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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With any decent TDR you can SEE all the connections so you can measure the
cable length (+/- a few mm) directly.
Regards,
David Partridge
-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf
Of Magnus Danielson
Sent: 03 April 2011 12:46
To:
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
A couple of years ago I picked up a surplus Aeroantenna choke-ring GPS
antenna that I think was intended for surveying use. I finally got it
installed today and noticed that it has an arrow on the bottom
indicating that the antenna should be oriented with the arrow facing north.
I'm trying
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
John:
Maybe it is not omni-directional.
Since the satellites don't go further north than about 55 degrees, then
(as long as you are in the northern hemisphere) you could reject both
reflections and also any direct signal low on the northern horizon.
--- Graham
==
On 4/3/2011 7:42 PM, John
A couple of years ago I picked up a surplus Aeroantenna choke-ring GPS
antenna that I think was intended for surveying use. I finally got it
installed today and noticed that it has an arrow on the bottom
indicating that the antenna should be oriented with the arrow facing north.
I'm trying
Hi John:
Exactly. There are about a dozen specific antennas that have been
thoroughly characterized for phase center at L1 and L2. I think to the
mm level.
Have Fun,
Brooke Clarke
http://www.PRC68.com
John Ackermann N8UR wrote:
A couple of years ago I picked up a surplus Aeroantenna
Hello! I've got a HP 8620C with a 86242D plugin (5.9 - 9.0GHz) that is in very
good physical condition. The machine powers up, and I can get a sawtooth wave
from the sweep out connector. The top row of knobs move the pointers in the
window as they should. I don't have a network analyzer (or
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