I am wondering if it's a tough road to get precise time and frequency.
How precise do you want? How much money do you have?
1/2 :), but you are asking on the time-nuts list so you should expect answers
like that.
I would love to discipline my counter and signal generator time bases to
jim...@earthlink.net said:
I sample at 100 kHz with 16 bits on a teensy3..
Neat. Thanks. How many effective bits? (when the input signal is 60 KHz it
that matters)
Can somebody give me a lesson in the tradeoffs between number of bits and
sampling rate?
I know of one special case. If
dan...@verizon.net said:
I had one with a dead thermistor; that was a little bit trickier. A lot in
the archives on these, I'm sure.
Good pictures and directions here:
http://www.realhamradio.com/GPS-oven-journey.htm
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# Delta GPS: 3659, Delta RTC: 3660
# Delta GPS: 3659, Delta RTC: 3659
# Delta GPS: 3658, Delta RTC: 1984
# Delta GPS: 3658, Delta RTC: 1984
# Delta GPS: 3659, Delta RTC: 3659
# Delta GPS: 3659, Delta RTC: 3660
I would like to ask if somebody did measurement for that Dallas DS32XX
jim...@earthlink.net said:
there's a BIG jump in cost when you cross that 18GHz boundary line.
What's magic about 18 GHz? Why not 16 or 20?
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rich...@karlquist.com said:
Solid dielectric cable and connectors of 3.5 mm size are mode limited to 18
GHz. That is why there is so much stuff rated at 18 GHz as opposed to 16 or
20 GHz.
Thanks. That's what I was looking for.
Wiki says that SMA works to 18 GHz and the 3.5 mm is good for
david.partri...@perdrix.co.uk said:
I looked around the with Google, and saw *numerous serial port splitters.
Which is recommended?
If your lines are short, you don't need fancy hardware. The RS-232 driver
will drive 2 lines. Just take 2 cables, cut them in half, connect the
wires...
b...@evoria.net said:
At least on the PIC I'm using, the CCP and timer interrupts don't seem to be
synchronous with the PIC clock. I could be mistaken.
Unless you have a very strange architecture, it doesn't make sense for an
interrupt to not be synchronous with the CPU clock. You are in
hau...@keteu.org said:
That being said, I find myself wondering as follows: Suppose that we count
OCXO cycles (at, say, 10 MHz) using one of the MCU's timer/counter
peripherals, and periodically sample the counter value with an interrupt
triggered on the rising edge of the GPS 1pps. Assume
I think a better solution would be to find a very large super cap and
power the BBB from that while giving it a power fail interrupt to quickly
sync the file system.
The advantage of something like the BBB is that it runs Linux so you have a
nice environment in which to run your code. The
I am trying to understand how this is done. Should I ever get a rubidium
standard, I'd want to check its calibration, and that's not a trivial
exercise.
If you assume your rubidium is stable, then it's pretty easy to check and/or
calibrate.
The trick is that you need someplace to stand.
li...@rtty.us said:
A number of them have sold recently on eBay for about $130.
Don't forget the antenna and power supply.
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bob91...@yahoo.com said:
But I thought conventional wisdom is that most crystals are AT cut and an
attempt at zero average coefficient is made, causing a nonlinear
characteristic. But perhaps over a limited range it's linear. The problem
of course is calibration.
Most crystals are low
tmiller11...@verizon.net said:
Is that 3 MHz OCXO one from Ridge? If so, I opened one up and was surprised
to find it did not have any foam insulation.
RDR Electronics
There were 2 per board, from some old telco/cell gear.
http://w9fz.com/ham/s3mhz2.jpg
http://w9fz.com/ham/3mhzocxo.txt
Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C
albertson.ch...@gmail.com said:
So does this mean I can epoxy a sandstone power resister to a junk crystal
and keep the frequency exactly perfect by varying the power in the resister?
Sure, for some values of perfect and such.
thol...@woh.rr.com said:
Hanging bridge? What is it; where is it found; and how does it form?
Tom Clark and Rick Hambly: Timing for VLBI
http://gpstime.com/files/tow-time2009.pdf
tvb: Motorola GPS M12+ Sawtooth
http://www.leapsecond.com/pages/m12/sawtooth.htm
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j...@jtmiller.com said:
I'm new at this obviously. I was just looking at the uBlox-6 info and I
don't see where in the NMEA sentences the sawtooth info is contained. Is it
a manufacturer specific option that needs be turned on? Or is it contained
within a standard NMEA sentence somewhere. I
jim...@earthlink.net said:
for $20, it's hard to beat.. the only downside is that you can't go down
to radio shack and buy one on the spur of the moment.
At that price, you can keep a couple on the shelf.
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j...@jtmiller.com said:
I may switch the GPS module at a later date to one which provides sawtooth
info if I really feel the need and add a delay line. Frankly I think I'll
never get around to it.
One nasty problem with hanging bridges is that if you don't believe in them,
then you won't
Yes indeed those plastic display covers do seem to fall out and get lost. I
have a 5730 with the same issue. Digikey sold (or used to) the red filtered
plastic and I have used that to fix an hp8505 that lost a window.
If you live in an area with lots of high-tech, there is probably a local
albertson.ch...@gmail.com said:
The M12 user manual hints at why, they say the newer receiver runs on a
faster internal clock.
Roughly, it's going to be within 1/2 clock cycle. If newer units have faster
clocks, the peak-peak sawtooth should be smaller.
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b...@evoria.net said:
A range of 0.715V-2.38V is totally outside my expectations. The only way I
can get close to these values is if the internal CHOLD in the PIC is only a
fraction of the 120pf they say it has - say 20pf. Any thoughts would be
appreciated.
My quick guess is a problem
a.. So how do I set it to read real time ?
My notes say that for a Z3801A:
:diag:gps:utc 1
It may need a reboot.
A google search for HP 58503A manual gets lots of hits that look
interesting. This is the top of the list:
58503B GPS Time and Frequency Reference ... - LeapSecond.com
So the question is, will this really stop the annoying survey every time ?
I'd browse the manual looking for fine print. The idea you are looking for
is that after a survey it will save the location. If it has a saved location
on power up it will use it rather than do a new survey.
The
xne...@luna.dyndns.dk said:
If you have a conditioning circuit betewwn the OCXO and the STM , i'd like
to see it. As i have the need for one , trying to interface a 5v OCXO to a
NXP 1114 Arm , that wants max 1.8v in the clockinput.
What's wrong with a simple resistive divider?
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mag...@rubidium.dyndns.org said:
Exponential averger takes much less memory. Consider this code:
x_avg = x_avg + (x - x_avg) * a_avg;
Where a_avg is the time-constant control parameter.
Also note that if a_avg is a power of 2, you can do it all with shifts rather
than multiplies.
Note that
So we know there are deviations in line freq. But it seems strange in this
era of very accurate and inexpensive freq references. How much is related to
the generation?
Controlling the line frequency is a giant PLL, with horrible complications.
The simple setup for a big generator is that if
b...@evoria.net said:
In the moving averages I'm doing, I'm saving the last bit to be shifted out
and if it's a 1 (i.e. 0.5) I increase the result by 1.
That's just rounding up at an important place. It's probably a good idea,
but doesn't cover the area I was trying to point out. Let me
[Context is maybe(?) withdrawing the proposal to stop keeping time on the US
power line.]
wb4...@wb4gcs.org said:
Since then, large amounts of generation (primarily coal) has been shut
down, so I was not at all surprised by the request.
I missed the announcement that the request was
albertson.ch...@gmail.com said:
We have to define best. I'd define it as the error integrated over time
is minimum. I think PiD gets you that and it is also easy to program and
uses very little memory. Just three values (1) the error, (2) the total of
all errors you've seen (in a perfect
li...@rtty.us said:
Timing at the Time Nuts level is about precision.
What's the term for a time-nut that's trying to be not-very-nutty?
--
b...@evoria.net said:
includes a 10-bit PWM dithered to 14 bits
When you get it all working, that's going to be one of the weak links, at
albertson.ch...@gmail.com said:
There seem to be two different class of Rb. One takes an EFC just like the
OCXO so the controller looks just like a GPSDO and the other class of Rb
accepts serial commends to adjust the frequency. These have an internal
DAC. But either way the logic is the
jleik...@leikhim.com said:
In retrospect it is kind of crazy that fleet owners will put tracking
devices on $100K semi trucks and cranes yet $100 million aircraft have to
rely upon 60 year old technology (Transponders) and ACARS to keep track of
them. I don't question the utility of TCAS and
albertson.ch...@gmail.com said:
Would you know which other systems include the PRUs? Is it only in the TI
products? It seems like an ideal solution to the problem of
non-deterministic latency.
There is a much simpler solution - avoid the latency by using a counter/timer
to capture the
4) How much do the DAC, reference, op-amps, resistors, capacitors, drift with
time?
Assuming constant temperature and supply voltage...
What is the time scale for parts drifting? Is it very low frequency so well
within the loop bandwidth or is it jumps that will be hard to filter out?
li...@rtty.us said:
If you have a source of noise that is not in your model *and* its
significant, then your model will not predict the outcome. Thats true if
its in or if its outside the loop bandwidth.
Does anybody have data on the drift of Rs or Cs? In this context, is it
csteinm...@yandex.com said:
Can I find a way to move the OXCO into the guts of a GPS receiver.
I don't know. Can you? That is essentially what the Thunderbolt does, and
it brings with it the tremendous advantage that it removes the sawtooth
error -- which is why some of us think so
mag...@rubidium.dyndns.org said:
I did a temporary hack on the PID code to convert the D-term into I^2 term,
by integrating the integrator output. First attempt was indeed quite
resonant just to show that I was in the unsafe region. Backing down on the
strength of the component sure did
Does anybody have data on the drift of Rs or Cs?
Rule of thumb:
...
Ah, thanks. But by Rs and Cs I meant plural or R/resistor and C/capacitor.
I know they change a lot with temperature, but how much do they drift if the
temperature is constant?
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b...@evoria.net said:
Thanks for the response. I've got a UT+ in the parts box. But that's not
the problem I'm trying to solve. I'm trying to make the best GPSDO that I
can make using a nav receiver at the moment. Call it an obsession if you
like. It's OK if I don't have corrections to
albertson.ch...@gmail.com said:
The assumption NTP makes is that you can judge the quality of a server by
the variance (of jitter) in the time it reports.
I think it's more complicated than that.
I think it also includes the non-jitter part of the round trip time. NTP
assumes the path is
ja...@extremeoverclocking.com said:
If there was some sort of feature in NTP (maybe there already is???), or
even a separate program that could test a list of NTP servers to try and
pick the lowest latency, I think that could have a positive benefit on
better time transfer.
The current
j...@jtmiller.com said:
I've spent a good part of the afternoon looking at all the plots, websites
and the few papers I could find mentioning the hanging bridge. As far as I
can tell as long as one is correcting for sawtooth there's nothing
additional to do about hanging bridges.
They
n1...@dartmouth.edu said:
I am surprised it took them this long. A number of satellite telemetry
systems can use doppler as a matter of course for locating transmitters,
such as Iridium and Argos.
It's more complicated than just computing the Doppler. You also have to
figure out what the
jim...@earthlink.net said:
Has anyone seen a similar behavior? I've tried the power cycling, and the
Garmin reset command. I've not done the clear non-volatile memory
which makes it forget the almanac.
I had one GPS-18x LVC go insane. I don't remember the details. I think it
didn't
martin.burni...@burnicki.net said:
Please note under Windows you should configure all upstream servers with a
line reading
server aa.bb.cc.dd iburst minpoll 6 maxpoll 6
There are lots of times when reducing maxpoll is reasonable, but I think an
unqualified suggestion is not appropriate.
[Nice description. Thanks.]
wd6...@gmail.com said:
I'm sure the short-term stability isn't as good as a PLL, but averaging the
errors over such a long period does have the advantage of making the
sawtooth error pretty much irrelevant.
You don't believe in hanging bridges?
What do you mean
wd6...@gmail.com said:
I'm sorry, I don't recognize the reference to hanging bridges.
I guess it was a good thing I mentioned it. Sometimes I feel like a broken
record. It gets discussed here occasionally. There will be lots of comments
in the archives.
Starter version:
tvb: Motorola
hol...@hotmail.com said:
I'm not sure how the Arduino environment handles interrupts, but in C you
need to declare any variables altered by an interrupt as volatile so that
the compiler optimization routines know not to assume they contain known
values.
Good point.
Also any code that
Actaully I don't care much about an off by one count because the problem
is corrected in the next second. If I happen to miss a count one second the
very next second this shows up as an extra count.I notice that something
like this happens every few hundred seconds.
I think you can
But I think you over looked one point that makes this project easier: We
KNOW 100% for certain that the interrupts happen only once per second. So
the foreground code knows for certain it has exclusive access to shared
variables for a given period of time. There is zero chance of a problem
I've been watching the discussions and graphs for a while. ADEV seems
appropriate for cases where the noise pattern is nice. How does ADEV work
if the noise isn't nice? Are there alternatives? What's the mathematical
term for the type of noise that works well with ADEV?
I can think of 3
t...@leapsecond.com said:
You only need enough bits to cover the worst case OCXO frequency drift or
the worst case GPS jitter error, per second. For example, if your OCXO stays
accurate to 1 ppm it can't possibly drift more than 1 us per second.
Similarly, it's a safe assumption that your GPS
But I still need to count all the cycles in the second and can't just let a
8 or 16 bit counter run free. The reason is I don't know where the
overflow happens. Overflow is not in sync with PPS.
OK this might work. I hope it does as it would allow a bit of code to be
removed. Let's
kd0...@mninter.net said:
I should have said warm start, not cold. I was referring to the code, not
the oscillator. So tell me, the OCXO is warm, there's no previous EFC
information to draw upon, and the oscillator is off-frequency by more than
can be measured with, let's say eight timer bits.
kd0...@mninter.net said:
Precisely my point. My oscillator's tuning range and the timer frequency and
the sampling interval dictated the minimum number of timer bits needed. In
my case, as I recall, eight was not enough. Once locked, yes, but not
initially.
I googled for TCXO tuning-range
Does anybody have a favorite low-cost ARM board? I'm looking for a simple
Arduino like setup rather than something that runs Linux. The idea is to get
32 bit counters so a bunch of the recent discussion can be ingnored.
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csteinm...@yandex.com said:
(Note that a 256 cycles per second error is 51 PPM at 5 MHz.)
You need a bit for the sign. That leaves only 25.6 PPM error from nominal,
51.2 peak-peak. Half that at 10 MHz.
In the real world, you should be able to trust that any oscillator that is
chosen
rich...@karlquist.com said:
Still, there was no way to guarantee that a crystal in the future would
never have a jump or sudden change in aging.
What was really needed was an ensemble of oscillators, but that was not
economically competitive with rubidium.
How many would you need? Is 3
dho...@gmail.com said:
The 32F4 (like lots of similar ARMs) uses a PLL to generate the internal
clocks from much lower frequency clock or crystal. Has anyone quantified
the stability of the synthesised clock?
I'm not familiar with the 32F4, but most of the SOC type ARM chips have ways
to
albertson.ch...@gmail.com said:
2) then switch to a mode where we look only at the last few bits of the
counter. I think this will actually perform better than mode #1 above
because there is zero chance of the two interrupts happening at the same
time causing your PPS sample to be delayed
I have a large LC tank, with a very lossy inductor. ...
So the question is, when actively driving a tank circuit, how do you know
you are driving it with the same frequency ad the same phase it naturally
oscillates at.
If it's lossy, the peak will be broad so tuning the driving frequency
albertson.ch...@gmail.com said:
My plan was to eventually fix this in software. Using ultra precision
resisters is not a good fix. I'm using normal 5% 1/4W resisters.
I don't think I will get stuck. if a step is to small it will simply move
up the next DAC value. The I term in the PID
i...@blackmountainforge.com said:
My concern is that the moving balance wheel could have an eddy current
induced into it and the resulting magnetic field might cause it to slow
down.
If that's a problem, it should be possible to measure it. That assumes the
pickup works when near but not
erm1ea...@ermione.com said:
In the lab, I would like to have an event counter that can double as
frequency/period counter, with maximum clock rate in the order of the tens
of Hz or so, better with TIC function (aka chronometer). Resolution need
not be better than 1/100s, counts to , but
b...@evoria.net said:
The reference pages indicate that a PPS interface is required.
Most times when somebody says that PPS is required, they leave off the for
decent timekeeping.
I don't have a UT+, but I'd be very surprised if NTP didn't work without PPS.
You can add noselect to the
What are using high school labs to time motion physics experiments?
Video cameras.
There are LED gadgets that blink fast enough to work well for that sort of
thing.
www.exploratorium.edu/baseball/ScienceOfBaseballTour.pdf
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j...@jtmiller.com said:
I spent some time reading the uBlox-6 documentation. I found the TIM-TP ubx
message and format. I see that there is also the ability to feed back to the
uBlox-6 time shift info for the PPS in 1ns increments.
Does it make sense to feed the TIM-TP info back this way to
br...@lloyd.com said:
As I think about the geometry of satellite position and path length, it
seems to me that, since the geometry is determined by the antenna position
and not the receiver position, additional antenna cable introduces a fixed
delay value and hence a fixed constant that gets
tn...@toneh.demon.co.uk said:
Can anyone point to figures for a typical non-TXCO low cost oscillator, 10
or 16MHz?
In general, low cost oscillators make pretty good thermometers.
I think you have a much better chance of getting good results if you are
willing to post-process the data.
I
tn...@toneh.demon.co.uk said:
In general, low cost oscillators make pretty good thermometers.
True, but it's short term stability that matters here - over 10s of seconds
the temperature shouldn't change much - especially if a bit of insulation
is used around the oscillator.
Ballpark is 1
wb0...@yahoo.com said:
As I am not using windows, I cannot make use of application program there to
test my interface. I do not wish to implement NTP on Linux as my eventual
target is not Linux, it is just my initial test environment.
You can use ntpd on Linux for initial testing.
You can
hol...@hotmail.com said:
Ahh, but with Lady Heather you can specify the time zone offset (down to
the second) and the when the daylight savings time switchovers occur. And
from experience, I can tell you that the code to do it is a royal pain in
the ass... not all that hard to do, but a
n...@lazygranch.com said:
You have to wonder who made this executive decision to have the cape cover
rather important pins.
How often do you need the serial port after you get SSH working?
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We'd have to guess the correct binary command to pt it into NMEA mode
One quick approach is to let gpsd try. It's very good at figuring out what
sort of device you have.
I normally use gpsmon. By default, it doesn't send anything, just listens
while searching baud rates. The i
The ref output is the minimal delay through the chip covering the input and
output pad buffers. It will vary slightly with temperature and voltage.
There are no negative delays in that sort of chip. It's just a bunch of
gates/buffers with a carefully calibrated delay. (For a negative delay,
Then I accidently touched the PPS wire to ground and fried the PPS output.
A short (duration) short (connection) to ground is unlikely to kill the
output buffer.
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wb0...@yahoo.com said:
I built a small CMOS divider connected to the UT+ 1 PPS output...
What do you mean by CMOS? Old 4000 series parts or HC or ... ?
Here's the problem: my counts vary significantly (+/- 1 or more) from
cycle to cycle, which is much higher than expected based on 50 nS
thol...@woh.rr.com said:
I'm not sure my Z3801 or any of my navigation receivers have the necessary
resolution to see even 10 mm.
In normal operation (post survey), a Z3801A knows the location and uses
that to work out a better time and/or the time with fewer satellites. So you
won't be
[Structure of Earth's core]
jim...@earthlink.net said:
Molten, but it's a composite material under a lot of pressure, so the
transition between liquid and solid isn't like between ice and water.
Think cold peanut butter.
Seismic evidence is how they knew it was liquid in the first place.
Always locate your DUTs physically orthogonal to each other.
Unless you have 3 clocks. (and everybody knows what happens if you only have
2)
From an old time-nuts message (Mar, 2009)
Allied to this discussion is the Loomis effect, discovered by the
American millionaire who had three
daniel.bu...@ieee.org said:
I have a HP/Symm 58530A that has the correct time, but date keeps defaulting
to 1994, Nov, 4 after GPS Lock. The pre-lock is 1996, so I do see a change
when it locks, just to the wrong date.time is exactly correct and
tracks.
Any ideas?
That looks like the
t...@leapsecond.com said:
Yes, I remember that I cut off the PS-2 connector before the UPS truck even
left the neighborhood. You are then left with nice 0/+5/Tx/Rx wires, which
is all you need for navigation and status. For 1PPS timing, in either the
serial or USB version, unscrew the case
namic...@gmail.com said:
Fibre optic would seem to be the answer for protection.
Assuming I use fibers for the data, how do I safely get power to the other
end?
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mag...@rubidium.dyndns.org said:
If your PRS-10 runs at +750 ns on every pulse then it has a frequency offset
of
It took me a while to parse that correctly.
In case anybody else is having the same problem, it works better for me if it
says something like:
If your PRS-10 offset gains
jwsm...@jwsss.com said:
I want a long run because where I plan to use it is some distance from
clear line of site.
It's often easier to use a long serial cable rather than a long antenna cable.
http://www.ebay.com/itm/321295751672
This one happens to be 5 meters long and is active. ...
To you and Hal who suggested it, is this unit suitable for outputing a1pps
timing signal? Wouldn't the long serial option Hal suggestion mess that
up, vs. using this method to put the Fastax as close as possible to a
system which which would have the systems gpio and serial ports attached?
albertson.ch...@gmail.com said:
I tried using a long serial cable. Just because I had some 100 feet of
cat-5 wire already installed. It did not work reliably I was using a MAX232
chip as a driver.
Were you using it as 8 separate wires or 4 pairs?
I'd expect RS-232 to work over 100 ft of
jl.on...@free.fr said:
AFAIK, the differential variant of RS-232 is RS-485. I'm not sure about the
levels.
RS-422 is the basic version:
http://en.wikipedia.org/wiki/RS-422
RS-485 is the multipoint version.
Interesting comment from http://en.wikipedia.org/wiki/EIA-485
The EIA once
albertson.ch...@gmail.com said:
For GPS you need to also include the microseconds long pulse per second. I
think it might by the very short duty cycle of the pulse that makes it hard
to transmit using RS-232 style signaling.
The problem with short PPS pulses is that some PCs don't catch
paulsw...@gmail.com said:
The key to these systems is that the transmitters have very good references.
In the US at least we have no requirement for that level of stability on the
MW broadcasts. Though evidently some stations are quite good. I think I have
a list some place have to re-look.
ja...@extremeoverclocking.com said:
A while back I even tried an old SveeSix receiver and those work too in the
TS2100.
I have a couple of SveeSixs in case anybody ever needs one.
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paulsw...@gmail.com said:
Trying to keep the message and attachements below the 128KB limit. I send a
119KB message and it gets held as a 165KB message. Can someone help me to
understand the difference please?
My guess would be base64 encoding? For binary files, you only get 6 bits per
edgecombe...@gmail.com said:
I am needing a GPS source of precise time, in three flavours - 10MHz (or
so), 1PPS, and ethernet NTP. In the beginning, the NTP will be most
important, and as time goes on, I'll need the 1PPS signal.
...
If a static CW12-TIM ethernet clock could be made, I would
albertson.ch...@gmail.com said:
1) It is set to use an NTP server called time.windows.com
to set the clock.
3) The above is working as well as it has ever worked.
Nothing has changed at Microsoft's end.
It may be more complicated than that.
time.windows.com is a cname for
mafl...@theflynn.org said:
I am working on a project where I need to transfer 1PPS approximately 120
meters between buildings.I cam borrow a pair of 62.5 fibers from IT/
telco to do so.
Google for fiber IRIG gets plenty of hits.
Raw PPS is a nasty case for fibers. You need some sort
alw.k...@gmail.com said:
Apparently, the forward biased silicon diode was temperature sensitive
enough that a small D.C. amplifier could drive a meter to read-out with
reasonable accuracy. Well, maybe not accurate by Time-nut standards but
close enough for its intended purpose.
I think that
docdai...@gmail.com said:
Ice water and boiling water coupled with altitude will give you two points.
Has anybody used a good thermometer to measure air pressure?
How much does the measured temperature vary between just barely boiling and a
good roiling boil? Or in various locations within
bro...@pacific.net said:
I expect that there's date and time information being sent in the header of
every phone call, maybe even before the first ring along with the Caller ID
info.
Wiki says CallerID is sent between the first and second ring, and includes
the date and time.
I think you can buy multi-frequency receivers. Remember GPS is not longer
the only system. There are stelites from the US, Europe, Russia, China and
Japan.Adding more more frequencies allows the receiver to detect multi
path and makes it harder to jam but the timing is not greatly
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