5-24 Service Guide E8364-90038
Theory of Operation PNA Series Microwave Network Analyzers
Frequency Offset Group Operation (Options 080 and 081) E8362C, E8363C, E8364C
Frequency Offset Group Operation (Options 080 and 081)
The frequency offset group provides the circuitry necessary to phase lock the analyzer while the source and
receiver are tuned to different frequencies. Figure 5-7 on page 5-25 is a simplified block diagram of the
frequency offset functional group.
In this section the following assemblies are described:
• A9 Fractional-N Synthesizer Board (Option 080)
• A13 Frequency Offset Receiver Assembly (Option 080)
• A45 and A46 Reference Transfer Switches (Option 081)
A9 Fractional-N Synthesizer Board (Option 080)
The A9 fractional-N synthesizer is identical to the A8 fractional-N synthesizer.
The A9 fractional-N synthesizer board uses the 5 MHz reference signal from the A10 frequency reference
board to tune two VCO circuits: one that sweeps from 1500 to 3010 MHz and one that is set to a CW
frequency of 2250 MHz. In bands 0–1, these two signals are heterodyned to produce the output frequencies
for A8 listed in Table 5-2 on page 5-8. In band 2, the output of the swept VCO is passed through a divide-by-2
circuit to produce the output frequencies for A8 listed in Ta b l e 5 -2 . In all other bands, the swept VCO signal
is sent directly to the synthesizer output.
At the output, an ALC circuit maintains the power level at 5 dBm ± 2 dB for bands 0–1 or 5 dBm ± 2 dB
for bands 2–25. In all bands, the output is sent to the A13 frequency offset receiver assembly.
A13 Frequency Offset Receiver Assembly (Option 080)
The A13 frequency offset receiver assembly consists of a frequency offset receiver board and a separate
receiver module.
The output of the A9 fractional-N synthesizer board is directed to the receiver module where it is mixed with
a signal from the A12 source assembly to produce a phase lock output signal.
This phase lock signal is sent to a multiplexer on the A35 receiver motherboard, the output of which is
routed to the A11 phase lock board to complete the phase lock loop. Refer to “Phase Lock Control” on
page 5-23.
A45 and A46 Reference Transfer Switches (Option 081)
The A45 and A46 reference transfer switches are used to direct the reference signal to either an external
reference mixer or directly to the A28 channel R1 first converter (mixer). Refer to “A27, A28, A29, and A30
Receiver First Converters (Mixers)” on page 5-21.
This allows an external reference mixer to be switched in or out of the measurement setup without the need
to manually disconnect and reconnect cables.
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