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

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