TFT 724A User manual
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SECTION
1
SECTION
2
SEC
TION
3
TABLE
OF
CO
NTENT
S
GENERAL
INFORMATION
1.1
Genera
l Descr
iption
...•.....
.
..•..••..
.
1.2
Spec
ifications
•.........
•...•.
•.
..
...
. .
1.
3 Accessory
Equipment
.•.
...
.
...
. .
...
...
..
1.4 Warranty
.....
....•.....
•
..
.
...
.•
.
.....•
1.5 Cl
aim
for
Damage
in Shipment
...
•....
. ••
IN
ST
ALLATION
Page
1-1
1-1
1-3
1-3
1-3
2
.1
2.2
2.3
2
.4
Unpacking
and
Inspection
.....•.
...
.
....
2
-1
Po
wer
Requ
i
rem
en
ts.
•. . •. . ••. .
..
•. . . ••. . . 2-1
lnstal
l
at
ion Procedures
..
.
...
..
...
.....
2
-1
Model
7
04C
Remote
Pane
l Meter
OPERATION
3.1
3.2
3.2.1
3.2.2
3.3
3.4
3.4.1
3.4.2
3. 4. 3
3.5
3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
3.6.6
3.6.7
3.
6.8
3.
6.9
3.6.10
3.6
.
11
3
.7
Connection
....
.
•.•.•
.
...
••
..•..•••
2-1
General
......
.
.....
..
....
.
......
......
.
Co
ntrol,
Co
nnections
and
Indica
tor
...
•.
F
ront
Pane
l
.••
••••..
•.
•.
•••
•....
..•
..••
Rear Panel
•..
.
•..
.
...
..
.
..
.•.•.••
....•.
Turn
On
and
Wann
Up
••
.•...
••
••.••.•.••
.
Ca
libration
Procedures
..
••
•.....
••...•.
Meter C
alibration
Usi
ng
Model
763
•.••
..
Meter Calibration with a
Composi
te
Input.
..
. .
....
..
....
.
......
..
..
...
.
P
ha
se
Ca
li
bra
tion
•• . ••• . .
.•.
.•
..•
•. . . •.
Use
of
th
e
Model
72
4A
for
Monitoring
••.
Use
of
the
Model
72
4A
for
Measurement
•.
Main-Channel
(L+R)
Mo
dulation.•• . .
•.
•
..
Stereo S
ub
channel
(L-R)
Modula
ti
on
•
.•
••
Pilot
Ca
rrier
Modulation
..
..••
•.
....•••
38
kHz
S
ub
c
arrier
Suppression
••••.•..••
S
tereo
Channel
Se
paration (Left
C
hann
el
Modulated
).
•.
...•.....•.•
•
Stereo
Channel
Se
paration (Right
Channel
Modulated) •• .
....•
.
•...•
..
Main
Chan
nel to S
ub
cha
nnel
Cross
talk
..
•
S
ub
channel
to
Main
Channel C
rosstalk
•••
FM
No
i
se
...
....
...
•
•.••..•
....
. .
..
..
...
Dis
tortion
.•
••
..
•..
. •
•..
•....•.
....•..
•
Pi
l ot Frequency
.......
•.
••
..•...
.•
..
. •.
Use
of
the
Model
70
4C
Remote
Meter
3-1
3-1
3-1
3-5
3-6
3-6
3-6
3-7
3-7
3-7
3-8
3-8
3-8
3-8
3-8
3
-9
3-9
3-9
3-10
3-10
3-1
1
3
-11
Panel........
....
.
...
.
....
.......
. 3
-11
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SECTION
4
SECTION
5
SECTION
6
TABLE
OF
CONTENTS
{Continued)
Page
THEORY
OF
OPERATION
4.1
4.1.1
4.
1.2
4.2
4.2
.1
4.2.2
4.2.3
4.2.4
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6
4.3.7
4.3.8
4.3.9
4.4
General Block
Diagram
Discussion
..
4-1
Modulation Monitoring Circu
its
....
4-1
Measureme
nt
Circuits
.•............
4-2
Meter Amplifier &Attenuator
Boa
rd (A-3) .
.....
.
..
.•...•...
4-2
Attenuator......
.
.................
4-3
Modulation/Test Meter Amplifier
...
4-3
Left-Channel
Meter
Amplifier
..•
...
4-3
Audio
Amplifiers......
..
..........
4-3
Demodulator &
Filter
Boa
rd
{A-2)
..
4-4
Buffer Amplifiers &F
un
ction
Sw
itche
s. .
.....
...
.
...
.
......
4-4
19-kHz
Filter
......
.
.......
.
....
..
4-4
38
-kHz
Filter
.....•.
. .
.....
.•....•
4-5
L+R
Channe
l
Filter
{FU)
..........
4-5
L-R
Cha
nn
el
Filter
{FL2)
..
. . .
..
••.
4-5
38-kHz
Phase-Locked
Loop
.....
.
..•.
4-5
Stereo Demodulator
•.
......•.
.
...••
4-6
Left-Channel
Filter
(Fl3)
and
Right
Channel
{FL4)
•...•....•
4-6
Phase
Calibrat
ion
..
•..•.•..••.....
4-6
Power
Supply
Board
{Al)
...
.
....
...
4-7
MAINTENANCE
5.1 General
...•
.
.............
...•.....
5.2 Periodic Maintenance
...
.
•.....
.
•..
5.3 Perfonnance
Checks
......•••.•.•
. . .
5.3.1
Ca
libration
Accuracy
Check
•••.....
5.3.2
Amplitude
Response
Check
.......
. . .
5.3.3
Stereo
Pilot
Indicator.
..........
.
5.3.4
Output
Check
...
..
•.
...
.
..
...
.•
.
...
5.3.5 Stereo Separation C
heck
.•..•••....
5.3.6
Crossta
lk
and
Distort
ion
Check
.
..
.
SCHEMATIC
DIAGRAMS
6.1
6.2
6.3
6.4
6.5
Block
Diagram
..
. .
•.•....•
•.
.....
. .
Wiring
D
ia
gram
-
Main
Chassis
Front & Rear
.....•.••.•....••
Audio
Meter Amplifier
(A3)
........
Demodulator/Filter
Board
{A2)
•.
...
Power
Supply
(Al)
.....
.
......
.
...
.
5-1
5-1
5-1
5-1
5-2
5-3
5-3
5-4
5-5
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SECTION
1
GENERAL
INFORMATION
General Description.
The
Model
724A
Stereo
Mo
nitor
is
intended
for
use with
the
TFT
Model
763
FM
Frequency
and
Modulation
Mon
itor
to
meet
all
FM
stereo
monitoring requirements
and
to
provide proof-of-perfonnance
measurements.
Two
separate meters allow monitoring of
right
and
left
channels simultaneously.
The
meters can also
be
used
to
measure
separation between
right
and
le
ft
channels,
crosstalk
between
main
and
sub
channels,
38
kHz
carrier
suppression,
19
kHz
injection
level,
and
FM
signa
l-t
o-n
oise
ratio.
The
various meter functions
are
selected
by
front-panel pushbutton switches.
Power
for
the
Model
724A
is
supplied
by
the
Mo
del
763
.
The
Model
724A
Stereo
Moni
tor,
when
used with the
Model
763
FM
Frequency
and
Mod
ulat
ion Monitor, meets the requirements
of
Section
73
.332, Sub-sections d
and
e,
of
the
FCC
regula
ti
ons
relating
to
FM
stereo
monitors.
1.2
Spec
ification
s.
Co
mposite input
Level
........
....
.....•.
.
..
.
500
mV
RMS
lmpedanc
e. . . . . . . . . . . . . . . . . . .
600
ohms
unba
1
anc
ed
Pilot
Measurements
Level
accuracy
.....
.
.......•
...
. .
+O.
5%
from
6%
to
12
%
-modulation
The
19
kHz
pilot
frequency
is
returned
to
the
digital
counter in the
Model
764
.
Accu
racy
and
resolution are ~0.1
Hz.
Mod
ulati
on
Meters
Frequency response measurements:
Left channel,
right
channel,
and
L+R
channel
..
....
...
...•
~4
%,
50
Hz
to
15
kHz
L-R
channel.
....
.•.
.......
..
~4
%,
23
kHz
to
53
kHz
1-1
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Ou
tp
ut
s
Separation measurements:
Left
to
right
and
right
to
l
eft
.......•...
.
......•••....
.
..
. . .
45
dB
m
in.
,
50
Hz
to
15
kHz
Crosstalk
measurements :
(L
+R)
to
(
L-R)
.
..
..
•. . . . . •. . . .
..
. •
60
dB
min.
(L-R)
to
(L+R)
.
...
.
.....
.
•.•••.•..
60
dB min.
SCA
to
(L-R) . .
••.•.
....•.
•••
..
.•..
66
dB
min.
SCA
to
(l+R)
•...•.•..•..••....•..•
66
dB
min
.
Left
and
right
channel monitoring:
Impedance
....••.••.•.......••.....
600
ohms
unbalanced
Level
•..••••
.
.•..••.•..•..•.•
.
....
1 V
RMS
at
100'.t
modulation,
400
Hz
Frequency response
(without de-emphasis)
•..•.......•.
+4
'.t
,
50
Hz
to
Ts
kHz
Distortion
.
.•
...
.
..•.•.•••..••••.•
0.5%
max.
No
ise level (
wi
th
de-emphasis)
....
...............••.
60
dB
min.
below
100
'.t
Remote
meter
...........................
Outp
ut
s
for
Model
704C
remote meter
panel
(bot
h
meters).
Pilot
frequency (19
kHz):
Leve
l
....
.
....•....
•
....
•
••..
••.
.•
100
mV
RMS
Composite Output
Impedance
•..••.•••••••.•
. .
......
..
10k
ohms
Level
......
....
.
......
...••
••
••..
. 1 V
RMS
(1001)
Power
Requirements
Requires 25.2
VAC,
center
tapped
from
Model
763
.
Physical
and
Environmental
Specifications
Operating temperature
•....
.
............
o0 to
so°
C
1-2
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1
Di
men
si
on
s. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
11
Wx 7
11
Hx
16
11
D
Weight
...
....
..
.
......
........
.
.......
.
15
pounds
Cabinet
...
.
.......
.
...
.
.........
•
......
Rack
mounting
1.
3 Accessory Equipment.
The
TFT
Model
704C
Remote
Readout
Pa
nel duplicates the
readings
of
the
two
Model
724A
front-panel meters.
1.4
Warranty.
TIME
&
FREQUENCY
TECHNOLOGY,
INC.,
warrants each
of
the
instruments
of
its
manufacture to
be
produced to meet the
specifications
delivered
to
the
BUYER;
and
to
be
free
from
defects in material
and
workmanship
and
will
repair
or
replace,
at
its
expense,
for
a period
of
one
year
from
the date
of
de
livery
of
equipment,
any
parts
which
are
defective
from
faulty
material
or
poor workmanship.
In
stru
ments
found
to
be
defective during the warranty
period shall
be
returned to the factory with
transportation
charges
prepaid
by
BUYER.
It
is
with
respect
to
any
nonconforming equipment
and
parts
there
of
and
shall
be
in
lieu
of
any
other
remedy
available
by
applicable
law.
Al
l returns to the factory
must
be
authorized
by
the
SELLER,
prior
to such
returns.
Upon
examination
by
the factory,
if
the
instrument
is
found
to
be defe
cti
ve
,
the
unit
will
be
repaired
and
returned to the
BUYER,
with
tran
spo
rtation
charges prepaid
by
SEL
L
ER.
Transportation charges
for
instruments
found
to
be
defective
within the
first
thirty
(30) days
of
the warranty period will
be
paid both ways
by
the
SE
LLER.
Transportation charges for warranty
returns,
wherein
failure
is
found
not
to
be
the
fault
of
the
SELLER,
shall
be
paid both
ways
by
the
BUYER.
-
NO
OTHER
WARRANTY
IS
EXPRESSED
OR
IMPLIED.
TFT
IS
N
OT
LIABLE
FOR
CONSEQUENTIAL
DAMAGES
.
1.5
Claim
for
Damage
in
Shipment.
Your
instrument should
be
inspected
and
tested as
soo
n as
it
is
received.
The
instrument
is
insur
ed
for
safe
delivery.
If
the
instrument is
damaged
in
any
way
or
fails
to
operate properl
y,
file
a
claim with the
carrier,
or
if
insured
separately,
with the insurance
company
.
WE
SINCERELY
PLEDGE
OUR
IMMEDIATE
AND
FULLEST
COOPERATION
TO
ALL
USERS
OF
OUR
PRECISION
ELECTRONICS
INSTRUMENTS.
1-3
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2.1
S
ECTION
2
INSTA
LL
ATION
Unpacking
and
Inspection.
Upon
receiving the instrument,
in
spect the packing
box
and
instrument
for
signs
of
possible shipping
damage.
Operate the
instrument in accordance with the procedures
of
Section 3
of
this
manual.
If
the instrument
is
damaged
or
fails
to operate properly,
file
a
cla
im
with
th
e
transportation
company,
or
with the insurance
company
if
insured
separatley
.
2.2
Model
Power
Reguirmen
ts.
Power
for the
Model
724A
(25.2
VAC)
is
s
up
plied
by
the
763
FM
Modulation Monitor. Refer to Paragraph 2.3
below
for
connections.
2.3
2.4
Installation
Procedures.
a.
Mount
the
Model
724A
in
the equipment rack.
b. Connect the furnished three-wire
power
cable
between
JlO
on
the
Model
724A
and
J2
on
the
Model
763.
A
ground cable
between
the
two
instruments
is
also
required.
Re
f
er
to Figure
2-1
for
connection.
c.
Connect the furnished coaxial cable
between
COMPOSITE
INPUT
connector
J7
on
the
rear
panel of
the
Mode
l
724A
a
nd
JS
(TO
STEREO
MO
NI
TOR)
outp
ut
on
the
Model
763.
d.
If
the studio
stereo
generator
is
to
be
monitored,
connect
it
s
compos
it
e ou
tput
to
COMPOSITE
INPUT
connector J7
on
Mode
l
724A
.
e. Connect another furnished coaxial cable
from
STEREO
PILOT
(19
kHz)
connector J3
on
the
Mode
l
724A
to
PILOT
CARR
co
nn
ector
on
the
rear
panel
of
the
Model
764.
NOTE
For information
on
installing
and
making
connections
to
the
Model
763, r
efer
to
the
Model
763
instruction
man
ual .
Model
704C
Remote
Panel Meter Connection.
Con
n
ect
the
50
foot,
three
wire cabl e furnished with the
Model
704C
to terminals
A,
B,
and
C
of
JlO
on
the
Model
724A
rear
panel .
Wraparound
labels
identify
the cable wires.
2-1
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3. 1 General.
SECTION
3
OPERATION
The
Model
724A
Stereo Monitor provides
all
the functions
required
for
the
FCC
proof-of-perfonnance
test,
as
well as for
daily
stereo
system monitoring. Left
and
right
channels can
be
monitored
simultaneous
ly.
Built-in
switchable
attenuators
permit
making
low-level
measurements
on
signals
that
are
small
compared
to
the
nonnal
modulation.
The
internal
calibrat
ion signal in the
Model
763
FM
Frequency
and
Modulation Monitor
is
used
in conjunction with the
LEVEL
CAL
control
on
the
Mo
del
724A
rear
pane
l
and
the
MOD
CAL/L+R
button
on
the
front
panel
to
calibrate
the
Mode
l
724A
.
3. 2
3.2.1
Fig.
3-1
Ref.
No.
1
2
Controls, Connectors,
and
Indicators.
Front Panel.
Name
PHASE
CAL
switch
and
control
LEFT
function switch
3-1
Function
When
the
PHASE
CAL
switch
is
depressed,
the
PHASE
CAL
control
can
be
adjusted
for
a
null
on
the
MODULATION/TEST
meter
to
indicate
that
the
internal
38
kHz
signal
is
in phase with the
19
kHz
pilot
signal.
This insures
that
the
best
channel
separation
has
been
attained
so
that
the
best
stereo
measurements can
be
made.
Note:
The
null
may
not be a zero
reading.
When
depressed, the
LEFT
CHANNEL
meter
reads the
left-channel-
modulation
unattenuated,
and
the
MODULATION
/
TEST
meter
reads
the
left-channel
modulation through the
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3.2.1
Fig. 3-1
Ref.
No.
3
4
5
6
Continued.
Name
RIGHT
function switch
38
kHz
function switch
PILOT
function switch
MOO
CA
L /
L+R
function
3-2
Function
selected
attenuator.
Each
meter
wi
11
indicate
90
%
when
the
left
channel
is
fully
modulated.
When
depressed, the
MODULATION/TEST
meter
reads the
right-
channel modulation
through the selected
attenuator.
A
fully
modul
ated
right
channel will indicate
90
%
on
the meter.
With
the
stereo
channel modulated
at
a
frequency
between
5
kHz
and
15
kHz,
depressing
this
permits reading the
38
kHz
sub-carrier
suppression
on
the
MODULATION/TEST
meter.
By
using the
appropriate
attenuator,
measurements can
be
made
to
60
dB
be
low
100
%.
When
depressed, the
MODULATION/TEST
meter
indicat
es
the
amplitude of the 19
kHz
pilot
signal
through the selected
attenuator
allowing
measurements over the
required 8 to
10
%
range.
These
measurements can
be
made
in the presence
of
modulation.
When
depressed, the
MODULATION/TEST
meter
indicates
the
amount
of
signal (attenuated
by
the
se
lected
attenuator)
www.SteamPoweredRadio.Com
I
I
3. 2
.l
(Continued). I
Fig.
3-1
Ref.
No.
Name
Function
in
monophonic
(main) I
channel in percent
of
100
'.t
modulation. This I
switch
is
also used
for
calibrating
the
meters in conjunction I
with
calibration
signal
from
the
Model
763.
7
L-R
function switch
When
depressed, the I
MODULATION/TEST
meter
indicates
the
amount
I
of
signal (attenuated
by
the
se
lected
attenuator)
in the
stereo
channel in I
percent
of
100
%
modulation.
8
FM
S/N
function switch
With
all
modulation I
turned
off,
depressing
this
switch causes the I
MODULATION/TEST
meter
to
indicate
the
residual modulation
(FM
noise) through the
selected
attenuator.
Depressing
this
switch I
automatically
inserts
I
a deemphasis
network
for
this
measurement.
9
METER
OUTPUT
Provides
an
A.C.
I
output
of
the signal
that
is
being
displayed
on
the I
MODULATION/TEST
meter.
Approximately
lOVPP
output
into
an
open
I
circuit
represents
100
'.t
on
the
MODULATION/TEST
meter. I
I
3-3 I
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3. 2.1
Fig.
3-1
Ref.
No.
10
11
12
(Continued).
Name
MODULATION/TEST
meter
MOD/TEST
METER
ATTENUATION
switches
STEREO
PILOT
lamp
3-4
Function
Indicates
the function
switched
in
by
the
MOD/TEST
METER
FUNCTION
switches.
Inputs
to
this
meter
are
always applied
through a
selected
attenuator.
Measurements can be
made
down
to
70
dB
below
10o
i .
Depressing
one
of
these
switches
inserts
the
attenuation
marked
thereon
into
the
MODULATION
/TEST
meter
input.
The
resulting
measurement
is
the
algebraic
sum
of
the
meter reading
and
the
the
inserted
attenuation.
For
example, a meter
indication
of
-2
dB
with the -30
dB
switch
depressed
would
indicate
a measurement
of
32
dB
below
100
%
modu
l
ation.
Three
of
the
switches
are
marked
1%,
1o
i ,
and
1oo
i . These
indicate
the actual modulation
percentage
when
the
meter needle
is
a the
100
%mark. For
example, a meter
reading
of
70
%with
the 1i switch
depressed
would
indicate
a measurement
of 0. 7%modulation.
Lights
when
the
19
kHz
pilot
signal
is
present.
www.SteamPoweredRadio.Com
I
3.2.1 (Continued). I
Fig.
3-1
Ref.
No.
Name
Function I
13
LEFT
CHANNEL
meter Indicates left-channel
modu
l
ation
independent
of
I
selected
function switch
position.
3.2.2 Rear Panel. I
Fig.
3-2
Ref.
No.
Name
Function I
1
DE-EMPHASIS
RIGHT
CHANNEL
Provides demodulation
connector J1 right-channel infonnation
through deemphasis I
network,
for
driving
mo
nit
or
systems
etc.
2
OE-EMPHASIS
LEFT
CHANNEL
Provides demodulated
left-
I
connector J2 channel infonnation
through deemphasis I
network,
for
driving
monitor systems
etc.
3
STEREO
PILOT
(19
kHz)
Provides
means
of
I
connector J3 delivering the
19
kHz
component
of the
composite signal to the I
Model
764
or
an
external
counter
for
frequency
measurement. I
4
RIGHT
CHANNEL
connector
J4
Provides demodulated
right-channel
infonnation, without I
deemphasis,
for
voltmeter
measurements,
etc.
5
LEFT
CHAN
NEL
connector
JS
Provides demodulated
left-
I
channel infonnation,
without deemphasis,
for
I
voltmeter measurements,
etc.
I
3-5
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3.2.2
Fig. 3-2
Ref.
No.
6
7
8
9
10
3.3
(Continued).
Name
SCOPE
OUTPUT
connector J6
LEVEL
CAL
control
COMPOSITE
INPUT
connector J7
POWER
SUPPLY
FRCJ,1
MODEL
763, JlO, F,
G,
H
Tenninal block JlO,
A,
B,
C
Turn-On
and
Wann-Up.
Function
Provides
demodulated
composite signal
for scope
observation.
Controls
amplitude
of
composite signal
for
calibration
of
front-panel
meters.
Provides
means
of
introducing a
composite signal
from
the
Model
763
or
a stereo
generator.
Provides
means
of
supplying
power
from
the
Model
763
to the
Model
724A.
Provides
means
of
connecting a
Model
704C
Remote
Panel
Meter
to
the
Model
724A
.
The
Model
724A
is
automatical
ly
turned
on
when
the
Model
763
is
plugged
in.
Since the
Model
724A
is
a completely
solid-state
design,
wann-up
time
is
very minimal.
One
or
two
minutes should
be
more
than adequate to allow
for
consistent
reading.
3.4
3.4
. l
Ca
li
bration Procedu
res.
Meter
Calibration
Using
Model
763.
With
the
C()1POSITE
INPUT
connector J7
on
the
Model
724A
connected to the composite output connector
JS
on
the
Model
763
proceed
as
follows:
3-6
www.SteamPoweredRadio.Com
3. 4.1
3.4
.2
(Continued) .
a.
Cal
ibrate
the
Model
763
modulation meter as
described
in
Model
763
instruction
manual.
b.
On
the
Model
724A
front
panel depress the
MOD
CAL/
L
+R
switch.
c.
On
the
Model
724A
rear
panel,
adjust
the
LEVEL
CA
L
control
so
that
the
MODULATION/TEST
meter reads
100
%.
Meter
Cal
ibration
with a Composite Input.
With
C(}iPOS
IT
E
INPUT
connector
J7
on
the
Model
724A
connected
to
a composite-signal source, proceed as follows:
3.4.3
3.5
a.
On
the
Model
724A
front
panel, depress the
PILOT
switch.
b.
On
the
Model
724A
rear
panel,
adjust
the
LEVEL
CA
L
control
so
that
the
correct
pilot
signal level
is
indicated
on
the
MODULATION/TEST
meter, using the
MOD/TEST
METER
ATTENUATION
switches
as
required.
c.
The
other
portions
of
the composite signal should
appear
at
their
proper
levels.
Phase
Ca
libration.
a.
Remove
all
modulation,
modulation.
left-channel
and
right-channel audio
leaving only the
pilot
signal
as
b. Depress the front-panel
PHASE
CA
L switch.
c.
Adjust the front-panel
PHASE
CAL
control
for
a
m1n1mum
reading
on
the
MODULATION/TEST
meter.
Note
that
this
minimum
reading will not be zero.
Use
of
the
Mode
l
724A
for
Moni
toring.
Fo
r
nonnal
monitoring, press the
RIGHT
function switch
and
the
100
% / 0
dB
MOD/TEST
METER
ATTENUATION
switch.
The
LEFT
CHANNEL
meter will then
indicate
the left-channel modulation percentage,
and
the
MODU
L
ATION/TEST
meter
will
indicate
the right-channel modulation
percentage simultaneously.
3-7
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www.SteamPoweredRadio.Com
10
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MON
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MODEL
72
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METE!<
FUNCTION
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3.6
3.6.l
Use
of
the
Model
724A
for
Measurements.
Main-C
hann
el
(L+R)
Modulation.
Press the
MOD
CAL/
L+R
function switch
and
the
100
%/ O
dB
MOD/TEST
METER
ATTENUATION
switch.
The
MODULATION/TEST
meter will
indicate
the main-channel modulation
direct
ly
in
percent. A
fully
modulated
right
or
left
channel only signal will
indicate
45
%
on
the
meter. A
fully
modulated
L=R
signal will
indicate
90
%
and
a
fully
modulate
L=
-R signal will
indicate
0.
3.
6.2
Stereo Subchannel
(L-R)
Modulation.
Press the
L-R
function switch
and
the
100
%/ 0
dB
MOD/TEST
METER
ATTENUATION
switch.
The
MODULATION/TEST
meter will
indicate
the
stereo
subc
hann
el modulation
directly
in percent. A
fully
modulated
right
or
left
channel only signal will
indicate
45
%
on
the modulation
meter. A
fully
modulated
L=-R
signal will
indicate
90%
and
a
fully
modulated
L=R
signal
wi
11
indi
cate
0.
3.6. 3
Pilo
t
Carrier
Modu
l
at
ion.
Press the
PILOT
Function
sw
it
ch
and
the
10
%/ -20 dB
METER
ATTENUATION
switch.
The
MODULATION/TEST
meter will
the
pilot
modu
lation
level,
with the
100
%
mark
on
the meter
10% modulation. Correct
pilot
mod
ulati
on
level
is
between
8%
MOD/TEST
indicate
denoting
and
10%.
modulation.
3.6.4
This
measuremen
t can
be
made
in the presence
of
program
38
kHz
Subcarri
er
Suppression.
a.
App
ly a
modu
lating signal
between
5
kHz
and
15
kHz
to
the
left
channel of the
transmitter
under
test,
and
adjust
its
le
vel
to
indicate
90
%
on
the
LEFT
CHANNEL
meter.
b.
Press the
38
kHz
function switch.
c.
With
the
MOD/TEST
METER
ATTENUATION
switches,
select
an
atten
uation
that
provides a usable reading
on
the
MODULATION/TEST
meter.
The
38
kHz
subcarrier
suppression
is
then the algebraic
sum
of
the meter
reading
and
the attenuation
inserted.
For example, a
meter reading
of
-2
dB
with the -50
dB
MOD/TEST
METER
ATTENUATION
switch depressed denotes a
38
kHz
subcarrier
suppression
of
52
dB
below
100
%
modulation.
3-8
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