WJ-8611 DIGITAL VHF/UHF RECEIVER
CIRCUIT DESCRIPTIONS
5-1
SECTION 5
CIRCUIT DESCRIPTIONS
5.1 WJ-8611 DIGITAL VHF/UHF RECEIVER FUNCTIONAL DESCRIPTION
The WJ-8611 Digital VHF/UHF Receiver is a Digital Signal Processor
(DSP) based receiver that provides frequency coverage in the 20 to
1000 MHz frequency range. The receiver circuitry consists of the Type
797228-1 RF Tuner Assembly (A3), the Type 797168-1 Digital Control
PC Assembly (A2), the Type 797229-1 Front Panel Assembly (A1), and
the Type 766032-1 Switching Power Supply (PS1). The functional
interconnection of these assemblies is illustrated in
to this illustration for the following overall functional description.
The RF Tuner Assembly (A3) provides coarse tuning of the RF signal and
down-conversion of the signal to an intermediate frequency (IF) that is
suitable for analog to digital conversion. It also performs the signal
conditioning that ensures that the Digital Control PC Assembly (A2) is
able to create an accurate digital representation of the analog signal of
interest. This section receives the incoming RF signal activity in the 20 to
1000 MHz frequency range, and using three mixing stages, provides an IF
output that is centered at 250 kHz. The 250 kHz IF output is bandwidth
limited to 200 kHz, thus providing an appropriate signal that is suitable for
digitization. It is then directed to the Digital Control PC Assembly (A2)
where it is digitized and sent to the DSP circuitry for further processing. A
second IF output that is centered at 21.4 MHz is sent to the rear panel. The
21.4 MHz IF output is a wide band output for use with an external signal
monitor or spectral display unit.
Control of the RF Tuner Assembly (A3) is obtained from the Digital
Control PC Assembly (A2) by way of a serial control bus and parallel
control lines. The parallel control lines (RF16, and IF 1/ 2/ 4/ 8/ 16) set the
gain of the RF signal path to ensure that the signal level does not overload
the digitizing circuitry in the Digital Control PC Assembly (A2). The
serial control bus lines (RFB DATA/ CLK/ STB/ A0/ A1/ A2) provide
synthesizer tuning and selection of the appropriate tuning band for the
five-band tracking preselector in the RF Tuner Assembly (A3).
Additionally, an analog tuning voltage line (PRE TV) provides a 0 to +5V
level that tunes the selected preselector tuning band to center its response
around the RF tuned frequency. The control signals supplied by the RF
Tuner Assembly (A3) provide the Digital Control PC Assembly (A2) with
an indication of its operating status. Four LOCK lines (1st/ 2nd/ 3rd/ REF
LOCK) indicate the operating status of each of the synthesizers in the RF
Tuner Assembly (A3). A logic ”1” on each of these lines indicates that the
respective synthesizer is locked on frequency and operating normally. The
Reference sensing line (REF SENSE) indicates when an external reference
is connected to the receiver. When an external reference signal is
connected to the receiver, this line assumes a logic “0” condition. It causes
the control processor in the Digital Control PC Assembly (A2) to send
Courtesy of http://BlackRadios.terryo.org
Summary of Contents for WJ-8611
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