Leslie Bai wrote:
Anyone there can share the experience to measure
cables' impedance thus to identify whether a BNC
is a 50 ohm or 75 ohm cable.
The SECOND simplest way I've found (short of using an SWR meter and a 1:1.5
transformer)_ is as follows:
If you have an impedance bridge operating in the high MHz region, you need
only measure a quarter wave of coax -- as evidenced by inverting the open
circuit at its far end, at any convenient frequency, then measure the
capacitive reactance at half the first frequency. Alternatively measure a
shorted quarter wave stub -- as evidenced by an infinite or very high
impedance reading -- and then look for the inductive reactance at half the
frequency.
The reactance of a 45 degree line is equal to its characteristic impedance,
with the sign depending on the termination.
This will not only tell you "higher or lower" but will identify odd ball
coax which might mess up a whole test. Don't ask how I learned THAT. (grin)
Good luck!
Cortland
---------
This message is coming from the emc-pstc discussion list.
To cancel your subscription, send mail to [email protected]
with the single line: "unsubscribe emc-pstc" (without the
quotes). For help, send mail to [email protected],
[email protected], [email protected], or
[email protected] (the list administrators).
