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| From [log in to unmask] Tue Jun 4 17: |
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AVNER,
WHAT YOU MAY BE EXPERIENCING IS A LOT TO LOT DIFFERENCE WITHIN THE
TOLERANCE RANGE. THE DIELECTRIC CONSTANT CAN AND OFTEN DOES VARY
ACROSS THE PWB ITSELF. THIS IS A PROBLEM WE HAVE RUN INTO AT HIGHER
FREQs. OUR ENGINEERS WOULD TUNE A CIRCUIT (50 OR 75 Ohm >500Mhz).
AND FIND OUT THAT THE TWEAK WOULDN'T WORK ON AN INDENTICAL BOARD
BECAUSE OF THE DIELECTRIC CONSTANT TOLERANCE. YOUR OPTIONS ARE TO USE
A BOARD MATERIAL WITH A TIGHTER TOLERANCE (MORE CONSTANT) OR USE
VARIABLE POTS, CAPS AND INDUCTORS EVERYWHERE. NEITHER IS A HAPPY
SOLUTION.
ROB BUTTERWORTH
SR PWB DESIGNER
ADC VIDEO SYSTEMS
999 RESEARCH PARKWAY,
MERIDEN, CT 06450
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Controlled Impedance - Dielectric Constant
Author: [log in to unmask] at internet-mail
Date: 5/21/96 8:15 AM
Subject: Controlled Impedance - Dielectric Constant
I like to know if anyone found that Dielectric Constant, for the same
material (e.g. FR-4),
might be different when used for calculation of Microstrip or for
calculation of Stripline.
Avner Drory
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