On Tue, 28 Jan 2014 13:03:35 -0600, 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.

Measure it again. That's an awfully high resistance for a piece of
coax cable of any length. Knowing the type of coax and the length
would be handy. Hopefully, you're not measureing the resistance of
teh broken pot cores. That won't work.

* 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.

The inductance of gapped and non-gapped ferrites are quite different.
Check to see if the inductance moves when you move the coax. Also,
RG-59/u is not the best coax on the planet. Try to find some RG-6/u
instead.

You might want to read through these papers on ferrites (especially
the first):
http://www.audiosystemsgroup.com/K9YC/K9YC.htm

--
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 2:26 PM, Jeff Liebermann wrote:
On Tue, 28 Jan 2014 13:03:35 -0600, 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.

Measure it again. That's an awfully high resistance for a piece of
coax cable of any length. Knowing the type of coax and the length
would be handy. Hopefully, you're not measuring the resistance of
teh broken pot cores. That won't work.

It is a lot. But when I put it together 15 years ago, I seem to
remember about 4000 ohms.
No, I'm measuring shield end to end.
Here's a picture, maybe that will give you a different opinion.
http://s395.photobucket.com/user/Qma...40099.jpg.html


* 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.

The inductance of gapped and non-gapped ferrites are quite different.

For sure, but I didn't care, I just wanted to see how it would act
when I put RG-58u (said 59 before, wrong) thru a bunch of cores.

Check to see if the inductance moves when you move the coax. Also,
RG-59/u is not the best coax on the planet. Try to find some RG-6/u
instead.

You will see in the picture I stabilized it and tapped the whole
thing.
The center hole is not big enough for RG-6/u.

You might want to read through these papers on ferrites (especially
the first):
http://www.audiosystemsgroup.com/K9YC/K9YC.htm

Will do.

When I did this I was thinking about choke baluns hams use on
coax driving antennas.
The whole think is just a curiosity.
Thanks, Mikek

On Tue, 28 Jan 2014 15:44:38 -0600, amdx wrote:

It is a lot. But when I put it together 15 years ago, I seem to
remember about 4000 ohms.
No, I'm measuring shield end to end.
Here's a picture, maybe that will give you a different opinion.
http://s395.photobucket.com/user/Qma...40099.jpg.html

The resistance from shield to shield should fairly close to zero. Same
with center pin to center pin. If you're not getting near zero, you
have an open somewhere in the circuit. My guess(tm) would be the
crappy old PL-259 connectors and UG-175 reducers. Check your
continuity.

You will see in the picture I stabilized it and tapped the whole
thing.

Perhaps you meant "taped" as in wrapped with duct tape?

The center hole is not big enough for RG-6/u.

Peel off the RG-6/u outer jacket and it will probably fit.


--
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 8:11 PM, Jeff Liebermann wrote:
On Tue, 28 Jan 2014 15:44:38 -0600, amdx wrote:

It is a lot. But when I put it together 15 years ago, I seem to
remember about 4000 ohms.
No, I'm measuring shield end to end.
Here's a picture, maybe that will give you a different opinion.
http://s395.photobucket.com/user/Qma...40099.jpg.html


The resistance from shield to shield should fairly close to zero.

My Kelvin resistance device says the the shield is 0.047 ohms end to end.



Same with center pin to center pin.


The center conductor is 0.105 ohms end to end.


If you're not getting near zero, you have an open somewhere in the circuit.

Looks good here.


My guess(tm) would be the crappy old PL-259 connectors and UG-175 reducers. Check your
continuity.

I just did.

You will see in the picture I stabilized it and tapped the whole
thing.

Perhaps you meant "taped" as in wrapped with duct tape?

That is what I meant.

The center hole is not big enough for RG-6/u.

Peel off the RG-6/u outer jacket and it will probably fit.

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

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 21:05:07 -0600, amdx wrote:

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*.

You previously said "I have measured the R at 3.85MHz, It is 3,350
ohms." Now, you change it to impedance. Please make up your mind.

However, I screwed up in my previous message. I forgot that you're
working with coax cable, where the center wire is shielded from the
effects of the inductors by the outside shield. So, you'll see the
equivalent of what you would get with a single wire going through all
the cores.

Got an Al value for a single core? I can't find a data sheet on the
new and useless Ferroxcube web pile. Here's roughly how I would do it
if I had the Al of your cores.

L(mH) = Al * N^2 * n / 10^6

N = number of turns, which in this case is 1.
n = number of cores, which in this case is 42.

Xl = 2 * Pi * f * L
Xl = 6.28 * 3.85*10^6 * L(mH)/10^3

The DC resistance is so small that it can be neglected.

You obtained a 22.5 degree phase angle which might be the capacitance
of the coax cable. I don't really know where it came from. That
angle would normally come from a resistance in the loop, but the coax
is nearly zero ohms. If there were any resistance, the phase angle
would be:
phase-angle = arctan(Xl/R)
If it is the cazapitance:

For RG-59/u 16.2 pf per foot for 12 ft would be 203 pf.
Xc = 1 / (2 * Pi * f * C)
Xc = 1 / (6.28 * 3.85*10^6 * 200*10-12)
Xc = 207 ohms

The vector sum of the reactances should give you the impedance.

Now, all you have to do is either supply a measured inductance or find
the Al of your cores.

Are you sure it's 3.85MHz and not the more common 3.58MHz? I smell a
transposition of numbers here.

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.

That's mostly because of the broken cores causing Al to change as they
move. More duct tape.

What are your thoughts, Jeff specifically and anyone else.

My thoughts are that I'm going to throw up. However, it's not your
questions or academic exercises. It's the junk food I excavated from
the back of the office fridge. Time to recycle everything.

--
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 10:29 PM, Jeff Liebermann wrote:
On Tue, 28 Jan 2014 21:05:07 -0600, amdx wrote:

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*.

You previously said "I have measured the R at 3.85MHz, It is 3,350
ohms." Now, you change it to impedance. Please make up your mind.

I did say that, I wrongly thought it was 3,350 ohms with 22.58 phase
shift, implying some as yet unknown amount of inductance. If you follow
the thread, I immediately followed my own thread with,
"The Total impedance is 3,350 ohms, this includes R and L."
I apologize for my screwups making it difficult for anyone reading to
follow along.
However, if I new what I was doing, I wouldn't be posting a question.


However, I screwed up in my previous message. I forgot that you're
working with coax cable, where the center wire is shielded from the
effects of the inductors by the outside shield. So, you'll see the
equivalent of what you would get with a single wire going through all
the cores.

Yes, a loss resistance and inductance of one turn.

Got an Al value for a single core?

I believe it is 9660 +/- 25%. This is for two core sandwiched. However,
does that have any use for calculations? I'm using the core in a manner
that is not normal. I don't remember how I placed the core halves, face
to face, back to back, mixed?


I can't find a data sheet on the
new

Ya, I found an exchange where I was asking for
that info back in back in 2007.
I got it privately from a friend with an old catalog.

and useless Ferroxcube web pile.

I thought the pile was ok, it just didn't have the 3B7,
must be old and obsolete.


Here's roughly how I would do it
if I had the Al of your cores.

L(mH) = Al * N^2 * n / 10^6

N = number of turns, which in this case is 1.
n = number of cores, which in this case is 42.

Xl = 2 * Pi * f * L
Xl = 6.28 * 3.85*10^6 * L(mH)/10^3


The DC resistance is so small that it can be neglected.


You obtained a 22.5 degree phase angle which might be the capacitance
of the coax cable.

The phase is inductive, E leads I.

I don't really know where it came from. That
angle would normally come from a resistance in the loop, but the coax
is nearly zero ohms. If there were any resistance, the phase angle
would be:
phase-angle = arctan(Xl/R)
If it is the cazapitance:

For RG-59/u 16.2 pf per foot for 12 ft would be 203 pf.
Xc = 1 / (2 * Pi * f * C)
Xc = 1 / (6.28 * 3.85*10^6 * 200*10-12)
Xc = 207 ohms

The vector sum of the reactances should give you the impedance.

Now, all you have to do is either supply a measured inductance or find
the Al of your cores.

I thought I had, but apparently it was in my secret code.
John S calculated "Therefore, R = 3072 ohms and X = 1336 ohms
As a sanity check, Z = sqrt(R^2 + X^2) = 3,350"

So if X = 1336 ohms at 3.85 MHz inductance is 55uH.

I'm a little surprised, I would have thought the reactance would have
been higher than the resistance.


Are you sure it's 3.85MHz and not the more common 3.58MHz? I smell a
transposition of numbers here.


I picked 3.85MHz to be in the 80 meter ham band.

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.

That's mostly because of the broken cores causing Al to change as they
move. More duct tape.

Yes and more, just putting your hand by the coax causes the current
to change.


What are your thoughts, Jeff specifically and anyone else.

My thoughts are that I'm going to throw up. However, it's not your
questions or academic exercises. It's the junk food I excavated from
the back of the office fridge. Time to recycle everything.


I had to stop eating cashews last night, I was moving in that green
feeling direction. Time to get ready for work.

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 1/28/2014 9:51 PM, Jeff Liebermann wrote:
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?

The cable is 12 ft long with a PL259 on each end. I plugged each PL259
into an SO239 panel mount connectors. I then drove 2ma of current
through the shield from panel mount connector to panel mount connector
in series with a 100 ohm resistor. I measured the voltage across the
resistor and calculated the current. This was done at 3.58MHz.
The input voltage was divided by the current to get the impedance.

btw, at one point I took a measurement and got around 800 ohms, took my
a second to figure out I had lowered my frequency to 350 kHz.

Reread, (or read) my response (3:17pm) to Wimpie about my setup and
look at the pictures, I think I laid it out pretty clearly. I was
impressed when I first started using the "setup". Simple, obvious idea,
but the strays need to be worked to a minimum. The "setup" is cheap and
simple and I'd like to refine for those that have a scope and frequency
generator but no other way to measure complex impedances.


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.

You're correct, I measured very low ohms and no phase difference.

Curious to hear your input on the "setup" and what else I can do to
give you more confidence in my measurement, OR fix my "setup".

I'll measure some known parts tomorrow evening.

Thanks Jeff.

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