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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 7:47 am
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.