Date   : Tue, 10 Aug 2010 16:14:24 +0100
From   : pete@... (Pete Turnbull)
Subject: Free Stuff Tranche III [Results]

On 10/08/2010 14:47, Rick Murray wrote:
> On 10/08/2010 00:44, Andrew Hancock wrote:
> 
>> "which is why maybe, circuit board tracks are curved and not right angles,
>> because electrons don't like corners!"
> 
> Oh no, it isn't because electrons don't like corners, it is because they 
> like them a little too much. They start to function less like a copper 
> circuit trace and more like an antenna, which involves all sorts of 
> scary maths and Dark Magic to understand. It can play havoc with rise 
> time in logic circuits.

Exactly, that's why I was taught (and most PCB CAD packages) to route 
lines with two 45-degree direction changes instead of one 90-degree one. 
  2 x 45 != 90 in this context ;-)   It's also why some older hand-drawn 
boards use curves instead of straight lines.  When you get high 
frequencies (short rise times) all sorts of interesting things happen; 
traces can behave like waveguides, and you can make tuned circuits out 
of odd lengths of coax (I had a UHF amp that used trimmed coax as part 
of the filter).

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York