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Table
9-1.
Internal
DVM Inputs
DVM Inputs
Function
+
Peak Voltage
Positive
modulation measurements
-
Peak
voltage
Negative modulation measurements
Carrier
Level
RF
output
level
RFINPUT PWR
Powe
r
level applied
to the RF
Input/Output port
EXT
FWDPWR
Forward
power
level
on
external
inline-wattmeter element
EXTRFLPWR
Reflected power level
on external in
line-wattmeter
element
BATT
VOLT
Voltage level at
de
input
port
on the rear
panel
divided
by 10
SIC
STRENGTH
DC
level
proportional to
the
level
in
dBm
of
the
received
VOLTAGE
signal
Distortion
Meter
Input
DC
level proportional
to
the
sil(nal
power
at the
input
of the
S INAD/DISTORTION
notch
filter
9.2.9
EXTERNAL DVM/DISTORTION CONTROL
External
DVM
and distortion inputs
to
the
front
panel
port are
ranged by
processor
control over
four
decades
on the
Front-Panel
Interface board
(A15).
The
resulting
output
is
routed to the DVM
FROM
RNG
SWITCH input of the
A7
board.
This
signal
is input
to
the
DVM/Distortion
Select
circuitry
(U30B
and
U:30C)
and the gain
stage of
6.5
(U62) preceding
the
1-kHz
notch
fi
lter.
9.2.1
0
DISTORTION
MEASUREMENT
In
the distortion
mode,
the DVMIDistortion Select
circuitry routes t
he
output
of
the
1-kHz notch
filter
(U62
and U63)
to
the
EXTERNAL DVM TO
AID
output pin. This
output
pin
is
connected
to the
rms-
to-dc converter on
the
All board. The output of
the
rms-to-dc
converter
is
multiplexed to the
AID
con-
verter
and
read
by the processor.
The
input to the
notch
fi
lter
is rectified
and filtered
by
U3,
and applied
to
the
Internal
DVM Select for
reading by
the proces-
sor
(as discussed
in paragraph
9.2.8).
To obtain
the
percent
distortion
for
a
1-kHz input,
t he
processor
divides
the
rms
output
voltage of the notch filter by the
average
rectified
input voltage
to the notch
filter.
The
notch
filter has a
processor-controlled
gain
that
is
switched
to
either
X
10
or
X
1.0,
depending
on input
distortion and
signal levels.
9.2.
11
EXTERNAL DVM MEASUREMENT
In
the
external DVM
mode,
the DVM
FROM
RNG
SWITCH
input
is
routed by
the
DVMIDistortion
Select
circuitry directly
to the EXT
DVM
TO
AID
output. At
t his
point,
it
is
connected to the rms-to-dc
converter
on
the
All
board. The output
of
the
rms-to-
dc
converter
is
multiplexed
to
the
AID
converter,
where it
is
read
by
the processor.
9.2.12
AUDIO AMPLIFIER AND ALARM
GENERATOR
An
a;;table mult
i-vibrator (U61 and
U50) operating
at
1.:.! kHz
is
the
alarm
generator.
The
alarm
signal,
eont
wlled
by
t he
processor,
is summed
with
the VOL
CNTL
AUD
RTN
signal
at the
input of the
aud
io
amplifier
(U7).
T
he SPEAKER
AUDIO
output of
the
amplifier
has a
0.5W
capability
and
is
connected
directly
to
the
system
speaker.
9.2.13
BOARD CONTROL
Processor
control of
the ScopeiDVM
Control
board
is
via three signal
lines:
the AF
ADD
BUS
0-3,
the
AF
DATA BUS
0-3,
and
the AF
BUS EN
1.
T
he fo
ur
address
bits
are
decoded
by
the
address
decoder
(U46)
to
determine
which
control latch
the four bits of
data
will be
latched
into.
The
latching process is synchro-
ni?.ed by the
AF
BUS
EN
1
line. Control
latches
in
addition to
those necessary
for controlling
this
board
(A7J provide
control for
the
Scope
Amplifier
board
(SCOPE
SWP
0-2) and part of t he
RF
Input
module
(A
TENNA
ENABLE).
9-3 /( 9-4
blank)
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