On Mon, 19 May 2008 13:40:24 -0700, Joerg
wrote:

John Larkin wrote:
On Sun, 18 May 2008 14:19:34 -0700, Joerg
wrote:

John Larkin wrote:
On Sat, 17 May 2008 22:39:43 -0700, "RST Engineering \(jw\)"
wrote:

The top dielectric layer is 12 mils, so a 50 ohm trace is only 20 mils
wide.
My calculator says 22 mils at one Gig, and not knowing your frequency of
operation puts me at somewhat of a disadvantage. I wonder if the mismatch
between 20 and 22 is honking things up.
It's wideband, DC to maybe 2.5 GHz, corresponding to roughly 150 ps
edges. I don't want something as simple as the pcb degrading what the
circuit can do, hence the desire to keep the traces very short. That
beats spending $1000 or so on better boards. Things are not yet honked
up; the board hasn't even been built.

Check with your fab houses whether they can do partial-Rogers boards.
Might be the ticket here.

We did that once. The board was curled up like a potato chip. I could
lay it flat on my desk, give it a twirl, and it would spin for about a
minute. Cool.

I still want to do this as a cheap proto-house board on FR-4. It's
really a test circuit, although I might call it a product if it works
well.


No idea what the old Duroid material would cost nowadays but if it were
my project I'd probably pick a really good material first, see what the
circuit can do and then ratchet down material qualities to reach a
compromise.

Or if you only have one or two longer stretches place rigid coax. That
looks really industrial and gives copycats a good scare ;-)

I've got the critical output trace, the one feeding J5 on the right,
down to 130 mils long. That should be fine at a mere 2.5 GHz.

John