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