fingers and use the absolute value trick as you have. You'll notice that's what I use in http://leapsecond.com/tools/3hat.c /tvb - Original Message - From: Ed Palmer ed_pal...@sasktel.net To: time-nuts@febo.com Sent: Wednesday, May 01, 2013 1:09 PM Subject: Re: [time-nuts] three cornered comparison tools I recently made some measurements between 3 oscillators. It wasn't a true 'Three-Cornered Hat' measurement because the measurements were made sequentially. When I do the three-cornered hat calculation for the hopefully 'better' oscillator, I end up trying to take the square root of a negative number. Is that a red flag that the data is invalid? If I ignore the minus sign, the results seem reasonable and I can successfully calculate from the result for each oscillator back to the measured results. Ed ___ 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.
