5-6 Service Guide E8361-90001
Theory of Operation PNA Series Microwave Network Analyzers
Source Group Operation E8361A
Source Group Operation
The source group produces a stable output signal by phase locking a yttrium-iron-garnet
(YIG) oscillator to a synthesized voltage-controlled oscillator (VCO). Refer to Table 5-2 on
page 5-8 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 5-4. For a simple block diagram of the source group, refer to Figure 5-2.
In this section the following characteristics and assemblies of the source group are
described:
• Band Modes
• A8 Fractional-N Synthesizer Board
• A17 L.O. Multiplier/Amplifier 12 (LOMA 12)
• A18 Multiplier/Amplifier 24 (MA 24)
• A19 Splitter
• A20 L.O. Distribution Assembly (LODA)
• A10 Frequency Reference Board (including rear-panel interconnects)
• A11 Phase Lock Board
• A12 Source 20
• A21 Source Multiplier/Amplifier 50 (SOMA 50)
• A16 Test Set Motherboard (including rear-panel interconnects)
Band Modes
Table 5-2 on page 5-8 lists the L.O. harmonic number, the synthesizer frequency, the
source frequency, and the frequencies at various other locations 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
8.333 MHz (1.0416 MHz for band 0) which is sent to the A11 phase lock board.
The A8 fractional-N synthesizer board produces an LO signal which is sent through the
A17–A20 LO distribution path to the A27–A30 first converters. The frequency is
synthesized such that the mixing product of this LO signal with the main source output is
a constant 8.333 MHz. In the A31–A34 receiver modules, this 1st IF signal is mixed with
the 2nd LO signals to produce a constant 2nd IF signal at 41.667 kHz.
A portion of the 1st IF signal is passed through the phase lock multiplexer on the A16 test
set motherboard back to the A11 phase lock board to complete the phase lock loop. For
Option 080 (frequency offset mode), this phase lock signal comes from the A13 frequency
offset receiver. Refer to “Frequency Offset Group Operation (Option 080)” on page 5-23.
The A10 frequency reference board also produces a constant 33.1667 MHz signal (4 MHz
for band 0) which is passed to the A35 receiver motherboard where the frequency is
divided by four to produce a constant 2nd LO signal of 8.29167 MHz (1 MHz for band 0). It
is then divided into two signals, the 2nd LO (a) and the 2nd LO (b). The 2nd LO (b) signal
is phase shifted +90° relative to 2nd LO (a). Both of these signals are then distributed to
each of the four receiver modules.
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