72 Chapter 2
Block Diagrams
A17 RF Assembly
21.4 MHz Output Buffer Amplifiers and Filter
The buffer amplifiers provide good isolation from the second converter
output to the input of the A12 analog IF assembly. The 21.4 MHz
bandpass filter is centered at 21.4 MHz, and has a 3 dB bandwidth of
approximately 12 MHz.
Pre-level Drive
The pre-level drive is part of the AGC loop. After detecting the level of
the LO on the RF board, the pre-level drive drives a variable attenuator
on the A19 synthesizer board, which then adjusts the level of the LO.
Interconnections to other assemblies
• A17P1. 21.4 MHz out to the A12 analog IF board
• A17P2. RF input (7 MHz to 4 GHz, from the front-panel port)
• A17P3. 321.4 MHz out (currently not in use)
• A17P4. LO input from the A19 synthesizer board
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