Service Guide N5242-90001 5-7
PNA Series Microwave Network Analyzers Theory of Operation
N5242A Synthesized Source Group Operation
Synthesized Source Group Operation
The source group produces a stable output signal by phase locking a synthesized
voltage-controlled oscillator (VCO). Refer to Table 5-2 on page 5-9 for the full frequency
range of the source. The outputs at the front panel test ports are swept, stepped or CW
signals. Maximum leveled output powers are listed in Table 5-1 on page 5-5. For a simple
block diagram of the source group, refer to Figure 5-3 on page 5-8.
In this section the following are described:
• Basic Operation
• A4, A13, and A11 13.5 GHz Synthesizer Boards
• A5 and A8 26.5 GHz Source Boards
• A21 Multiplier/Amplifier 26.5 Board (HMA26.5)
• A10 Frequency Reference Board (including rear-panel interconnects)
• A19 Test Set Motherboard (including rear-panel interconnects)
Basic Operation
Table 5-2 on page 5-9 lists the L.O. harmonic number, the synthesizer frequencies (A4,
A13, and A11), and the main source frequency (A5 and A8) within the analyzer for each
band. This table is referred to throughout this chapter and also appears on the overall
block diagram at the end of Chapter 4, “Troubleshooting.”
The A10 frequency reference board produces a constant phase locked reference signal of
50 MHz that is sent to the A4, A13, and A11 13.5 GHz synthesizer boards.
The A11 13.5 GHz synthesizer board produces an LO signal that is sent through the A21
multiplier/amplifier 26.5 to the A23 and A24 mixer bricks (via the A22 splitter). The
frequency is synthesized such that the mixing product of this LO signal with the test
signal output is a constant 7.606 MHz IF; except for frequencies below 53 MHz when the
IF is 2.535 MHz. This IF signal is sent to the A12 SPAM board for digital processing.
The A4 and A13 13.5 GHz synthesizer boards each produce an incident signal that is sent
to the front panel outputs. A portion of these signals are coupled off and sent to the A23
and A24 mixer bricks (A
–D and R1–R4) where they are mixed with the LO signal from the
A22 splitter to produce the 7.606 MHz (or 2.535 MHz) IF signal.
The A4, A13, and A11 13.5 GHz synthesizer boards each contain their own phase lock
circuitry. The A11 board is used to phase lock the LO signal while the A4 and A13 boards
are used to phase lock the test signal. This makes it possible for the LO signal to be tuned
to a different frequency than the test signal, which is necessary since the LO signal is
normally 7.606 MHz higher than the test signal. Since the A4, A13, and A11 13.5 GHz
synthesizer boards each receive their 50 MHz input reference signal from the exact same
source, frequency drift error is eliminated.
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