rotary attenuator
I would add some personal opinions about the question.
I agree with respect the marcomdd's answer.
Perhaps, FD357 woul'd also know
Why one shoul'd use the rotary attenuator (instead the more cheaper types) ?
The anser is:
The Rotary Vane attenuator is a metrology standard attenuator. It means that the accuracy is very high.
It's needed to calibrate other attenuators.
Also it's attenuation level is stable across frequency.
Of course, due to its funcuion, it is an expensive instruments.