Re: [time-nuts] Using 5335 frequency counter for timing

[Jerry Hancock]

Tim, I understand all about TDRs, was doing communications cable tests going 
back to '76 at IBM.  This was a simple experiment to show my son (who is 
thinking of becoming an engineer) how precise certain equipment is.


> On May 8, 2017, at 6:03 AM, Tim Shoppa  wrote:
> 
> Jerry, it's very different than the equipment you currently have, but there
> are specialized microwave TDR's that are used to quantify and localize
> impedance bumps down to the fractional inch level (which would be tens of
> picoseconds). You can "see" every connector and PCB/cable transition using
> these TDR's.
> 
> Tim N3QE
> 

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Re: [time-nuts] Using 5335 frequency counter for timing

[Tim Shoppa]

Jerry, it's very different than the equipment you currently have, but there
are specialized microwave TDR's that are used to quantify and localize
impedance bumps down to the fractional inch level (which would be tens of
picoseconds). You can "see" every connector and PCB/cable transition using
these TDR's.

Tim N3QE

On Sun, May 7, 2017 at 8:52 PM, Jerry Hancock  wrote:

> I was showing my son how we could measure the difference in cable lengths
> by using the velocity of light and cable velocity factor.  I used a scope
> to measure the offset and was then thinking the 5335 could do it more
> accurately, but I was wrong, as it only reports to the nanosecond.  I
> thought I had seen somewhere where people were getting higher resolution
> using software along with the 5335, no?
>
> Thanks
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Re: [time-nuts] Using 5335 frequency counter for timing

[Bob kb8tq]

HI

Timing resolution of what we’re talking about:

53342 ns single shot.   
http://literature.cdn.keysight.com/litweb/pdf/5952-7900.pdf?id=172178:epsg:dow
 

53351 ns single shot
http://www.keysight.com/upload/cmc_upload/All/EPSG084786.pdf 

53131   0.5 ns single shot  
http://www.keysight.com/upload/cmc_upload/All/EPSG084786.pdf 

53132   0.15 ns singla shot (above)
53700.02 ns single shot 
http://literature.cdn.keysight.com/litweb/pdf/05370-90031.pdf?id=713250 

TICC0.05 ns single shot. https://www.febo.com/pages/TICC/ 


Many of the devices above will do strange (and possibly incorrect) things to 
generate some extra digits here and there. Most toss
up all sorts of extra digits in frequency mode. We have discussed the issues 
with those extra digits at great length here many times
before.

Random piece of coax around the shop will have a delay of < 1 us. A 1 ppm 
timebase on a scope will give you 
an accuracy of 1 ppm out of 1 us. That would be 1 ps. If you have a scope that 
will show you better than 1 ps, 
that’s even faster than what I would call a real fast scope. 

Bob






On May 8, 2017, at 12:48 AM, Jerry Hancock  wrote:
> 
> I tried reading the 5335 over GPIB.  In the case where I am measuring 
> frequency I get the expected number of digits.  In the case where I am 
> measuring A->B, I only get nanoseconds (e.g 3E-9; or 4E-9).  On my scopes, I 
> was able to measure the delta at 3.28 nanoseconds with both scopes close 
> within .01 nanoseconds.  I was measuring the delta between 1M and 11.5” of 
> RG316 cable.  With a published velocity factor of .695 and 3.28E-9 seconds 
> difference, the delta came out to 27” vs the measured 27.87”.  Of course the 
> RG316 VF wasn’t accurate to the number of digits needed to get any closer.  I 
> was demonstrating the precision of the equipment I was using to my son who is 
> becoming somewhat of a mad scientist like his father.
> 
> 
>> On May 7, 2017, at 8:15 PM, Hal Murray  wrote:
>> 
>> 
>> je...@hanler.com said:
>>> I thought I had seen somewhere where people were getting higher resolution
>>> using software along with the 5335, no?
>> 
>> I don't know about the 5335, but if you talk to a 5334 via GPIB, you can get 
>> more digits than fit on the display.
>> 
>> 
>> -- 
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
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Re: [time-nuts] Using 5335 frequency counter for timing

[Bill Byrom]

First I should disclose that I work for Tektronix, and have done so for
30 years. So I have worked directly with many generations of
oscilloscopes. Good oscilloscopes can make timing measurements of up to
about a millisecond with timing errors of 10's of nanoseconds.

There are a very large range of oscilloscopes using different
technologies over the past few decades, so there are several different
answers to your questions. The range of bandwidths and new instrument
prices range over a factor of roughly 1,000. Bandwidths range from about
30 MHz to 70 GHz, and prices from a few hundred dollars to a few hundred
thousand dollars US.

Many high-end scopes do have external clock inputs (usually 10 MHz), but
this feature is not usually available on lower end or older
oscilloscopes. This only affects the accuracy of longer time interval
measurements (over 1 us), where the internal clock error is usually not
any better than 1 ppm (and 50 ppm for low cost oscilloscopes). Internal
timebase error for a 1 second measurement interval is in the several
10's of ppm for most low-end to mid-range oscilloscopes.

Short-term time measurement error for high-end oscilloscopes can be
under 1 ps, and in equivalent time mode is limited by trigger and
aperture jitter. Lower cost oscilloscopes might have short term timing
errors of several ns, limited by jitter and risetime (bandwidth).

Analog oscilloscopes have analog timebases which have large errors
compared to digital oscilloscopes. They have been obsolete for about
20-25 years.

There are several digital oscilloscope technologies. 
*  The easiest to understand is real time sampling, where you have a
sampler running at a high sampling rate and each sample is converted in
to a digital value in real time. A single trigger event results in a
waveform capture, but the instrument can capture a waveform without a
trigger event. The memory length can be large (1 G sample in some
cases), but the sampling rate is limited by the need for the A/D to
complete the conversion in real time. Using internal A/D interleaving,
waveform sampling rates up to 200 GS/s are available, but the cost is
very high in such cases. Lower cost recent models typically have
sampling rates of 1 to 5 GS/s.
*  Many (but not all) real time oscilloscopes also offer random
equivalent time sampling. In this case the instrument samples at a much
lower sampling rate than would be required for the chosen time/division
setting and waveform length. So, for example, every 10th waveform point
might be filled after each trigger. In this mode, the signal has to
trigger the instrument multiple times (in some cases thousands of
trigger events) before all of the waveform record points are filled. The
sample points are purposely randomly delayed at the start of each
sub-acquisition cycle and the displayed points appropriately skewed so
that all waveform samples are filled without aliasing. This gives you
much better time resolution than with real time sampling, but the
trigger must be extremely accurate and the signal being measured must
have low jitter. Unless you want to get an eye pattern, the signal must
be repetitive (same exact waveform on each trigger). A trigger is
required for this mode to build up a waveform.
*  Sequential sampling oscilloscopes: These instruments are often
referred to as "sampling scopes", although this is now a misnomer since
all digital (and some analog) oscilloscopes use a sampler. This is a
sequential form or equivalent time sampling, and only one sample (or
less) is acquired for each trigger event. So a 1,000 point waveform
requires that 1,000 triggers must be accepted, and since the trigger
processing rate is usually on the order of 200 k/sec only about 1/1000
of the trigger events are actually used if the trigger signal is 200
MHz. An external separate trigger input is usually required. This
instrument has the highest time resolution and short-term timing
accuracy and vertical accuracy of any oscilloscope type, but must be
used for stable repetitive signals.

The waveform update rate of equivalent time mode (repetitive or
sequential) is much slower than real time mode due to the many waveforms
which must be acquired in equivalent time mode to build up a waveform
record. 
--
Bill Byrom N5BB
Tektronix RF Application Engineer

- Original message -
From: Hal Murray <hmur...@megapathdsl.net>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Cc: hmur...@megapathdsl.net
Subject: Re: [time-nuts] Using 5335 frequency counter for timing
Date: Sun, 07 May 2017 20:11:58 -0700


kb...@n1k.org said:
> None of them will do as well as a really fast scope.

How accurate is the clock in a scope?  Do the high end scopes have an 
external clock input?

I remember playing with a scope many years ago.  Trigger on a PPS from a
GPS, 
look at the next PPS.  It should be 1 second later.  I think the scope I
was 
using was off by 6 PPM.

I'd expect that t

Re: [time-nuts] Using 5335 frequency counter for timing

[Jerry Hancock]

I tried reading the 5335 over GPIB.  In the case where I am measuring frequency 
I get the expected number of digits.  In the case where I am measuring A->B, I 
only get nanoseconds (e.g 3E-9; or 4E-9).  On my scopes, I was able to measure 
the delta at 3.28 nanoseconds with both scopes close within .01 nanoseconds.  I 
was measuring the delta between 1M and 11.5” of RG316 cable.  With a published 
velocity factor of .695 and 3.28E-9 seconds difference, the delta came out to 
27” vs the measured 27.87”.  Of course the RG316 VF wasn’t accurate to the 
number of digits needed to get any closer.  I was demonstrating the precision 
of the equipment I was using to my son who is becoming somewhat of a mad 
scientist like his father.


> On May 7, 2017, at 8:15 PM, Hal Murray  wrote:
> 
> 
> je...@hanler.com said:
>> I thought I had seen somewhere where people were getting higher resolution
>> using software along with the 5335, no?
> 
> I don't know about the 5335, but if you talk to a 5334 via GPIB, you can get 
> more digits than fit on the display.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Using 5335 frequency counter for timing

[David]

My Racal-Dana 1992 is the same way; its time interval mode is limited
to the 1 nanosecond interpolated resolution of the counter.

Some counters support time interval averaging which will produce much
much higher resolution but often they have a minimum time interval.

If the transmission line to be measured is configured as a shorted
line, then the pulse width can be measured instead to determine the
line length and pulse width averaging is much more commonly supported.

On Sun, 7 May 2017 22:05:58 -0400, you wrote:

>Hi
>
>The 53131 and 53132 will get you more resolution. The TICC, the 5370, and the 
>SR620 will do even better. None
>of them will do as well as a really fast scope.
>
>Bob
>
>> On May 7, 2017, at 8:52 PM, Jerry Hancock  wrote:
>> 
>> I was showing my son how we could measure the difference in cable lengths by 
>> using the velocity of light and cable velocity factor.  I used a scope to 
>> measure the offset and was then thinking the 5335 could do it more 
>> accurately, but I was wrong, as it only reports to the nanosecond.  I 
>> thought I had seen somewhere where people were getting higher resolution 
>> using software along with the 5335, no?
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Re: [time-nuts] Using 5335 frequency counter for timing

[Gian-Paolo Musumeci]

On Sun, May 7, 2017, at 20:11, Hal Murray wrote:
> kb...@n1k.org said:
> > None of them will do as well as a really fast scope.
> How accurate is the clock in a scope?  Do the high end scopes have an 
> external clock input?

My scope (Keysight MSOX3104, so 1 GHz) is rated at ±1.6 ppm (after a 30
minute warmup and ±10C from calibration temperature). The 3000 series
and below don't have 10 MHz external reference inputs; I know the 4000
series does. /gp
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Re: [time-nuts] Using 5335 frequency counter for timing

[Hal Murray]

kb...@n1k.org said:
> None of them will do as well as a really fast scope.

How accurate is the clock in a scope?  Do the high end scopes have an 
external clock input?

I remember playing with a scope many years ago.  Trigger on a PPS from a GPS, 
look at the next PPS.  It should be 1 second later.  I think the scope I was 
using was off by 6 PPM.

I'd expect that there would be a crossover.  For short times, the scope would 
be better.  For long times, the better crystal (or external input) in the 
5335 would take over.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Using 5335 frequency counter for timing

[Hal Murray]

je...@hanler.com said:
> I thought I had seen somewhere where people were getting higher resolution
> using software along with the 5335, no?

I don't know about the 5335, but if you talk to a 5334 via GPIB, you can get 
more digits than fit on the display.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Using 5335 frequency counter for timing

[Bob kb8tq]

Hi

The 53131 and 53132 will get you more resolution. The TICC, the 5370, and the 
SR620 will do even better. None
of them will do as well as a really fast scope.

Bob

> On May 7, 2017, at 8:52 PM, Jerry Hancock  wrote:
> 
> I was showing my son how we could measure the difference in cable lengths by 
> using the velocity of light and cable velocity factor.  I used a scope to 
> measure the offset and was then thinking the 5335 could do it more 
> accurately, but I was wrong, as it only reports to the nanosecond.  I thought 
> I had seen somewhere where people were getting higher resolution using 
> software along with the 5335, no?
> 
> Thanks
> ___
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[time-nuts] Using 5335 frequency counter for timing

[Jerry Hancock]

I was showing my son how we could measure the difference in cable lengths by 
using the velocity of light and cable velocity factor.  I used a scope to 
measure the offset and was then thinking the 5335 could do it more accurately, 
but I was wrong, as it only reports to the nanosecond.  I thought I had seen 
somewhere where people were getting higher resolution using software along with 
the 5335, no?

Thanks
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