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 Tuesday, January 28, 2014 2:12:53 PM UTC-6, John S wrote:
Therefore, R = 3072 ohms
and X = 1336 ohms

Looks like it might be #77 ferrite material.

In rec.radio.amateur.antenna amdx wrote:
On 1/28/2014 1:32 PM, wrote:
In rec.radio.amateur.antenna 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.

The real resistance should not change with frequency so just measure it
with an ohmmeter.

I'm not sure, it might change with frequency, this is a ferrite around a
wire, so the ohm meter won't work. It's loss in the ferrites.

Correct, but if there is any significant loss in the ferrites at the
frequency of interest you probably shouldn't be using that ferrite.

Something like an AIM 4170 is very handy for measuring this and a whole
bunch of other things though a bit pricy.


Total impedance is the square root of the sum of the squares of resistance
and reactance.

The phase angle will tell you if the reactance is inductive or capacitive.

Yup, Eli the Ice man.
Mikek


--
Jim Pennino

On 1/28/2014 4:02 PM, wrote:
In rec.radio.amateur.antenna amdx wrote:
On 1/28/2014 1:32 PM, wrote:
In rec.radio.amateur.antenna 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.

The real resistance should not change with frequency so just measure it
with an ohmmeter.

I'm not sure, it might change with frequency, this is a ferrite around a
wire, so the ohm meter won't work. It's loss in the ferrites.

Correct, but if there is any significant loss in the ferrites at the
frequency of interest you probably shouldn't be using that ferrite.

Something like an AIM 4170 is very handy for measuring this and a whole
bunch of other things though a bit pricy.



Ok.

On Tuesday, January 28, 2014 4:02:39 PM UTC-6, wrote:
Correct, but if there is any significant loss in the ferrites at the
frequency of interest you probably shouldn't be using that ferrite.

OTOH, if one doesn't dissipate the common-mode energy,
the reactance of the ferrite choke may make common-mode
problems worse by bringing the common-mode circuit
impedance to series resonance, i.e. low impedance.
I personally prefer to dissipate common-mode energy
rather than risk making the mischief worse.
--
73, Cecil, w5dxp.com

On 1/28/2014 3:50 PM, W5DXP wrote:
On Tuesday, January 28, 2014 2:12:53 PM UTC-6, John S wrote:
Therefore, R = 3072 ohms
and X = 1336 ohms

Looks like it might be #77 ferrite material.


It's a Ferroxcube 3B7 material.
Here's some info.
http://www.ferroxcube.com/Ferroxcube...asheet/3b7.pdf
Don't know how it compares to #77.

Mikek

W5DXP wrote:
On Tuesday, January 28, 2014 4:02:39 PM UTC-6, wrote:
Correct, but if there is any significant loss in the ferrites at the
frequency of interest you probably shouldn't be using that ferrite.

OTOH, if one doesn't dissipate the common-mode energy,
the reactance of the ferrite choke may make common-mode
problems worse by bringing the common-mode circuit
impedance to series resonance, i.e. low impedance.
I personally prefer to dissipate common-mode energy
rather than risk making the mischief worse.
--
73, Cecil, w5dxp.com

Yeah, I was thinking of other stuff...

Sometimes you want it lossy, sometimes you don't; for a choke you do.


--
Jim Pennino

On Tuesday, January 28, 2014 5:16:36 PM UTC-6, amdx wrote:
It's a Ferroxcube 3B7 material.

Overall, #77 is much better for HF with the resistance/reactance curves crossing at about 18 MHz. 3B7 is better for MF with the resistance/reactance curves crossing at about 1.5 MHz. The curves indicate that it should be more reactive than resistive at 3.8 MHz. Makes me wonder if the phase angle is actually 90-23.5=66.5 degrees?
--
73, Cecil, w5dxp.com

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