Use an antenna analyzer!

At 1/8 wavelength, from either a short or an open, the input impedance
will be purely resistive. The resistive value is the Zo of the line.

DD, W1MCE

Jack Twilley wrote:

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This is a little bit off the original topic, but I have a question.

Given two unmarked pieces of coax, how do you determine if they're "50
ohm" or "75 ohm" or whatever? Shorting them doesn't work.

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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"Dave" =3D=3D Dave Shrader writes:

Dave Use an antenna analyzer!

Umm, assume that instead of an antenna analyzer, I've got a VOM.

Dave At 1/8 wavelength, from either a short or an open, the input
Dave impedance will be purely resistive. The resistive value is the
Dave Zo of the line.

Without being able to send a signal, I won't be able to test it?

Jack.
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Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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NO! You can't test it with a VOM. You need a signal with wavelength
[frequency] characteristics.

Someone in your area should have an MFJ 259B. Ask around.

Deacon Dave, W1MCE

Jack Twilley wrote:

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"Dave" == Dave Shrader writes:


Dave Use an antenna analyzer!

Umm, assume that instead of an antenna analyzer, I've got a VOM.

Dave At 1/8 wavelength, from either a short or an open, the input
Dave impedance will be purely resistive. The resistive value is the
Dave Zo of the line.

Without being able to send a signal, I won't be able to test it?

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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Dave Shrader wrote:
At 1/8 wavelength, from either a short or an open, the input impedance
will be purely resistive. The resistive value is the Zo of the line.

Don't you mean purely *reactive*, Dave, like 0+jZ0 or 0-jZ0?
--
73, Cecil http://www.qsl.net/w5dxp



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