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Today's Topics:
1. Re: Leviton VTP24 Is this Time Accurate enough? (Dana Whitlow)
2. Re: Leviton VTP24 Is this Time Accurate enough? (Lux, Jim)
3. Re: uncertainty/SNR of IQ measurements (Joseph Gwinn)
4. Stanford Research SR620 GBIB (Julien Goodwin)
----------------------------------------------------------------------
Message: 1
Date: Fri, 27 Aug 2021 05:30:14 -0500
From: Dana Whitlow <k8yumdoo...@gmail.com>
Subject: [time-nuts] Re: Leviton VTP24 Is this Time Accurate enough?
To: Discussion of precise time and frequency measurement
<time-nuts@lists.febo.com>
Message-ID:
<CADHrwpcec+LWq8hE1nWeW=5MmZJL8cUAf0AuFEYpLff==
uq...@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
If my watch were that bad, I'd toss it out and go shopping for a new
one.
I wonder if Leviton offers a version with an external ref input.
Dana
On Fri, Aug 27, 2021 at 12:12 AM D. Resor <organlis...@sonic.net>
wrote:
I inquired with Leviton as to the accuracy of the VTP24 24 Hour
Programmable
Timer with DST.
https://www.leviton.com/en/products/vpt24-1pz
Don Resor
Here is the reply I received:
Hello,
Thank you for contacting Leviton technical support. According to the
code
it
meets, it is required to have time keeping accuracy within 5 minutes
every
year.
It also uses a crystal to keep time, as it must maintain the time
even
during power outages.
Regards,
Virgilio Dominguez
Technical Services Representative II
Leviton Manufacturing Co., Inc.
201 North Service Road., Melville, NY 11747
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------------------------------
Message: 2
Date: Fri, 27 Aug 2021 06:25:06 -0700
From: "Lux, Jim" <j...@luxfamily.com>
Subject: [time-nuts] Re: Leviton VTP24 Is this Time Accurate enough?
To: time-nuts@lists.febo.com
Message-ID: <d4c921a7-126f-d599-b042-f98e4746b...@luxfamily.com>
Content-Type: text/plain; charset=utf-8; format=flowed
On 8/27/21 3:30 AM, Dana Whitlow wrote:
If my watch were that bad, I'd toss it out and go shopping for a new
one.
I wonder if Leviton offers a version with an external ref input.
Dana
When your requirement is "turn the lights on and off with the sun" 5
min/year is pretty good.
OTOH, Perhaps there's an aftermarket for a modified version. Maybe
you've got a niche business opportunity there, Dana.
"Now, with improved accuracy!
Ovenized for better performance!
30 millsecond error in one year!
"
You might need to gradually change the frequency you feed it, though,
because I'll bet their sunrise/sunset algorithm doesn't implement the
equation of time. But if you're doing milliseconds, you'll need it.
On Fri, Aug 27, 2021 at 12:12 AM D. Resor <organlis...@sonic.net>
wrote:
I inquired with Leviton as to the accuracy of the VTP24 24 Hour
Programmable
Timer with DST.
https://www.leviton.com/en/products/vpt24-1pz
Don Resor
Here is the reply I received:
Hello,
Thank you for contacting Leviton technical support. According to
the
code
it
meets, it is required to have time keeping accuracy within 5
minutes
every
year.
It also uses a crystal to keep time, as it must maintain the time
even
during power outages.
Regards,
Virgilio Dominguez
Technical Services Representative II
Leviton Manufacturing Co., Inc.
201 North Service Road., Melville, NY 11747
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------------------------------
Message: 3
Date: Fri, 27 Aug 2021 12:02:02 -0400
From: Joseph Gwinn <joegw...@comcast.net>
Subject: [time-nuts] Re: uncertainty/SNR of IQ measurements
To: time-nuts@lists.febo.com
Message-ID: <20210827120202402955.e8b2b...@comcast.net>
Content-Type: text/plain; charset=us-ascii
On Fri, 27 Aug 2021 03:30:28 -0400, time-nuts-requ...@lists.febo.com
wrote:
Send time-nuts mailing list submissions to
time-nuts@lists.febo.com
time-nuts Digest, Vol 208, Issue 20
----------------------------------------------------------------------
Message: 1
Date: Thu, 26 Aug 2021 10:36:46 -0700
From: "Lux, Jim" <j...@luxfamily.com>
Subject: [time-nuts] uncertainty/SNR of IQ measurements
To: Discussion of precise time and frequency measurement
<time-nuts@lists.febo.com>
Message-ID: <f8252b36-d0d8-e197-a57a-e21922f9d...@luxfamily.com>
Content-Type: text/plain; charset=utf-8; format=flowed
This is sort of tangential to measuring time, really more about
measuring phase.
I'm looking for a simplified treatment of the uncertainty of I/Q
measurements. Say you've got some input signal with a given SNR and
you
run it into a I/Q demodulator - you get a series of I and Q
measurements
(which might, later, be turned into mag and phase).
If the phase of the input happens to be 45 degrees relative to the
LO
(and at the same frequency), then you get equal I and Q values, with
(presumably) equal SNRs.
But if the phase is 0 degrees, is the SNR of the I term the same as
the
input (or perhaps, even, better), but what's the SNR of the Q term
(or
alternately, the sd or variance) - Does the noise power in the input
divide evenly between the branches? Is the contribution of the
noise
from the LO equally divided? So the I is "input + noise/2" and Q is
"zero + noise/2"
If one looks at it as an ideal multiplier, you're multiplying some
"cos
(omega t) + input noise" times "cos (omega t) + LO noise" - so the
noise
in the output is input noise * LO + LO noise *input and a noise *
noise
term.
I'm looking for a sort of not super quantitative and analytical
treatment that I can point folks to.
There are many treatments of phase-detector noise available outside
of the time world. The following may help.
.<https://en.wikipedia.org/wiki/Rice_distribution>
.<http://www.seas.ucla.edu/brweb/papers/Journals/HRTCASMar13.pdf>
By and large, these sources assume that the I and Q noise components
are statistically independent, which may be only partially true in
time-nut service. A phase detector implements the pointwise multiply
operation, yielding sum and difference terms. The sought-for phase
is in the difference term, in which noise in common will cancel out
(in the voltage domain), while the noise not in common will add as
power.
The easiest analytical approach to sorting this out is to draw the
block diagram, and trace AM and PM phase noise expressed as
band-limited zero-mean random functions of time through the block
diagram.
Joe Gwinn
------------------------------
Message: 4
Date: Sat, 28 Aug 2021 17:03:09 +1000
From: Julien Goodwin <time-n...@studio442.com.au>
Subject: [time-nuts] Stanford Research SR620 GBIB
To: Discussion of precise time and frequency measurement
<time-nuts@lists.febo.com>
Message-ID: <4e137f33-67e5-c00c-0293-16276e591...@studio442.com.au>
Content-Type: text/plain; charset=utf-8
For an upcoming (very time-nutty, and hopefully to be shared soon)
project I need to finally do some frequency datalogging.
I've had a Stanford SR620 sitting around, and plugged it in to a
handy
GPIB adapter (*not* a major commercial one, one of the community
ones).
While I can get it to talk GPIB there seems to be some reliability
issues, with what looks to be some form of read buffering happening,
with measurement results coming in as the answer to some later
command.
A few times I've even restarted it as it stopped responding (luckily
that hasn't happened once measurements had started).
Since I'm hoping to actually use measurements as part of a control
loop
this is obviously a bad thing.
Does anyone have any experience with the SR620 & GPIB as to why this
might be happening?
I've not experienced this with other instruments (ancient HP, modern
Keysight, recent Keithley, 90s Anritsu) I've used with the same GPIB
adapter.
The SR620 has version 1.48 firmware.
------------------------------
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End of time-nuts Digest, Vol 208, Issue 21
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