I'll take advantage of the opportunity to get something clear.
When I studied microwaves, the teacher told us that at high frequencies, when the wavelength of the signal approaches the size of the components in the circuit, the reflexions have to be taken in account. So, impedances should be matched to achive the maximun power transfer to the load. Ok, this also applies in any circuit at any frequency, even in DC. Impedances should be equal. But, no reflexions happend if frequency is not high enough.
From that moment, I started to see a microwave circuits as a different kind of circuit than "standard" AC circuits, where reflexions don't happend (or are negligible). Now, relating this to what have been said, I suppose I need to use a 50 ohm coaxial cable for frequency counter 50 ohm input, and a 1Mohm oscilloscope probe for the high impedance input.
Now, as Roff talked about reducing the reflexions in coax cable, should I suppose that they do happend at 100 MHz - 300 MHz frequencies of an hipotetical CMOS bus / signal ?
If they do, then a impedance far away from 50 ohm would cause a terrible standing wave ratio,... maybe I'm confused. To be honest, I didn't like microwaves too much