Circuit Description; Microprocessor Front Panel Assembly Circuit Descriptions; Type 791202-5 Encoder Assembly (Mfp-A2); Optical Encoder (Vi) - Watkins-Johnson Company WJ-8718A/MFP Instruction Supplement

WJ-8718A/MFP
SECTION
m
CIRCUIT DESCRIPTION
CIRCUIT DESCRIPTION
3.1
MICROPROCESSOR FRONT PANEL ASSEMBLY CIRCUIT DESCRIPTIONS
Figure 3-1 is a functional block diagram of the front panel section of the
WJ-8718A/MFP Option which includes Encoder Assembly MFP-A2 and Front Panel
Switch/Encode Assembly MFP-Al. The front panel assemblies interface all front panel
features (except the power switch) with the I/O section of the receiver. Paragraph 2.4.4 of this
manual con.tains a functional description of all front panel controls, indicators, displays, and
connections. Refer to the schematic diagrams, Figures 6-1 through 6-8 when reading the
following circuit descriptions.
3.1.1
3.1.1.1
TYPE 791202-5 ENCODER ASSEMBLY (MFP-A2)
Optical Encoder (U1)
The optical encoder (Ul) converts the front panel tuning wheel rotation into
electrical inputs to the Front Panel Encode Board (MFP-AIAl), described in paragraph 3.1.3.
When the tuning wheel is rotated,both of the encoder output lines, CLK and DIR, swing
repeatedly between 0 and +5 Vdc. Due to the internal mechanics of the .encoder, the transitions
of the two outputs are square wave trains staggered in time in relationship to each other, as
shown in Figure 3-2. When the tuning wheel is rotated clockwise to increase tuned frequency,
the square wave on the DIR line will appear to lead that on the CLK line. When the tuning
wheel is rotated counterclockwise, the DIR square wave lags the CLK square wave. The two
encoder inputs go through approximately 120 cycles per revolution of the input shaft, causing a
tuning step for roughly each 3 0 of shaft rotation.
3.1.2 TYPE 794310-X FRONT PANEL SWITCH/ENCODE ASSEMBLY (MFP-Al)
The Front Panel Switch/Encode Assembly (MFP-Al) is located directly behind the
front panel (Figure 6-2). The module contains two subassemblies, interconnecting track, and
the amplifiers for the front panel phones jack audios. The microprocessor referenced
throughout the following circuit descriptions is located on the IF Interface Board, MFP-A3
(Figure 6-5).
3.1.2.1
Headphone Audio Amplifiers (MFP-A1, U1A, U1B)
Audio amplifiers UIA and UIB are low-power operational amplifiers with differen-
tial inputs. The non-inverting input to each amplifier is a dc voltage varied by the f-ront panel
PHONE LEVEL potentiometer (R7). In all detection modes except ISB, the non-inverting
amplifier inputs, AUDIO 1 and AUDIO 2, are the same audio signal. In ISB detection mode, the
audio to UIA is USB information (AUDIO 1) and audio to UIB is LSB information (AUDIO 2).
UIA outputs to the tip of the front panel stereo phones jack and UIB outputs to the ring.
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