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Source Theory
he source group consists of the A3 fractional-N/reference assembly and the A4 source
assembly.
A3 Fractional-N/Reference Assembly
he A3 fractional-N/reference assembly consists of two boards connected together. he
reference board generates the various reference signals used in the analyzer, while the
fractional-N assembly generates a 30 to 60 MHz synthesized signal for use in the A4 source
assembly.
he reference board uses either the internal 10 MHz crystal oscillator or an external 10 MHz
reference signal to generate three reference signals. he 100 kHz signal is used in the
fractional-N VCO phase lock loop. he 10 MHz signal is used by the A4 source assembly.
A 5 MHz signal goes to the backplane, where it is routed to the A2 CPU and A5 receiver
assemblies for use in signal processing.
he fractional-N board is the synthesizer for the source. he 30 to 60 MHz fractional-N VCO
output is used for phase-locking the source LO signal, which in turn is used to generate the
source RF output.
A4 Source Assembly
he source assembly provides two output signals. One signal, which covers the 0.3 to 1300
(or 3000 MHz for HP 8713C/14C) range, is the main source RF output signal. It goes to the
A5 receiver assembly and through an optional AM delay modulator and/or step attenuator
before it gets to the RF OU (REFLEC ION) port on the front panel. he other signal serves
as the internal receiver LO for downconverting narrowband signals. he two signals are
independently phase-locked, and they are separated from one another by the receiver IF
(intermediate frequency) of 27.778 kHz.
Note
he following paragraphs describe an HP 8711C/12C/30A. he HP 8713C/14C is
very similar. See the section \Di erences Between the HP 8711C/12C/30A and
HP 8713C/14C (1300 MHz vs 3000 MHz)" at the end of this chapter.
hese two signals are generated from 3 phase-locked VCOs, as shown in Figure 6-2. In
normal operation, the RF1 VCO is phase-locked to a 1 MHz reference signal to produce a
stationary 2340 MHz signal. ( he 1 MHz signal is derived from the 10 MHz output of the
A3 fractional-N/reference assembly.) Similarly, the RF2 VCO is also phase locked to the
1 MHz reference to produce a stationary signal that is o set from RF1 by the receiver IF of
27.778 kHz. he source LO VCO supplies the LO drive for the two source mixers. It covers a
2340.3 to 3640 MHz range. It is phase-locked to a fractional-N sweeping synthesizer (on the A3
fractional-N/reference assembly). As this phase lock loop sweeps, the main source RF output
is generated as the mixing product of the 2340 MHz RF1 signal and the sweeping 2340.3 to
3640 MHz source LO signal. Similarly, the receiver LO output is generated by the RF2 signal
mixing with the sweeping source LO, resulting in a signal that is o set from the source RF
output by the receiver IF.
6-4
Theory of Operat on
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