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b. The scale fidelity is warranted with ADC dither set to Medium. Dither increases the noise level by nominally only 0.24
dB for the most sensitive case (preamp Off, best DANL frequencies). With dither Off, scale fidelity for low level
signals, around 60 dBm or lower, will nominally degrade by 0.2 dB.
c. Reference level and off-screen performance: The reference level (RL) behavior differs from some earlier analyzers in a
way that makes this analyzer more flexible. In other analyzers, the RL controlled how the measurement was performed
as well as how it was displayed. Because the logarithmic amplifier in these analyzers had both range and resolution
limitations, this behavior was necessary for optimum measurement accuracy. The logarithmic amplifier in this signal
analyzer, however, is implemented digitally such that the range and resolution greatly exceed other instrument
limitations. Because of this, the analyzer can make measurements largely independent of the setting of the RL without
compromising accuracy. Because the RL becomes a display function, not a measurement function, a marker can read
out results that are off-screen, either above or below, without any change in accuracy. The only exception to the
independence of RL and the way in which the measurement is performed is in the input attenuator setting: When the
input attenuator is set to auto, the rules for the determination of the input attenuation include dependence on the
reference level. Because the input attenuation setting controls the tradeoff between large signal behaviors (third-order
intermodulation and compression) and small signal effects (noise), the measurement results can change with RL
changes when the input attenuation is set to auto.
d. Mixer level = Input Level - Input Attenuator
e. The relative fidelity is the error in the measured difference between two signal levels. It is so small in many cases that
it cannot be verified without being dominated by measurement uncertainty of the verification. Because of this
verification difficulty, this specification gives nominal performance, based on numbers that are as conservatively
determined as those used in warranted specifications. We will consider one example of the use of the error equation to
compute the nominal performance.
Example: the accuracy of the relative level of a sideband around 60 dBm, with a carrier at 5 dBm, using attenuator =
10 dB, RBW = 3 kHz, evaluated with swept analysis. The high level term is evaluated with P1 = 15 dBm and P2 =
70 dBm at the mixer. This gives a maximum error within 0.025 dB. The instability term is 0.018 dB. The slope
term evaluates to 0.050 dB. The sum of all these terms is 0.093 dB.
f. Errors at high mixer levels will nominally be well within the range of 0.045 dB × {exp[(P1 Pref)/(8.69 dB)]
exp[(P2 Pref)/(8.69 dB)]}. In this expression, P1 and P2 are the powers of the two signals, in decibel units, whose
relative power is being measured. Pref is 10 dBm. All these levels are referred to the mixer level.
g. Slope error will nominally be well within the range of 0.0009 × (P1 P2). P1 and P2 are defined in footnote
Description
Available Detectors
Specifications
Normal, Peak, Sample,
Negative Peak, Average
Supplemental Information
Average detector works on RMS,
Voltage and Logarithmic scales
f
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