Re: [time-nuts] time-nuts Digest, Vol 148, Issue 28
Hello,
-
The comments in Lady Heather are placed there by Mark Sims. There are
comments for all kinds of events during the year. -
Yes, the output of the HP 5065A is 5MHz (and also 1MHz and 100kHz). I
have a board from another HP instrument that multiplies 1MHz to 10MHz
(there is no identification on the board other than an HP logo, at first I
thought it was a 5MHz to 10MHz doubler, but the signal generator and
spectrum analyzer set me straight). -
I actually saw a 5065A recently that had a modification to decrease the
C-field sensitivity. It had two 10-turn dial pots, the normal and another
that was about 2x10E-14 per division. Unfortunately, I did not take note
of the circuit to see how it was implemented.
Regards,
Skip Withrow
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Today's Topics:
1. Re: Thermal impact on OCXO (Scott Stobbe)
2. Re: Thermal impact on OCXO (Hal Murray)
3. Re: Subject: Re: I love the smell of tantalum in the morning
(Jeremy Nichols)
4. Re: Subject: Re: I love the smell of tantalum in the morning
(Charles Steinmetz)
5. This may be my new favorite old oscillator (Skip Withrow)
6. This may be my new favorite old oscillator (Mark Sims)
7. Re: This may be my new favorite old oscillator (Ruslan Nabioullin)
8. Re: This may be my new favorite old oscillator (paul swed)
Message: 1
Date: Mon, 7 Nov 2016 16:47:28 -0500
From: Scott Stobbe scott.j.stobbe@gmail.com
To: Bob Stewart bob@evoria.net
Cc: Discussion of Precise Time and Frequency Measurement
time-nuts@febo.com
Subject: Re: [time-nuts] Thermal impact on OCXO
Message-ID:
<CALg-KtP_UN9qdXH7B-whmG1WHWrXPscLKRS+DhB2kUS9g4A_
hg@mail.gmail.com>
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Deeper into the rabbit hole :)
I'm not sure what specific pic you are you using but most of them have at
least one timer that will run fully asynchronously and its timer input is
usually shared with one of the 32k osc pins. Which you can then use to wake
the prossesor from one of its sleep states. Do you end up hitting a clock
sync with the pwm block?
Good old 74 series to the rescue.
On Monday, 7 November 2016, Bob Stewart bob@evoria.net wrote:
Hi Scott,
I wish I had some long term data, but I don't. I had initially set out
to
build an accurate GPS frequency reference type of GPSDO. So, aging
wasn't
an issue. It's either on and locked or it's not. So, I didn't worry
about
leaving a unit running for months and collecting aging data.But then I had this crackpot idea of using the latches in a 7474 to
stabilize the 1PPS from the receiver to the OCXO. Tom had a bit of a
misunderstanding about what I was doing and we had a bit of a discussion
until he caught on to what I was doing and its limitations.But, somewhere along the line, I realized that the idea was sound but my
implementation was poor. The basic problem with using a timer in the
dsPIC33 is that they use a PLL to generate the internal clock - even if
you
supply a clock. That gives you a 1-count jitter in any output pulse you
try to create. So, I realized that I could use the latches in a 7474 to
latch the OCXO to the output of a timer on the PIC. With the PIC running
at 40MHz, I have plenty of room for the jitter without the worry of a
phase
slip. I think I've proved that that works, so now I have the possibility
of using my system as a time server. And that means I now have to deal
with such arcane matters as holdover, aging, and generating the time from
the OCXO. The learning curve has been a bit steep.Bob
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
From: Scott Stobbe <scott.j.stobbe@gmail.com
javascript:_e(%7B%7D,'cvml','scott.j.stobbe@gmail.com');>
To: Bob Camp <kb8tq@n1k.org
javascript:_e(%7B%7D,'cvml','kb8tq@n1k.org');>
Cc: Bob Stewart <bob@evoria.net
javascript:_e(%7B%7D,'cvml','bob@evoria.net');>; Discussion of precise
time and frequency measurement <time-nuts@febo.com
javascript:_e(%7B%7D,'cvml','time-nuts@febo.com');>
Sent: Monday, November 7, 2016 9:34 AM
Subject: Re: [time-nuts] Thermal impact on OCXOHere is a sample data point taken from http://tycho.usno.navy.mil/
ptti/1987papers/Vol%2019_16.pdf; the first that showed up on a google
search.Year Aging [PPM] dF/dt [PPT/Day] 1 180.51 63.884 2 196.65 31.93 5 218 12.769 9 231.69 7.0934 10 234.15 6.384 25 255.5 2.5535If you have a set of coefficients you believe to be representative of
your
OCXO, we can give those a go.On Mon, Nov 7, 2016 at 7:08 AM, Bob Camp <kb8tq@n1k.org
javascript:_e(%7B%7D,'cvml','kb8tq@n1k.org');> wrote:Hi
On Nov 5, 2016, at 10:43 PM, Bob Stewart <bob@evoria.net
javascript:_e(%7B%7D,'cvml','bob@evoria.net');> wrote:Hi Scott,
D'oh. Thanks for the correction! Like I said, I don't do these
calculations often.If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit
stumped. I do have an op-amp in the EFC string with a voltage divider
for
gain. The resistors are Panasonic ERA-6AEDxxxV resistors. Mouser says
they're temperature stable to 25PPM/C, but of course they don't mention
an
aging rate. I don't really see anything else, other than the OCXO, that
is
likely to be prone to a linear type of aging.OCXO’s don’t age in a linear fashion. At least 90% of them don’t. If you
dig into the FCS papers there are various
curves proposed as models. Mil-O-55310 has one of them as the “official”
approach. All of them have the basic
issue of mistakenly fitting to to short a time constraint.Bob
The aging rate appears to be stable from unit to unit, so naturally I
considered the OCXO first.There is one other bit in the EFC string that might be controversial,
but I don't see that it would be a candidate for the symptoms of aging.Bob
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/ GFS-GPSDOs/info
<http://groups.yahoo.com/neo/groups/GFS-GPSDOs/info?soc_
src=mail&soc_trk=ma>From: Scott Stobbe <scott.j.stobbe@gmail.comjavascript:_e(%7B%7D,'cvml','scott.j.stobbe@gmail.com');>
To: Bob Stewart <bob@evoria.net
javascript:_e(%7B%7D,'cvml','bob@evoria.net');>
Cc: Discussion of Precise Time and Frequency Measurement <
time-nuts@febo.com javascript:_e(%7B%7D,'cvml','time-nuts@febo.com');>
Sent: Saturday, November 5, 2016 9:19 PM
Subject: Re: [time-nuts] Thermal impact on OCXOIf your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the
EFC range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1
LSB
is ~1PPT. So, if everything else is stable the DAC code reflects changes
solely due to the OCXO, which would be an aging of 24 PPT/day.
On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <bob@evoria.net
javascript:_e(%7B%7D,'cvml','bob@evoria.net');> wrote:Hi Scott,
The 20 bits span about 6 volts. The EFC range spans about 8Hz
(+/-4Hz). I don't do these calculations every day, but that's about
4.5PPT?
Bob ------------------------------ ------------------------------
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/
http://groups.yahoo.com/neo/groups/?soc_src=mail&soc_trk=ma
GFS-GPSDOs/infoFrom: Scott Stobbe <scott.j.stobbe@gmail.com
javascript:_e(%7B%7D,'cvml','scott.j.stobbe@gmail.com');>
To: Bob Stewart <bob@evoria.net
javascript:_e(%7B%7D,'cvml','bob@evoria.net');>; Discussion of precise
time and frequency measurement <time-nuts@febo.com
javascript:_e(%7B%7D,'cvml','time-nuts@febo.com');>
Sent: Saturday, November 5, 2016 8:38 PM
Subject: Re: [time-nuts] Thermal impact on OCXOI think that's a nice plot, it looks like you have stepped 160 LSB over
7 days or roughly 1 LSB per hour. With a 20bit dac you are trimming
maybe 1
ppt/LSB to 4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB,
solely
due to drift, you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the case of
4ppt/hour your at 1E-12 at 1280 s. Seems reasonable.
On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <bob@evoria.net
javascript:_e(%7B%7D,'cvml','bob@evoria.net');> wrote:Oh dear. I attached the wrong file. Here's the correct one.
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/
http://groups.yahoo.com/neo/groups/?soc_src=mail&soc_trk=ma
GFS-GPSDOs/info
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Message: 2
Date: Mon, 07 Nov 2016 14:26:10 -0800
From: Hal Murray hmurray@megapathdsl.net
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Cc: hmurray@megapathdsl.net
Subject: Re: [time-nuts] Thermal impact on OCXO
Message-ID:
20161107222610.5667F406061@ip-64-139-1-69.sjc.megapath.net
Content-Type: text/plain; charset=us-ascii
kb8tq@n1k.org said:
Yes, that���s a bit of a long winded reply ��� sorry about that.
It was also valuable. Thanks.
--
These are my opinions. I hate spam.
Message: 3
Date: Mon, 7 Nov 2016 15:31:35 -0800
From: Jeremy Nichols jn6wfo@gmail.com
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] Subject: Re: I love the smell of tantalum in
the morning
Message-ID:
<CAPv4gjQ-ZWu3FYcWX0pRFJaR99PeeTP6kheAcj
usDJ4Y1vThYA@mail.gmail.com>
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Amazon indicates the different lenses simply snap in and out. Any idea how
easy/practical this is? It it better to have two completely different
visors each holding different magnification lenses?
Jeremy
On Monday, November 7, 2016, Scott Hamilton scottha@me.com wrote:
https://www.amazon.com/Donegan-OptiVISOR-Headband-
Magnifier-Magnification/dp/B0068OSIIS/ref=sr_1_4?ie=UTF8&
qid=1478548961&sr=8-4&keywords=headset+magnifiersFinally, I can offer a contribution to this list. I have found the
Donegan
magnifiers in the above Amazon link with 3.5X lenses to be very
comfortable
and indespensible for SMD work. Different lenses can be obtained for
other
work but the 3.5X is a minimum for me.Scott Hamilton
W3SEH
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Message: 4
Date: Mon, 7 Nov 2016 22:54:47 -0500
From: Charles Steinmetz csteinmetz@yandex.com
To: time-nuts@febo.com
Subject: Re: [time-nuts] Subject: Re: I love the smell of tantalum in
the morning
Message-ID: 58214C87.1050704@yandex.com
Content-Type: text/plain; charset=utf-8; format=flowed
Jeremy wrote:
Amazon indicates the different lenses simply snap in and out. Any idea
how
easy/practical this is? It it better to have two completely different
visors each holding different magnification lenses?
Quite easy -- the lens plates are held onto the front of the visor by
two plastic pins that just snap in and out. You can see the heads from
the outside (as opposed to the eye-side) at the far left and right of
the lens plate.
That said, IMO it is always more convenient to have each lens plate
mounted in its own visor.
I have to say that contrary to the original post, I find the 3.5x lenses
WAY too strong for SMD work. The working distance is only 3-4" -- not
nearly enough to work safely with hot tools, or comfortably. Even the
2.5x lenses, with 6-8" of working distance, are too strong for me. For
anything that requires working on the object you're looking at (as
opposed to just examining it), I recommend staying at 2x and below (2x,
1.75x, 1.5x).
Finally, Donegan makes two series of lenses -- rectangular plastic
frames with optical glass lenses, and rectangular plastic frames with
molded-in plastic lenses. The glass lenses are more expensive, but the
large difference in optical quality makes them the only real choice, IMO.
At substantially greater cost, you can get "surgical loupes" (a/k/a
"dental loupes"). These have compound optical systems, so you can get
longer working distances at a particular magnification than you can with
a single lens (like the OptiVisor has).
Best regards,
Charles
Message: 5
Date: Mon, 7 Nov 2016 22:16:48 -0700
From: Skip Withrow skip.withrow@gmail.com
To: time-nuts time-nuts@febo.com
Subject: [time-nuts] This may be my new favorite old oscillator
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Hello Time-Nuts,
I recently acquired an HP 5065A rubidium oscillator (with 10811 10MHz
OCXO). I think I pretty much have it running now and have been letting it
cook for the last couple of weeks. I offset the C-field + and - and
measured the frequency to calculate the C-field sensitivity. My unit came
out to 1.96x10E-12 per dial unit, which agrees with the manual stated
2x10E-12. So, calculated the on frequency C-field value and dialed it in.
Attached is a Lady Heather plot of the frequency over the last 3 days. The
purple line is the 1pps plot with the vertical scale being 20ns per
division. So, the unit is off about 125ns over the last 72 hours (running
about 4.92x10E-13 slow). So my C-field setting is off about 1/4 of a
division, but I think I'm going to leave well enough alone.
The yellow line is the NTBW50AA temperature sensor, and you can clearly see
when the furnace cycles. I was away for the weekend, and you can also
clearly see when I came home this evening and turned up the heat. At the
very end of the plot is the spike when I turned on the lights in the shop.
I love using a Thunderbolt/NTBW50AA for making frequency measurements this
way. I remove the OCXO, and insert the 10MHz from the DUT. Then disable
disciplining so the DAC voltage doesn't try to chase the open loop
oscillator. Of course the short-term performance looks worse than it
actually is because of measuring against GPS, but the long-term
measurements are very good.
I want to log this unit at regular intervals to see what the aging looks
like. Also need to do some measurements against the cesium to see what the
short-term performance might be. But, I think this oscillator will be a
good reference in many cases in lieu of using the cesium.
Regards,
Skip Withrow