5-20 Service Guide E8361-90001
Theory of Operation PNA Series Microwave Network Analyzers
Receiver Group Operation E8361A
Receiver Group Operation
The receiver group measures and processes the input signals into digital information for
processing and eventual display. Figure 5-6 on page 5-21 is a simplified block diagram of
the receiver functional group.
In this section the following assemblies are described:
• A27, A28, A29, and A30 Receiver First Converters (Mixers)
• LO Reject/Filter Board
• A31, A32, A33, and A34 Receiver Modules
• A6 SPAM Board (Analog Description)
• A35 Receiver Motherboard
• A16 Test Set Motherboard
A27, A28, A29, and A30 Receiver First Converters (Mixers)
The four receiver first converters (mixers) function identically and are completely
interchangeable.
Each first converter receives the RF reference or test signal and mixes it with the 1st LO
signal from the A20 LODA to create the 1st IF signal at a constant 8.333 MHz for bands
1–26 or 1.0416 MHz for band 0. This 1st IF signal is sent to the LO reject/filter board.
LO Reject/Filter Board
In each of the four channels, a 1.3 MHz lowpass filter is switched into the signal path for
band 0, to allow only the 1st IF signal of 1.0416 MHz to pass but all higher frequencies to
be blocked.
A31, A32, A33, and A34 Receiver Modules
The four receiver modules function identically and are completely interchangeable.
The 8.333 MHz 1st IF signal is filtered and amplified. For bands 16–26, additional
amplification is applied to overcome conversion loss of the A27–A30 first converters in
their third-order conversion mode.
A portion of the 8.333 MHz 1st IF 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. The 8.333 MHz 1st IF signal is also filtered, amplified, and routed to the
2nd converter.
The 2nd converter divides the 8.333 MHz signal into two paths and mixes each with a
separate LO signal, designated 2nd LO (a) and 2nd LO (b). These 2nd LO signals are
8.29167 MHz for bands 1–26 and 1 MHz for band 0. The 2nd LO (b) signal is phase shifted
+90° relative to the 2nd LO (a) signal. The two generated 2nd IF (a) and 2nd IF (b) signals
are a constant 41.667 kHz and are phase shifted −45 degrees and +45 degrees, respectively.
These signals are summed together and routed to the A6 signal processing and ADC
module (SPAM) board.
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