"dave" wrote in message
...
I don't consider 500 Ohms to be "high impedance".

Compared to 50 ohms it's high. :-) Granted, this is a bit subjective, but in
my mind a "high impedance RF probe" is often 500 ohms (a 450 ohm resistor +
the 50 ohm terminator in a scope"), and the implication is that it doesn't
significantly load down whatever it is that you're probing.

(Note that a "1Mohm in parallel with 10pF" "high impedance" probe ends up
being ~110ohm by the time you hit 144MHz...)

I was taught that MMICs were 50 Ohms in and out.

True, most are reasonably close in the bands they were designed for. I
probably shouldn't have said "MMIC amplifier" there -- just plain "amplifier."