WJ-8611 DIGITAL VHF/UHF RECEIVER
CIRCUIT DESCRIPTIONS
5-13
The six gain control lines (RF 16, and IF 1/2/4/8/16) set the RF and IF
attenuation level to prevent the 250 kHz IF output (A2P1) from
overdriving the analog-to-digital converter in the Digital Control PC
Assembly (A2). The data provided at these lines are the result of the
sampling in the Digital Control PC Assembly (A2) of the signal amplitude
after it has been digitized, and is not a direct result of manual or automatic
gain control. The overall attenuation ranges from 0 to approximately 47
dB, controlled in 1 dB increments. This attenuation is intended to prevent
the signal level at the 250 kHz output from exceeding 0.2 V peak-to-peak.
The IF 16/8/4/2/1 control lines set the level of an attenuator contained in
the 2nd LO/2nd Converter PC Assembly (A3A2). A 4-bit control word,
formed by the IF 1/2/4/8 lines, sets the attenuation of a 0 to 15 dB
programmable attenuator. It provides from 0 to 15 dB of attenuation
selectable in 1 dB increments. IF 16 controls the selection of a 16 dB
attenuator. With IF 16 at logic “1” the 16 dB attenuator is in the signal
path, inserting an additional 16 dB of attenuation into the signal path. A
logic “0” at this input bypasses the 16 dB attenuator. The result of these
control lines is a selectable attenuation ranging from 0 to approximately 31
dB that may be injected into the signal path between the 1350 MHz IF
Input (A2E5) and the 250 kHz IF Output (A2P1) of the 2nd LO/2nd
Converter PC Assembly (A3A2). This attenuation has no affect on the
21.4 MHz signal at the Signal Monitor Output (J1).
The RF 16 control line enters the 2nd LO/2nd Converter PC Assembly
(A3A2) at A2P3, pin 18 and is sent directly to the 1st LO/1st Converter
Assembly through J10, pin 16. This line controls the selection of a 16 dB
attenuator in the 1st LO/1st Converter PC Assembly (A3A1). This
attenuator is activated only during strong signal conditions, after the 2nd
LO/2nd Converter PC Assembly (A3A2) attenuation has been set to
maximum.
5.3 TYPE 797168-1 DIGITAL CONTROL PC ASSEMBLY (A2) CIRCUIT DESCRIPTION
The Digital Control PC Assembly (A2) consists of four major functional
sections: the Control and Interface section; the IF Digitization section; the
Digital Signal Processing section, and the Analog Reconstruction and
Output section. The combination of these functional groups provides
receiver control and performs many of the signal processing tasks
associated with signal conditioning and demodulation of the intelligence.
Digitization of the analog IF, and the use of digital signal processing
algorithms, permits a broad range of operating functions without additional
hardware requirements. Refer to
following functional description.
Courtesy of http://BlackRadios.terryo.org
Summary of Contents for WJ-8611
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