gpsd 1pps pulse?
I would like to set up a NTP server on a machine running Linux
(currently Korora 18).
What are the requirements for the 1 PPS signal fed to the carrier detect
pin?
I presume the 10 us 1pps from the Thunderbolt is too narrow.
I assume the rising edge of CD is the one gpsd triggers on.
--
Chuck Forsberg WA7KGX caf@omen.com www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430
Yes, the rising edge is the usual UTC reference for the PPS pulse. The PPS
is used to trigger the interrupt on its rising edge so a 10uS long pulse
should be enough.
On Mon, May 6, 2013 at 3:38 PM, Chuck Forsberg WA7KGX N2469R
caf@omen.comwrote:
I would like to set up a NTP server on a machine running Linux
(currently Korora 18).
What are the requirements for the 1 PPS signal fed to the carrier detect
pin?
I presume the 10 us 1pps from the Thunderbolt is too narrow.
I assume the rising edge of CD is the one gpsd triggers on.
--
Chuck Forsberg WA7KGX caf@omen.com www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430
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and follow the instructions there.
The computer only looks at the leading edge so the pulse width does
not matter as long as the cable is short. look at what kind of signal
is required by the serial port on the PC. Many of them will accept a
TTL level 5 volt signal but you may have to level sift it to RS-232
levels (plus and minus about 9 volts) If you are driving a long
cable you may have to buffer it.
Whatever you do make sure the polarity is correct. RS232 data signals
use "negative logic" with 0 meaning 1 but rs232 control signls use the
other convention. If you get the polarity wrong the timing is "off"
by the width of the pulse. So you get a 10 uS bias. Having the PPS
inverted is a common error.
On Mon, May 6, 2013 at 6:38 AM, Chuck Forsberg WA7KGX N2469R
caf@omen.com wrote:
I would like to set up a NTP server on a machine running Linux
(currently Korora 18).
What are the requirements for the 1 PPS signal fed to the carrier detect
pin?
I presume the 10 us 1pps from the Thunderbolt is too narrow.
I assume the rising edge of CD is the one gpsd triggers on.
--
Chuck Forsberg WA7KGX caf@omen.com www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430
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.
--
Chris Albertson
Redondo Beach, California
Hi
Unless you have a holdover requirement (running without a GPS antenna for
x,xxx hours), a TBolt is major overkill for NTP. A cheap / simple / low
power GPS receiver with a pps out is plenty good enough. Save the TBolt (and
it's complicated power demands) for a place where you need it.
Depending on the exact hardware you have in your PC, 10 us may (or may not)
be to narrow. It's easy enough to hook up a TTL to RS-232 chip and try it
out.
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Chuck Forsberg WA7KGX N2469R
Sent: Monday, May 06, 2013 9:39 AM
To: time-nuts
Subject: [time-nuts] gpsd 1pps pulse?
I would like to set up a NTP server on a machine running Linux
(currently Korora 18).
What are the requirements for the 1 PPS signal fed to the carrier detect
pin?
I presume the 10 us 1pps from the Thunderbolt is too narrow.
I assume the rising edge of CD is the one gpsd triggers on.
--
Chuck Forsberg WA7KGX caf@omen.com www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430
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.
On 5/6/2013 9:38 AM, Chuck Forsberg WA7KGX N2469R wrote:
I would like to set up a NTP server on a machine running Linux
(currently Korora 18).
What are the requirements for the 1 PPS signal fed to the carrier detect
pin?
I presume the 10 us 1pps from the Thunderbolt is too narrow.
I assume the rising edge of CD is the one gpsd triggers on.
Chuck,
10 microseconds? That sounds fine actually... You could simply try it?
Really, I mean it. Just try and it might work with your serial port.
I don't recommend any clever hardware hacks which will somehow piggyback
the 1 PPS output onto the DCD line on the same serial port you're using
for the TSIP protocol.
If you have problems with PPS, just set the serial port to a higher baud
rate... This is the reason I recommend against using the DCD line on the
same serial port you're using for TSIP. Trimble tends to use 9600 baud
on the TSIP port, and the signaling on that is too narrow.
For PPS, you'll be fine with 115200 BAUD (bit/s) ... This speed comes
out to 8680.55 nanoseconds, more than a full microsecond "narrower" than
the 10 microsecond wide PPS.
I had trouble getting the right headers to connect to the onboard serial
port on the motherboard (not installed by default) ... So I tried a
USB-serial, and ultimately switched to a "PCI Express to Serial Port"
version.
This is from the product description on my current setup:
(quote) Based on a native single chip design (no bridge chip), this
2-port serial adapter card allows you to harness the full capability
offered by PCI Express (PCIe), and reducing the load applied to the CPU
by as much as 48% over conventional serial cards.
^ I'm really not sure if this helps the latency for hardware interrupts,
or makes them worse, but it DEFINITELY works better than the USB-serial
adapter I was trying to use before.
At less than $100, the price is right though (And now my PPS hardware
interrupts are via "native PCIe" so it only makes sense that it would
work better than USB)
Hope this helps
--Sarah
P.S. If anyone needs a good serial port and not sure where to look, I
got mine from newegg, they have tons: http://goo.gl/CEzZA ... Mine was
specifically, this model, made by startech: http://goo.gl/S9EHx
This might be slightly off-topic, but probably there is a time-nut who
knows the answer.
I am trying to adjust the 10 MHz OCXO in a Cushman 5110 service
monitor. I am using a frequency counter driven by a GPSDO. Perhaps
someone can educate me about a couple problems I am encountering.
I tried making small incremental adjustments but after I am done, the
frequency drifts several Hz and then re-stabilizes at a new value. When
I make further adjustments, I notice strange behavior. For example, if I
initially turned the adjustment clockwise to increase the frequency, it
will now decrease if I turn it clockwise and increase if I turn it
counter-clockwise. On the next adjustment, it will reverse again.
Is there some correct procedure to adjust an OCXO?
Many thanks for any suggestions.
Fred Bray
Hi Fred,
It sounds like you are turning it too far and too fast and expecting too much
from it. In old items, like what you have, those adjustments are fairly coarse
and required a very slight touch, then a wait and see, then another very slight
touch, etc.,. It sounds like you are turning a physical capacitor. If it is the
kind that has two little ceramic discs and a small screw type head for
adjustment, often the variable ceramic disc part would become lose where the
screw head would not really be fully attached to the disc causing backlash.
Oscillators that only have a single adjustment like that are not at the high
quality end of things.
When you make a mechanical adjustment there will need to be some time for the
mechanically induced stresses, along with some electrically induced stresses upon
the quartz blank to dissipate before the final results of the adjustment will be
realized. All of the above is assuming no temperature change.
The time frame of the Cushman 5110 was back when very high quality oscillators
were very expensive and for the intended purpose were not really necessary. The
Cushman only needed a given amount of accuracy to meet the requirements over a
certain time frame to qualify for adjusting commercial radios to FCC
specifications.
With that said, to improve the time base of the Cushman, you should consider
replacing the internal reference oscillator with one of the modern oven
controlled 14 or 8 pin IC size oscillator packages. They are way above what is
in the Cushman, of very small size and can be adjusted via a resistive ten turn
potentiometer to a much higher degree and will hold its frequency to a much
closer degree.
You do need to be careful which one you select as most of the small IC size
oscillators do not have a voltage tuned connection. On eBay, you can find ads
for a Marion 89A which is the kind you would want for such a project, that is
assuming the base reference of the Cushman is 10 MHz. If it is lower there a
ways to use the Marion and achieve the needed frequency without a lot of space
consumed.
Of course you could disassemble the Cushman oscillator and replace the variable
capacitor. That would improve things a little but no where near what can be done
with the Marion 89A.
Hope this is helpful,
Bill....WB6BNQ
Frederick Bray wrote:
This might be slightly off-topic, but probably there is a time-nut who
knows the answer.
I am trying to adjust the 10 MHz OCXO in a Cushman 5110 service
monitor. I am using a frequency counter driven by a GPSDO. Perhaps
someone can educate me about a couple problems I am encountering.
I tried making small incremental adjustments but after I am done, the
frequency drifts several Hz and then re-stabilizes at a new value. When
I make further adjustments, I notice strange behavior. For example, if I
initially turned the adjustment clockwise to increase the frequency, it
will now decrease if I turn it clockwise and increase if I turn it
counter-clockwise. On the next adjustment, it will reverse again.
Is there some correct procedure to adjust an OCXO?
Many thanks for any suggestions.
Fred Bray
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.
Fred,
What I do is to apply the GPSDO to the trigger input of a scope and the
output of the OCXO to be adjusted to the vertical input of the scope. Set
the time base to something line 100 nSec or faster and watch the output of
the OCXO after it has warmed up for 30 minutes or so.
This is an option only if you have an output from the OCXO you can watch.
If no output, try a x10 probe attached to a 10 MHz connection from the OCXO
inside the monitor. However, be careful that the probe does not 'load' the
OCXO and shift the frequency.
Adjust the OCXO for a stable display, not drifting left or right.
If the sine wave (or square wave) is moving to the left, the OCXO is high in
frequency. If it is moving to the right, the OCXO is low in frequency. If
stable, it is matched to the GPSDO. This is useful as long as the OCXO and
GPSDO are within a few Hz of each other. The amount of time it takes for
the display to shift 1 cycle tells you how close the OCXO is to the GPSDO.
For instance, if it takes 10 seconds for the display to shift one cycle,
100,000,000 +/- 1 cycles went by in that 10 seconds or 1 part in 10E9 if I
have my math correct.
Joe
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Frederick Bray
Sent: Tuesday, May 07, 2013 9:25 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] OCXO Adjustment Question
This might be slightly off-topic, but probably there is a time-nut who knows
the answer.
I am trying to adjust the 10 MHz OCXO in a Cushman 5110 service monitor. I
am using a frequency counter driven by a GPSDO. Perhaps someone can educate
me about a couple problems I am encountering.
I tried making small incremental adjustments but after I am done, the
frequency drifts several Hz and then re-stabilizes at a new value. When I
make further adjustments, I notice strange behavior. For example, if I
initially turned the adjustment clockwise to increase the frequency, it will
now decrease if I turn it clockwise and increase if I turn it
counter-clockwise. On the next adjustment, it will reverse again.
Is there some correct procedure to adjust an OCXO?
Many thanks for any suggestions.
Fred Bray
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.
Fred wrote:
I tried making small incremental adjustments but after I am done,
the frequency drifts several Hz and then re-stabilizes at a new value.
That is to be expected. Adjusting an oscillator is an iterative
process. After a while, you should get a feel for how far it drifts
after adjustment, and whether or not the direction of drift depends
on the direction you were turning the adjustment when you
stopped. In future iterations, you will stop adjusting about that
far from the exact frequency and let the oscillator drift onto
frequency (instead of adjusting for dead on and watching it drift away).
It would be good to get an educated guess (or information from the
service documentation) about what you are turning (i.e., air variable
capacitor, compression trimmer, or potentiometer setting bias on a
varactor -- and if the latter, whether it is a multiturn or
single-turn pot). This information will help you understand how to
cope with the inevitable mechanical backlash. If it is a multiturn
pot, you should always adjust, then back away just enough so that
there is no further mechanical bias applied that might cause further
motion of the wiper contact (i.e., put the adjustment screw in the
middle of the backlash, biased neither one way or the other). Also,
if it is a potentiometer or air variable cap, the wiper (or capacitor
rotor contact) may be dirty at the spot where you need to set it --
it is often helpful to exercise the pot or cap by running it
significantly farther in both directions than you will need to go to
set it on frequency, to try to clean the contact.
You should expect to see significant drift over a period of ten
minutes to several hours, then slower drift for days to weeks until
the crystal settles into its new frequency. Every crystal is
different -- some adjust right up with no fuss (a distinct minority,
IME), some you chase for several months (again, a minority
IME). Note also that oscillators exhibit some sensitivity to
gravitational orientation, so it is best to adjust it in the
orientation in which it will be used (or else characterize its
gravitational drift and set your target adjustment frequency
accordingly). Ovens aren't perfect, so if the ambient temperature
around the oscillator is different when the instrument is buttoned up
than it is when you are adjusting it, that can introduce another small shift.
How hard it is depends on the accuracy you expect and the resolution
of your counter -- it is much easier to get it "spot on" (as far as
you can tell) if you are using a seven digit counter than if you are
using a twelve digit counter.
Best regards,
Charles
This is the method I use for my 5110. There are two 10 mhz outputs on the
osc - you can unplug one of the plugs and use a 10x probe there. My unit
will hold a couple of parts in
10-8 for months.
73,
Bill, WA2DVU
Cape May, NJ
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of J. L. Trantham
Sent: Tuesday, May 07, 2013 11:52 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] OCXO Adjustment Question
Fred,
What I do is to apply the GPSDO to the trigger input of a scope and the
output of the OCXO to be adjusted to the vertical input of the scope. Set
the time base to something line 100 nSec or faster and watch the output of
the OCXO after it has warmed up for 30 minutes or so.
This is an option only if you have an output from the OCXO you can watch.
If no output, try a x10 probe attached to a 10 MHz connection from the OCXO
inside the monitor. However, be careful that the probe does not 'load' the
OCXO and shift the frequency.
Adjust the OCXO for a stable display, not drifting left or right.
If the sine wave (or square wave) is moving to the left, the OCXO is high in
frequency. If it is moving to the right, the OCXO is low in frequency. If
stable, it is matched to the GPSDO. This is useful as long as the OCXO and
GPSDO are within a few Hz of each other. The amount of time it takes for
the display to shift 1 cycle tells you how close the OCXO is to the GPSDO.
For instance, if it takes 10 seconds for the display to shift one cycle,
100,000,000 +/- 1 cycles went by in that 10 seconds or 1 part in 10E9 if I
have my math correct.
Joe
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Frederick Bray
Sent: Tuesday, May 07, 2013 9:25 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] OCXO Adjustment Question
This might be slightly off-topic, but probably there is a time-nut who knows
the answer.
I am trying to adjust the 10 MHz OCXO in a Cushman 5110 service monitor. I
am using a frequency counter driven by a GPSDO. Perhaps someone can educate
me about a couple problems I am encountering.
I tried making small incremental adjustments but after I am done, the
frequency drifts several Hz and then re-stabilizes at a new value. When I
make further adjustments, I notice strange behavior. For example, if I
initially turned the adjustment clockwise to increase the frequency, it will
now decrease if I turn it clockwise and increase if I turn it
counter-clockwise. On the next adjustment, it will reverse again.
Is there some correct procedure to adjust an OCXO?
Many thanks for any suggestions.
Fred Bray
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.
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and follow the instructions there.
Le 7 mai 2013 à 20:00, Sarah White a écrit :
On 5/6/2013 9:38 AM, Chuck Forsberg WA7KGX N2469R wrote:
I would like to set up a NTP server on a machine running Linux
(currently Korora 18).
What are the requirements for the 1 PPS signal fed to the carrier detect
pin?
I presume the 10 us 1pps from the Thunderbolt is too narrow.
I assume the rising edge of CD is the one gpsd triggers on.
Chuck,
10 microseconds? That sounds fine actually... You could simply try it?
Really, I mean it. Just try and it might work with your serial port.
snipped
If you have problems with PPS, just set the serial port to a higher baud
rate... This is the reason I recommend against using the DCD line on the
same serial port you're using for TSIP. Trimble tends to use 9600 baud
on the TSIP port, and the signaling on that is too narrow.
For PPS, you'll be fine with 115200 BAUD (bit/s) ... This speed comes
out to 8680.55 nanoseconds, more than a full microsecond "narrower" than
the 10 microsecond wide PPS.
Sara, I'd be interested to know if you ran into the problem and changing baud rate fixed it. I ask that as my understanding of the most common UART indicates that the DCD signal line is not managed with the baud rate clock. At least for the most common 16550x variety, the DCD level changes are signaled in the MSR and then if interrupts are enabled an interrupt is queued. However t there is an anti-metastability filter of 2 CLK cycles before pin level changes are reflected in the MSR. So.. if your UART is on a slow clock, it could be that a 10us transition will be too fast to pass the filter. However, I do agree that trying is the easiest test.
Hi
Full blown, troublesome OCXO set procedure:
-
Touch the adjustment gizmo with your tuning tool. Don't adjust it. Watch the frequency, does it bounce? (change over several minutes). If so, your tuning tool is cooling off the oven. Find a lower thermal conductivity tool.
-
Take a toothpick, Push on the trimmer. Does the frequency move? If so, you likely have a broken / worn / cheap trimmer. Adjustment will take a long time.
-
Mark your tuning tool, mark the adjustment hole, call that point zero. Track your adjustments relative to that point.
-
Let the 5110 warm up for at least a couple of days. Record the frequency. Wait a day or two and check it again. If it's not settled wait a bit more. The normal approach with this box when new was to leave it on all the time.
Now you're ready to adjust the OCXO. Record the frequency, rotate the trimmer 1/8 turn clockwise. Watch what happens for at least a couple of minutes. Maybe it goes from +3 to +3.5 Hz relative to 10 MHz. What matters here is the start and finish frequencies, not what it does in-between. Rotate it back 1/8 turn. I'm guessing it goes from 3.5 to 3.2 Hz. That's backlash, if it's present the answer is to only adjust (slowly) in one direction.
Next adjust it another 1/8 turn CCW. One would hope that the frequency goes from 3.2 to 2. 7 Hz. If it goes from 3.2 to 3.3 Hz, that's non-linearity. If it's that significant, you will need to spend some quality time doing the adjustment. The trick here is to do a search for one of the many possible zeros.
Next step is to move in the appropriate direction, 1/8 turn at a time, until you go from x.x Hz high to x.x Hz low. Once that happens, take a break. Come back in a half hour and check it again.
Finally, bump the trimmer small fractions of a turn back towards zero. The idea is to get it closer with each bump, but not past zero. There's always some backlash ….
Lots of fun. All this is why cheap trimmer caps went out of favor a while back.
Bob
On May 7, 2013, at 10:24 PM, Frederick Bray fwbray@mminternet.com wrote:
This might be slightly off-topic, but probably there is a time-nut who knows the answer.
I am trying to adjust the 10 MHz OCXO in a Cushman 5110 service monitor. I am using a frequency counter driven by a GPSDO. Perhaps someone can educate me about a couple problems I am encountering.
I tried making small incremental adjustments but after I am done, the frequency drifts several Hz and then re-stabilizes at a new value. When I make further adjustments, I notice strange behavior. For example, if I initially turned the adjustment clockwise to increase the frequency, it will now decrease if I turn it clockwise and increase if I turn it counter-clockwise. On the next adjustment, it will reverse again.
Is there some correct procedure to adjust an OCXO?
Many thanks for any suggestions.
Fred Bray
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.
I use this method too, but I also find it little use trying to get the
internal reference down to the last squeak in 10^11 on this kind of kit. It
will not hold the setting for vey long and it takes ages to get the
adjustment spot on. I get as close as I can easily.....then allow the
unknown to stabilise and do an estimate of the error and stick a label with
thay value on the front until the next check is required eg "2 in 10^9 high
6thApr13" ......would not suit an avid "time-nut" but then the equipment is
often barely "time-nut quality" :-))
Alan G3NYK
.
----- Original Message -----
From: "Bill Riches" bill.riches@verizon.net
To: "'Discussion of precise time and frequency measurement'"
time-nuts@febo.com
Sent: Wednesday, May 08, 2013 11:52 AM
Subject: Re: [time-nuts] OCXO Adjustment Question
This is the method I use for my 5110. There are two 10 mhz outputs on the
osc - you can unplug one of the plugs and use a 10x probe there. My unit
will hold a couple of parts in
10-8 for months.
73,
Bill, WA2DVU
Cape May, NJ
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of J. L. Trantham
Sent: Tuesday, May 07, 2013 11:52 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] OCXO Adjustment Question
Fred,
What I do is to apply the GPSDO to the trigger input of a scope and the
output of the OCXO to be adjusted to the vertical input of the scope. Set
the time base to something line 100 nSec or faster and watch the output of
the OCXO after it has warmed up for 30 minutes or so.
This is an option only if you have an output from the OCXO you can watch.
If no output, try a x10 probe attached to a 10 MHz connection from the
OCXO
inside the monitor. However, be careful that the probe does not 'load'
the
OCXO and shift the frequency.
Adjust the OCXO for a stable display, not drifting left or right.
If the sine wave (or square wave) is moving to the left, the OCXO is high
in
frequency. If it is moving to the right, the OCXO is low in frequency.
If
stable, it is matched to the GPSDO. This is useful as long as the OCXO
and
GPSDO are within a few Hz of each other. The amount of time it takes for
the display to shift 1 cycle tells you how close the OCXO is to the GPSDO.
For instance, if it takes 10 seconds for the display to shift one cycle,
100,000,000 +/- 1 cycles went by in that 10 seconds or 1 part in 10E9 if I
have my math correct.
Joe
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Frederick Bray
Sent: Tuesday, May 07, 2013 9:25 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] OCXO Adjustment Question
This might be slightly off-topic, but probably there is a time-nut who
knows
the answer.
I am trying to adjust the 10 MHz OCXO in a Cushman 5110 service monitor.
I
am using a frequency counter driven by a GPSDO. Perhaps someone can
educate
me about a couple problems I am encountering.
I tried making small incremental adjustments but after I am done, the
frequency drifts several Hz and then re-stabilizes at a new value. When I
make further adjustments, I notice strange behavior. For example, if I
initially turned the adjustment clockwise to increase the frequency, it
will
now decrease if I turn it clockwise and increase if I turn it
counter-clockwise. On the next adjustment, it will reverse again.
Is there some correct procedure to adjust an OCXO?
Many thanks for any suggestions.
Fred Bray
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 mailing list -- time-nuts@febo.com To unsubscribe, go to
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To unsubscribe, go to
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and follow the instructions there.
Thanks for all the helpful suggestions and comments so far. I will
answer a few of the questions that have been raised.
The device definitely is an OCXO as it is in an oven and gets warm. It
is an Ovenaire 73-25.
As one person commented, there are two 10 MHz outputs on the device.
Actually, it appears that the Ovenaire has one output and there is a
resistor network external to the device that splits the signal.
So far, the range seems to be from around 9.999975 to 10.000025 and it
has been on for over 18 hours.
I am going to let it sit for a bit and then try the various tool options
that have been suggested.
One suggestion was to replace the Ovenaire with something like a Morion
MV89. That would seem to be a good long-term option.
All of this started as an attempt to track down an "unlock" problem with
the 5110 to see whether there was any output from the Ovenaire. When it
turned out that the OCXO was working, I gave into the temptation to
tweak the frequency.
Fred
One point of clarification. In my last post I said:
So far, the range seems to be from around 9.999975 to 10.000025 and it
has been on for over 18 hours.
That is not how much it drifts, but rather the range over which the
frequency on the counter has varied as I have tried to touch up the
adjustment.
I was going to write the same thing. That the DCD line has nothing at
all to do with baud rate. But that applies to a "real" serial port.
If this is being done on a Serial->USB dongle that all bets are off
and you'll never get really good result as USB adds to many software
laters.
You can buy a new motherboard with a real rs232 port for under $100
and used ones for even less. I'd not recommend uSB for the PPS
signal. It is OK for serial data but not for PPS. (that is if you
care about best accuracy.)
On the USB converter the fact that the dCD signal changed has to go
over the USB bus in a serial data packet and gt queued and then read
and acted on. It is orders of magnitude worse.
But all that said, if you get NTP sync'd to within 20 uSec you are
more than good enough. It takes some effort to get to the 2 uSec
level and heroic effort to break 1 uS. For practical purposes you
have to decide what is good enough. Some people are happily with 10
milli Sec.
Sara, I'd be interested to know if you ran into the problem and changing baud rate fixed it. I ask that as my understanding of the most common UART indicates that the DCD signal line is not managed with the baud rate clock. At least for the most common 16550x variety, the DCD level changes are signaled in the MSR and then if interrupts are enabled an interrupt is queued. However t there is an anti-metastability filter of 2 CLK cycles before pin level changes are reflected in the MSR. So.. if your UART is on a slow clock, it could be that a 10us transition will be too fast to pass the filter. However, I do agree that trying is the easiest test.
--
Chris Albertson
Redondo Beach, California
Fred,
Be careful about the 'tweaking'. It can become very addicting. Short of a
GPSDO, you'll always have to tweak from time to time. The problem is being
able to define what tolerance you are willing to accept and how often you
don't mind tweaking.
Otherwise, you never get any work done, just spend your time 'tweaking'.
Joe
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Frederick Bray
Sent: Wednesday, May 08, 2013 11:21 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] OCXO Adjustment Question
Thanks for all the helpful suggestions and comments so far. I will answer a
few of the questions that have been raised.
The device definitely is an OCXO as it is in an oven and gets warm. It is an
Ovenaire 73-25.
As one person commented, there are two 10 MHz outputs on the device.
Actually, it appears that the Ovenaire has one output and there is a
resistor network external to the device that splits the signal.
So far, the range seems to be from around 9.999975 to 10.000025 and it has
been on for over 18 hours.
I am going to let it sit for a bit and then try the various tool options
that have been suggested.
One suggestion was to replace the Ovenaire with something like a Morion
MV89. That would seem to be a good long-term option.
All of this started as an attempt to track down an "unlock" problem with the
5110 to see whether there was any output from the Ovenaire. When it turned
out that the OCXO was working, I gave into the temptation to tweak the
frequency.
Fred
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One of the things I hadn't adequately considered was how quickly / much
the oven cycling affects things. I wasn't really thinking about this
when tweaking the adjustment so I wasn't doing them at a consistent
point in the cycle.
Now, it looks like it may be cycling from a low of 10.000001 to a high
of 10.000017. I have watched this pattern repeat a number of times now.
I guess my goal for this device should be to get it to the point that it
cycles from about 9.999992 to about 10.000008, thus putting the center
point around 10 MHz.
I forgot to mention in my earlier email, a +/- 25 Hz range for the OCXO is
fairly large. I have an OVENAIRE OCXO in an EIP 545A that has a range (by
20 turn pot) of about +/- 2.5 Hz.
I suspect you are adjusting a capacitor, not a pot.
Joe
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Frederick Bray
Sent: Wednesday, May 08, 2013 11:44 AM
To: time-nuts@febo.com
Subject: Re: [time-nuts] OCXO Adjustment Question
One point of clarification. In my last post I said:
So far, the range seems to be from around 9.999975 to 10.000025 and it
has been on for over 18 hours.
That is not how much it drifts, but rather the range over which the
frequency on the counter has varied as I have tried to touch up the
adjustment.
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and follow the instructions there.
On 5/7/2013 2:00 PM, Sarah White wrote:
If you have problems with PPS, just set the serial port to a higher baud
rate... This is the reason I recommend against using the DCD line on the
same serial port you're using for TSIP
((snip))
On 5/8/2013 6:53 AM, mike cook wrote:
Sara, I'd be interested to know if you ran into the problem and changing
baud rate fixed it. I ask that as my understanding of the most common
UART indicates that the DCD signal line is not managed with the baud
rate clock. At least for the most common 16550x variety, the DCD level
changes are signaled in the MSR and then if interrupts are enabled an
interrupt is queued. However t there is an anti-metastability filter of
2 CLK cycles before pin level changes are reflected in the MSR. So.. if
your UART is on a slow clock, it could be that a 10us transition will
be too fast to pass the filter. However, I do agree that trying is the
easiest test.
--- begin reply ---
[CITATION] --> http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm
(section) 6.2.4.6.1. What is the shortest Width for a Pulse
connected to the DCD Pin of an RS-232 Interface?
That depends. The higher the quality your serial port is, the longer
pulses will be needed. This is because of the ESD protection of the chip.
26 usec should be about the bit time for a 38400 serial line, so you
could connect it to the RxD line instead and see if you receive
characters that way when the port is set for 38400 or faster.
Another thing to try is to configure the serial port for 115200, some of
the chips base their deglitching on the baud rate, often requiring a
full symbol before they react.
[END CITATION]
Mike, I think that's basically what you were saying:
(quote of mike cook)
... there is an anti-metastability filter of 2 CLK cycles before pin
level changes are reflected in the MSR. So.. if your UART is on a slow
clock, it could be that a 10us transition will be too fast to pass the
filter.
(end of last quote)
Or did I misunderstand what you said?
Yes. On principle, for some but not 100% of serial ports, the baud rate
clock won't matter at all, and the hardware interrupts will still happen
with low latency, regardless of the baud rate setting. What will change
however, is filtering which MIGHT be related to the baud rate setting.
(as per the citation I included in this post)
--Sarah
P.S. I had trouble understanding the quote & reply style / layout...
... refactored the layout by band to look cleaner (my own tastes)
... basically made it easier for me to proofread everything, etc.
Also, seems the person who started this topic is currently silent...
... I think it was: "Chuck Forsberg WA7KGX N2469R" caf@omen.com