OK, Thanks Fred. I don't really need a new design. I'm just trying to

understand what I already did :^) Is the above "tee" circuit any better

than 450 followed by 56 ohms to ground? It certainly attenuates more.

It looks more like 50 ohms. Not perfect, since you don't know an accurate

source impedance. Attenuation is less important than termination accuracy,

here, provided you can still see what you want to see.

500 series, and 56 shunt from a 500 source looks like 45.2 ohms, or 1.1

VSWR. OK for RF, but maybe not for pulse reflections.

What I'd do is load your source with a known resistor, and calculate the

source resistance from the voltage drop, then calculate a suitable pad.

However:

Instead of source termination, use a 450 ohm resistance in series with the

coax, at the sending end, and terminate the scope end with 50 ohms. That's

effectively a 10:1 probe without reflection. I do that all the time, with

50 ohm wideband vertical amplifiers. If it loads too much, try a 100:1

4950/50 version instead.

The main application of source termination is where you want to get pulse

power down a line into a load that can't be matched, such as measuring trr

of a diode.