In message [EMAIL PROTECTED], David M. Witten II writes:
Can I still expect to see similar performance using more recent versions
of FreeBSD than you originally used?
Yes, the timestamping is done in hardware, so it does not depend on
the OS version.
Will a usable build of FreeBSD 7.x run in
Poul-Henning Kamp wrote:
#--
Actually, the best hardware for the job is the Soekris NET4501
which can timestamp a signal to a quarter microsecond.
That's why we use it for NTP servers in the first place.
All the software you need is in the FreeBSD kernel, and there
is a handy userland program
In message: [EMAIL PROTECTED]
David M. Witten II [EMAIL PROTECTED] writes:
: Will a usable build of FreeBSD 7.x run in the memory available on the
: older Soekris boards? (64 MB RAM)
No. My router/dhcp server, mail forwarding anti-spam agent, external
DNS server are all on my
In message: [EMAIL PROTECTED]
M. Warner Losh [EMAIL PROTECTED] writes:
: In message: [EMAIL PROTECTED]
: David M. Witten II [EMAIL PROTECTED] writes:
: : Will a usable build of FreeBSD 7.x run in the memory available on the
: : older Soekris boards? (64 MB RAM)
:
: No.
Tom Van Baak [EMAIL PROTECTED] wrote:
Now I am confused. I thought it used the internal crystal clock
for the timing, and selected which pulse to output for the 1PPS,
and this is what causes the sawtooth. If so, the timing is
determined by the crystal.
Correct. For
Mike,
So where did the 1ns granularity come in?
For example, Motorola receivers output the sawtooth correction as
an 8-bit signed binary field in the @@En/Hn TRAIM message. The
range of said byte is -128 to +127; the scale, the granularity, the
units of that field are 1 ns. Make sense now?
On 10/13/08 8:54 PM, Mike Monett [EMAIL PROTECTED] wrote:
Mike,
So where did the 1ns granularity come in?
For example, Motorola receivers output the sawtooth correction as
an 8-bit signed binary field in the @@En/Hn TRAIM message. The
range of said byte is -128 to +127; the
Mike,
Comments below...
I have to learn more about how you do your measurements. A 53132A is
way out of my price range at the moment. But I do have a 53310A
which should give comparable results.
Yes, if you can get a clean series of 1PPS sub-ns time interval
measurements over GPIB
Tom Van Baak [EMAIL PROTECTED] wrote:
Mike,
Comments below.
I have to learn more about how you do your measurements. A 53132A
is way out of my price range at the moment. But I do have a
53310A which should give comparable results.
Yes, if you can get a clean series
Now I am confused. I thought it used the internal crystal clock for
the timing, and selected which pulse to output for the 1PPS, and
this is what causes the sawtooth. If so, the timing is determined by
the crystal.
Correct. For example, if the xtal were 20.00 MHz then the hardware
Mike Monett wrote:
Bruce Griffiths [EMAIL PROTECTED] wrote:
Mike
They actually use an augmented form of GPS common view for which
the GPS PPS signal and its timing variations are largely common to
both locations and thus largely cancel when comparing the
The single-shot is supposed to eliminate the 1PPS jitter? So it must
be triggered on the 1PPS, and the variable delay gives an average of
half the clock period?
Yes, right.
Note another equivalent technique is to use two serial ports;
one for the receiver (record sawtooth corrections) and
Bruce Griffiths [EMAIL PROTECTED] wrote:
Mike
They actually use an augmented form of GPS common view for which
the GPS PPS signal and its timing variations are largely common to
both locations and thus largely cancel when comparing the
frequencies at the customer
Hi Mike,
Rick's CNSC02-O1 implementation has been discussed here
a number of times over the years (google the archives). It uses
a programmable digital delay line to compensate for the receiver
reported quantization error on each pending 1 pps.
Here's a quick plot of an M12+ receiver without
Mike Monett wrote:
For more detail see:
http://tf.nist.gov/timefreq/service/fms.htm
Thanks very much for the link. It is curious they don't seem to
spend much effort on correcting the user's frequency errors. They
just want to report how much they are off.
Why is
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Testing frequency using NTP Bruce GPS ps
Mike Monett wrote:
For more detail see:
http://tf.nist.gov/timefreq/service/fms.htm
Thanks very much for the link. It is curious they
don't seem
Tom Van Baak [EMAIL PROTECTED] wrote:
Hi Mike,
Hi Tom,
I want to thank you for the very nice reply you gave to my email a
while ago. Unfortunately, I am still learning about precision
frequency references, and I don't have enough knowledge yet to give
you an intelligent
In message [EMAIL PROTECTED], Steve
Rooke writes:
2008/10/2 Bruce Griffiths [EMAIL PROTECTED]:
Save yourself a counter and just divide the frequency down to about 1Hz
and time stamp the 1Hz transitions with the Linux box.
As long as you know the division factor its easy enough to calculate
I'd planned on a simple interface to the PC via using the parallel,
suitably strapped, as a basic output port. Now, I could use it as an
input but I'd probably have to poll the port which would be somewhat
inefficient but an option I guess. Think I could just record the
staring time of the
2008/10/2 Poul-Henning Kamp [EMAIL PROTECTED]:
In message [EMAIL PROTECTED], Steve
Rooke writes:
2008/10/2 Bruce Griffiths [EMAIL PROTECTED]:
Save yourself a counter and just divide the frequency down to about 1Hz
and time stamp the 1Hz transitions with the Linux box.
As long as you know the
Scuse me for top posting.
Guess I'm going to do something a bit like plan 3 but mostly in
hardware. My plan for the PC is just to use it to gate the oxco output
into the pre-scalier divider chain for a specific time period. The
output of the pre-scalier will be a series of pulses which can be
I'm not planning to use this oxco to sync the NTP on my PC, just using
NTP to check the frequency of my oxco so I can use it to calibrate my
counters, as a timebase and hence to allow me to lock amateur radio
transceivers to a precise frequency for QRP (very low power long
distance work). If
inside!
73s de Ulrich, DF6JB
-Ursprungliche Nachricht-
Von: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Im Auftrag von Steve Rooke
Gesendet: Donnerstag, 2. Oktober 2008 07:37
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] Testing frequency using
Ulrich Bangert wrote:
Steve,
Hmmm... If I measured a 10MHz oscillator for a 1/10 second, I
could achieve, at best, 1ppm accuracy. Now my measuring
system has a non accumulating error in the ms range, say 1s,
so this would be totally unworkable. If I sampled for 1s,
best would be
On 10/1/08 10:18 PM, Steve Rooke [EMAIL PROTECTED] wrote:
2008/10/2 Bruce Griffiths [EMAIL PROTECTED]:
Save yourself a counter and just divide the frequency down to about 1Hz
and time stamp the 1Hz transitions with the Linux box.
As long as you know the division factor its easy enough to
I'm wondering about the possibility of checking the frequency of my
oscillator by using a NTP synced RT Linux system. What I'm thinking of
An all-PC frequency counter is a great idea. True, the
performance is limited compared to GPS time sources and
hardware frequency counters, but there's
Mike Monett wrote:
Hello Bruce,
This is my first attempt to post so I'm not sure if it will work.
I have been researching the forum archive and find it is by far the
best resource on time and frequency available anywhere. Also, your
posts are extremely helpful to a newcomer.
Tom Van Baak wrote:
I'm wondering about the possibility of checking the frequency of my
oscillator by using a NTP synced RT Linux system. What I'm thinking of
An all-PC frequency counter is a great idea. True, the
performance is limited compared to GPS time sources and
hardware
When using a sound card for frequency comparisons the zero crossing time
stamp resolution is improved if the slew rate of the input signal is
slow enough that several (3 or more) samples are taken in the vicinity
of the zero crossing. One can then make use of WKS (Whittaker,
Kotelnikov,
Tom Van Baak wrote:
When using a sound card for frequency comparisons the zero crossing time
stamp resolution is improved if the slew rate of the input signal is
slow enough that several (3 or more) samples are taken in the vicinity
of the zero crossing. One can then make use of WKS
In message [EMAIL PROTECTED], Tom Van Baak writes:
I'm wondering about the possibility of checking the frequency of my
oscillator by using a NTP synced RT Linux system. What I'm thinking of
An all-PC frequency counter is a great idea.
Actually, the best hardware for the job is the Soekris
Tom Van Baak wrote:
The instability of the sound card LO isnt completely cancelled if the
zero crossings of the the 2 signals aren't coincident.
That seems right for absolute event timing with a stereo sound card
but I think for a frequency measurement the delay, if any, between
Tom
The short term phase instabilities of the sound card LO that occur
during the finite interval between the zero crossing times for one
channel and the zero crossing time for the other channel can be
significant.
...
Bruce,
I'm all ears for details about the phase stability of
At 5:32 PM -0700 10/2/08, Tom Van Baak wrote:
Tom
The short term phase instabilities of the sound card LO that occur
during the finite interval between the zero crossing times for one
channel and the zero crossing time for the other channel can be
significant.
...
Bruce,
I'm all
Tom Van Baak wrote:
Tom
The short term phase instabilities of the sound card LO that occur
during the finite interval between the zero crossing times for one
channel and the zero crossing time for the other channel can be
significant.
...
Bruce,
I'm all ears for details about
Tom
The major source of interchannel phase shift instability will be the
phase shift instabilities of the sound card input RC coupling network
particularly if electrolytic capacitors are used and the input
frequencies are too close to the high pass RC filter 3dB frequency.
Amplifier
Bruce Griffiths wrote:
Tom
The major source of interchannel phase shift instability will be the
phase shift instabilities of the sound card input RC coupling network
particularly if electrolytic capacitors are used and the input
frequencies are too close to the high pass RC filter 3dB
The time constant should have been 22ms and the phase shift 1.16us with
a tempco of 580ps/C.
Since both channels have the same nominal low frequency cutoff the
differential phase shift tempco will be somewhat smaller.
Thanks for the calculations. So it's probably safe to say the
Tom Van Baak wrote:
Anyway, I think it would make a fun project to see how well a
typical PC sound card actually does as a 1PPS or LF phase
comparator and frequency counter. I wouldn't expect better
results than a $50 surplus eBay time interval counter, but it
would be interesting to see just
I'm wondering about the possibility of checking the frequency of my
oscillator by using a NTP synced RT Linux system. What I'm thinking of
doing is building a long chain of dividers feeding a standard freq
counter in totallise mode such that I can count the number of cycled
over a long time
Steve Rooke wrote:
I'm wondering about the possibility of checking the frequency of my
oscillator by using a NTP synced RT Linux system. What I'm thinking of
doing is building a long chain of dividers feeding a standard freq
counter in totallise mode such that I can count the number of cycled
It depends on how accurately you want to measure the oscillator
frequency with your approach short term you probably would not be able
to measure the oscillator offset any better than a few parts in 10-5
longer term probably a few parts in 10-7 might be possible as you
could compute the allen
But wouldn't, over time, all this ntp/OS/network noise average away
because ultimately the whole system is being locked to an atomic clock? I
know any given measurement will have errors in the order of milliseconds,
but the long term average ought to be good. Ought it?
You could test it by giving
2008/10/2 Bruce Griffiths [EMAIL PROTECTED]:
Save yourself a counter and just divide the frequency down to about 1Hz
and time stamp the 1Hz transitions with the Linux box.
As long as you know the division factor its easy enough to calculate the
frequency.
I'd planned on a simple interface to
Hi Jim,
That's exactly what I was thinking too. Indeed, if I had a decent freq
std I'd use that to measure my oxco. Guess I'm just bouncing ideas
around here and looking for any input.
Cheers,
Steve
2008/10/2 Jim Palfreyman [EMAIL PROTECTED]:
But wouldn't, over time, all this ntp/OS/network
Your results are considerably better than mine but these are just off
my busy workstation taken as a snapshot. I have no local time standard
so dependant on the external servers. Perhaps I could do better on a
dedicated system running a RT Linux:-
ntpdc peers
remote local st
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