McMartin TBM-4500A User manual

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•
McMARTIN
INDUSTRIES, INC.
605
Norfh
13th
Street
Omaha, Nebroslca
68102
TBM-4500A
FM
STEREO
MON
1
ITOR

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I.
II.
III.
r:v.
v.
VI.
VII.
VIII.
TABIE
OF
CONl'ENI'S
Technical
Specifications••••••••••••••••••••••••••••••••••••
3
Module,
Transistor
and Diode
Complement•••••••••·•••••••••••
6
Plug-In
Modules,
Transistor
and
Diode Complement
••••••••••••
8
General
Description
•••••••••••••••••••••••••••••••••••••
••••
11
Block
Diagram•••••••••••••••••••••••••••••••••••••••••••••••
13
Circuit
Description•·•••••••••••·••••••••••·••••••••••••••••
14
Installation
••••••••••••••••••••••••••••••••••••••••••••••••
18
Operation
•••••••••••••••••••••••••••••••••••••••••••••••••••
19
Adjustment
of
Input
Level•••••••·••·•••••••••••••••••••
19
Monitoring
Total
Modulation••••••••••••••••••••••
••••••
19
Polarity
Switch••••••••••••••••••••••••••••··••·•••••••
19
Peak
Modulation
Adjustment•••••••••••••••••••••••••••••
19
Monitoring
the
Pilot
Injection••·••••••••••••••••••••••
20
Internal
19
kHz
Phase
Calibration••••••••••••••••••••••
20
Pilot
Phase
Adjustment
of
Transmitter••••••••••••••••••
20
Operation
of
Separation
Switch
•••••••••••••••••••••••••
20
Measurement
of
L
Into
R Channel
Separation
•••••••••••••
21
Measurement
of
R
Into
L Channel
Separation•••••••••••••
21-22
Measurement
of
Crosstalk
-
Stereo
Sub-Channel
Into
Main
Channel••·•••••••••••••••••••••••••••••••••
22
Measurement
of
Crosstalk
-Main Channel
Into
Stereo
Sub-Channel••·••••••••••••••••••••••••••••••••
22-23
Measurement
of
the
38
kHz
Suppressed
Carrier
Without
Modulation•••••••••••••••••••••••·•••••••••••
23
Measurement
of
the
38
kHz
Suppressed
Carrier
With Modulation (5kHz
to
15kHz)••••••••••••••••••••••
23
Measurement
of
Distortion
of
the
Left
and
Right
Channel
••••••••••••••••••••••••••••••••••••••••••
••••
24
Measurement
of
Distortion
of
Monaural
Signal
•••••••••••
24
Measurement
of
AM
Signal
to
Noise
Ratio
of
the
Transmitter••••••••••••••••••••••••••••••••••••••••••
24-25
Measurement
of
FM
Signal
to
Noise
Ratio
of
the
Transmitter••••••••••••••••••••••••••••••••••••••••••
25
IX.
Maintenance•••••••••••••••••••••••••••••••••••••••••••••••••
26
x.
Table
of
Audio
Frequencies
vs.
Percent
of
Modulation
••••••••
28
XI.
Trouble
Shooting
••••••••••••••••••••••••••••••••••••••••••••
38
nr.
Callouts
••••••••••••••••••••••••••••••••••••••••••••••••••••
39
XIII.
WarrantY••••••••••••••••••••••••••••••••••••••••••••••••••••
43
xr:v.
Parts
List
xv.
Schematic

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TECHNICAL
SPECIFICATIONS
Operating
Range
Modulation
Range
RF
Demodulator
Input
Impedance
Sensitivity
Composite
Input
Impedance
Sensitivity
Outputs
-
Left
&
Right
Audio
output
for
monitoring
circuits
Source
Impedance
Level
Distortion
Audio
output
for
distortion
measurement
Impedance
Level
Frequency
Response
Distortion
Monaural
Stereo
Noise
Level
Stereo
phones
output
Impedance
Level
- 3 -
88
-
108
MHz
+
75
kHz
deviation
-
1001.
mod.
+
100
kHz
deviation
-
1331.
mod.
50 ohms
unbalanced
0
.1
to
1
watt
S
OK
ohms
1
to
1.
5
vo
lts
pe
ak-to-pe
ak
600 ohms
balanced
+ 4 dbm@
100%
modulation
at
400
Hz
Less
than
1%
(50 -
15,000
Hz
)
lOK
or
greater
7 vo
lts
@
100%
modulation
at
400
Hz
30 -
15,000
Hz±
0.S
db
0.25% (30 -
15,000
Hz)
0.5% (30 -
15,000
Hz)
-66 db
below
100%
modulation
at
400
Hz
20K ohms
2.0
volts

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TECHNICAL SPECIFICATIONS (Cont'd.)
Outputs - Left & Right (Cont'd.)
Composite output
Source Impedance
Level
Frequency Response
Pilot Injection Circuit
Accuracy
Meter Indication
Indicator
Peak Flasher
Peak flasher meets FCC requirements
Modulation Meters
Left or Right
Total
Accuracy
Frequency Response
Meter characteristic meets
FCC requirements
Accuracy
Frequency Response
Meter characteristic meets
FCC requirements
Separation
Left into right
Right into left
67 kHz into either channel
- 4 -
300 ohms
0.30 volts peak-to-peak
50 - 100,000 Hz± 0.2 db
+ 0.5%
6 - 12%
Pilot lamp (operates at 6% injection
or higher)
Peak light adjustable to read
positive and negative peaks from
50% to 120% modulat ion
± 0.5 db
30 -
15,000 Hz± 0.5 db
± 0.5 db
30 -75,000 Hz± 0.5 db
35 db
or better (50 15,000 Hz)
35 db
or better (50 - 15,000 Hz)
-60 db or better
NOTE: SEPARATION CAN BE MEASURED
INTERNALLY DOWN TO -70 db

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TECHNICAL
SPECIFICATIONS
(Cont'd.)
Measurement
of
Suppressed
38
kHz
Carrier
Modulated
100%
with
frequencies
above 5 kHz
No
modulation
Cross
Talk
Main
to
stereo
sub
Stereo
sub-channel
to
main
67
kHz
into
main
or
stereo
Power
Requirements
Fuse
Ambient
Temperature
Range
Dimensions
Width
Height
Depth
Weight
Finish
- 5 -
Better
than
46
db
Better
than
55 db
46
db
or
better
46
db
or
better
66 db
or
better
105 -125
volts
AC,
50/60
Hz,
45
watts
0.5
amp.
slo-blo
10
-
so°
C
Standard
19
inch
rack
panel
mount
8\
inches
14
inches
overall
25
pounds
McMartin
blue
and
brushed
aluminum

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MODULE, TRANSISTOR & DIODE COMPLEMENT
Symbol
Description Function
MM-601 1 per unit Plug-in
composite amplifier
MM-602
1 per unit Plug-in amplitude correction amplifier
MM-603
5 per
unit Plug-in audio amplifier
MM-604 3
per unit Plug-in
DC meter amplifier
MM-606
1 per unit FM wide-band
demodulator
MM-607
1 per unit
Peak flasher
MM-608
1 per unit
Phase inv erter
MM-609
l per un it db
amplifier
MM-611
1 per unit 19
kHz
amplifier
MM-612
1 per u nit
19 kHz amplifier
doubler
MM-613
1 per
unit 19 kHz phasing amplifier
Q-1 SE-4010
Emitter follower
-- \ :::
SE-4001*
Right
channel amplifier
2N2102
Right
channel amplifier
Q-4 SF-4863A
Composite amplifier
Q-5
SF-4863A db
amplifier
Q-6 2N3053 db
amplif i er
Q-7
SE-4001*
Left channel amplifier
Q-8 2N2102
Left channel
amplifier
Q-9
40328
Voltage
regulator
Q-10
40328
Voltage regulator
- 6 -

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MODULE, TRANSISTOR & DIODE COMPLEMENT {Cont'd.)
Symbol
Description
Function
Q-11
40328
Voltage regulator
D-1
1N3604 Demodulator diode
D-2 1N3604
Demodulator
diode
D-3 1N3604
Demodulator diode
D-4 1N3604
Demodulator diode
D-5 1N3606
Voltmeter diode
D-6
1N3606
Voltmeter
diode
D-7 1N3606
Voltmeter diode
D-8
BY127
Power rectifier
D-9
BY127
Power rectifier
Z-1
24V
Zener diode
Z-2 36V
Zener diode
. Z-3
24V
Zener
diode
Z-L~ 24V
Zen er diode
Z-5
90V
Zener diode
Z-6
36V
Zener diode
'kSelected in production for optimum performance
- 7 -

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Q-1
Q-2
Q-1
Q-2
Q-1
Q-2
Q-1
Q-2
Q-3
PLUG-IN MODULE, TRANSISTOR & DIODE COMPLEMENT
COMPOSITE AMPLIFIER MM-601
SE-4001
2N3053
SE-4001
2N3053
Voltage amplifier
Audio amplifier
Voltage amplifier
Audio amplifier
AMPLITUDE CORRECTION AMPLIFIER MM-602
SE -4001
SE-4001
Left channel amplifier
Right channel amplifier
WIDE-BAND PLUG-IN AUDIO AMPLIFIER MM-603
SE-4001
2N2102
DC METER AMPLIFIER MM-604
SF-4863A
SF-4863A
Amplifier
Amplifier
\ of DC amplifier
~ of DC amplifier
WIDE-BAND FM DEMODULATOR MM-606
40245
40243
40245
- 8 -
Local oscillator
Mixer
Limiter

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PLUG-IN MODULE, TRANSISTOR & DIODE COMPLEMENT (Cont'd.)
Q-4
Q-5
Q-6
Q-7
D-1
D-2
D-3
Q-1
Q-2
Q-3
Q-4
Q-5
Q-6
Q-7
Q-1
Q-2
Q-3
Q-4
WIDE-BAND FM DEMODULATOR MM-606 (Cont'd.)
40245
40245
SE-4001
2N2102
lNSl
1N3604
1N3604
PEAK FLASHER CIRCUIT MM-607
SF-4863A
SE-4001
SE-4001
2N3053
SF-4863A
2N2102
2N2102
PHASE SPLITTER MM-608
2N2102
2N2102
2N2102
2N2102
- 9 -
Limiter
Lirni ter
Audio amplifier
Audio amplifier
RF doubling diode
Counter detector
Counter detector
Isolation amplifier
\ of a Schmitt trigger
\ of a Schmitt trigger
Low impedance pulse amplifier
DC amplifier
Buffer
Switching transistor
Anode follower
Phase splitter
Negative peak amplifier
Positive peak amplifier

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PLUG-IN MODULE, TRANSISTOR & DIODE COMPLEMENT (Cont'd.)
Q-1
Q-2
Q-1
Q-2
Q-3
Q-1
Q-2
Q-3
HI-GAIN AUDIO AMPLIFIER MM-609
SE-4001
2N2102
19 kHz AMPLIFIER MM-611
SE-4010
SE-4001
SE-4001
Amplifier
Amplifier
Hi-Z amplifier
Hi-Z amplifier
Emitter follower
19 kHz AMPLIFIER DOUBLER MM-612
SE-4001
2N2102
2N2102
Hi-Z amplifier
38 kHz pulse amplifier
DC relay control
19 kHz PHASING AMPLIFIER MM-613
SE-4001
SE-4001
SE-Lf001
- 10 -
Hi-Z amplifier
Hi-Z amplifier
Emitter follower

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GENERAL
DESCRIPTION
The McMartin TBM-4500A,
all
silicon
solid-state
stereo
monitor,
is
a
completely
self-contained
unit
for
measurements
of
all
modula-
tion
characteristics
of
the
FM
broadcast
station.
The
TBM-4500A
features
three
modulation
meters
for
simultaneous
measurements
of
left
channel,
right
channel,
and
total
modulation.
For
simplicity
of
operation
the
various
metering
functions
are
incorporated
in
one
switch
to
measure
all
the
important
character-
istics
of
the
stereo
signal.
These
functions
include
RF
input
level,
pilot
inj
ection,
left
channel
modulation,
L
+
R {main
channel
modula-
tion),
L - R
(stereo
sub-
c
hannel
modulation),
proper
phasing
of
inter-
nal
19
kHz
and
38
kHz
circuits,
38
kHz
carrier
suppression,
FM-S/N,
and
AM-S/N.
In
addition,
the
TBM-4500A
will
measure
separation
between
the
left
and
right
channels,
cross
talk
between
main
and
stereo
su
b-
channel,
cross
talk
between
the
67
kHz
SCA
channe
l and
the
stereo
sub-
channel
or
the
main
channel.
The
modulation
meters
are
peak
indicating
devices
capable
of
mea-
sur
ing
true
peak
value,
regardless
of
waveform.
The
right
and
left
meters
are
also
used
as
audio
voltmeters
which
are
used
to
measure
sep-
aration
between
the
left
and
ri
ght
channels,
cross
talk
between
the
main
and
the
stereo
sub-channels,
FM-S/N
and
AM-S/N.
When
the
function
switch
is
in
the
FM-S/N
or
AM-S/N
position,
the
signal
is
automatically
de-emphasized.
Also,
the
meter
is
highly
damped
in
all
the
db
positions.
With
the
separation
switch
in
the
operate
position,
the
meter
ballistics
conform
to
the
FCC
requirements.
NOTE;
TiiE
VOLTMETER
IS
PROTECTED
AGAINST
SEVERE
OVERLOAD.
The
level
is
automatically
compensated
between
the
stereo
and
monaural
mode.
When
no
stereo
is
broadcasted,
all
three
meters
will
read
identica
lly.
A
BNC
connector
located
on
the
left
side
of
the
front
panel
gives
a
true
display
of
the
modulation
present.
It
is
also
switche~
so
that
the
pilot,
main
channel,
stereo
sub-channel
or
the
composite
signal
can
be
seen
separately
depending
on
the
position
of
the
function
switch.
The
output
impedance
is
low,
minimizing
error
when
a
reasonable
length
of
cable
is
used.
A
wide-band
oscilloscope
can
be
used
to
verify
all
measurements.
Also,
a
frequency
measuri
ng
device,
such
as
the
McMartin
TBM-3005
frequency
counter,
can
be
connected
and
the
pilot
frequency
meas
ur
ed
at
any
time
without
removi
ng
the
main
channel
modulation.
The
TBM-4500A
features
modular
cons
truction;
almost
all
of
the
circuits
are
plug-in
units
for
simplified
service
in
the
field.
Each
plug-in
module
is
isolated
from
th
e power
supply
so
that
in
case
of
failure
or
short
circuit
in
any
one
unit,
it
will
not
short
circuit
the
power
supply,
disabling
the
rest
of
the
monitoring
functions,
-
11
-

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GENERAL DESCRIPTION (Cont'd.)
All the critical circuits have double regu l ation in the power
supply for added stability. All transistors are operated at one -
half or less of their rated voltage for greater reliability.
The wide - band demodulator automatically mutes if the RF input
signal falls below proper operating level, thus eliminating noise in
the monitoring s ystem in case of loss of RF input.
A high speed peak indicating light, located on the front panel,
is adjustable from 50 -120% modulation. The light remains on for a
period of two to four seconds as required by the FCC, regardless of
the duration of the overmodulation peak. A jack is provided for a
remote peak indicator light. The addition of the cable capacity will
not affect the performance. The peak indicatin g light will flash when
positive and negative peaks exceed the preset level. In addition, a
polarity switch is provided to measure modulation in both positive and
negative directions read only on the modulation meter.
An indicator light, located on the front panel, lights when the
19 kHz pilot carrier exceeds 6% main channel modulation, thus indicat-
ing stereo transmission. A phasing control , located on the front panel,
allows adjustments of the internal 19 kHz circuits for a precise zero
crossing. This may be checked at any time with or without modulation.
Two terminal strips, located on the rear of the chassis, provide
connections for aural monitoring of either left or right channel, also
fo r connection of an external distortion meter.
A composite/normal function switch, located on the rear of the
chassis, allows direct monitoring of a stereo generator, bypassing the
exciter and the transmitter's P.A. This is adjustable from 0.35 to
l.SV RMS.
Remote metering kit (RM-M45) contains the rack panel assembly, left
and right meters, total peak indicator light and remote amplifiers.
- 12 -

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CIRCUIT DESCRIPTION
The sampled RF from the transmitter is fed to the adjustable RF
input attentuator. The RF is adjusted by the RF level control , located
on the rear of the unit, to a level suitable for proper operation. The
correct level is indicated by the left meter (with the function switch
in the RF level position). Two diode rectifiers convert the RF into
a DC voltage to drive the meter. A meter reading of 100% indicates that
the proper RF level is being fed to the input of the wide-band demodu-
lator (MM-606). T his adjustment is not critical except when making an
AM-S/N reading.
The RF signal from the variable attenuator is further attenuated
by a fixed resistor which feeds the MM-606 FM wide-band demodulator.
An output from the MM-606 is fed through isolation resistor R-1 (5600
ohms)
to the input of phase splitter MM-608. A front panel polarity
switch is used to select modulation in either the positive or negative
direction as read on the modulation meter only. The output from the
polarity switch is fed to Q-1, an isolation stage used to eliminate
loading of the phase splitter. The output of Q-1 feeds R-3 (SK ohm)
calibration poten tiometer. This controls the amount of modulation fed
to the input of the wide-band audio amplifier (MM-603). The output
impedance of this amplifier is very low, suitable for feeding diode D-5,
thus charging capacitor C-4 to a peak value. This peak value ' is measured
with an extremely high input impedance VTVM type circuit. DC meter
amplifier MM-604 consists of two FET's in a balanced differential
amplifier. Modulation meter M-1 is connected between the two source
elements. Thus, the meter sees an extremely low impedance. This gives
a met er circuit with rapid rise time and excellent damping.
A second output from the MM-608 which contains both negative and
positive pulses is fed to the peak light calibration potentiometer.
This controls the level of the MM-607. The peak flasher amplifier
will respond to negative and positive modulation peaks of very short
duration. Capacitor C-10 and resistor R-13 comprise a RC time delay
which will hold the light on for at least two to four seconds, regard-
less of the length of the ovennodulation pulse. The power supply is
double regulated to insure stable operation under all conditions. A
socket is provided on the rear of the chassis for an external peak
light . The capacity of the cable will not affect the performance in
any way.
A second output from the MM-606 wide-band FM demodulator is fed
to the rear chassis switch SW-1. This switch enables the operator to
bypass the RF section of the system and sample a composi te signal
directly from the stereo generator. The signal from switch SW-1 is fed
through capacitor C-12 to the input of 19 kHz amplifier MM-611. The
low output impedance of MM-611 is fed through capacitor C-21 to the
- 14 -

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CIRCUIT DESCRIPTION (Cont'd.)
center of the stereo switching bridge. This amplifier consists of two
stages of amplification using low impedance Hi-Q coils giving high
selectivity and rejecting all frequencies excepting the 19 kHz pilot.
Another output from MM-611 is fed through capacitor C-15 to the input
of the amplifier doubler (MM-612). The output of the amplifier doubler
consists of 38 kHz pulses, which feeds L-3, a 38 kHz phasing coil.
This restores the 38 kHz pulses into a sine wave. The output of the
38 kHz phasing coil is fed through capacitor C-20 (6800 pf) to matching
transformer L-4. This transformer feeds the stereo demodulator. The
stereo demodulator circuit separates the original left and right audio
channels from the composite signal. This demodulation is accomplished
by alternately switching the incoming composite signal at a 38 kHz rate.
This switching is accomplished in diodes D-1, D-2, D-3 and D-4.
The left and right audio channels from the stereo demodulator are
fed to the amplitude correction amplifier (MM-602). The amplitude
correction amplifier corrects for the inefficiency in the switching
diodes. The left and right outputs of the correction amplifier are
fed through 15 kHz low-pass filters FL-4 and FL-5 which remove all
frequencies present above 15 kHz.
The
output of filters FL-4 and FL-5 feeds the right and left
amplifier modules. De-emphasis is accomplished by a feedback network
in each unit. A de-emphasis switch is provided in each channel by
SW-3 and SW-4 which are located on the rear chassis. The left and
right audio outputs from the two MM -603 amplifiers are fed to thei r
respective terminal boards marked Hi-Z on the rear of the chassis.
Strapping the two Hi-Z terminals gives a balanced 600 ohms output at
the 600 ohm terminals.
The right and left signals from FL-4 and FL - 5 are fed through the
function switch to the separation switch. In the operate position the
signal is fed directly to the right and left meter amplifiers (MM-603).
In any of the other positions of the switch the signal is amplified by
the audio voltmeter amplifier module (MM-609). The signal is ampli-
fied in 10 db steps as the separation switch is rotated. A maximum of
50 db gain is available.
A second output from SW-1 is fed through capacitor C- 17 (5 mfd)
to the input of the composite amplifier (MM-601). The low output
impedance of the MM-601 is suitable for driving the three filters
(Oto 15 kHz low-pass filter, 23 to 53 kHz bandpass filter and 38 kHz
bandpass filter). Potentiometers in the output of these filters allow
for calibration of the peak reading meter through the function switch
SW-5.
The
composite output circuit primarily cons i sts of Q-4, a field-
effect transistor with extremely high input impedance and a low source
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CIRCUIT DESCRIPTION (Cont'd.)
impedance. This eliminat _ es any error when a reasonable length of cable
is used in feeding an oscilloscope. The composite output is available
through a BNC connector on the front panel. This output is switched to
the output of the bandpass filters. Thus, you can view the L plus R,
L
minus R, composite, or 19 kHz pilot at any time on an oscilloscope.
The FET also gives complete isolation so that no loading is reflected
on any of the circuits.
The audio voltmeter consists of amplifiers Q-5 and Q-6 in con-
junction with R-60, R-61, R-62, R-63 and R-64. Q-5 is a FET with very
high input impedance which will not load the voltage divider, thus
minimizing error . The output of Q-6 is low which makes it suitable for
driving either the right or left meter amplifier.
To insure proper zero crossing of the 19 and 38 kHz signals, a
switch is used to measure the voltage difference that occurs betweeen
the junction of diodes D-1, D-2, D-3 and D-4. The 19 kHz pilot carrier
voltage across the demodulator diodes will be unbalanced if the phasing
is incorrect. Switching the function switch from positive pha se to
negative phase samples the voltage present on each side of the demodulator
diodes. If the voltage is equal, exact zero crossing is achieved. This
voltage is measured with the 19 kHz phasing amplifier (MM-613).
A second output from Pin No. 5 of the amplifier doubler (MM-612)
drives relay RLY-1. The relay control circuit performs the following
functions:
1. Activates the stereo pilot light PL-1.
2. Short circuits R-39 in the stereo mode and feeds a
small positive voltage which back - biases the switch-
ing diode to insure low distortion in the monaural
mode .
3. Short circuits R-44 which is the monaural calibrate
potentiometer. This increases the gain of the
correction amplifier to give exactly the same audio
output as when in the monaural mode.
Lf. Short circuits Points W& Z compensating the diode
D-5 th reshol d point. D-5 will not conduct until a
potential of 0.35 volts is applied. This corrects
for the approximate 0.3 db error when measuring a
c
omposite signal.
The audio voltmeter is automatically damped when the separation
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CIRCUIT DES CRIPTION (Cont 'd . )
switch is t urn ed to any po si tion except operate. Capaci to rs C-36 and
C-45 are shunted ac ros s the meter movement, w hich hi ghly dam ps the
meter for more precis e noi se measurement.
The ballistics of the mete rs are co ntrol led by R-6, C-3, R-59 ,
C-34, R-76 and C-44. The rise time is controlled by th ese c apacitors.
Meter decay is controlled by resistors sh unted across diodes D-5, D-6.
and D-7. The resistors are selected at the f a ctory for prope r decay.
The three DC meter amplifiers (MM-604) are stabilized by a special
balancing circuit and double regu lation i n the po wer su pply.
The power suppl y is well regula ted, using a Darlington t ype e mitter
follower employing t hree tran sisto rs and two Ze ner re f er ence vol tage
diode s . The circuit also functions as a capacity mu lt ipl ie r, el iminating
any AC rip p le in t he power su ppl y. Severa l of the plug-in amplif ie rs
are further regulated by Zener diodes. The voltage is he ld wi thin 1%
wi th the li ne voltage varying from 105 to 150 volts. Al l st ages are fed
through isolat ion resist oc.s and are all d ecoupled. An y one st age could
be sh ort circuited with o ut seriously aff e cting t he others.
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INSTALLATION
Upon r ece ipt of your TBM-4SOOA, remove it from the shipping carton
and i nspec t c arefull y f or any damage caused in transit due to rough
handli ng. If damage is found, notify the shipping agency and advise
McMa r t in In d ustri es , In corporated of such action.
The t op cover of th e TBM -4500A should be removed and the packing
materia l rem oved. An inspection of the plug-in modules should be made
to in s ur e that the y are firmly seated in their proper sockets.
The TBM-4500A sh ould be mounted where there is adequate ventilation.
Th e unit s hould n ot be mou nted above high heat producing equipment.
CAUTI ON :
TilE T EMP ERATURE SHOULD N OT EXCEED 110° F
Connect th e AC co rd to the 117 vol t AC source. Connect the RF
ca ble fr om t he p ick -up loop to the inpu t jack on the rear of the
chassis.
CAU TI ON:
DO NO T EXCEED 1 WATT RF INPUT
The TBM-4 500A h as been thoroughly checked and calibrated prior to
sh ipment and sh ould require no adjustment . However, after the unit has
be en insta l led, t he f ollowing checks should be made.
1. Check t
he mechanical zero setting of each meter before
turni ng the monitor on .
2. T urn po wer on and allow sufficient time for stabiliza-
tion. The monitor has extensive filtering and requires
some time for stabilization .
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OPERATION
ADJUSTMENT OF RF INPUT LEVEL:
CAUTION: BEFORE APPLYIID RF INPUT, TURN THE RF LEVEL CONTROL
TO MINJMUM. Slowly adjust RF level for a reading of 100% on
left meter (with function switch in RF level position). If the
meter tends to reverse when increasing the level control, this
indicates too much RF applied to monitor.
NOTE: MONITOR NEED NOT HAVE AC POWER APPLIED FOR THIS ADJUSTMENT
This is the only adjustment required for monitoring the RF
output of the transmitter.
CAUTION: THE COMPOSITE INPUT LEVEL CONTROL MUST BE FULLY CLOCK-
WISE AND FUNCTION SWI'.OCH IN NORMAL OPERATION POSITION.
The unit is now ready for operation. If the station is trans-
mitting monaural, all three meters will read the same. One-hundred
percent modulation reading is equivalent to ±75 kHz deviation of the
transmitter. The center meter will read total peak modulation at all
times.
MONITORIID TOTAL MODULATION:
Total modulation may be read on the center meter at all times.
POLARITY SWITCH:
The switch may be left in either the positive or negative posi-
tions, as the peak flasher automatically will respond to positive and
negative peaks.
PEAK MODULATION ADJUSTMENT:
This adjusts the overmodulation peak indicator, and should never
be set to exceed 100%. This is the most important function of the
monitor. The peak light will remain on for at least two seconds every
time overmodulation occurs, in either positive or negative direction.
SPECIAL NOTE: With normal broadcast program material, it will not be
uncommon for the peak flasher to light at a 100% setting while the
total modulation will average about 50 to 70"/, on peaks. The peak
flasher will catch modulation peaks which are much too short for complete
meter response. THE PEAK LIGHT MUST BE THE PRIME SOURCE OF INDICATIN:;
OVERMODULATION •
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OPERATION
(Cont'd.)
MONITORING
THE
PILOT
INJECTION:
If
the
station
is
transmitting
stereo,
place
the
function
switch
in
the
pilot
injection
position,
then
adjust
the
pilot
injection
of
the
transmitter
to
get
the
desired
injection
(8-10%
is
required
by
the
FCC),
read
on
the
upper
scale
of
the
left
meter.
(The 19 kc
pilot
may
be viewed on a
scope
through
the
BNC
connector
on
the
front
panel).
Return
the
function
switch
to
the
operate
position.
INTERNAL
19
kHz
PHASE
CALIBRATION:
A
19
kHz
pilot
carrier
must be
present
and
adjust
to
approximately
1Cil,
injection.
Turn
the
function
switch
to
positive(+)
~base
and
note
the
reading
on
the
left
meter.
Switch
to
the
negative(
- )
phase
posi-
tion.
If
the
two
readings
are
not
identical,
adjust
the
phase
control
located
on
front
panel
while
swit
ching
between
the
readings.
Exact
zero
crossing
or
perfect
phase
occurs
when
the
positive(+)
and
negative
(-)
readings
are
equal.
This
function
may
be checked
at
any
time
with
or
without
modulation.
It
is
suggested
that
this
be done
daily
to
insure
accurate
monitoring,
PILOT
PHASE
ADJUSTMENT
OF
TRANSMIT.I'ER:
The
internal
19
and
38
kHz
phasing
of
the
monitor
must be
adjusted
before
making
any
phase
adjustment
in
the
transmitter.
Applying
equal
out-of-phase
signals
(L=
-R)
(80
-100 Hz)
to
the
left
and
right
input
of
the
transmitter.
Adjust
the
pilot
phase
of
the
transmitter
for
maxi-
mum
reading
on
either
left
or
right
meter.
If
a good wide-band
oscillo-
scope
is
available,
t
he
adjustment
ma
y be
verified
by
connecting
a low
capacity
cable
to
the
BNC
connector
located
on
the
front
panel.
CAUTION:
IF A
COMPENSATED
PROBE
IS
USED,
CARE
MUST
BE
TAKEN
TO
SEE
THAT
IT
IS
PROPERLY
ADJUSTED.
NOTE:
IT
IS
D1PERATIVE
THAT
CORRECT
PHASE
IS
MAINTAINED
AT
ALL
TIMES.
The
display
should
resemble
Figur
e
6A
.
The two
points
in
the
dia-
mond
should
coincide.
Figure
6B
sho
ws
incorrect
pilot
phase.
OPERATION
OF
SEPARATION
SWITCH:
The
separation
switch
is
in
effect
an
audio
voltmeter
calibrated
in
10 db
steps.
Turning
the
switch
to
either
the
left
or
right
increases
the
g
ain
10 db
in
each
position.
However,
the
high
gain
amplifier
is
auto-
matically
switched
to
the
appropriate
left
or
right
meter.
An
example
for
reading
s/N
ratio:
If
the
met,er
reads
-3
db
in
the
50 db
positio
n,
the
noise
ratio
would
be
-53
db below
10C/1,
modulation.
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