On Sun, 21 Sep 2014 01:32:22 -0400, rickman wrote:

On 9/20/2014 11:01 PM, Jeff Liebermann wrote:
For RF, rounded corners are a problem due to impedance bumps.

From the source you cite:
"If you use a radius greater than three times the line width, you will
have a transmission line that is almost indistinguishable in impedance
characteristics from a straight section."

So where is the problem?

The real problem is with using cut corners. Many companies and
schools taught different techniques of making 90 degree turns with
traces. I was taught to use the Xacto knife to cut half way across
the trace, before "bending" the tape 90 degrees to make a corner. That
eliminated a messy looking corner produced then the trace is cut all
the way across, and overlaid with tape at 90 degrees to make the
corner. That produced a radius of about 1/3rd the width of the trace.
However, such corner cutting takes time, and it's much easier to make
sweeping turns, which is what I did on this PCB. This also has the
advantage in RF where it produces shorter trace lengths than with
corners. However, none of this is important for this PCB. It was
designed for the IBM PC ISA bus, where the highest frequency it might
encounter would be about 14.3 MHz.

Sharp
corners are equally bad due to reflection problems. The compromise is
a chamfered corner (mitered bend):
http://www.microwaves101.com/microwave-encyclopedia/480-mitered-bends
which unfortunately also makes a tolerable fuse at the bend.

My understanding the reflection idea is also a myth but rather the real
issue is the impedance change due to the added capacitance of the
corner, which is also supported by your reference. Impedance changes
will also cause reflections, but the signal does not reflect from the
corner itself like a light beam.

Agreed. I should have said "impedance bump problem" instead of
"reflection problem".

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558