I stand firm that the only proper way to do this is with a 100%
deterministic architecture.
..only proper way to do what? The goal is to discipline the internal
software clock to GPS. A typical application is a database server
that is running a web e-comerse site so that transactions get
Nice toy, but the question of the necessity of a fully fledged OS for
most tasks thrown at such a small system still remains (integrated
network connectivity is a plus).
NTP isn't capable to improve the precision of a system's clock, as it
works over a heterogeneous path, which is quite
Hi Brooke,
RAM mat is a good idea, but I'm not sure that signal blocking is a good test,
it could just be reflecting. A better test is to put a small piece in a
microwave along with a cup of water (as dummy load) and see how hot it gets.
Best done at low power and short time when household
I asked this on an NTP list, got some guesses, but no knowledgeable
responses.
[]
So, running a process(es) which keep the CPU completely busy reduces the
jitter. The busier, the better. Why? I'm guessing it has something to do
with interrupt latency, but why does a busy CPU make it more
Jim,
There's a new choke ring style antenna (patented, of course, and they
deserve it) which uses spikes instead of solid rings. And, they wrap the
choke over a hemispherical surface as opposed to on a plane.
Much tougher to design and fabricate (no buying sets of cake pans any
more), but
On a side note, speaking of deterministic systems, why has no one built a
GPSDO with an FPGA yet? Or an NTP server? :)
Yes, I have: I have a GPSDO entirely on a 50Kgates FPGA (Spartan3 XC3S50)
without microprocessor. GPS is the iLotus M12M and OCXO is a Morion MV201,
the DAC is... well, not
On 4/5/2012 2:51 AM, David J Taylor wrote:
Mike, have you tried FreeBSD instead? Does it show the same problems?
I have a couple of Soekris Net 4501s running FreeBSD and NTP. They don't
have much jitter, but they're a very different architecture. The machine
with the jitter is my home do
El 05/04/2012 12:20, Azelio Boriani escribió:
On a side note, speaking of deterministic systems, why has no one built a
GPSDO with an FPGA yet? Or an NTP server? :)
Oh, I've done that (an NTP server, not GPSO) in a Cyclone III FPGA. But
well... it has a Nios-II CPU and runs Linux, so I
What sort of interference?? What is causing it? Any possibility of
correcting it?
I am interested in more information. Will look for whats later in the
thread. I have a situation where there is interference coming from a
specific direction (close to the horizon). Is it feasible to
How do you know it is coming from a specific direction? There is a
terrestrial L-band transmitter? A radio link? Try to put a screen
n*lambda+lambda/2 from the GPS antenna to create a null for the offending
L-band frequency...
On Thu, Apr 5, 2012 at 2:49 PM, Chuck Forsberg WA7KGX N2469R
'Navipedia': the reference for satellite navigation know-how. Satellite
navigation is progressing swiftly, in fact so swiftly that its printed
textbooks can't keep pace - so ESA has introduced its own wiki-based
information source, Navipedia, which is also the first ever ESA technical
wiki
There was some discussion on this here a while back. I had issues with bad
reflections and wanted to know if there was a possibility of creating a
variable mask angle. I had found a reference to a program developed by Leica to
do just that. The links however ended in a dead end.
It would be a
On 03/26/2012 01:38 AM, John Ackermann N8UR wrote:
[ Apologies if this is a duplicate. ]
We are happy* to announce that TAPR is now accepting orders for the
TADD-2 Mini (or T2-Mini) pulse-per-second (PPS) frequency divider:
http://www.tapr.org/kits_t2-mini.html.
Congratulations!
Good work!
On 03/26/2012 10:34 AM, Rex wrote:
On 3/24/2012 3:54 PM, Magnus Danielson wrote:
and the Hanbook of Frequency Stability Analysis
You didn't mention looking at that one. Any comments about it?
Considering that it is available from NIST as SP 1067 and that it is
also downloadable as PDF from
On 04/03/2012 01:10 PM, Jim Lux wrote:
On 4/3/12 12:49 AM, Azelio Boriani wrote:
Yes, but nonetheless why not develop more stable primary clock
sources? We
can always take care of the dissemination in the meantime and try to
develop a more precise time transfer method.
On Tue, Apr 3, 2012 at
My guess on the original question is that keeping the CPU busy puts junk into
the cache so the whole interrupt processing path takes every possible cache
miss. NTP doesn't care how fast that code is as long as it's consistent.
(Of course, you probably get a different answer, but we are
On Thu, Apr 5, 2012 at 11:11 AM, Hal Murray hmur...@megapathdsl.net wrote:
My guess on the original question is that keeping the CPU busy puts junk into
the cache so the whole interrupt processing path takes every possible cache
miss.
Cache misses are nanosecond level events not tens of
An older laptop (Pentium M for instance) can be had for $80 or so any day of
the week, won't take much space, is completely standalone (built-in keyboard
and display, built-in battery backup) and sips power when idle, which it will
be most of the time.
The only issue is that you might be
Old doesn't necessarily mean it sips power. Power consumption is based
on buckets of charge shuffled through the chips. Older processes have
more capacitance, hence bigger buckets for the same amount of work.
Further, notebooks have all the power saving features that are causing
(potentially)
On 5 Apr, 2012, at 13:03 , shali...@gmail.com wrote:
An older laptop (Pentium M for instance) can be had for $80 or so any day of
the week, won't take much space, is completely standalone (built-in keyboard
and display, built-in battery backup) and sips power when idle, which it will
be
Hi,
Are you sure that the Oncore VP sends the right voltage to the antenna?
This type needs 5 V and most pucks are designed for 3.3 V . According
to the manual the VP sends 5 V to the antenna but anyway it is easy to
measure.
Regards,
Ignacio, EB4APL
On 05/04/2012 3:43, Morris Odell
On Thu, Apr 5, 2012 at 2:28 PM, EB4APL eb4...@cembreros.jazztel.es wrote:
Hi,
Are you sure that the Oncore VP sends the right voltage to the antenna?
This type needs 5 V and most pucks are designed for 3.3 V . According to
the manual the VP sends 5 V to the antenna but anyway it is easy to
On Thu, Apr 5, 2012 at 1:03 PM, shali...@gmail.com wrote:
An older laptop (Pentium M for instance) can be had for $80 or so any day of
the week, won't take much space, is completely standalone (built-in keyboard
and display, built-in battery backup) and sips power when idle, which it will
Thanks for the replies.
Yes it's definitely 5V from the receiver.
That advice re the pipe mount sounds good - that will be the next step!
Morris
--
Are you sure that the Oncore VP sends the right voltage to the antenna?
This type
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