On Mon, 02 Jan 2006 13:34:54 -0800, dansawyeror
wrote:

Owen,

That idea seems to work. I set it up and then looked and the 'interference', the
change in phase based on changing the pad. Zero pad showed several degrees phase
shift from -40 dbm, 10 dbm showed small shift, and 20, 30, and 40 were all about
equal. I decided on 20 dbm as a practical base.

This doesn't make sense... are you using "dbm" to mean decibels of
attenuation, usually written "dB".

The units "dBm" are usually written to qualify a power level with
respect to one milliwatt.

The attenuator on your sig gen might be marked in dBm, but that
applies to the combination of the oscillator, possibly its level
meter, and the attenuator as a system.

Using the wrong terms for things is often a result of a concept gap!

A 20dB attenuator will reduce the effect of the reflected component to
about the same level as you would expect from a practical directional
coupler, more attenuation is better if you have the power from the sig
gen and the VVM probe chan can operate at the higher input level.

Owen
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