On 1/28/2014 8:34 PM, amdx wrote:
On 1/28/2014 8:11 PM, Jeff Liebermann wrote:
No need for that, This is just a curiosity.

Not sure where we have disagreement, do you disbelieve the 3,350ohms at
3.58MHz?

If I short one end shield to center pin, and measure the other end
would that double impedance?
I'm going to find out.
Mikek

Nope, almost zero ohms, shorting one end and measuring center to shield
on the other end at 3.58MHz.
To reiterate, measuring this 12ft of RG58/u with 42 half cores of 3B7
(material) (size 3019) slide over the coax, shows an impedance of about
3,350 ohms with an inductive phase angle of 22.5*.

The whole system is touchy, putting your hand on the coax changes the
current shown on the scope, also reorienting the coax will change the
current.

What are your thoughts, Jeff specifically and anyone else.

Thanks, Mikek

On Tue, 28 Jan 2014 20:34:21 -0600, amdx wrote:

Not sure where we have disagreement, do you disbelieve the 3,350ohms at
3.58MHz?

Yep. I am a heretic. You stated:
"I have measured the R at 3.85MHz, It is 3,350 ohms"
From where to where did you measure 3.35K, presumably with an ordinary
ohms-guesser?

If I short one end shield to center pin, and measure the other end
would that double impedance?
I'm going to find out.

It's like winding two turns on a toroid in opposite directions. The
inductances cancel and you get zero inductance. Replace the coax
cable with a single loop length of wire and see if it makes more
sense. Only turns that go AROUND the toroid in the same direction
provide useful inductances.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Tuesday, January 28, 2014 8:11:33 PM UTC-6, Jeff Liebermann wrote:
The resistance from shield to shield should fairly close to zero.

Jeff, he is measuring the choking impedance of a w2du
choke-balun. It is like running one wire through a
number of ferrite beads/toroids.
--
73, Cecil, w5dxp.com

On Tue, 28 Jan 2014 20:19:40 -0800 (PST), W5DXP
wrote:

On Tuesday, January 28, 2014 8:11:33 PM UTC-6, Jeff Liebermann wrote:
The resistance from shield to shield should fairly close to zero.

Jeff, he is measuring the choking impedance of a w2du
choke-balun. It is like running one wire through a
number of ferrite beads/toroids.

Thanks. Enlightenment arrived a few milliseconds after I clicked
send. I forgot that it was a coax cable and that the center wire was
shielded from the effects of the inductors by the coax shield. Sorry
for the muddle.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 1/28/2014 1:03 PM, amdx wrote:
I have beads* on a coax and want to know the R and the L.
I have measured the R at 3.85MHz, It is 3,350 ohms.
I have also measured the phase shift, voltage leading
by 17ns. The period of 3.85Mhz is 260ns.

I want to calculate the impedance of the reactance.

Can anyone solve this for me?
I would like to see the math, because I want to measure again
at 7.5MHz.

My first step was to find the phase angle, 23.5*.
Do we agree there?

Thanks, Mikek


* it is actually a bit more than beads. Years ago, we were sent a box of
ferrite potcores, the cores arrived broken. I slide 42 broke halves onto
a piece of RG59, and now I'm measuring it.


Hi, Mike -

I have reviewed your pictures and re-read the posts and I have a couple
of new comments.

* I don't know how you verified that your probes are a problem, but I
suggest applying the same signal to both, recording the results,
swapping channels, and see if the problem follows the probes or not. If
the problem follows, it's the probes. If not, it's the scope channels.

* The ll feet of coax alone will cause almost 11ns of delay. Since you
have it coiled on each end, the delay will be more than that. This
leaves us in an even worse situation to explain high R and low L.

* If you, by any chance, have another 11-feet piece of coax without the
cores, try measuring that.

Good luck.

John S

On 1/31/2014 6:49 AM, John S wrote:
On 1/28/2014 1:03 PM, amdx wrote:
I have beads* on a coax and want to know the R and the L.
I have measured the R at 3.85MHz, It is 3,350 ohms.
I have also measured the phase shift, voltage leading
by 17ns. The period of 3.85Mhz is 260ns.

I want to calculate the impedance of the reactance.

Can anyone solve this for me?
I would like to see the math, because I want to measure again
at 7.5MHz.

My first step was to find the phase angle, 23.5*.
Do we agree there?

Thanks, Mikek


* it is actually a bit more than beads. Years ago, we were sent a box of
ferrite potcores, the cores arrived broken. I slide 42 broke halves onto
a piece of RG59, and now I'm measuring it.


Hi, Mike -

I have reviewed your pictures and re-read the posts and I have a couple
of new comments.

* I don't know how you verified that your probes are a problem, but I
suggest applying the same signal to both, recording the results,
swapping channels, and see if the problem follows the probes or not. If
the problem follows, it's the probes. If not, it's the scope channels.

Yes that's what I did, problem follows the probes. I'm not surprised,
I have done a major repair to the metal housing that was broke in two
pieces. I seem to have ruined a solder tip soldering the metal the
housing is made off. The probes are at least 30 years old. I didn't
receive my new probes yesterday (as told) maybe today.


* The ll feet of coax alone will cause almost 11ns of delay. Since you
have it coiled on each end, the delay will be more than that.

I'll have to check that, an see if my "setup" verifies that.

This
leaves us in an even worse situation to explain high R and low L.

Ya, hmm.
I did find a data sheet for 3B7 but the loss graph only goes to 500kHz.
I'll take the book with me to work and see how the losses of this
material compare to others. Don't know if it is high loss or low loss.


* If you, by any chance, have another 11-feet piece of coax without the
cores, try measuring that.

I will be busy all weekend, working for a living, I hope I can try
something sooner, but it might be next Tuesday.

Good luck.

John S

On 1/31/2014 7:21 AM, amdx wrote:
On 1/31/2014 6:49 AM, John S wrote:
On 1/28/2014 1:03 PM, amdx wrote:
I have beads* on a coax and want to know the R and the L.
I have measured the R at 3.85MHz, It is 3,350 ohms.
I have also measured the phase shift, voltage leading
by 17ns. The period of 3.85Mhz is 260ns.

I want to calculate the impedance of the reactance.

Can anyone solve this for me?
I would like to see the math, because I want to measure again
at 7.5MHz.

My first step was to find the phase angle, 23.5*.
Do we agree there?

Thanks, Mikek


* it is actually a bit more than beads. Years ago, we were sent a box of
ferrite potcores, the cores arrived broken. I slide 42 broke halves onto
a piece of RG59, and now I'm measuring it.


Hi, Mike -

I have reviewed your pictures and re-read the posts and I have a couple
of new comments.

* I don't know how you verified that your probes are a problem, but I
suggest applying the same signal to both, recording the results,
swapping channels, and see if the problem follows the probes or not. If
the problem follows, it's the probes. If not, it's the scope channels.

Yes that's what I did, problem follows the probes. I'm not surprised,
I have done a major repair to the metal housing that was broke in two
pieces. I seem to have ruined a solder tip soldering the metal the
housing is made off. The probes are at least 30 years old. I didn't
receive my new probes yesterday (as told) maybe today.

Okay. Use one probe to measure both amplitudes. Use both probes to
measure the phase (at zero-crossing only) while ignoring the amplitudes.

Otherwise, use your new (calibrated by you and verified by you) probes.


* The ll feet of coax alone will cause almost 11ns of delay. Since you
have it coiled on each end, the delay will be more than that.

I'll have to check that, an see if my "setup" verifies that.

This
leaves us in an even worse situation to explain high R and low L.

Ya, hmm.
I did find a data sheet for 3B7 but the loss graph only goes to 500kHz.
I'll take the book with me to work and see how the losses of this
material compare to others. Don't know if it is high loss or low loss.

I would not expect 3B7 to be of significant inductance at your frequency
of interest. It might be instructional to insert the coax into a piece
of conduit of the same length and measure it.


* If you, by any chance, have another 11-feet piece of coax without the
cores, try measuring that.

I will be busy all weekend, working for a living, I hope I can try
something sooner, but it might be next Tuesday.

I understand. I don't mean to push you.

John S

On 1/31/2014 8:44 AM, John S wrote:
On 1/31/2014 7:21 AM, amdx wrote:
On 1/31/2014 6:49 AM, John S wrote:
On 1/28/2014 1:03 PM, amdx wrote:
I have beads* on a coax and want to know the R and the L.
I have measured the R at 3.85MHz, It is 3,350 ohms.
I have also measured the phase shift, voltage leading
by 17ns. The period of 3.85Mhz is 260ns.

I want to calculate the impedance of the reactance.

Can anyone solve this for me?
I would like to see the math, because I want to measure again
at 7.5MHz.

My first step was to find the phase angle, 23.5*.
Do we agree there?

Thanks, Mikek


* it is actually a bit more than beads. Years ago, we were sent a
box of
ferrite potcores, the cores arrived broken. I slide 42 broke halves
onto
a piece of RG59, and now I'm measuring it.


Hi, Mike -

I have reviewed your pictures and re-read the posts and I have a couple
of new comments.

* I don't know how you verified that your probes are a problem, but I
suggest applying the same signal to both, recording the results,
swapping channels, and see if the problem follows the probes or not. If
the problem follows, it's the probes. If not, it's the scope channels.

Yes that's what I did, problem follows the probes. I'm not surprised,
I have done a major repair to the metal housing that was broke in two
pieces. I seem to have ruined a solder tip soldering the metal the
housing is made off. The probes are at least 30 years old. I didn't
receive my new probes yesterday (as told) maybe today.

Okay. Use one probe to measure both amplitudes. Use both probes to
measure the phase (at zero-crossing only) while ignoring the amplitudes.

Otherwise, use your new (calibrated by you and verified by you) probes.


* The ll feet of coax alone will cause almost 11ns of delay. Since you
have it coiled on each end, the delay will be more than that.

I'll have to check that, an see if my "setup" verifies that.

This
leaves us in an even worse situation to explain high R and low L.

Ya, hmm.
I did find a data sheet for 3B7 but the loss graph only goes to 500kHz.
I'll take the book with me to work and see how the losses of this
material compare to others. Don't know if it is high loss or low loss.

I would not expect 3B7 to be of significant inductance at your frequency
of interest. It might be instructional to insert the coax into a piece
of conduit of the same length and measure it.


* If you, by any chance, have another 11-feet piece of coax without the
cores, try measuring that.

I will be busy all weekend, working for a living, I hope I can try
something sooner, but it might be next Tuesday.

I understand. I don't mean to push you.

John S

Please, I don't feel pushed, this stuff is fun, I want to get back to
it. Can't wait to retire, so I can play all day.
I seem to recall a video of an aging Navy lady, she was teaching. She
ask what is a nanosecond, then held up 1 foot of wire and said, this is
a nanosecond. So, ya, 11 ft, 11ns, thanks for the memory jog.
I found the video, Admiral Grace Hopper, fun to watch.
http://www.youtube.com/watch?v=9eyFDBPk4Yw
http://www.youtube.com/watch?v=9eyFDBPk4Yw

It amazes me that I can see the the delay in a short piece of wire.
All of the sudden I see a value in my new 300 Mhz scope. Lower time base.

Let me setup the proposed experiment.
I'm measuring the delay in the shield of a coax. The R will be near zero
ohms so I'll probably change my sense resistor to a low value,
maybe one ohm, if I can find one. I should probably use a series 50 ohm
resistor to protect the 50 ohm in the signal generator.
Halt.
I'm rethinking that, I already have a 47.5 ohm sense resistor, so I
think I'm all set.
Won't there me some additional delay caused by the inductance of the
wire?
What is the inductance of a ft of wire.
Found this calculator.
http://www.consultrsr.com/resources/eis/induct5.htm
I picked 0.5 cm for the dia. of coax shield. (?) I'm at work can't
measure, I don't know how a braided shield compares to a solid wire.
The calculator gives me 3.2uH for 11 ft of wire. Please check that for
me, seems high, but it is a weak, seems :-)
Anyway, my first guess is I have a delay caused be length and a delay
caused by inductance. We will see.


Mike

"amdx" wrote in message
...


It amazes me that I can see the the delay in a short piece of wire.
All of the sudden I see a value in my new 300 Mhz scope. Lower time base.

OFF TOPIC, SLIGHTLY:

With a wideband scope, you see many interesting things, including some that
might surprise you. Years ago, while looking at some short pulses (to
evaluate the response of a new amplifier), I saw unexpected "steps" in the
traces. I was using BNC T-connectors and my test setup had accidentally
duplicated a TDR function. The impedance change reflections were plainly
evident in a few feet of 50-ohm coax. (I've since seen plans for a
home-brew TDR similar to my accident. :-)

I enjoy amazement, too.

"Sal"
(KD6VKW)

On 1/31/2014 10:49 AM, amdx wrote:

On 1/31/2014 8:44 AM, John S wrote:
On 1/31/2014 7:21 AM, amdx wrote:
On 1/31/2014 6:49 AM, John S wrote:
On 1/28/2014 1:03 PM, amdx wrote:
I have beads* on a coax and want to know the R and the L.
I have measured the R at 3.85MHz, It is 3,350 ohms.
I have also measured the phase shift, voltage leading
by 17ns. The period of 3.85Mhz is 260ns.

I want to calculate the impedance of the reactance.

Can anyone solve this for me?
I would like to see the math, because I want to measure again
at 7.5MHz.

My first step was to find the phase angle, 23.5*.
Do we agree there?

Thanks, Mikek


* it is actually a bit more than beads. Years ago, we were sent a
box of
ferrite potcores, the cores arrived broken. I slide 42 broke halves
onto
a piece of RG59, and now I'm measuring it.


Hi, Mike -

I have reviewed your pictures and re-read the posts and I have a couple
of new comments.

* I don't know how you verified that your probes are a problem, but I
suggest applying the same signal to both, recording the results,
swapping channels, and see if the problem follows the probes or not. If
the problem follows, it's the probes. If not, it's the scope channels.

Yes that's what I did, problem follows the probes. I'm not surprised,
I have done a major repair to the metal housing that was broke in two
pieces. I seem to have ruined a solder tip soldering the metal the
housing is made off. The probes are at least 30 years old. I didn't
receive my new probes yesterday (as told) maybe today.

Okay. Use one probe to measure both amplitudes. Use both probes to
measure the phase (at zero-crossing only) while ignoring the amplitudes.

Otherwise, use your new (calibrated by you and verified by you) probes.


* The ll feet of coax alone will cause almost 11ns of delay. Since you
have it coiled on each end, the delay will be more than that.

I'll have to check that, an see if my "setup" verifies that.

This
leaves us in an even worse situation to explain high R and low L.

Ya, hmm.
I did find a data sheet for 3B7 but the loss graph only goes to 500kHz.
I'll take the book with me to work and see how the losses of this
material compare to others. Don't know if it is high loss or low loss.

I would not expect 3B7 to be of significant inductance at your frequency
of interest. It might be instructional to insert the coax into a piece
of conduit of the same length and measure it.


* If you, by any chance, have another 11-feet piece of coax without the
cores, try measuring that.

I will be busy all weekend, working for a living, I hope I can try
something sooner, but it might be next Tuesday.

I understand. I don't mean to push you.

John S

Please, I don't feel pushed, this stuff is fun, I want to get back to
it. Can't wait to retire, so I can play all day.
I seem to recall a video of an aging Navy lady, she was teaching. She
ask what is a nanosecond, then held up 1 foot of wire and said, this is
a nanosecond. So, ya, 11 ft, 11ns, thanks for the memory jog.
I found the video, Admiral Grace Hopper, fun to watch.
http://www.youtube.com/watch?v=9eyFDBPk4Yw
http://www.youtube.com/watch?v=9eyFDBPk4Yw

I saw a complete program on PBS about her. It was fascinating.

It amazes me that I can see the the delay in a short piece of wire.
All of the sudden I see a value in my new 300 Mhz scope. Lower time base.

Let me setup the proposed experiment.
I'm measuring the delay in the shield of a coax. The R will be near zero
ohms so I'll probably change my sense resistor to a low value,
maybe one ohm, if I can find one. I should probably use a series 50 ohm
resistor to protect the 50 ohm in the signal generator.
Halt.
I'm rethinking that, I already have a 47.5 ohm sense resistor, so I
think I'm all set.
Won't there me some additional delay caused by the inductance of the
wire?
What is the inductance of a ft of wire.
Found this calculator.
http://www.consultrsr.com/resources/eis/induct5.htm
I picked 0.5 cm for the dia. of coax shield. (?) I'm at work can't
measure, I don't know how a braided shield compares to a solid wire.
The calculator gives me 3.2uH for 11 ft of wire. Please check that for
me, seems high, but it is a weak, seems :-)

I use 1nH/mm as a rule-of-thumb for a straight wire. For an 11-foot
straight wire, that would give about 3.3uH. But, remember that your wire
has additional inductance in the coiled portions.

Anyway, my first guess is I have a delay caused be length and a delay
caused by inductance. We will see.


Mike