How to Construct a Dynamic Range Chart

All this says that dynamic range depends upon the signal level at the
mixer. How do we know what level we need at the mixer for a particular
measurement? Most analyzer data sheets include graphs to tell us how
dynamic range varies. However, if no graph is provided, we can draw
our own 2.

We do need a starting point, and this we must get from the data sheet. We
shall look at second-order distortion first. Let's assume the data sheet says
that second-harmonic distortion is 75 dB down for a signal 40 dBm at the
mixer. Because distortion is a relative measurement, and, at least for the
moment, we are calling our dynamic range the difference in dB between
fundamental tone or tones and the internally generated distortion, we have
our starting point. Internally generated second-order distortion is 75 dB
down, so we can measure distortion down 75 dB. We plot that point on a
graph whose axes are labeled distortion (dBc) versus level at the mixer
(level at the input connector minus the input-attenuator setting). See
Figure 6-2. What happens if the level at the mixer drops to 50 dBm? As
noted in Figure 6-1, for very dB change in the level of the fundamental at
the mixer there is a 2 dB change in the internally generated second harmonic.
But for measurement purposes, we are only interested in the relative change,
that is, in what happened to our measurement range. In this case, for very
dB that the fundamental changes at the mixer, our measurement range also
changes by 1 dB. In our second-harmonic example, then, when the level at
the mixer changes from 40 to 50 dBm, the internal distortion, and thus our
measurement range, changes from 75 to 85 dBc. In fact, these points fall
on a line with a slope of 1 that describes the dynamic range for any input
level at the mixer.

2. For more information on how to construct a
dynamic range chart, see the Agilent PSA
Performance Spectrum Analyzer Series Product
Note, Optimizing Dynamic Range for Distortion
Measurements , literature number 5980-3079EN.