Keysight N9038A - Page 323

Keysight N9038A MXE Service Guide 323
Analog & Digital IF
A2 Analog I.F. Assembly Description
Mixer
There are two mixers that reside on this assembly. The first mixer is used to
down convert the 322.5 MHz input to the final 22.5 MHz IF. The other mixer
is described in the IF Comb Cal section.
3rd LO
The 300 MHz 3rd L.O. signal comes from the A16 Reference assembly and
conditions it for use as an LO in the two mixers that reside on this assembly.
The third LO power is ~+10 dBm to optimize the conversion efficiency of the
mixer.
I.F. Comb Cal
The 2nd mixer on this assembly is used to mix the 300 MHz LO from the A16
Reference assembly with the 22.5 MHz cal comb signal from the A3 Digital
IF to allow calibration of the prefilters and overall passband phase and
amplitude. The signal is attenuated by 20 dB if necessary. A limiter is used
to reduce amplitude variation effects.
Post Down Conversion Amplification and Prefiltering
The 22.5 MHz IF goes through a fixed gain amplifier. Then prefilters are
switched in and out. The signal then goes through a variable gain amplifier.
The prefilters provide four single-pole filters to limit the bandwidth of the
signal reaching the ADC on the A3 Digital IF assembly. There are five
different signal paths for the 22.5 MHz IF when using Signal Analyzer swept
mode, as shown in Table 10-1.
Table 10-1 A2 Analog IF Assembly 22.5 MHz Prefilter Signal Paths
Filter Path Instrument RBW (3 dB) Filter BW
Through Path 430 kHz to 8 MHz n/a
LC Wide 180 kHz to 390 kHz 1 MHz
LC Narrow 30 kHz to 160 kHz 300 kHz
Crystal Wide 4.3 kHz to 27 kHz 75 kHz
Crystal Narrow 1 Hz to 3.9 kHz 10 kHz
In IQ Analyzer mode or in Spectrum Analyzer mode with Sweep Type of FFT, the analyzer span
setting determines the pre-filter settings.