Table of Contents
Advertisement
2.5.3.3
Signal-Present
Detector
During
Scan
Lock
operation,
a wideband-signal
detector
indicates the
presence
of a signal within 20
MHz
of the
L.O. frequency.
The 10.7 MHz IF
input
is
amplified
and applied
to
a diode
detector.
When
the
signal level is above about
-
30
dBm
and
within
20
MHz
of
the
L.O.
freq
uency, the
WB SIG PRES
output
goes
low, indicating signal presence.
2.5.3.4
Frequency-Error Indicator
One of three
signals
internal to
the Receiver may
be
switched
to the
IF/BFO
output
for use in
frequency-
error
indication.
During AM
and
FM monitor opera-
tion, the
limited, linear IF
output
is
selected
and routed
to
the
frequency counter on
the Processor Interface
board (All).
The
difference
between
this
frequency
and 700
kHz is
computed
by the processor
and
dis-
played
as frequency
error.
During SSB monitor
oper-
ation,
the BFO
output
is
switched
to the IF/BFO
output.
The difference
between this frequency
and
700
kHz is
computed and
displayed
as
BFO
error.
During
Scan
Lock
operation, the wideband-signal
detector's
output
is
switched to the
IF /BFO
output.
The
fre-
quency
of this
signal
is
equal
to the difference
between
the RF input
frequency
and the
L.O.
frequency.
2.6
DUPLEX GENERATOR
(ST
ANDARO AND
ENHANCED)
Simultaneous generate
and monitor functions are
available with the
Duplex
Generator.
The frequency
spread
between
generate and monitor
frequencies
is
limited
to
a range
of 0
to
10
MHz and
a
fixed
fre-
quency
of
45
MHz.
(Also 39
and
55
MHz for enhanced.)
A
block diagram
of the Duplex Generator function
is shown at the end of the section in
Figure
2-6.
The
Duplex
Generator signal
is
generated
by mix-
ing the
L.O.
signal for the
first receive mixer
with a
signal
from the
offset
phase-locked-loop
(PLL).
The
frequency of the offset PLL equals the
desired spread
between
generate and
monitor
frequencies,
minus
the
10.7-MHz IF
offset. The
monitor
function is
unaf-
fected
by
the
Duplex
mode and operates as
described
in paragraph
2.5.
Frequency
modulation
of
the
Duplex
output
is
obtained by modulating
the offset PLL via the
OFF-
SET
MOD
signal
line.
The
OFFSET MOD
signal is
generated
on the
Audio
Synthesizer
board
(AlO).
The
offset PLL is controlled via the
RF
CONTROL
BUS.
2.7
CODE SYNTHESIZER
Three simultaneous modulation sources are
possi-
ble
with the
internal
code
synthesizer.
The
levels
of a
private line
(PL) or digital private line (DPL) source,
a
fixed 1-kHz
source,
and
external
modulation
sources
can be
individually
controlled and
summed
together to
2-6
give the composite modulation
signal. T
he code
syn-
thesizer
provides
the
modulation
source for the
sys-
tem in
the
generate
mode
and can be
used
as an audio-
frequency
source.
For the
IEEE
option,
modulation
levels
can
be
controlled
by
the
processor.
A block diagram
of the code synthesizer
is
shown at
the end
of
the
section
in Figure
2-7.
T
he PL signaling-sequence is generated
by an
audio
synthesizer with an
output frequency
range
from 5
Hz
to 20
kHz in 0.1-Hz
steps.
The
frequency is pro-
grammed by
the processor
in response
to
the
opera-
tor's
request
from the
keyboard
through the CRT
display.
The programmable
attenuator
following
the
audio
synthesizer provides attenuation
levels of
10 dB
and 30
dB for
the
Tone-Remote-Access
Sequence.
DPL
code
words are
generated
by
the
processor
in
response
to the code entered
by
the operator.
The
23-
bit DPL word is stored
in
the
DPL
generator and con-
tinuously output
when
selected.
Either PL
or
DPL
signals
are switched
to the code synthesizer
level
con-
trol (Code Synth
Lvl)
on the front panel.
A
1-kHz reference
signal from the
RF
Synthesizer
is
bandpass-filtered to
provide
a
low
distortion,
1-kHz
sinewave to the front
panel's
1 KHz
Level
control.
Two
sources of
external modulation
are possible
through two
ports
on
the
front
panel:
a standard
Motorola
microphone-interface
port and
a
BNC
port.
The
microphone input
(Mic)
is
connected to an
instantaneous deviation-control
(IDC) circuit
for
peak-
limiting.
The composite
of
the
two external
modula-
tion sources is the signal which goes to the
Ext
Level
control
on
the
front
panel.
On systems without one of the Remote
options,
the
wipers of the
level-control potentiometers will be
jumpered from their
respective
inputs to the
summa-
tion
amplifier
on the
Audio
Synthesizer
board
(AlO).
On
those
systems
with
one
of the
Remote
options,
select switches on the
IEEE/RS-232
Interface board
send
either the tops of the
level
controls (Code Synth,
1
KHz, or Ext) or their
respective
wipers to the
pro-
grammable attenuators.
For remote
control,
they
select
the tops;
for local
control, the wipers.
During
the
Remote control mode, the
processor-controlled
pro-
grammable attenuator on the
IEEE/RS-232
board
controls
the
modulation level.
For the
local
mode,
the
attenuators are
programmed
for
zero
attenuation
so
that
the
wipers of the
level
control
set the
modulation
levels
directly.
The
three modulation sources are
summed
together
on
the Audio
Synthesizer
board
according
to
what
is
set
on the
level
controls. This composite
modulation
signal is
applied to 1)
the
appropriate
modulator,
2)
the
modulation-measuring circuitry (MOD CAL AUDIO),
3)
the audio amplifier (SPKR AUDIO) and
4)
the
front
panel's modulation
output
port (Mod Out). To
pro-
vide
a
low-impedance
output,
the
signal
to
the
front
panel's port
is
driven by a buffer amplifier.
For AM, the composite
modulation
is
summed
with
+5 Vdc. This
signal
(5V
+
AM
MOD)
is applied to
Advertisement
Table of Contents
Troubleshooting
