Anritsu 682XXB, 683XXB 2-4

Step Sweep

Mode Step (digital) frequency sweeps of the YIG-tuned os-

cillator RF output consist of a series of discrete, syn-

thesized steps between a start and stop frequency.

Each frequency step is generated by applying the

tuning signal (from the A12 Analog Instruction

PCB) to the YIG-tuned oscillator’s main tuning coil,

then phase-locking the RF output. Every frequency

step in the sweep range is phase-locked.

2-4 ALC/AM/PULSE

MODULATION TheALC, AM, and pulse modulation subsystem provides automatic

level control (ALC), amplitude modulation (AM), and pulse modulation

of the signal generator’s RF output signal. The ALC loop consists of

circuits located on the A10 ALC PCB, the A9 PIN Control PCB, and

the A14 SDM, SQM Driver PCB. These circuits interface with the

Switched Filter assembly,the Down Converter assembly, the Source

Quadrupler Module (SQM), and the Directional Coupler/Level Detec-

tor (all located on the RF deck). AM modulation circuits (located on

the A10 ALC PCB) are included in this loop.

Pulse modulation of the RF output signal is provided by circuits lo-

cated on the A6 Pulse Generator PCB. These circuits interface directly

with the Switched Filter assembly located on the RF deck. (In 682X5B/

683X5B models, these circuits interface directly to the Digital Down

Converter assembly and from there to the Switched Filter assembly.)

The overall block diagram of the ALC and modulation subsystem is

shown in Figure 2-3, page 2-17. The following paragraphs describe the

operation of the subsystem components.

ALC Loop

Operation In the 682XXB/683XXB, a portion of the RF output

is detected and coupled out of the Directional Cou-

pler/Level Detector as the feedback input to the

ALC loop. The feedback signal from the detector is

routed to the A10 ALC PCB where it is compared

with a reference voltage that represents the desired

RF power output level. If the two voltages do not

match, an error correction signal is fed from the A10

ALC PCB to the modulator shaper amplifier circuits

located on the A9 PIN Control PCB and the A14

SDM, SQM Driver PCB, if installed. The resulting

modulator control voltage output causes the modu-

lators, located in the Switched Filter assembly,the

SQM, and the Digital Down Converter assembly

(682X5B/683X5B models only), to adjust the RF out-

put level. Thus, the feedback signal from the detec-

tor will be set equal to the reference voltage.

FUNCTIONAL ALC/AM/PULSE

DESCRIPTION MODULATION