🚀 go-pugleaf

John Larkin wrote:
> On Tue, 10 Jan 2012 15:39:08 -0800 (PST), Bill Sloman
> <bill.sloman@ieee.org> wrote:
> 
>> On Jan 10, 5:50 pm, John Larkin
>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>> On Tue, 10 Jan 2012 17:29:35 +0100, Jeroen Belleman
>>> <jer...@nospam.please> wrote:
>>>> John Larkin wrote:
>>>>> On Tue, 10 Jan 2012 01:28:22 -0800 (PST), Bill Sloman
>>>>> <bill.slo...@ieee.org> wrote:
>>>>>> On Jan 10, 7:47 am, "David L. Jones" <altz...@gmail.com> wrote:
>>>>>>> Just thought some might be interested in hearing our recent guest on
>>>>>>> our Amp Hour radio show, Dr Howard Johnson of "Handbook of Black
>>>>>>> Magic" fame[...]
>>>>> Yeah, his book is half nonsense. If you can tell which half is which,
>>>>> you don't need the book. His ideas on "return currents" and bypassing
>>>>> are absurd. And the writing is dreadful.
>>>> I haven't got the book handy, but I'll pick it up tomorrow or so.
>>>> Do you mind expounding on why his "return currents" make no sense?
>>>> Did he mean something different from image currents?
>>> He says that a transmission-line pcb trace must always be "referenced"
>>> to the same "return current" plane it started with and shouldn't pass
>>> through vias to become referenced to a different plane, or else the
>>> return currents will get confused or go on strike or something. If
>>> that were true, 98% or the multilayer boards on Earth would quit
>>> working.
>>>
>>> He also says that you should add bypass caps and stitching vias to
>>> conduct these return currents whenever a trace does via to a different
>>> "reference plane."
>>>
>>> All silly.
>> Not completely silly. One of the more avoidable hold-ups in the
>> development of the electron beam tester at Cambridge Instruments from
>> 1988 to 1991 was when the drafting office sent out a six layer board
>> for manufacture without specifying the order of the inner planes -[...]
>> The next board had the inner planes in the right order, amongst other
>> changes, and worked a lot better.
>>
>> --
>> Bill Sloman, Nijmegen
> 
> 
> Of course the stackup and order matter, if not to get the DC
> connections right, then to get the impedances right. But the obsession
> with return currents and "reference planes" is mostly silly.
> 
> As is the admonition to never cross slits in planes, fr'instance
> running a trace above a plane that has multiple pour pours.
> 
> John

A track across a slit is an antenna. Unless there's another plane
underneath covering the slit, in which case it probably doesn't
matter.

Jeroen Belleman