: Sun, 3 Apr 2011 16:37:05
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] T.I. experimenting - newbie question
I assume you mean that impedance has an effect
Hal,
Here are the results I got using your suggestion. The numbers may be a
bit different than last night as I'm not sure I'm using the same
cable.
A+, B+ = 18.9 ns
A-, B- = 19.4 ns
Obviously there is some difference in delay between the A and B
channels. Otherwise, the two numbers would have
I'm keeping the newbie question in the subject for those who wish to
ignore this thread. To those who respond, your contribution to the
diminution of my ignorance is appreciated :-)
I had borrowed two different 5328A counters. I just compared them,
using the exact same coax, connectors and
Does the counter have setable input threasholds? Most do. Are they set the
the same?
-John
I'm keeping the newbie question in the subject for those who wish to
ignore this thread. To those who respond, your contribution to the
diminution of my ignorance is appreciated :-)
I
Here are the results I got using your suggestion. The numbers may be a bit
different than last night as I'm not sure I'm using the same cable.
A+, B+ = 18.9 ns
A-, B- = 19.4 ns
Obviously there is some difference in delay between the A and B channels.
Otherwise, the two numbers would have
John,
Yes, they both do. However, only one has the DVM option that lets me
measure the voltage trigger levels. When I turned off preset and set
the levels manually to match, I got similar numbers to using preset.
On Mon, Apr 4, 2011 at 10:13 PM, J. Forster j...@quik.com wrote:
Does the counter
Hal, replies inline.
On Mon, Apr 4, 2011 at 10:21 PM, Hal Murray hmur...@megapathdsl.net wrote:
Here are the results I got using your suggestion. The numbers may be a bit
different than last night as I'm not sure I'm using the same cable.
A+, B+ = 18.9 ns
A-, B- = 19.4 ns
Obviously there
Another interesting measurement would be to use the timebase output and
external reference to compare the readings using the same timebase.
Or are you already using a gpsdo?
On Apr 5, 2011, at 12:08 AM, Joseph Gray jg...@zianet.com wrote:
I'm keeping the newbie question in the subject for
If I understand you correctly, then I did not have things setup
symetrically. Now I have a tee on each of the A and B inputs. The unused
port on the B tee has a 50 Ohm terminator. Is this what you mean?
Symmetry makes it easier to see what is going on. If you use a Tee on the B
input, then
On 04/03/2011 12:40 PM, Hal Murray wrote:
If I understand you correctly, then I did not have things setup
symetrically. Now I have a tee on each of the A and B inputs. The unused
port on the B tee has a 50 Ohm terminator. Is this what you mean?
Symmetry makes it easier to see what is going
At 09:42 PM 4/2/2011, Joseph Gray wrote...
I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should
calculate out to a length of 3.74 M. When I measure the coax, I get
3.8 M.
Your calculation is incorrect. If the velocity factor only has 2
significant digits, the result of the
Thanks again to everyone who replied. I obviously have much more to
learn about this topic. I will do some reading and more experimenting.
The comments so far have put me on the right track.
Joe Gray
W5JG
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To: time-nuts@febo.com
Subject: Re: [time-nuts] T.I. experimenting - newbie question
On 04/03/2011 12:40 PM, Hal Murray wrote:
If I understand you correctly, then I did not have things setup
symetrically. Now I have a tee on each of the A and B inputs. The
unused port on the B tee has a 50 Ohm
On 04/03/2011 09:33 PM, David C. Partridge wrote:
With any decent TDR you can SEE all the connections so you can measure the
cable length (+/- a few mm) directly.
No, you can't. You can measure the electrical length. I do have a decent
TDR at hand.
You would have to assume the speed in the
For extra points, test with the same long cable at different
temperatures.
Say from soaking in a 150 deg F oven and a zero degree freezer.
Bill Hawkins
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That's an interesting question. Does temperature have an effect on the
dielectric that changes the VOP? I'll have to try your experiment. Is
that worth ten extra credit points? :-)
The copper in the coax has a positive temperature coefficient, which
will contribute to an increased impedance
It does change vop
On Sun, Apr 3, 2011 at 5:52 PM, Joseph Gray jg...@zianet.com wrote:
That's an interesting question. Does temperature have an effect on the
dielectric that changes the VOP? I'll have to try your experiment. Is
that worth ten extra credit points? :-)
The copper in the coax
On 04/03/2011 11:52 PM, Joseph Gray wrote:
That's an interesting question. Does temperature have an effect on the
dielectric that changes the VOP? I'll have to try your experiment. Is
that worth ten extra credit points? :-)
The copper in the coax has a positive temperature coefficient, which
I assume you mean that impedance has an effect on VOP? Can you point
to any internet sources that explain this effect? Preferably something
not overly technical.
Joe Gray
W5JG
On Sun, Apr 3, 2011 at 4:11 PM, paul swed paulsw...@gmail.com wrote:
It does change vop
Hi Joe,
Both VoP and impedance depend on relative permittivity (dielectric
constant). See the section Derived Electrical Parameters on Wikipedia.
http://en.wikipedia.org/wiki/Coaxial_cable
Brent
On 4/3/2011 4:37 PM, Joseph Gray wrote:
I assume you mean that impedance has an effect on VOP?
But, does the impedance have any effect on VOP?
Not normally. It's 1/sqrt(dielectric constant * magnetic permeability)
For most materials used as insulators, the magnetic permeability is 1 so we
tend to drop that part.
http://en.wikipedia.org/wiki/Coaxial_cable
There are a couple of
Joe,
The coax can be viewed as a series of lumped constants; that is, series
inductors with many shunt capacitors to ground in between the
inductors. In essence, a delay line. At standard temperature /
pressure / etc. the delay line assumes a given value. If any external
Bottom line is that using a chunk of coax (even air line) as a time delay
standard is like using a ruler made of a rubber band to check the accuracy
of a SS maxchinist's scale.
YMMV,
-John
===
Joe,
The coax can be viewed as a series of lumped constants; that is, series
John,
I wasn't expecting the coax to be a precision standard. However, since
you bring it up, can you recommend something that I could use as a
precision standard to test a T.I. counter? Preferably something that
is inexpensive and easy to make.
Joe Gray
W5JG
On Sun, Apr 3, 2011 at 6:11 PM, J.
Air dielectric coax is about the best you can do, AFAIK.
-John
==
John,
I wasn't expecting the coax to be a precision standard. However, since
you bring it up, can you recommend something that I could use as a
precision standard to test a T.I. counter? Preferably something
The electrical length of a piece of coax does change with temp.
The Gore catalog, for instance, has a graph of it. And it has a most annoying
bump right around 20 to 25 C, at least for the stuff I use at work.
As to why... The length changes for one thing. I think, also, there will be a
change
I have a borrowed HP 5328A with the Universal Module. I'm using
averaging mode and auto triggering. Counter does not have the OCXO
option. I'm using the internal oscillator, not locking to my GPSDO.
I was just messing around with a length of Belden 9273 and the 100 KHz
square wave output from my
Joseph Gray wrote:
I have a borrowed HP 5328A with the Universal Module. I'm using
averaging mode and auto triggering. Counter does not have the OCXO
option. I'm using the internal oscillator, not locking to my GPSDO.
I was just messing around with a length of Belden 9273 and the 100 KHz
square
Interesting followup. With the exact same setup, but replacing the tee
with a Wenzel power divider, I get 18.6 ns.
On Sat, Apr 2, 2011 at 7:42 PM, Joseph Gray jg...@zianet.com wrote:
I have a borrowed HP 5328A with the Universal Module. I'm using
averaging mode and auto triggering. Counter does
Bruce Griffiths wrote:
Joseph Gray wrote:
I have a borrowed HP 5328A with the Universal Module. I'm using
averaging mode and auto triggering. Counter does not have the OCXO
option. I'm using the internal oscillator, not locking to my GPSDO.
I was just messing around with a length of Belden
Joseph Gray wrote:
Interesting followup. With the exact same setup, but replacing the tee
with a Wenzel power divider, I get 18.6 ns.
Resistive or rf power divider?
Using the latter may result in significant reflections.
On Sat, Apr 2, 2011 at 7:42 PM, Joseph Grayjg...@zianet.com wrote:
Seems like you are asking where the reference plane of a BNC is. The
distance between the reference planes defines the electrical length of a
cable or adapter or L or T.
Unlike precision connectors like the APC-7 or GR 900, the reference
plane of a BNC is not well defined. A quick Google turned
On Sat, Apr 2, 2011 at 8:06 PM, Bruce Griffiths
bruce.griffi...@xtra.co.nz wrote:
Resistive or rf power divider?
Using the latter may result in significant reflections.
RF divider. Perhaps I should make a resistive divider.
Joe Gray
W5JG
___
Thanks for the input. I'll try a bit more experimenting and see what I get.
As for the measured cable length, do I include the BNC connectors or not?
Joe Gray
W5JG
On Sat, Apr 2, 2011 at 8:03 PM, Bruce Griffiths
bruce.griffi...@xtra.co.nz wrote:
Bruce Griffiths wrote:
The measured delay
As for the measured cable length, do I include the BNC connectors or not?
You want the difference in path lengths. Is there an asymmetry in the setup?
If so, count the BNC connectors that don't have a match on the other path.
If you have input-Tee-coax-Tee-terminator, then the difference is
I've always been partial to differential measurements.
So many things fall out when you do the subtraction.
Make short and long cables using the same wire and connectors.
Measure the time delay for each. Subtract the short delay from
the long delay to get Td. Subtract the length of the short
Yes, that is a better way of phrasing my question. If you are correct,
then that would make about 14 mm difference in my measured length,
which would bring me even closer to my calculated length. And the tee
may also be adding to my error margin. Time for more experiments :-)
Joe Gray
W5JG
On
On 04/03/2011 04:03 AM, Bruce Griffiths wrote:
Bruce Griffiths wrote:
Joseph Gray wrote:
I have a borrowed HP 5328A with the Universal Module. I'm using
averaging mode and auto triggering. Counter does not have the OCXO
option. I'm using the internal oscillator, not locking to my GPSDO.
I was
If I understand you correctly, then I did not have things setup
symetrically. Now I have a tee on each of the A and B inputs. The
unused port on the B tee has a 50 Ohm terminator. Is this what you
mean?
With the above setup, using the shortest cable I have gives me 1.5 ns.
Adding the longer cable
Speaking of the 5328A, for strictly T.I. use, would having the OCXO
option be better? I have a different frequency counter that is much
better for that purpose.
Joe Gray
W5JG
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I would not trust the VOP of any coax cable of a non-precision types.
Generally, if you need that kind of precision, you use air line or hard
line and measure it with a TDR.
-John
=
If I understand you correctly, then I did not have things setup
symetrically. Now I have a tee on
Oops. I just noticed that I had previously punched the wrong button
and had the wrong frequency out of the Spectracom. Using the loweset
frequency of 100 KHz (as I thought I was using before), the T.I.
readings are much more stable. Using these new numbers gets me even
closer to the measured cable
John, the intent was not to precisely measure the VOP, although I
would expect Belden cable to be fairly close. I'm just messing around
with a piece of equipment that I haven't used before and doing simple
experiments to see if I get reasonable results. I used to own a 5370A,
but it had something
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