coaxial cabel - need to find its chacteristic-impedance

[accountme05]

Finding CH-impedance??

hi !

a coaxial cabel is given to me,
i am required to find it's chacteristic-impedance..
how can i find that??

regards!

 

[biff44]

Re: Finding CH-impedance??

I would hook it up to a network analyzer with a 50 ohm load at the far end, and measure s11. As the frequency is stepped, it will draw a circle on the smith chart, centered somewhere along the real axis, and the center point of that circle will be the cable characteristic impedance.

Another less accurate way would be to hook a tee junction. On one side of the tee, hook up a high impedance scope probe going to an oscilloscope. On the other side hook the cable. At the far end of the cable, hook various resistors, 35 ohm, 50 ohm, 75 ohm, 100 ohm. Figure out which resistor kills any pulse ringing you see on the oscillosope, and that is the value of your characteristic impedance.

There are other ways, but that is a start.

Rich

www.maguffinmicrowave.com