
8712ET/ES and 8714ET/ES Theory of Operation
RF Network Analyzers System Theory
Service Guide 6-9
8712ET/ES Source Assembly (A4)
The source assembly provides two output signals. One signal is the main source RF output
signal which has a range of 0.3 to 1300 MHz. The other signal serves as the internal
receiver local oscillator (LO) for downconverting narrowband signals. The two signals are
independently phase-locked, and they are separated from one another by the receiver
intermediate frequency (IF) of 27.778 kHz.
The RF and the receiver LO output signals are generated from 3 phase-locked VCOs,
called RF1, SOURCE LO and RF2 (refer to Figure 6-3). In normal operation the following
occurs:
• The RF1 VCO is phase-locked to a 10 MHz reference signal, from the fractional-N
board, to produce a stationary 2340 MHz signal.
• The RF2 VCO is also phase locked to the same 10 MHz reference to produce a
stationary signal that is offset from RF1 by the receiver IF of 27.778 kHz.
• The SOURCE LO VCO is phase locked to the 30 to 60 MHz output from the fractional-N
board.The output of the SOURCE LO VCO is a swept frequency of
2340.3 to 3640.0 MHz that mixes with the VCO outputs of the RF1 and RF2.
Figure 6-3 Simplified Block Diagram of the 8712ET/ES A4 Source
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