CDR-3250/80 TECHNICAL MANUAL
Issue 2.2
4-5
demodulation using an independent BFO input. USB is
provided by the normal channel during ISB operation.
FM demodulation is accomplished with FIR differentiator
functions that determine frequency as a time derivative of
phase. The IF FIR filtered I&Q components are applied to
the FM demodulator where the FM demodulation is done
mathematically. Instantaneous digital gain control is
derived from the AM signal to effect hard limiting. The FM
video output is available in all modes except ISB.
The NBIF signal is reconstructed from the digital IF data as
follows: The complex (I&Q) IF data having a selectable
bandwidth is centered at zero frequency. This data is
upsampled from 24 ks/s to 96 ks/s, then translated by -25
kHz. The result is a real signal at 96 ks/s which is then
applied to a D/A converter. The analog output has the
desired bandwidth centered at
K
25 kHz, with spectral
images centered at
K
25 kHz ±N
C
96kHz, where N is an
integer. The pulse shaper shortens the analog pulse
sufficiently that the spectral images corresponding to N
.
5 are enhanced. Thus the images centered at (
K
25±5
C
96) =
±455 kHz are enhanced.
The signal is then applied to a multipole bandpass filter
centered at 455 kHz to suppress the other spectral images
before it is applied to the rear panel as the NBIF signal.
Since this filter has a greater bandwidth than any of the
digital IF filters, the bandwidth at the NBIF connector is
determined by the digital IF filter selection.
The D/A converter converts the digital signals from the
digital signal processor into the required analog signals.
Input signals from the processor are applied to the
converter where they are converted into analog signals for
application to the appropriate circuits. Four signals are
multiplexed through one D/A converter and separated
using four sample/hold circuits. The signals then go
through 4-pole active lowpass filters before leaving the
circuit.
The signal outputs of the DSP section are selected by the
firmware as determined by data from the Control Section.
Signal outputs include:
GAIN CONT
Automatic or manual gain control for the
RF Analog module.
NORM AUDIO Either AM, FM, CW, USB, LSB, or USB
audio in ISB mode when selected by the
Control Section.
ALT AUDIO
LSB audio in ISB mode when selected by
the Control Section.
FM VIDEO
FM output to rear panel (except in ISB
mode). DC coupled.
NBIF
Reconstructed narrowband IF signal to the
rear panel for external equipment.
I & Q
Digital IF signals to the rear panel for
external equipment.
4-2.7
Serial Bus (Optional)
.
If the unit is optionally
configured for serial bus remote control operation, the unit
will contain the Serial Bus Remote Interface Board and the
Serial Bus Cable Assembly. Each is described in the
following paragraphs.
4-2.7.1
Serial Bus Remote Interface Board.
The Serial Bus
Remote Interface Board converts serial data from the bus to
parallel data for the Control Section. It also converts
parallel data from the Control Section to serial data for the
serial bus. This board is installed at the factory as a plug-in
daughter board in the Digital module, and uses a serial
receiver-transmitter integrated circuit. The board contains
line drivers and line receivers for both RS-232 and RS-422
bus types.
4-2.7.2
Serial Bus Cable Assembly.
The optional Serial
Bus Cable Assembly allows connection of the Serial Bus
Remote Interface board to the rear panel, and contains a
multipurpose connector for operation of either a RS-232C or
RS-422A external serial bus.
4-2.8
IEEE-488 Bus (Optional).
If the unit is optionally
configured for IEEE-488 bus remote control operation, the
unit will contain the IEEE-488 Remote Interface Board and
the IEEE-488 Cable Assembly. Each is described in the
following paragraphs.
4-2.8.1
IEEE-488 Remote Interface Board.
The optional
IEEE-488 Remote Interface Board contains an IEEE-488
controller, line transceivers, and associated circuits to
provide a smooth and orderly flow of data between the
Control Section in the Digital module and the external IEEE-
488 bus. This board is installed at the factory as a plug-in
daughter board in the Digital module.
4-2.8.2
IEEE-488 Cable Assembly.
The optional IEEE-488
Cable assembly allows connection of the IEEE-488 Remote
Interface Board to the rear panel, and contains a D-type
connector for connection to the external bus.
4-2.9
Front Panel.
The Front Panel contains a phones
jack, power/volume control, main adjustment knob, 19-key
conductive rubber keypad, and full graphic vacuum
fluorescent display. The volume control uses +12V to
Courtesy of http://BlackRadios.terryo.org
