Mad Scientist wrote:
What do consumer A/B video boxes use to get around this?

Open one up and see... most of them use active switching electronics, but
it is amazing to see how the PC boards are designed.... very short lead
lengths on everything, and the spacing of the traces on the board are designed
to keep impedances constant.

Take the cover off on one of the better VGA switches and just see how
the board is designed as a transmission line.

Are there special shielded relays that would work?

You can buy constant impedance coaxial switches. They are very, very
expensive, but they are commonly used in RF switching applications.

Can I modify the circuit in some other way to fix the problem?

You might be able to get by using the existing relays and running micro
coax right up to them, cutting the board traces off. You'd still get a
bump, but it might not be too bad of one depending on how much smearing you
are willing to tolerate. It would definitely be a lot more work than it's
worth, though.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."