Agilent Technologies M90XA, Руководство для стартапов

Страница: 77 / 79

X-Series Measurement Applications for Modular Instruments Startup Guide
73
Image Protection Differences
Analyzers use super heterodyne techniques, where input signals are shifted to lower frequencies using one
or more mixers. Without any filtering or image suppression signal processing, the analyzer will respond at
both the desired frequency and also at an image frequency. The image-susceptible frequency range is
typically 400 MHz to 800 MHz above or below the analyzer center frequency. To optimize measurement
speed, modular analyzers use different image protection techniques.
The X-Series benchtop analyzers (MXA, PXA) utilize fixed filtering below 3.6 GHz, and a YIG-tuned
preselection filter above 3.6 GHz.
Below 3.6 GHz all measurements are image protected.
Above 3.6 GHz measurements are image protected only when the RF preselector is on. There
is no image protection when the RF preselector is bypassed. Modulation accuracy usually
bypass the preselector and so are
to images. susceptible
The M9391A Modular PXI analyzer can be configured to use single mixer conversion mode without
image protection, or image-protected double conversion mode. For best EVM and phase noise
performance, the X-apps use the single mixer conversion mode for all measurements except
Spurious Emissions. Spurious Emissions uses image protected double downconversion mode.
The M9393A Modular PXI microwave analyzer utilizes fixed filtering below 3.6 GHz, and may be
configured to use image suppression signal processing above 3.6 GHz.
. Below 3.6 GHz all X-app measurements are image protected
Above 3.6 GHz X-app measurements are not image protected, with the exception of Spurious
Emissions.
The Spurious Emissions measurements are always image protected using image suppression
signal processing. This technique performs multiple acquisitions at each frequency and is
described in application note
Achieving Excellent Spectrum Analysis Results Using Innovative
Noise, Image and Spur-Suppression Techniques
. Because multiple acquisitions http://cp.literature.agilent.com/litweb/pdf/5991-4039EN.pdf
are combined (see Figure 7 of the note), this technique requires the use of gating when
measuring burst signals, and requires a low video bandwidth value to reduce the variance of
time-varying signals.
When making measurements without image protection, insure the signal at the analyzer input does not
include power in the image-susceptible frequency range.