off at a rate determined by the modulating square
wave.
The 0.01 to 2.2 GHz RF signal from the modulator is
amplified and routed via PIN switches to the
switched low-pass filters. PIN switch drive current
is generated by internal drivers that are controlled
by signals received from the A12 Analog Instruction
PCB via the A14 PCB. There are 16 switched low-
pass filters covering the 0.01 to 2.2 GHz frequency
range. These low-pass filters provide rejection of un-
wanted harmonics. After routing through the appro-
priate filter path, the 0.01 to 2.2 GHz RF signal is
multiplexed by PIN switches to the output connec-
tor J3. A portion of the down converter’s RF output
signal is detected, amplified, and coupled out for use
in internal leveling. The detected RF sample is
routed to the A10 ALC PCB.
The 0.01 to 2.2 GHz output from the digital down
converter goes to input connector J1 of the switched
filter assembly. There, the 0.01 to 2.2 GHz RF signal
is multiplexed into the switched filter’s output path.
In units with Option 22, the 0.01 to 2.2 GHz RF out-
put of the digital down converter is diplexed with
the 0.01 to 10 MHz output of the A13 10 MHz DDS
PCB. The resulting 0.00001 to 2.2 GHz signal is
then diplexed with the RF signal from the swtiched
filter assembly (or switched doubler module for
>20 GHz models) into the RF path to the directional
coupler.
Switched
Doubler
Module
The switched doubler module (SDM), found in
>20 GHz models is used to double the fundamental
frequencies of 10 to 20 GHz to produce RF output
frequencies of 20 to 40 GHz.
The RF signal from the switched filter assembly is
input to the SDM at J1. During CW or swept fre-
quency operations in the 20 to 40 GHz frequency
range, the 10 to 20 GHz RF signal input is routed by
PIN switches to the doubler/amplifiers. PIN switch
drive current is provided by the A9 PCB and bias
voltage for the doubler/amplifiers is supplied by the
A14 YIG, SDM, SQM Driver PCB. The RF signal is
amplified, then doubled in frequency. From the dou-
bler, the 20 to 40 GHz RF signal is routed by PIN
switches to the bandpass filters. There are three
bandpass filter paths to provide good harmonic per-
2-28
690XXB/691XXB MM
FUNCTIONAL
RF DECK
DESCRIPTION
ASSEMBLIES
Summary of Contents for 680 C Series
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