Agilent Technologies 8753ES Option 011 Service Manual page 384

Theory of Operation
Receiver Theory
The Mixer Circuit
The 1st IF and the 2nd LO are combined in the mixer circuit. The resulting difference
frequency (the 2nd IF) is a constant 4 kHz in both bands, as shown in
Table 12-4 Mixer Frequencies
Band
a 0.010 to 0.300 MHz
Super Low
Low 0.300 to 16.0 MHz
High 1.000 MHz
a. Analyzers with Option 006 only.
A10 Digital IF
The three 4 kHz 2nd IF signals from the sampler/mixer assemblies are input to the A10
digital IF assembly. These signals are sampled at a 16 kHz rate. A fourth input is the
analog bus, which can monitor either an external input at the rear panel AUX IN
connector, or one of 31 internal nodes. A multiplexer sequentially directs each of the
signals to the ADC (analog-to-digital converter). Here they are converted to digital form
and sent to the A9 CPU assembly for processing. Refer to
page 12-9 for more information on signal processing.
12-30
1st IF
0.014 to 0.304 MHz
0.304 to 16.004 MHz
0.996 MHz
2nd LO 2nd IF
4.0 kHz
4.0 kHz
4.0 kHz
"Digital Control Theory" on
Table 12-4.
Chapter 12