Amplitude Uncertainlty & Comparison

Examples
Let's look at some amplitude uncertainty examples for various measurements.
Suppose we wish to measure a 1 GHz RF signal with an amplitude of 20
dBm. If we use an Agilent E4402B ESA-E Series spectrum analyzer with Atten
= 10 dB, RBW = 1 kHz, VBW = 1 kHz, Span = 20 kHz, Ref level = 20 dBm, log
scale, and coupled sweep time, and an ambient temperature of 20 to 30Â° C, the
specifications tell us that the absolute uncertainty equals Â± 0.54 dB plus the
absolute frequency response. An E4440A PSA Series spectrum analyzer
measuring the same signal using the same settings would have a specified
uncertainty of Â± 0.24 dB plus the absolute frequency response. These values
are summarized in Table 4-2.

Table 4-2. Amplitude uncertainties when measuring a 1 GHz signal

At higher frequencies, the uncertainties get larger. In this example, we wish
to measure a 10 GHz signal with an amplitude of 10 dBm. In addition, we
also want to measure its second harmonic at 20 GHz. Assume the following
measurement conditions: 0 to 55Â° C, RBW = 300 kHz, Atten = 10 dB, Ref
level = 10 dBm. In Table 4-3, we compare the absolute and relative amplitude
uncertainty of two different Agilent spectrum analyzers, an 8563EC (analog
IF) and an E4440A PSA ( digital IF).

Table 4-3. Absolute and relative amplitude accuracy comparison (8563EC and E4440A PSA)