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Post subject: How to measure 50-ohm impedance on pcb trace?
Unread postPosted: Wed Jun 08, 2005 12:51 am
Joined: Tue Mar 22, 2005 5:29 pm
If i have a PCB
layout with impedance of 50-ohm trace. What equipment will i need to
use to measure the trace is actually 50-ohm. How do i do that and what
is the concept behind it. At this point i know simple ohmmeter is not
the way to do it since it is measuring in dc.
Unread postPosted: Wed Jun 08, 2005
Hopefully you have a network analyzer to do the job.
Terminate one end of the trace with a high quality 50 ohm surface mount
resistor to a nearby ground. Solder a piece of 0.141 or smaller semirigid
coax to the the other end and ground, and measure S11 (after doing a
good cal on the NetAn).
The more difficult, and less accurate
way is to use a directional coupler to measure the reflected vs. incident
power and use the ration to calculate S11. You won't get the angle part
of the S11 that way, though.
There are lots of descriptions for
diong the measurement on the Web - just do a search.