In a message dated 4/23/2007 20:51:28 Pacific Daylight Time, bruce
[EMAIL PROTECTED] writes:
Of course one can always resort to annealing out the retrace by
controlled thermal cycling of the reference as Fluke (optionally) do in
their 7000 series references whenever continuous power is
* The Vref output of most OCXO's is from a Zener diode inside the can.
These
typically have aging, thermal sensitivity and very poor voltage accuracy,
and there are much better monolithic high-precision, low-tempco voltage
reference available on the market now (Digikey etc). Depending
Tom
Attached images are drift plots for:
1) VRE430 reference utilising a buried zener.
2) LM199
3) LTZ1000
Bruce
___
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Question - does Vref drift matter for a GPSDO? It seems it is
either too low to be of concern or the effect of Vref drift is in
fact indistinguishable from OCXO frequency drift and is thus
transparently compensated by any 3rd order loop?
I don't know for sure, but is 1 ppm/day drift in Vref
Tom
Attached images are drift plots for:
1) VRE430 reference utilising a buried zener.
2) LM199
3) LTZ1000
Bruce
OK, thanks very much. What I read from the slopes in
those long-term plots are Vref drift rates on the order of:
-6 ppm / 1000 hours (= 2e-12/d)
-2 ppm / 1000 hours (=
Tom Van Baak wrote:
Can someone do a similar numerical analysis of these two
factors: tempco and noise? It's not that I don't believe you;
it's just that I'd rather see numbers and plots than words.
Tom
When the reference is temperature cycled hysteresis may be significant.
Hysteresis
Tom
Attached is some hysteresis and other data for various references.
NB take the claimed XFTE reference ADR293 drift figure with a large dose
of salt, its 2 orders of magnitude lower than ADI claim.
Bruce
___
time-nuts mailing list
In a message dated 4/23/2007 06:05:12 Pacific Daylight Time,
[EMAIL PROTECTED] writes:
-6 ppm / 1000 hours (= 2e-12/d)
-2 ppm / 1000 hours (= 6e-13/d)
-2 ppm / 3000 hours (= 2e-13/d)
+6 ppm / 5 months (= 5e-13/d)
+10 ppm / 12 months (= 3e-13/d)
-1 ppm / 10 days (= 1e-12/d)
-1.5 ppm / 30
Can someone do a similar numerical analysis of these two
factors: tempco and noise? It's not that I don't believe you;
it's just that I'd rather see numbers and plots than words.
Tom attached plot of zener noise is also from Eickes 1964 paper.
Bandpass is a little unclear as its
In a message dated 4/23/2007 11:03:07 Pacific Daylight Time,
[EMAIL PROTECTED] writes:
So you can imagine that Vref noise on the order of 1e-12 might
just start being noticeable in the plot, meaning that if you want
short-term performance down in the low 12's and if you have
an OCXO that
Hi Tom:
Appendix H of Linear App Note 86 A Standards Lab Grade 20-Bit DAC with
0.1ppm/C Drift on pdf page 43 describes the 1,000 X amplifier they used and
the need for an out of production analog scope with to see sub 1 uV noise as
well as the need for a totally shielded measurement system.
Tom Van Baak wrote:
Also an idea - is there an easy way to artificially increase Vref
noise, by say 10x, so one could see if that change made any
measurable change in OCXO output ADEV or phase noise?
/tvb
Tom
1) Increase the cutoff frequency of any low pass filter used.
2) With a
Hi Colin:
That's one sweet meter. Years ago at work I used them and we had both flavors.
One used the old definition of the volt and the other used the new volt.
Although our cal lab was not good enough to calibrate them we could feed them
signals and measure their readings. They differed
Tom Van Baak wrote:
Also an idea - is there an easy way to artificially increase Vref
noise, by say 10x, so one could see if that change made any
measurable change in OCXO output ADEV or phase noise?
/tvb
Tom
Another possibility is to use a low noise instrumentation amplifier with
a
attachment did not make it, there it is:
http://www.ko4bb.com/ham_radio/Manuals/Tektronix -
7L5/Tek-7L5-PhaseNoise.png
Didier
Didier Juges wrote:
Tom Van Baak wrote:
Related - does anyone have equipment in your home/lab that
can directly measure, at uV or sub-uV levels, noise on the
In a message dated 4/23/2007 18:54:54 Pacific Daylight Time,
[EMAIL PROTECTED] writes:
If an unheated reference exposed to wide ambient temperature swings is
used then hysteresis may be significant when the OCXO is continuously
powered.
The significance and magnitude of the effect
Dr Bruce Griffiths wrote:
Tom Van Baak wrote:
Bruce, I'm getting the idea you don't like _any_ of the
hobbyists GPSDO's that have come out in the last ten
years...
So I'm curious what then would qualify as a well designed
GPSDO in your opinion? (and please don't bring up the
Quartzlock
12) provision for measuring OCXO case temperature and power supply
current to allow compensation for variable internal wiring voltage
drops for those OXCOs that do not allow Kelvin sensing of the EFC
varactor voltage.
Some OCXO's (FTS1200 etc) do not have independent sensing of the EFC
In a message dated 4/22/2007 01:11:30 Pacific Daylight Time,
[EMAIL PROTECTED] writes:
Does anybody have a list of OCXOs with a separate ground pin for the oven?
Some of the OCXO data sheets I've looked at have a Vref output. Seems like
a
good idea. They already have good
I made a hardware sawtooth remover a couple of years ago as an
experiment, but where I used it I didn't seen much difference. I just
checked again recently, but the sawtooth errors seem very small
compared to overall instability, even for just an M12 to Rb at a
fairly stable temperature. The
Dr Bruce Griffiths wrote:
Said
[EMAIL PROTECTED] wrote:
Hi guys,
Some comments:
* The Vref output of most OCXO's is from a Zener diode inside the can.
These
typically have aging, thermal sensitivity and very poor voltage accuracy,
and there are much better monolithic
In a message dated 4/22/2007 06:30:46 Pacific Daylight Time, [EMAIL PROTECTED]
writes:
If you want the lowest tempco and drift available try using an LTZ1000
(used in HP 8 1/2 digit DVMs).
In those cases where a thermally stabilized reference is undesirable
(power consumption,
The VP is still distinctly worse until tau 1000sec.
The plots are not conclusive evidence that correcting for the sawtooth
error isn't advisable.
What about hanging bridges and similar artifacts?
Bruce
It would be interresting to see exactly how much the sawtooth on an
M12 affects actual
There are plenty of times when sawtooth removal would be of use/
interest, but in a typical GPSDO which has a heap of other errors, I
do wonder what improvements in performance would actually be seen in
the output from the oscillator - which is all that a lot of people are
really interrested
Hal Murray wrote:
There are plenty of times when sawtooth removal would be of use/
interest, but in a typical GPSDO which has a heap of other errors, I
do wonder what improvements in performance would actually be seen in
the output from the oscillator - which is all that a lot of people are
One has to be careful not to misuse such statistics to mask the
shortcomings of a poorly designed GPSDO.
Bruce, I'm getting the idea you don't like _any_ of the
hobbyists GPSDO's that have come out in the last ten
years...
So I'm curious what then would qualify as a well designed
GPSDO in
Tom Van Baak wrote:
Bruce, I'm getting the idea you don't like _any_ of the
hobbyists GPSDO's that have come out in the last ten
years...
So I'm curious what then would qualify as a well designed
GPSDO in your opinion? (and please don't bring up the
Quartzlock thing; it's a hundred times
From: Christopher Hoover [EMAIL PROTECTED]
Subject: Re: [time-nuts] GPS: ADEV or MDEV?
Date: Sat, 21 Apr 2007 20:06:59 -0700
Message-ID: [EMAIL PROTECTED]
Bruce wrote:
6) Doesn't rely on the relative phase of an independent oscillator being
random with respect to the PPS signal or the OCXO
Surely its better to detect the pseudorange instability in software (if
one has access) rather than attenuating the signal from all SVs.
Another option is to use multiple GPS antennae operating as a phased array.
Bruce
Of course but I think that approach is part of sub nanosecond time transfer
From: Peter Schmelcher [EMAIL PROTECTED]
Subject: Re: [time-nuts] GPS: ADEV or MDEV?
Date: Sat, 14 Apr 2007 02:40:57 -0700
Message-ID: [EMAIL PROTECTED]
Surely its better to detect the pseudorange instability in software (if
one has access) rather than attenuating the signal from all SVs
On Sat, April 14, 2007 13:32, Magnus Danielson said:
From: Peter Schmelcher [EMAIL PROTECTED]
Subject: Re: [time-nuts] GPS: ADEV or MDEV?
Date: Sat, 14 Apr 2007 02:40:57 -0700
Message-ID: [EMAIL PROTECTED]
Surely its better to detect the pseudorange instability in software (if
one has
Surely it would be much simpler (in principle at least) to just to add
sufficient Gaussian phase noise to the GPS receiver clock so that
potential coherence problems are virtually eliminated.
The noise only really needs to be added to the PPS positioning
algorithm/hardware.
My two
Dr Bruce Griffiths wrote:
Peter
I only intended to indicate that not all GPS timing receivers need
exhibit hanging bridges.
The Trimble Resolution T for example may (or may not) exhibit hanging
bridges.
If anyone has any evidence either way it would be interesting to look at it.
If one
Hal Murray wrote:
Surely it would be much simpler (in principle at least) to just to add
sufficient Gaussian phase noise to the GPS receiver clock so that
potential coherence problems are virtually eliminated.
It doesn't look reasonable to me, but I'm not good at this sort of math.
From: Dr Bruce Griffiths [EMAIL PROTECTED]
Subject: Re: [time-nuts] GPS: ADEV or MDEV?
Date: Tue, 10 Apr 2007 17:49:03 +1200
Message-ID: [EMAIL PROTECTED]
Poul-Henning Kamp wrote:
In message [EMAIL PROTECTED], Brooks Shera writes:
The impact of time averaging to suppress white phase
[context is avoiding hanging bridges]
Ovenize it to control the sawtooth frequency?
Temperature controlled oscillator! :-)
Should be fairly simple to acheive, really just a FLL.
I was wondering about that a while ago. Is the basic idea feasible?
Assume you had a good crystal with an A/D
Hal Murray wrote:
[context is avoiding hanging bridges]
Ovenize it to control the sawtooth frequency?
Temperature controlled oscillator! :-)
Should be fairly simple to acheive, really just a FLL.
I was wondering about that a while ago. Is the basic idea feasible?
Assume you had
Brooks Shera wrote:
In view of recent interest in the Allan Deviation of GPS-based 1 pps time,
it should be mentioned that the calculation of ADEV is based on a
statistical model which is not completely appropriate for noise sources
present in GPS signals and their decoding hardware/software.
Poul-Henning Kamp wrote:
In message [EMAIL PROTECTED], Brooks Shera writes:
The impact of time averaging to suppress white phase noise is illustrated
by a new plot TVB has created and placed on his website
http://www.leapsecond.com/pages/3gps/gps-adev.gif.
These revealing plots show
39 matches
Mail list logo
