Porting Lady Heather
Yeah, rightey-oh we got flow charts, gantt charts, pi charts, tart charts, all with the circles and the arrows and the paragraphs on the back explain' what each is all about...
The significance of the pickle boils down to reading the comments at the start of the heather.cpp file pertaining to system dependencies. Then search the code for "def DOS" and "def WINDOWS".
At a minimum you need kbhit() and getch() for the keyboard. serial_data_available(), get_serial_char(), sendout() for the com port. dot() and vidstr() for the screen output, some code to initialize the serial port and screen, and you're off and rolling.
For performance you can add a real line() routine and erase_area(). For prettiness, a filled_circle() routine. And it really helps to be able to render the screen to a background buffer that is moved to the display with refresh_page().
It also helps to support a couple of different font sizes (like 8x8, 8x12, 8x14, 8x16)... probably 8x12 or 8x14 if you only do one font (there are font files in the package). And it's nice to be able to change the window/screen size.
A get_pixel() routine for doing screen dumps (the program uses a max of 16 colors). The ability to set/get the system time. For temperature control the ability to diddle modem control signals and read a millisecond-ish counter. For silliness, the ability to play a .WAV file.
Do you have a high-level schematic of the code in design form as it's
really just a coding exercise from that onto another platform or into
a form that would work cross-platform
Hotmail: Free, trusted and rich email service.
http://clk.atdmt.com/GBL/go/171222984/direct/01/
2010/1/5 Mark Sims holrum@hotmail.com:
Yeah, rightey-oh we got flow charts, gantt charts, pi charts, tart charts, all with the circles and the arrows and the paragraphs on the back explain' what each is all about...
So do you have all 27 of them, including the approach, the get away,
NW corner, the SW corner and not to mention the aerial photography?
Anyway, the only problem is that I have a seeing-eye-dog :-(
Do you have a link to the source then please? ... preferably in
braille or scratch and sniff so my dog can read it to me :-)
No offence intended to any blind people reading this posting!
Steve Rooke
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.
I am new to the list (although lurking now a while) and also new to
the more precise species of frequency and time measurement. I have
recently powered up an LPro and a Thunderbolt, both of which appear
to be working by the book. Connecting the TBolt to my scope external
sync and the LPro as an "unknown" I see the pattern moving one
division (cm) to the left in 295 seconds with a 0.05 us-per-division
setting on the scope (the fastest setting available). This, if my
newly-learned calculations are correct, indicates a difference of 1.7
X10-10 (0.0017 Hz). This appears to be confirmed by my HP 5335A
counter, which shows the LPRO 1or 2 thousandths of a Hz low, using
the TBolt as an external time source. An HP manual I have indicates
that a low unknown pattern should be moving to the right, not the
left, on the scope, so this sort of puzzles me.
I have a few questions that I'm hoping some of you more experienced
hands can help with:
- Can someone tell me the meaning and significance of the "Timing
Outputs" numbers in the lower left corner of the TBolt monitor
window? (Mine right now is showing plus 3.75 ns and plus 0.01 ppb).
The TBolt manual does not describe these, although on one page it
lists them as "estimates of UTC/GPS offsets." Do these numbers show
the difference between my receiver outputs and the time being kept by
my present satellites? Or is it the difference between my receiver
outputs and master gps time (somewhere)? Neither of these? The use
of two decimal places on nanoseconds implies great accuracy. Is this
obtained in practice? My ppb on 10 MHz usually lies between plus 0.1
and minus 0.1, often hanging around 0.01 or 0.02. I have not so far
put in any compensation for cable delay.
If the TBolt "knows" what these differences are, why doesn't it just
factor them into its outputs? Or does it?
-
What is a reasonable expectation of TBolt accuracy (at any given
time that I use it for measurement) for the 10 MHz relative to NIS?
How accurate would it be, say, 90 percent of the time? (Looking for
just an experienced guesstimate here). -
What format do I use to put in pps nanoseconds compensation for
cable delay (I use about 19 feet of RG-58U). I understand this
should be a negative number. -
Does anyone know a way to force the 5335A counter to display
another decimal place in frequency measurements? I am getting to
0.001 Hz by using the "mean of 100 counts" function on the counter,
but I think the counter has at least one more digit available which I
would like to use when accuracy justifies it (e.g. when using the
TBolt as an external time source).
Any comments and suggestions appreciated
Jim, KF7A
Jim,
Attached is some info on how to measure/calibrate a time base or oscillator
which you might find useful per your e-mail.
Tom
Tom Duckworth
tomduck@comcast.net
----- Original Message -----
From: "Jim Mandaville" zygo@dakotacom.net
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Tuesday, January 05, 2010 11:17 AM
Subject: [time-nuts] Newbie questions
I am new to the list (although lurking now a while) and also new to the
more precise species of frequency and time measurement. I have recently
powered up an LPro and a Thunderbolt, both of which appear to be working by
the book. Connecting the TBolt to my scope external sync and the LPro as
an "unknown" I see the pattern moving one division (cm) to the left in 295
seconds with a 0.05 us-per-division setting on the scope (the fastest
setting available). This, if my newly-learned calculations are correct,
indicates a difference of 1.7 X10-10 (0.0017 Hz). This appears to be
confirmed by my HP 5335A counter, which shows the LPRO 1or 2 thousandths of
a Hz low, using the TBolt as an external time source. An HP manual I have
indicates that a low unknown pattern should be moving to the right, not the
left, on the scope, so this sort of puzzles me.
I have a few questions that I'm hoping some of you more experienced hands
can help with:
- Can someone tell me the meaning and significance of the "Timing
Outputs" numbers in the lower left corner of the TBolt monitor window?
(Mine right now is showing plus 3.75 ns and plus 0.01 ppb). The TBolt
manual does not describe these, although on one page it lists them as
"estimates of UTC/GPS offsets." Do these numbers show the difference
between my receiver outputs and the time being kept by my present
satellites? Or is it the difference between my receiver outputs and
master gps time (somewhere)? Neither of these? The use of two decimal
places on nanoseconds implies great accuracy. Is this obtained in
practice? My ppb on 10 MHz usually lies between plus 0.1 and minus 0.1,
often hanging around 0.01 or 0.02. I have not so far put in any
compensation for cable delay.
If the TBolt "knows" what these differences are, why doesn't it just
factor them into its outputs? Or does it?
-
What is a reasonable expectation of TBolt accuracy (at any given time
that I use it for measurement) for the 10 MHz relative to NIS? How
accurate would it be, say, 90 percent of the time? (Looking for just an
experienced guesstimate here). -
What format do I use to put in pps nanoseconds compensation for cable
delay (I use about 19 feet of RG-58U). I understand this should be a
negative number. -
Does anyone know a way to force the 5335A counter to display another
decimal place in frequency measurements? I am getting to 0.001 Hz by
using the "mean of 100 counts" function on the counter, but I think the
counter has at least one more digit available which I would like to use
when accuracy justifies it (e.g. when using the TBolt as an external time
source).
Any comments and suggestions appreciated
Jim, KF7A
time-nuts mailing list -- time-nuts@febo.com
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One should of course be aware that the number notation used is no longer
considered correct.
Also even after correcting for the non standard notation the last set of
numbers is incorrect:
eg
40.000 000 003 GHz is equivalent to an error of +7.5 parts in 1E11 not
7.5 parts in 1E-11.
Bruce
Tom Duckworth wrote:
Jim,
Attached is some info on how to measure/calibrate a time base or
oscillator which you might find useful per your e-mail.
Tom
Tom Duckworth
tomduck@comcast.net
----- Original Message ----- From: "Jim Mandaville" zygo@dakotacom.net
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Tuesday, January 05, 2010 11:17 AM
Subject: [time-nuts] Newbie questions
I am new to the list (although lurking now a while) and also new to
the more precise species of frequency and time measurement. I have
recently powered up an LPro and a Thunderbolt, both of which appear
to be working by the book. Connecting the TBolt to my scope external
sync and the LPro as an "unknown" I see the pattern moving one
division (cm) to the left in 295 seconds with a 0.05 us-per-division
setting on the scope (the fastest setting available). This, if my
newly-learned calculations are correct, indicates a difference of 1.7
X10-10 (0.0017 Hz). This appears to be confirmed by my HP 5335A
counter, which shows the LPRO 1or 2 thousandths of a Hz low, using
the TBolt as an external time source. An HP manual I have indicates
that a low unknown pattern should be moving to the right, not the
left, on the scope, so this sort of puzzles me.
I have a few questions that I'm hoping some of you more experienced
hands can help with:
- Can someone tell me the meaning and significance of the "Timing
Outputs" numbers in the lower left corner of the TBolt monitor
window? (Mine right now is showing plus 3.75 ns and plus 0.01 ppb).
The TBolt manual does not describe these, although on one page it
lists them as "estimates of UTC/GPS offsets." Do these numbers show
the difference between my receiver outputs and the time being kept by
my present satellites? Or is it the difference between my receiver
outputs and master gps time (somewhere)? Neither of these? The use
of two decimal places on nanoseconds implies great accuracy. Is this
obtained in practice? My ppb on 10 MHz usually lies between plus 0.1
and minus 0.1, often hanging around 0.01 or 0.02. I have not so far
put in any compensation for cable delay.
If the TBolt "knows" what these differences are, why doesn't it just
factor them into its outputs? Or does it?
-
What is a reasonable expectation of TBolt accuracy (at any given
time that I use it for measurement) for the 10 MHz relative to NIS?
How accurate would it be, say, 90 percent of the time? (Looking for
just an experienced guesstimate here). -
What format do I use to put in pps nanoseconds compensation for
cable delay (I use about 19 feet of RG-58U). I understand this
should be a negative number. -
Does anyone know a way to force the 5335A counter to display
another decimal place in frequency measurements? I am getting to
0.001 Hz by using the "mean of 100 counts" function on the counter,
but I think the counter has at least one more digit available which I
would like to use when accuracy justifies it (e.g. when using the
TBolt as an external time source).
Any comments and suggestions appreciated
Jim, KF7A
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 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
- Can someone tell me the meaning and significance of the "Timing
Outputs" numbers in the lower left corner of the TBolt monitor
window? (Mine right now is showing plus 3.75 ns and plus 0.01 ppb).
The TBolt manual does not describe these, although on one page it
lists them as "estimates of UTC/GPS offsets." Do these numbers show
the difference between my receiver outputs and the time being kept by
my present satellites? Or is it the difference between my receiver
outputs and master gps time (somewhere)? Neither of these?
They're basically what the manual says -- estimates of the current
oscillator performance versus what the Thunderbolt thinks the satellites are
telling it.
The use
of two decimal places on nanoseconds implies great accuracy. Is this
obtained in practice? My ppb on 10 MHz usually lies between plus 0.1
and minus 0.1, often hanging around 0.01 or 0.02. I have not so far
put in any compensation for cable delay.
To be meaningful, the reported data should ideally be filtered with a time
constant close to the VCO disciplining time constant, which you can do in
Lady Heather but not TBoltMon. If not, it will seem artificially noisy.
Without filtering I don't think I'd pay much attention to the LSD (1E-11)
and possibly the next one (1E-10).
If the TBolt "knows" what these differences are, why doesn't it just
factor them into its outputs? Or does it?
This is basically what happens, but it has to be done through the VCO
control loop's filter, which is a lowpass function (integrator) whose time
constant is typically 100 to 1000 seconds.
You can't get good clean timing data from GPS satellites at timescales much
shorter than that; the performance of your local OCXO will always be better.
You can set your disciplining time constant to 1 second and let the
Thunderbolt try to jerk the OCXO around as needed to zero out the reported
PPS and/or frequency error... but the actual result, if measured
independently at the Thunderbolt's 1-pps and 10 MHz outputs, will be fairly
noisy.
The situation is basically that of a PLL with a very good VCO (your OCXO)
and a noisy reference (the GPS signal). Such cases call for long loop time
constants.
- What is a reasonable expectation of TBolt accuracy (at any given
time that I use it for measurement) for the 10 MHz relative to NIS?
How accurate would it be, say, 90 percent of the time? (Looking for
just an experienced guesstimate here).
This sort of question can't be answered without specifying the timescale,
which is why you commonly see people discussing Allan deviation and other
graph-friendly representations. If you gather statistics once a day, the
answer is "very accurate indeed," down in the parts per 1E14, thanks to GPS.
At shorter timescales the accuracy will be worse, again because of the
compromise between GPS S/N ratio and your local OCXO's stability. Tom's
pages at http://www.leapsecond.com/pages/gpsdo/ and
http://www.leapsecond.com/pages/tbolt-8d/ are extremely informative in
this regard.
- What format do I use to put in pps nanoseconds compensation for
cable delay (I use about 19 feet of RG-58U). I understand this
should be a negative number.
Not sure, never used this feature. If you aren't trying to synchronize your
1-PPS output with other stations, there's not much point.
- Does anyone know a way to force the 5335A counter to display
another decimal place in frequency measurements? I am getting to
0.001 Hz by using the "mean of 100 counts" function on the counter,
but I think the counter has at least one more digit available which I
would like to use when accuracy justifies it (e.g. when using the
TBolt as an external time source).
Unfortunately you can't even do that. :( The counter's jitter and
resolution limits will dominate the performance of a GPSDO at timescales <
100 seconds or so. Averaging isn't as informative as you might think,
because you don't know if the noise being averaged out is drift from the
DUT, phase noise from the DUT, quantization artifacts from the counter,
jitter from the counter, or all of the above. (Hint: it's pretty much all
from the counter in this case.)
The best conventional time-interval counters have resolution+jitter floors
in the 20-50 ps neighborhood. So stability measurements at 1-second
intervals can't be made below 20-50 parts per trillion with these
counters.... and traditional "frequency counters" are much worse.
Meanwhile, a Thunderbolt-class GPSDO will normally be accurate to better
than 10 parts per trillion at 1-second timescales (again, see Tom's pages).
Characterizing the stability of these sources requires specialized hardware
(which can be primarily digital or analog-based.) Even with a better timing
analyzer, you'll eventually find that your LPRO is noisier than the
Thunderbolt at shorter timescales as well.
Use of a microwave synthesizer and counter, as in the document TomD
mentioned, isn't likely to be beneficial, because what's the first thing the
microwave counter is going to do with a 40 GHz signal? Divide it by 4000 or
so, undoing the multiplicative effect of the synthesizer. One figure of
merit for frequency counters is "digits per second," which is a way of
stating its usable resolution in a way that's independent of the displayed
frequency. Given the same 1-second gate time, a hypothetical microwave
frequency counter that displays 11 digits per second can resolve 100 Hz at
10 GHz or 0.0001 Hz at 10 MHz. You're getting the same amount of
information from the counter either way, at the same rate.
Any comments and suggestions appreciated
Run away while you still can? :-P
-- john, KE5FX
Jim,
We use a benchmark 1 ns per foot of coax (RG-59).
You could measure the delay by using a resistive splitter (50 ohms) and two
cables (say a 2 foot and a three foot, each terminated at the far end with a
50 ohm pass through terminator). Drive the splitter with your 10 MHz signal
and measure, at the far end, using an appropriate 2-channel scope or counter
with the necessary resolution, the difference in time delay between the two,
which will give you a pretty accurate delay per foot. Both cables should be
the same coax type.
Tom
Tom Duckworth
tomduck@comcast.net
----- Original Message -----
From: "Jim Mandaville" zygo@dakotacom.net
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Tuesday, January 05, 2010 11:17 AM
Subject: [time-nuts] Newbie questions
I am new to the list (although lurking now a while) and also new to the
more precise species of frequency and time measurement. I have recently
powered up an LPro and a Thunderbolt, both of which appear to be working by
the book. Connecting the TBolt to my scope external sync and the LPro as
an "unknown" I see the pattern moving one division (cm) to the left in 295
seconds with a 0.05 us-per-division setting on the scope (the fastest
setting available). This, if my newly-learned calculations are correct,
indicates a difference of 1.7 X10-10 (0.0017 Hz). This appears to be
confirmed by my HP 5335A counter, which shows the LPRO 1or 2 thousandths of
a Hz low, using the TBolt as an external time source. An HP manual I have
indicates that a low unknown pattern should be moving to the right, not the
left, on the scope, so this sort of puzzles me.
I have a few questions that I'm hoping some of you more experienced hands
can help with:
- Can someone tell me the meaning and significance of the "Timing
Outputs" numbers in the lower left corner of the TBolt monitor window?
(Mine right now is showing plus 3.75 ns and plus 0.01 ppb). The TBolt
manual does not describe these, although on one page it lists them as
"estimates of UTC/GPS offsets." Do these numbers show the difference
between my receiver outputs and the time being kept by my present
satellites? Or is it the difference between my receiver outputs and
master gps time (somewhere)? Neither of these? The use of two decimal
places on nanoseconds implies great accuracy. Is this obtained in
practice? My ppb on 10 MHz usually lies between plus 0.1 and minus 0.1,
often hanging around 0.01 or 0.02. I have not so far put in any
compensation for cable delay.
If the TBolt "knows" what these differences are, why doesn't it just
factor them into its outputs? Or does it?
-
What is a reasonable expectation of TBolt accuracy (at any given time
that I use it for measurement) for the 10 MHz relative to NIS? How
accurate would it be, say, 90 percent of the time? (Looking for just an
experienced guesstimate here). -
What format do I use to put in pps nanoseconds compensation for cable
delay (I use about 19 feet of RG-58U). I understand this should be a
negative number. -
Does anyone know a way to force the 5335A counter to display another
decimal place in frequency measurements? I am getting to 0.001 Hz by
using the "mean of 100 counts" function on the counter, but I think the
counter has at least one more digit available which I would like to use
when accuracy justifies it (e.g. when using the TBolt as an external time
source).
Any comments and suggestions appreciated
Jim, KF7A
time-nuts mailing list -- time-nuts@febo.com
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https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Tom Duckworth wrote:
Jim,
We use a benchmark 1 ns per foot of coax (RG-59).
This sounds fast. The normal taxiometer is at 66% of speed of ligth in
vaccum, which for 1 ns is about 3 dm so for the RG-59 that would be
about 2 dm.
Some cables reach 78%, but RG-58 and RG-59 is down at normal 66%.
You could measure the delay by using a resistive splitter (50 ohms) and
two cables (say a 2 foot and a three foot, each terminated at the far
end with a 50 ohm pass through terminator). Drive the splitter with your
10 MHz signal and measure, at the far end, using an appropriate
2-channel scope or counter with the necessary resolution, the difference
in time delay between the two, which will give you a pretty accurate
delay per foot. Both cables should be the same coax type.
Being a time-nut, using time-interval counters or TDR would be my
choice, but these tools/toys outnumbers the scopes...
Cheers,
Magnus
Run away while you still can? :-P
-- john, KE5FX
Nope, not ready to run away by any means, John! And I do thank you
much for your time in these helpful comments. Thanks also to Tom for
that somewhat different scope method. I was indeed wondering about
that short-term stability issue when making quick "point-in-time"
frequency measurements. You have clarified my thinking on this. My
conclusion now is that there is not much point in trying to adjust
the LPRO to the TBolt frequency when the difference, as now, is only
0.001 or 0.002 Hz I should just probably make comparisons once in a
while to check the LPRO for aging rate, etc.
But what about making comparisons with the counter using very long
gate times, such as 1000 seconds. Wouldn't that make things more
accurate. Or would I still be limited by the counter (obviously I am
still limited by the number of digits being displayed).
By the way, I noticed that the blurb for that just-announced (here)
TBolt-disciplined LPRO is "adjusted at the factory for down to 0.1
ppb accuracy" That is just about the limit of accuracy I see for
the indicated 10 MHz output on the TBolt monitor (although for much
of the time mine seems to run somewhat better than that).
Jim
Nope, not ready to run away by any means, John! And I do thank you
much for your time in these helpful comments. Thanks also to Tom for
that somewhat different scope method. I was indeed wondering about
that short-term stability issue when making quick "point-in-time"
frequency measurements. You have clarified my thinking on this. My
conclusion now is that there is not much point in trying to adjust
the LPRO to the TBolt frequency when the difference, as now, is only
0.001 or 0.002 Hz I should just probably make comparisons once in a
while to check the LPRO for aging rate, etc.
But what about making comparisons with the counter using very long
gate times, such as 1000 seconds. Wouldn't that make things more
accurate. Or would I still be limited by the counter (obviously I am
still limited by the number of digits being displayed).
You can use long gate times to measure long-term frequency differences, as
long as the counter has enough "storage" to accumulate that many cycles. At
some point you may find that increasing the gate time doesn't give you any
more digits of precision. Unfortunately I'm totally unfamiliar with the
5335A so can't say offhand what the best settings would be.
-- john, KE5FX
Magnus,
We've made this measurement using a 20 ps time interval counter and a GPS
disciplined Rubidium frequency standard as the time base; making many
concurrent measurements with no dead time between. The resultant measurement
was very close to the 1 ns/ft benchmark with RG-59 (BNC connectors), 10 MHz
source. So we felt ok with using the 1 ns/ft estimate.
Tom
Tom Duckworth
tomduck@comcast.net
----- Original Message -----
From: "Magnus Danielson" magnus@rubidium.dyndns.org
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Tuesday, January 05, 2010 7:26 PM
Subject: Re: [time-nuts] Newbie questions
Tom Duckworth wrote:
Jim,
We use a benchmark 1 ns per foot of coax (RG-59).
This sounds fast. The normal taxiometer is at 66% of speed of ligth in
vaccum, which for 1 ns is about 3 dm so for the RG-59 that would be about
2 dm.
Some cables reach 78%, but RG-58 and RG-59 is down at normal 66%.
You could measure the delay by using a resistive splitter (50 ohms) and
two cables (say a 2 foot and a three foot, each terminated at the far end
with a 50 ohm pass through terminator). Drive the splitter with your 10
MHz signal and measure, at the far end, using an appropriate 2-channel
scope or counter with the necessary resolution, the difference in time
delay between the two, which will give you a pretty accurate delay per
foot. Both cables should be the same coax type.
Being a time-nut, using time-interval counters or TDR would be my choice,
but these tools/toys outnumbers the scopes...
Cheers,
Magnus
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and follow the instructions there.
But the result disagrees with the manufacturer's specs for RG59.
There's an error somewhere in your measurement setup.
For example, it could be a time offset error (or even differing trigger
levels with a sinewave input) between the time interval counter start
and stop channels.
Bruce
Tom Duckworth wrote:
Magnus,
We've made this measurement using a 20 ps time interval counter and a
GPS disciplined Rubidium frequency standard as the time base; making
many concurrent measurements with no dead time between. The resultant
measurement was very close to the 1 ns/ft benchmark with RG-59 (BNC
connectors), 10 MHz source. So we felt ok with using the 1 ns/ft
estimate.
Tom
Tom Duckworth
tomduck@comcast.net
----- Original Message ----- From: "Magnus Danielson"
magnus@rubidium.dyndns.org
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Tuesday, January 05, 2010 7:26 PM
Subject: Re: [time-nuts] Newbie questions
Tom Duckworth wrote:
Jim,
We use a benchmark 1 ns per foot of coax (RG-59).
This sounds fast. The normal taxiometer is at 66% of speed of ligth
in vaccum, which for 1 ns is about 3 dm so for the RG-59 that would
be about 2 dm.
Some cables reach 78%, but RG-58 and RG-59 is down at normal 66%.
You could measure the delay by using a resistive splitter (50 ohms)
and two cables (say a 2 foot and a three foot, each terminated at
the far end with a 50 ohm pass through terminator). Drive the
splitter with your 10 MHz signal and measure, at the far end, using
an appropriate 2-channel scope or counter with the necessary
resolution, the difference in time delay between the two, which will
give you a pretty accurate delay per foot. Both cables should be the
same coax type.
Being a time-nut, using time-interval counters or TDR would be my
choice, but these tools/toys outnumbers the scopes...
Cheers,
Magnus
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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and follow the instructions there.
Except the 1nS/ft figure is a good approximation to C (speed of light in
vacuo). In RG58, you would expect to see 0.66C or about that.
So 1nS for 8" of cable is a good ROT. Or put the other way round, about
1.5nS per foot.
Dave
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Tom Duckworth
Sent: 06 January 2010 02:23
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Newbie questions
Jim,
We use a benchmark 1 ns per foot of coax (RG-59).
You could measure the delay by using a resistive splitter (50 ohms) and two
cables (say a 2 foot and a three foot, each terminated at the far end with a
50 ohm pass through terminator). Drive the splitter with your 10 MHz signal
and measure, at the far end, using an appropriate 2-channel scope or counter
with the necessary resolution, the difference in time delay between the two,
which will give you a pretty accurate delay per foot. Both cables should be
the same coax type.
Tom
Tom Duckworth
tomduck@comcast.net
----- Original Message -----
From: "Jim Mandaville" zygo@dakotacom.net
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Tuesday, January 05, 2010 11:17 AM
Subject: [time-nuts] Newbie questions
I am new to the list (although lurking now a while) and also new to the
more precise species of frequency and time measurement. I have recently
powered up an LPro and a Thunderbolt, both of which appear to be working by
the book. Connecting the TBolt to my scope external sync and the LPro as
an "unknown" I see the pattern moving one division (cm) to the left in 295
seconds with a 0.05 us-per-division setting on the scope (the fastest
setting available). This, if my newly-learned calculations are correct,
indicates a difference of 1.7 X10-10 (0.0017 Hz). This appears to be
confirmed by my HP 5335A counter, which shows the LPRO 1or 2 thousandths of
a Hz low, using the TBolt as an external time source. An HP manual I have
indicates that a low unknown pattern should be moving to the right, not the
left, on the scope, so this sort of puzzles me.
I have a few questions that I'm hoping some of you more experienced hands
can help with:
- Can someone tell me the meaning and significance of the "Timing
Outputs" numbers in the lower left corner of the TBolt monitor window?
(Mine right now is showing plus 3.75 ns and plus 0.01 ppb). The TBolt
manual does not describe these, although on one page it lists them as
"estimates of UTC/GPS offsets." Do these numbers show the difference
between my receiver outputs and the time being kept by my present
satellites? Or is it the difference between my receiver outputs and
master gps time (somewhere)? Neither of these? The use of two decimal
places on nanoseconds implies great accuracy. Is this obtained in
practice? My ppb on 10 MHz usually lies between plus 0.1 and minus 0.1,
often hanging around 0.01 or 0.02. I have not so far put in any
compensation for cable delay.
If the TBolt "knows" what these differences are, why doesn't it just
factor them into its outputs? Or does it?
-
What is a reasonable expectation of TBolt accuracy (at any given time
that I use it for measurement) for the 10 MHz relative to NIS? How
accurate would it be, say, 90 percent of the time? (Looking for just an
experienced guesstimate here). -
What format do I use to put in pps nanoseconds compensation for cable
delay (I use about 19 feet of RG-58U). I understand this should be a
negative number. -
Does anyone know a way to force the 5335A counter to display another
decimal place in frequency measurements? I am getting to 0.001 Hz by
using the "mean of 100 counts" function on the counter, but I think the
counter has at least one more digit available which I would like to use
when accuracy justifies it (e.g. when using the TBolt as an external time
source).
Any comments and suggestions appreciated
Jim, KF7A
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Tom Duckworth wrote:
Magnus,
We've made this measurement using a 20 ps time interval counter and a
GPS disciplined Rubidium frequency standard as the time base; making
many concurrent measurements with no dead time between. The resultant
measurement was very close to the 1 ns/ft benchmark with RG-59 (BNC
connectors), 10 MHz source. So we felt ok with using the 1 ns/ft estimate.
Well, I think you should reconsider. Theory says that
v = 1/sqrt(my*epsilon) = 1/sqrt(my_r * epsilon_r) * c
For a coaxial cable, we have the magnetic properties about the same as
vacuum, so my_r = 1 is a fair approximation. RG-58 and RG-59 use solid
polyethylene having epsilon_r = 2,25 and that cranks out as v = 0,66*c,
in agreement with tabulated values:
http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/diel.html
http://www.epanorama.net/documents/wiring/coaxcable.html
Notice how foam-PE rates at 0,78c rather than 0,66c. This is due to
the lower dielectric constant (about 1,64) of foam PE.
I think it this relationship is wellfounded. I use 2 dm/ns for coax and
fiber myself for my reality check calculations and found good
correlation with reality whenever I tried it.
Oh, did you use sine as waveform? A few different frequencies and/or
amplitude would be good to ensure that biases could be canceled out. I
do that for reality check myself. Swapping the cables is another.
You have to excuse me, but the value you have measured does not really
correlate well with my experience or view of theory.
Cheers,
Magnus
Hi
The thing that always gets me is when I pick up a piece of air dielectric
coax (like a line stretcher). I have to recalibrate all over again....
Bob
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Magnus Danielson
Sent: Wednesday, January 06, 2010 8:17 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Newbie questions
Tom Duckworth wrote:
Magnus,
We've made this measurement using a 20 ps time interval counter and a
GPS disciplined Rubidium frequency standard as the time base; making
many concurrent measurements with no dead time between. The resultant
measurement was very close to the 1 ns/ft benchmark with RG-59 (BNC
connectors), 10 MHz source. So we felt ok with using the 1 ns/ft estimate.
Well, I think you should reconsider. Theory says that
v = 1/sqrt(my*epsilon) = 1/sqrt(my_r * epsilon_r) * c
For a coaxial cable, we have the magnetic properties about the same as
vacuum, so my_r = 1 is a fair approximation. RG-58 and RG-59 use solid
polyethylene having epsilon_r = 2,25 and that cranks out as v = 0,66*c,
in agreement with tabulated values:
http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/diel.html
http://www.epanorama.net/documents/wiring/coaxcable.html
Notice how foam-PE rates at 0,78c rather than 0,66c. This is due to
the lower dielectric constant (about 1,64) of foam PE.
I think it this relationship is wellfounded. I use 2 dm/ns for coax and
fiber myself for my reality check calculations and found good
correlation with reality whenever I tried it.
Oh, did you use sine as waveform? A few different frequencies and/or
amplitude would be good to ensure that biases could be canceled out. I
do that for reality check myself. Swapping the cables is another.
You have to excuse me, but the value you have measured does not really
correlate well with my experience or view of theory.
Cheers,
Magnus
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