TFT EBS 760 Series Service manual

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,
operating
and
Service
Ma
,
nua
:1
EBI
IYITEffl
fflODEt
760
TIMEAND FREQUENCY
TECHNOLO,
GY,
INC.

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Warranty
TIME & FREQUENCY TECHNOLOGY, INC. , warrants each of the in-
struments of its manufacture to be produced to meet the specificationsdelivered to the
BUY ER: and to be free from defects in mater ial and workmanship and will repair or
replace, at its expense, for a period of one year from the date of delivery of equipment,
any parts wh i ch are defective from faulty material or poor workmanship.
I
nstruments found to be defective during the warranty periodshall be returned
to the factory with transportation charges prepaid by BUYER. It is expressly agreed
that replacement and repair shall be the sole remedy of BUYER with respe ct to any
nonconforming
equipment and parts thereof and shall be in lieu of any other remedy
available by applicable
law . All returns to the factory must be authorized by TFT ,
prior to such returns. Upon examination by the factory, if the instrument is found to be
defective, the unit will be repaired and returned to the BUYER , with transportation
charges prepaid by TFT.
Transportation charges for instruments found to be defective within the first
th i rty (30) days of the warranty period will be paid both ways by the TFT.
Transportation charges for warranty returns, wherin failure is found not to be
the fault of the SELLER, shall be paid both ways by the BUYER.
This Warranty does not apply to instruments which, in the opinion of the
SELLER , have been altered or misused.
NO OTHER WARRANTY IS EXPRESSED OR IMPLIED . TFT IS NOT
LIABLE FOR CONSEQUENT I AL DAMAGES.
Claim for Damage in Shipment .
Your instrument should be inspected and tested as soon as it is received. The
instrument is insured for safe delivery. If the instrument is damaged in any way or fails
to operate properly, file a claim with the carrier, or if insured separately, with the in-
surance company.
WE SINCERELY PLEDGE OUR IMMEDIATE AND FULLEST COOPER-
ATION TO ALL USE RS OF OUR PRECISION ELECTRON IC
I
NS TRUMENTS.
PLEASE ADVISE US IF WE CAN ASSIST YOU IN ANY MANNER.
fflEffL
TIME AND FREQUENCY
TECHNOLOGY, INC.
3000 Olcott St.
Santa Clara, CA 9 5 051
40 B -2 4 6- 6 365
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' .
IMPORTANT
MODEL
NO . 760
REVISION A
Effective Serial No. 1000
MODEL 760 MANUAL CHANGES
2. 4 Antenna Installation
Delete Resistor
Figure 6-2 AM Receiver (Schematic only)
AD:p X 100 KHz,.
~ 1MHz and Xl.0 KHz to S1 as Shown
SI
XIOOKt\z I
: I
XI Ml-12. .
8
4
2.
I
XI -z.
•, · .·.
•· •l
, Figure 6-3 ., 1 FM Receiver (Schematic only) .
1 , • •
ADD: Line from the junction of Zl-6 ' and R43 to center tap of L3
·' ! -'.
Figure 6-:-4 Tone Generator (Schematic & Material List)
. ,Change: . C2 lO00pf Part No. 1005-1000 to a 1200pf Part No. 1007-0012
Figure 6-5 Tone Decoder (Schematic & Material List)
REMOVE: Fl a 2A Slo Blo Fuse, Part No . 1900-0002,
Replaced with a jumper
Figure 6-6 Dual Purpose Decoder (Schematic & Material List)
REMOVE: Fl a 2a Slo Blo Fuse, Part No. 1900-0002, replaced
with a jumper
CHANGE: P . C. Board No. 6609-0970 to 6608-0970
CHANGE: Switch
Sl, reverse nomenclature of LISTEN/OPERATE
CHANGE: On Material List Z3 to a 74132 Part No. 1100-4132
CHANGE: On Schematic C27 from a 7000µf capacitor to a8000µf
capacitor

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-.,,,--,.._
IMPORTANT
MODEL 760 MANUAL CHANGES
MODEL NO. 7G0
REVISION B
Effective Serial No . 1000
2. 4 Antenna Installation
Figure 6-2
Sl
Figure 6-3
Figure 6-4
Figure 6-5
Figure 6-6
Figure 2-1
Delete Resistor
AM Receiver (Schematic and Material List)
ADD X 100 KHz, X 1MHz and XlO KHz to Sl as Shown
8
4
2
I
')(\00 1(1,1-z.
t
')(.\MHZ.8
4
'l
I
X 10 \(~?.
Change: Ql 40841 Part No. 1271-4084 to a 40673 Part No. 1271-4067
Change: R14 330Q Part No . 1065-0330 to a 240 QPart No. 1065-0240,
factory select.
FM Receiver (Schematic only)
ADD:
Line from the junction of Zl-6 and R43 to center tap of L3
Tone Generator (Schematic & Material List)
Change: C2 l000pf Part No. 1005-1000 to a 1200pf Part No. 1007-0012
Tone Decoder (Schematic & Material List)
REMOVE: Fl a 2A Slo Blo Fuse, Par t No. 1900-0002,
replaced. with a jumper
Dual Purpose Decoder (Schematic & Material List)
REMOVE: Fl a 2A Slo Blo Fuse, Part No . 1900-0002, replaced with
a jumper
CHANGE: P, C. Board No. 6609-0970 to 6608-0970
CHANGE: Switch Sl, reverse nomenclature of LISTEN/OPERA TE
CHANGE: On Material List Z3 to a 74132 Part No. 1100-4132
CHANGE: On Schematic C27 from a 7000µf capacitor to a 8000µf
capacitor
CHANGE: As Shown Below
TFT MODEL 760
K1: POTTER & BRUMFIELD R10-E1-Y2-
V185. TOTAL RELAY CURRENT
MUST NOT EXCEED 250 mA .

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-
..........
APPLICATION
BULLETIN:
75-02
TO:
Model 760 EBS
System
Users
FROM:
F.
Stolten,
Customer
Service
Manager
DATE:
December
15,
1975
SUBJECT:
Automatic
Reset
of
Two-Tone
Generator
TFT
has
recently
received
inquiries
from
the
field
requesting
information
on
how
to
modify
the
Model
760-04
Two-
Tone
Generator
to
make
the
RESET
automatically
function
after
the
23. 5
second
two-tone
transmission
period.
This
change
is
desired
because
some
broadcasters
want
to
make
EBS
announcements
on
their
nprmal
program
line
and
thus
do
not
want
to
manually
reset
the
Two-
Tone
Generator
after
each
tone
transmission
before
making
Emergency
announccments
-
-or
maybe
forget
to
reset??
There
are
several
ways
to
implement
the
automatic
reset.
. One
way
is
to
modify
the
generator
directly.
This
is
done by
removing
C20,
lµf,
and
placing
a
0.
22µ.f
capacitor
between
Z3
pin 11 and
Zl
pin
13.
An
alternate
approach
to
automatically
rcsef
the
generator
would
be:
1.
Do
not
route
the
normal
program
audio
through
Kl
on
the
Two-Tone
Generator.
2.
Connect
a
pair
of
lines
from
the
AUDIO
OUTPUT
terminals
of
the
Two-
Tone
Generator
to a
mixer
on
the
audio
console
.
.
This
would
inject
the
,
two-tone
's
on
the
program
iine
without
interrupting
it.
However,
the
Generator
must
be
reset
either
manually
or
automatically
before
the
next
tone
transmission.
. ;
..
.
.
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':-,
.
',J;
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Sect.Ion '1
Table af Cant:ent:s
caeneral Informal.Ion
1.1 General Description ...................................... . ............... .
1.2 Specificaitons ................... .... ... .......... .... .... . ............... .
7.2.1 Model 760-07 AM Receiver ...... . ...................... ... ...... . ....... .
1.2.2 Model 760-02
FM Receiver . ...... . .. . .......... . ........ . . .. ... . ......... .
7.2.3 Model 760-03 Tone
Decoder ............. . ...... . .. . ... . . . .. . ... . ......... .
Page
1-1
1-1
1-1
1-1
1-2
1.2.4 Model 760-04 Two-Tone Generator...... . . . .................... . ... ...... . .. 1-2
7.2.5 Model 760-05 Dual Purpose Decoder.......... . ................. . . . .......... 1-2
Sect.Ion 12 lnat.allat.lon
2.1 Unpacking and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.2 Power Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.3 Installation and Hookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.3. 7 Receiver AM or FM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.3. 7d External Carrier Fail Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.3.2 Two-Tone Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.3.2b Combined AM/FM/TV Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . 2-1
2.3.3 Tone Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.3.4 Dual-Purpose Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
2 .4 Antenna Installation
2-4
Sect.Ion 3 Dperaclon
Sect.Ion 4
Section 15
3.1 General ...... ... . ... .... . ......... . ............ . .... ... . . ............... .
3.2
AM Receiver ................... . . ........ . ............ . ...... . ..... ..... .
3.3 FM Receiver ......... . .... . ... . .... . . . .................. . .......... . ..... .
3.4 Two-Tone Generator ... . ......... . . . . . . .......... . .... . . . . .. ............ . .
3.4.1 Basic Operation ........ . .............. . ...................... .. ........ .
3.4.2 Remote Control .
...... . .......... .................. ........... . . . .. ..... .
3.4.3 External Audio Switching .
............ ... . . ..... ............. . ... . .. . . . ... .
.3.5 Tone Decoder ................................... . ...................... . .
3.6 Dual Purpose Decoder .. . ...... . ..... ........... .. ..... ................. . .
Theory of 0peraclon
4.1 System ....................... . ........ . ........ . ...... . . . .... . .......... .
4.2
AM · Receiver ............................................................ .
4.3 FM Receiver ....... . ......... . ... .... ... . ............... . . .. ...... . .. . . . . .
4.4 Two-Tone Generator ................ . . . ........... . .. . .... . ...... ... ..... .
4.5
Tone Decoder .................................. . .............. . ......... .
4.6
Dual Purpose Decoder
Malncenanca
5.1 General ................... . .......... . .... . ..... . .................... ... .
3-1
3-1
3-1
3-1
3-1
3-1
3-1
,3-1
3-2
4-1
4-1
4-1
4-1
4-2
4-2
5-1
5.2 Periodic Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5. .3 Performance Checks........ . ........................ . ........... . . .. ... . .. 5-1
5.3.1
AM Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.3.2 FM Receiver............ . ........................ . . . . ........... . ...... 5-1
5.3.3 Tone
Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.3.4 Two Tone Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . 5-1
5.3.5 Dual
Purpose Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
Section B Schematic Diagram•
6.1 Block Diagram
6.2 AM Receiver
.,.......,.,_ *6.3 FM Receiver
6.4 Two-Tone Generator
6.5 Tone Decoder
*6.6 Dual Purpose Decoder
*These Diagrams are only included when applicable.

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Section 1
General Information
1.1 General Description.
The TFT EBS System is designed to meet the
FCC Two-Tone EBS interstation signal ing require-
ments. It normally consists
of three modules- the model
760-04
Two-Tone Generator, the Model 760-01 AM
Receiver or the Model 760-02 FM Receiver, and the
Model 760-03
Tone Decoder- mounted in a cabinet for
installation in a 19-i
nch relay rack.
1.2 Specifications.
EBS Cabinet Assembly
Module Capacit y .............. . ..... .... .
Input Power* .... , . . .. . ... . .... . ... .. . . . .
Operating Temperature* ......... . ... . . . . .
Operating Humidity* ................ . ... .
Size
..... .. ..... .... . ...... . ...... ... .. .
Weight .
...... . . .. .............. . . . ... . .
7. 2. 7 Model 760-07, Frequency-Synthesized AM Recei ve r
FrequencyRange ...... . .... . .... .. .. . . . . .
Local OscillatorStability
............. • . . ..
Tuning Method ... ............ . ....... . . .
Antenna Input ........... . .............. .
Sensitivity .
... ................ .. . . .. .... .
Image Rejection
...... . ................. . .
AGC .. ......... . ...... . ....... . ....... .
IF Bandwidth, 6dB . . ... . .... ... . . .. ..... .
Harmonic Distortion ... ... .. ..... . . ...... .
Noise
... . ...... .. . ................. . . . . .
Audio
Outputs , 600 ohms ............... . . .
Carrier-Off Output .. . . . ... . . ......... , .. .
7.2.2 Model 760 - 02, Crystal Controlled FM R ece i ver
FrequencyRange . , ....... . . ............ . .
Channel Frequency . .
.... ... .......... . .. .
Antenna Input . .... . ... .. . . ... ...... ... . .
Sensitivity
.... ....... . .. •. ... . .......... .
IFBandwidth, 6dB ... . .. . ............... .
Image Rejection
..... ... . . . . ....... . ... . . .
AGC . ...... . ..... ................ . .... .
Audio Frequency Response
..... . .... ... ... .
Harmonic Distortion ..................... .
S/N Ratio ........ . . .. ... .. ... . . . ....... .
*Specifications apply to all system modules.
1-1
An emergency two-tone signal received from the
AM or FM station being monitored will be heard on the
EBS System speaker after such a tone has been received
for
at least 8 seconds. The EBS System provides the
means for interruptingnormal
programming and broad -
casting the two-tone emergency signal for 23.4 seconds,
and for inserting emergency announcements. Normal
operation can be restored by operation of two reset
switches.
willaccept
up to three EBSmodules (Models 760-01, -02,
-03, -04,
and -05). Blank panels are provided when fewer
th
an three modules are in use.
117
VAC ± 15 %, 50/60 Hz , 20 watts maximum.
0 °
to 50 °C.
95% Relative..
3.5" (8.9 cm) high x 19" (48.3 cm ) wide x 12" (30.5 cm)
deep.
Approx. 10
pounds (4 .5 kg)
540-1620
kHz
±500 Hz per year
Channel frequency digitally set m 10 kHz steps by
thumbwheel switches.
75 ohms nominal, unbalanced.
30 µ V for 20 dB S/N at 30% modulation.
SO dB
70 dB
±5 kHz
Less than 3% at 90% modulation.
45
dB or greaterbelow100%modulationwith 10 MV RF
Balanced: +8 dBm. Unbalanced: 1 V rms
Active pullup to 10 V, 10 ma
88-108 MHz
Speci fy frequency, either one or two channel versions
available.
75 ohms nominal, unbalanced.
2 µ V for 30 dB
of quieting.
±150 kHz
40 dB
80 dB
±1 dB, 50 Hz -15 kHz
1%
60 dB or greater below 100% modulation at SO µV RF
i nput

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De-emphasis .......................... . . .
Audio
Outputs, 600 ohms .... . .. . ......... .
Carrier-Off Output ............ . .. . ... ... .
1.2. 3 Model 760-03, Two-Tone Decoder
Input Le vel Requir ed .. ..... ...... .. ..... . .
Tone Frequencies"'* ....... .. ..... . ...... . .
Bandwidth**
..... ..... ...... . . .... ..... .
Listen
Operate Switch ......... . .......... .
Audio
Output .............. . .. . .... . .. .. .
Re set Switch ........................... . .
Remote Operation ....................... .
Time DelayforDe-muting"'* . ... . ......... .
External
Alarm Cont ra cts ................. .
1.2 .4 Model 760-04 , Two-Tone Generator
Output Frequencies"'* . . ...... .. .......... .
Frequency Accuracy*"'
................... .
Output Level ........... . ..... . .. . ...... .
Output Impedan ce ............ .. ........ .
Harmoni c Distortion"'* ......... . ......... .
Tone Duration•• .... .......... . ....... .. .
Tone Level Adjust** ............. . ....... .
Program Audio Routing
..... . .. .. ..... ... .
Emergency
Program
Audio I nput ... . ................ ...... .
Test Switch ... . ........... . ............ . .
Tone Switch ...... . ..... ....... . . . . ..... .
Command Switches ... • ...................
ResetSwitch , ....... . ................ .. . .
Remote Operation . . . • ........ . . ..........
l.2.5 /lfudel 760-05, Dual-Purpo se Decoder
75 µ sec
Balan ced: +8 dBm. Unbalanced: I V rms
Active pullup to IOV, 10ma.
l00 mV into 600
ohms
053 Hz and 960 Hz
±5 Hz
In Operate mode the loudspeaker is muted until an EBS
alert is decoded.
fn Listen mode,
the loudspeaker is demuted .
I
Watt, in ternal loudspeaker
Resets
decoder and mutes loudspeaker
The RESET switch wiring is brought out to the rear
panel.
12 seconds ±4 seconds
SPOT relay contacts brought out to rear panel.
853
Hz and 960 Hz
±0.25 Hz , crystal controlled
+8 dBm nominal (per tone)
600
ohms, balanced
Less th~n 2%
23.4 seconds,
±0.15 seconds
Front panel pot, -2 dBm to +8 dBm
Rear panel DPDT relay contacts. Balanced input and
output. Switchover and latch to EBS programming is
automatic.
Unbalanced input. Internally inserted into program line.
Connects
Generator to De coder for testing without inter-
rupting program audio.
Enables one tone at a time for setting level and checking
distortion.
2 toggle switches.
Must be activated in opposite direc-
tions
to turn on Generator .
Releases
latch to restore normal program audio.
The COMMAND and RESET switch wiring is brought
to the rear panel.
See M ode! 760 - 03, T wo -Tone Decoder for Two- Tone Spec1fications
CarrinBrf'ak/ J(XX} H{Speczfzcations:
Input Le vel Required ................... .. .
Tone
Fr equency ... .................... . . .
B
andwidth ..... . ...... ............ . . ... .
Time to demute after start of Carrier
Breaksequence ............. .. ....... . . .. .
RE SET switch ........................ .. .
Listen/Operate Switch . ........ ........ . . .
Audio
Output ............. . ........... . . .
Remote
Operation . . ............. . ....... .
External Alarm
Contacts ...... . .. .. ....... .
100 mV into 600 ohms
1000
Hz
±50 Hz
23 to 27 sec.
Resets decoder
and mutes loudspeaker.
fn
Operate mode the loudspeaker is muted until an EBS
alert is decoded. In List en mode the loudspeaker is
demuted.
1
Watt , internal loudspeaker
The RESET switch is brought out to the rear panel.
SP
OT relay contacts brought out to rear panel.
Specifications
are typical except those identified by ** which are guaran teed.
1-2

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Section 2
Installation
2.1 Unpack ing and Inspection.
Upon receiving the instrument, inspect the
packingbox and instrument forsi gns of possible sh i pping
damage. Operate the instrument in accordance with the
procedures of Section3 of this manual. If the instrument
is damaged or fails to opera te properly, file a claim with
the t ransportation company, or with the insurance com-
pany if insured separate ly.
2.2 Power Requirements.
The Model 760 EBS System operates from a
117-volt Ac Source.
The line frequency must be between
50
and 60 hertz. Maximum power requ i red is 20 watts.
2.3 Installation and Hookup.
When the EBS System Cabinet assemb ly is
mounted in a 19-inch relay rack with all modules in
place,
make the following connections to the module
terminalstripsat the rear of the cabinet. Afterall connec-
tions have
been made, plug the power cord into a 117-
volt, 60-hertz source.
There is no power switch in the
system: it is energized wheneverits power cord is plug g ed
m.
2.3.7 R eceiver AM or FM.
2.3.2
ii- a. If an AM or FM Receiveris installed, connect
a 75 ohm coax cable from the antenna to the
rear-panel ANTENNA connector.
,.~ b. Connect the rear-panel UNBAL AUDIO
terminal to the DECODER AUDIO I NPUT
terminal.
c. If desired, the rear-pan el BALA NCE D
AU DIO t erminals can be connected to a
monitor or other device. Output at these
terminals is +8dBm at 600 ohms for 100%
modulation.
d. ff a remote indication of car rier fail ure is to
be provided, connect the rear-panel CARRIER
FAIL termina l to the remote indicator. Output
from th is terminal is+ 10 volts @ 10 ma for
normal carrier level, and O volts wi th 5 ma
current sinking for car rier failure. For operating
an external carrier fail ala rm relay, see Figure2-
1 for suggested circuit. Total external relay
current must not exceed 250 ma.
Two- Tone Generator.
a. If the monaural program audio is to be
looped through the Two - Tone Generator,
connect the program input line to the rear -panel
AUDIO IN terminals and connect t he program
output li ne to the rear-panel AUDIO OUT
term inals.
b. If the program line is not to be looped
2-1
TFT MODEL 760
EXTERNA
AUDIO
RELAY
K1: POTTER
Ii BRUMFIELD R10-E1- Y2 -
V185. TOTAL RELAY CURRENT
MUST NOT EXCEED 250 mA.
Fi gure 2 -1
through the Two -T one Generator, or if
combined AM/FM/TV program audio is to be
controlle d, external circuitry like that
diagrammed in Figure 2-2 is recommended.
Relays
Kl, K2, and K3 shown in Figure 2-2
should have 12 - vo lts coils, and the total coil
current must not exceed 250 milliamperes.
Relay power
and EBS audio input come from
connect
or J2 on the rear panel of the Two -T one
Gene ra tor .
c-~ c. Connect a wire from the rear-panel TEST
OUT terminal to the DECODER TEST
INPUT terminal. This provides a means to test
the Two -T one Generator and Tone Decod er
together without interrupting the program.
o '-'- d. Connect t he emergency announcement
audio line (unba l anced) to the rear -panel AN
INPUT terminal.
i~ e. ff remote control of the command and reset
functions is desired,
connect the rear - pan el
COMMAND and RESET terminals to remote
switches.
Groundi ng the se lines activates the
functions.
NOTE: Pursuant to Section 73.940 (j ) of the FCC Rules &
Regulations, the remotely located command switch must be guarded
such as to prevent accidental operation .
2. 3.3 Tone decoder.
ti\L a. Connect the rear-panel AUDIO INPU T
terminal
to the REC EI VER UN BAL AUDIO
as previously stated in Subsecti on 2.3.1 b or to
another EBS monitor receiver if used. The
sentitivity of the Tone Decoder is factory
adjust ed so that a 100 per cent modulatedsignal
(+8 d Bm at the DECODER AU DIO I NPUT
terminal) will produce 10 vo l ts peak - to - peak at
the rear-panel LEVEL terminal when used with
---------
-

www.SteamPoweredRadio.Com
,..,...........
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www.SteamPoweredRadio.Com
a TFT Model 760-01 or Model 760-02 Receiver.
If a different receiver is used, the audio input
should not be less
than 250 mV rms for a 100%
modulated signal (100mV rms for 40% modul-
ation),
and internal potentiometer R6 can be
adjustedfor
10 vol ts peak-to-peak at the LEVEL
terminal.
ef" b. Connect the rear-panel TEST INPUT
terminal to the GENERATOR TEST OUT
terminal as described in Subsection 2.3.2c.
c.
If remote control of the Tone Decoder reset
function is desired, connect the
rear panel
RESET terminal to the remote switch.
Grounding the RESET terminal effects a reset.
d. If a received two-tone signal is to actuate a
stat i on alarm , connect the alarm device to the
rear-panel
DECODER RELAY terminals. The
normally open and normally closed contacts of
the internal
alarm relay together with the relay
common, are internally connected to these ter-
minals.
2.3.4 Dual Purpose Deco der.
The Model 760-05 EBS Dual-Purpose Decoder
operates
on boththe EBS signalto be used afterApril 16,
1976, and t
he EBS signal used before that date.
After
the new EBS goes into effect, it is impor-
tant todisable thecircuitwhichwas used to detect theold
EBS signal by removing Resistor R46 from the module.
The board on which this Resistor is mounted is marked
"CUT" in two places to facilitate the removal.
2-3
a. Connect the rear -panel AUDIO INPUT
terminal to the RECEIVER UNBAL AUDIO
or to another EBS monitor receiver ifused. The
sensitivity of the Tone Decoder is factory
adjusted so that a 100-percent modulated signal
(+8 dBm at the Decoder AUDIO I NPUT
terminal) will produce 10 volts peak-to-peak at
the rear-panel DECODER LEVEL terminal
when used with a
TFT Model 760-01 or Model
760-02 Receiver.
If a different receiver is used,
the audio input should not exceed 5V rms,
and
internal potentiometer RS can beadjustedfor 10
volts peak-to-peak
at the LEVEL terminal
(signal should be adjusted just into limiting).
b. Connect the rear-panel TEST INPUT
terminal to the GENERATOR TEST OUT
terminal.
c. If remote control
of the Tone Decoder reset
function is desired, connect
the rear - panel
RESET terminal to the remote switch.
Grounding the RESET terminal effects a reset.
d. If a received two-tone signal is to actuate a
station alarm, connect the alarm device to the
rear-panel
DECODER RELAY terminals. The
normally open and normally closed contacts of
the internal alarm relay, together with the relay
common , are internally connected to these
terminals.
e. Connect the rear-panel CARRIER FAIL
terminal to
the CARR IE R FAIL terminalof the
Receiver.
,,.-...

www.SteamPoweredRadio.Com
,,--...__
,,..--.,,
1/2
11
Threaded Union
or
11
U11 Clamp
Antenna Suggested
per drawing at right
Mounting
Surface
3T
To 75Q
Load
Tune C so that antenna
resonates at desired freq.
1600 kHz C~30pf
540 kHz C~600pf
Model 760 Rear Panel
2.4 Antenna Installation
If a local FM antenna is not available, any conventional FM or TV antenna is satisfac-
tory.
If a local AM antenna is not available, an end-fedlongwire antenna (approximately250ft.)
can be used with good results. One end of the long wire should be connected at the rear-panel
ANTENNA connector
For moderately strong signal areas, the above illustration is an alternative to the long-
wire
antenna.
2-4

www.SteamPoweredRadio.Com
Sect:ian 3
Operation
3.1 General.
After the installation procedures of Section 2
have been
carried out, the EBSSystem is ready for oper-
ation.
The system is energized whenever the power cord
is plugged into an
appropriate power receptacle. Figure
3-1, the EBS System front panel, illustrates the controls
and indicators referred to in the following paragraphs.
When
an emergency two-tone signal is received
from the stationto which the receiveris tuned,
and when
the tone is present for at least 8 seconds, the speaker will
be demuted, allowing the two-tone signal to be heard.
The operator can then transmit the two-tone emergency
signal by moving the handles
of the two COMMAND
toggle switches in opposite directions. This will inter-
rupt normal programming, transmit the tones for 23.4
seconds,
and allow emergency announcements to be
tr
ansmitted. At any time after operating the
COMMAND switches, the operator can resume normal
programming by moving the
RESET /TEST switch to
RESET. He can also mute the speaker by operating the
Tone Decoder RESET switch.
Detailed operating instructions for each module
are presented in Subsections 3.2 through 3.6.
3.2 AM Receiver.
a. Dial in the desired frequency on the thumb-
wheel switches. These switches indicate the
frequency in tens of kilohertz.
b. Tune the preselector for the best signal as
determined by maximum speaker volume with
the
Tone Decoder LISTEN/OPERATE switch
in the LISTEN position, and by the CAR R lamp
being lighted.
3.3 FM Receiver.
a. Press the channel selector switch for the
desired channel, if ordered with two channels.
The single channel receiver is fixed tuned to the
specified channel.
b.
The CARR lamp must be lighted, indicating
sufficiently strong signal for satisfactory oper-
ation.
3.4 Two Tone Generator.
3.4.7 Basic Operation.
a. Check that the POWER lamp is lighted,
indicating
that the Two-Tone Generator is
receiving DC power from the Tone Decoder.
b. To transmit an emergency signal, operate
the two COMMAND switches in opposite
directions as indicated by thearrows on the front
panel.
The COMMAND lamp should light,
indicating
that the dual-tone audio signal is
being delivered to the
transmitter for a period of
23.4 seconds. At the end of the tone period,
emergency announcements
can be made on the
audio circuit connected to the rear-panel AN.
INPUT terminal.
c. To restore normal programming, move the
RESET /TEST switch to the RESET position.
d. To test the operation of the Two-Tone
Generator with the Tone Decoderwithout inter-
rupting normal programming, move the
RESET /TEST switch to the TEST position.
The Dual-tone signal should be present at the
speakerfor 23.4 seconds, with
the Decoderin the
listen mode.
e. To test the tones separately, move the 853
Hz/OPERATE/960 Hz switch to the desired
tone position.
The tone should be heard on the
speaker
as long as the switch is held in the
selected posiiton.
f. The GAIN control allows adjustment of the
Two-Tone Generators' two-tone audio output to
interface with the stations audio system.
3.4.2 Remote Control.
Both the COMMAND and RESET functions
can beremotely controlledif the connectionsdescribed in
Subsection2.3.3ehavebeen made. Operating the remote
COMMAND switch performs the same functions
described in Subsection3.4.1a,
and operating the remote
RESET switch is the same as operating the front-panel
RESET switch as described in Subsection 3.4.1b.
NOTE: Pursuant to Section 73.940 (j) of the FCC Rules &
Regulations, the remotely located command switch must be guarded
su ch as to prevent accidental operation.
3.4.3 External Audio Switching.
If audio switching is to be accomplished ex-
ternally be means ofcircuitrylike
that of Figure2-2, move
the
AM/FM/TV /OPERATE switch to either AM
TEST , FM TEST , or TV TEST to test these circuits
individually.
3.5 Tone Decoder.
The POWER lamp shouldbeon, indicating that
DC power is available from the Tone Decoder power
supply. When the
LISTEN/OP ERATE switch is set to
OPERATE , the speaker circuit will be muted until a
dual 853
Hz/960 Hz tone is received for 8 seconds, at
which time the sepaker circuit will be enabled and the
alarm relay will energize. This condition will exist until
the RESET switch is operated, at which time thespeaker
circuit will again be muted
and the alarm will de -
energize.
When the
LISTEN/OPERA TE switch is set to
LISTEN the speaker is demuted an d incoming audio is
continuously monitored.

www.SteamPoweredRadio.Com
----.
.3.6
Dual
Purpose
Decoder
The
POWER
lamp
should
be
on
, indicating
that
DC
power
is
avail
able
from
the
Tone
Decoder power
supply.
Wh
en
the
LIST
EN/
OPER
ATE
switchis
set
to
OPERATE
,
the
speaker circuit will
be
muted
until
an
EBS signal is received.
Thi
s will enable
the
speaker
circuit
and
the
alarm
relay will energize.
This
condition
will exi
st
until
the
RESET
switch
is
oper
ated,
at
whi
ch
time
the
spea
ker circuit will
aga
in
be
muted
and
the
alarm
relay will
be
deenergized.
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Section
4
Theory
of
Operation
4.1
System.
(
Bl
ock Diagram: Figure 6-1)
The
received si
gna
lis demodulated
in
the
AM
or
FM
Receiver,
and
the resulting
audio
is
app
lied to
the
Tone
Decoder.
ff
an
EBS emergency signal is present
(853
Hz
and
960
Hz
tones present simultaneously for
at
least 8seconds), the
Tone
Decoderdemutes itsspeakerso
that
the
audio
can
be
heard
,
and
e
ner
gizes a relay to
actuate
an
external alarm.
The
station's
program
audio
is normally fed through closed relaycontacts in
the
Two
-
Tone
Generator. However, when
the
COMMAND
switches
are
closed,
the
program
is interrupted, the EBS
two-tone signal
is
placed
on
the
programlineto
the
trans-
mitter
for
23.4 seconds,
and
a local announcement lineis
activated so
that
emergency
anno
un
cements
can
be
made.
The
Tone
Decoder external
alarm
cir
cuit
and
speaker
muting
can
be reset
by
a front-panel switch
or
by
ground
ing a remote reset line.
The
Two
Tone
Generator
can
be reset for norm
al
programming
by
a front panel
switchor
by
groun
ding
a remote reset line. Provisions
are
made
for testing the
Two
Ton
e Gene
ra
tor
with the T
one
Decoder without interrupting the programming,
and
for
separatelychecking the generation
of
the two emergency
tones,
as
described in the following
paragr
aphs.
B
oth
the
AM
and
FM
Receiver furni
sh
an
output
for a remote
carrier-fail
alarm.
4.2
AM
Receiver
Model
760-01.
(Schematic Diagram: Fi
gur
e 6-2)
Thi
s
module
is a
superheterodyne
receiver
covering the
AM
broadcast
band
from 540-1620
kHz
in
10
kHz
steps.
RF
amplifier
Qt
is
tuned
by
a front-panel
control to
peak
the
received signal. Its
output
is mixed
by
Q2
with a local-oscillator input from a frequency synthe-
sizer (described in the next
pa
ragrap
h.)
The
450-kHz
IF
signal
is
amplified
by
Q4
and
Q5,
and
detected
by
CR3.
The
resulting audio signal
is
amplified by
216
and
fed
to
the
UN
B
ALANCED
audio
output
terminal: itisalso fed
through transformer
Tl
to
the
BALANCED
audio o
ut-
put
terminals.
The
output
from detector CR3 is also
amplified by
Q3
and
appli
ed
as
an
AGC voltage to
RF
amplifier
Qt
an
d mixer
Q2.
The
LO
input
to the mixer comes from
dua
l
retriggerable monostable multivibrator
Zl
1 functioning
as
a voltage controlled oscillator.
The
phase-locked loop
consists
of
oscillator
Zt
1,
a divide-by-N divid
er
(ZS
through
ZI0)
,
and
a phasedete
ctor
(Zl
2). Aprecision 10
kH
z reference signal for
the
phase
detector
is
obtained
from 5
MHz
crystal oscilla
tor
Q10
by dividing by 500
in
ZI
5,
214,
and
Z13.
Th
e logic ones
and
zeroes from the
front-panel thumbwheel switches (St )
are
decoded
by
the
logic circuitry
of
gates
21
throug
h
24
to cause
the
divide-by-N divider to divide
the
output
frequency
of
4-1
oscillator
Zt
1
by
the
appropriate
number
to
produce a
10
-kH
z
input
to pin
1
of
phase
detector Z12 when
the
oscillator
output
is exactly 450 kHz above the frequ
en
cy
indicated by
the
thumbwheel switches. Any
pha
se
difference between the
output
of
the
divide-by-N-circuit
and this 10-kHz reference is dete
cte
d in
212,
which
produces a voltage to retune the oscillator by means
of
Qtl.
The
IF
signal
at
the
output
of
mixer Q2 is
detected in Q7
/Q8,
and
used to
turn
on
the
CARR
LED
CR7 to indicate the reception
of
a
ca
rrier.
The
output
of
detector
Q7
/Q8
is also amplified by
Q6
and
fed
to rear-
panel connector
J3-
5 to operate a carrier-fail
alarm;
this
output
is +
10
volts
at
10 ma whan a
car
ri
er
is present,
an
d
O
vol
ts
(2000 o
hm
r
eturn
to ground) for carrier
failure.
4.3
FM
Receiver
Model
760-02.
(Schematic Diagram: Figure 6-3)
The
FM
Receiveris
capab
le
of
receiving
any
two
preselected frequencies within the
FM
broadcast
band
of
88 to 108
MHz.
Th
e
RF
amplifier
an
d mixer are each
one
-h
alf
of
a
MOSFET
dual-gate transistor pair.
In
the
RF
amplifier the
RF
input
is applied to
one
gate
and
AOC
to the
oth
er.
In
the Mixer, the
RF
input
is
applied
to one gate,
and
the
LO
signal to
the
ot
her.
The
LO
is a
crystal oscillator
(Q2)
whose
output
is
tuned
totwice
the
crystal freq
uen
cy.
One
crystal is
stan
dard
, the second
optional crystal is selectable bya front-panel switch.
Thi
s
switchalsoconnects
an
additional
tuning
capacitor
in
the
crystal oscillator and
RF
amplifier circuits
when
the
switch is in the position
that
selects
the
lower
of
the
two
channel frequencies. The
LO
output
frequency is 10.7
MHz above the desired
RF
signal.
The
10.7 M
Hz
mixer
output
is fed
through
two
ceramicfilters
(FL
1
and
FL2) toprovide hi
gh
selecti
vi
ty,
and
into integrated circuit
22,
which functions
as
an
IF
amplifier, squelchc
ir
cuit, detector, AOC,
and
AFC.
The
IF
amplifier
is
factory-tuned to10.7
MHz
by
L9
and
C32.
The
AGC
voltage
at
pin
15
of
22
controls
the
gain
of
the
RF
amplifier.
The
squelch voltage
at
pin
12
of
Z2 is amplified by Z3
and
used to l
ight
CARR
LED
CR1
when received carrierdevelops sufficient squelch voltage.
The
squelch
is
also further
amp
lifi
ed
by
Q3
to drive
an
externa
I
carrier
ala
rm
c
ircuit
through
rear-panel
te
rminal 5; this
outp
ut is +
10 volts
at
10
ma
when a
ca
rrier is present
and
O
volts (2000
ohm
return
to
ground.)
fo
r
carrier
failure.
4.4
Tone
D
ec
oder
Model
760-03.
(Schematic Diagram: Figure 6-5)
This
module detects t
he
presence
of
the
853
Hz
a
nd
960
Hz
tones in
the
receiver
au
dio output.
If
both
tones
are
present sumultaneously for
at
least 8 seconds,

www.SteamPoweredRadio.Com
the
Tone
Decoder demutes its speakercircuit so
that
the
receiver
audio
can
be
heard; it also energizes a relay
whose cont
act
s
can
be
connec
ted
to
an
external
alarm
circuit. Provision is
made
for
testing system operation
by
using
the
test signals from the
Two
Tone
Generator.
The
audio input from the
AM
or
FM
receiver
is
applied to thepiezoelectric filters,
FLl
and
FL2, through
a section
of
buffer amplifier
21.
The
filter
outputs
are
amplified in different sections
of
Z1
and
drive detector
diodes
CR
1
and
CR2.
21
input
stage, pins 11, 12,
and
10,
is
configured to limit significant overdrives
in
input
level.
Wheneither 853
Hz
or
960
Hz
are present, voltagesbuild
up
across capacitor
C9
or
Cl
1 driving
the
collector
of
Ql
or
Q2
low.
If
one
of
the two tones is present only one
of
collectors
Ql
or
Q2
will be low
and
transistor
Q3
will be
on, holding the voltage
at
TP3
close to ground.
LED
s
CR3
and
CR4
turn
off
as
collectors
Ql
and
Q2
go low,
respectively.
These
LEDs
are
inside the module
and
may
be used
for
maintenance test purposes.
If
both tones
are
present, collectors
Ql
and
Q2
are
low
and
Q3
is
off,
allowing C13 to charge through
R26.
At
the
end
of
8 seconds, the voltage across C13,
amplified
by
Q4/Q5,
is highenough tofire
SCR
Q7,
thus
energizing relay K
1,
and
turning onspeakeramplifier
22
to
demute
thespeakeraudio, which is normally
muted
as
described below.
To
reset the relay
and
speaker,
RESET
switch S2 is operated to either position,
or
RESET
terminal
J2-4
is
grounded.
This
turns
off
Q6
and
therefore Q7.
The
unbalanced audio input from the Receiver
is
also applied to
the
speaker amplifier
22
through
volume control RS with switch
Sl
in
the
OPERA
TE
position, pin 2
of
Z2
is
pulled
up
to a positive voltage
causing speaker ampl
ifi
er
22
to mute. Placing
S1
in the
LISTEN
position removes thispositive voltage
at
pin2
of
22
and
thus
demutes
the
speaker amplifier.
The
audio
output
of
buffer
Zl
is also fed to
LEVEL
terminalJ2-2.
GAIN
control
R4
is
factory
set
so
that
at
100-perccnt modulation, the voltage
at
the
LEVEL
terminal
is
10 volts peak-to-peak, when used
with
the
760
-01
or
760-02 Receivers.
The
power supply
fo
r the entire EBS System is
contained
in
the
Tone
Decoder
module,
with
the
exception
of
the 12-volttransformerwhich is mounted
on
the
cabinet. Power connections to
the
receiver
and
the
Two
Tone
Generator
are
made
through
Jl
and
J3.
4.5
Two
Tone
Generator
Model
760-04.
(Schematic Diagram: Figure 6-4)
This
modulegenerates the twotone, 23.4second
tone pulse required
by
the system.
It
also contains
the
circui
tr
y
for
switching the
transmitter
modulation from
normal programmingtoemergencytones
and
announce-
ments. Provision is
made
for testing the 853
Hz
and
960
Hz
tones separately,
and
for testing
the
operation
of
the
Generator
with
the
Tone
Decoder without interrupting
normal programming.
The
853
Hz
tone is generated
by
dividing the
3.2552
MHz
output
of
crystaloscillator
Q2
by3840
in
the
4-2
divider
chain
consisting
of
216
,
215,
214,
and
213.
When
pin
9
of
Z2
is
held
at
logic 1 by
the
control cir-
cuitry,
the
853
Hz
tone
is
gated through
an
active 1-KHz
low-pass filter (218), level control R23,
and
GAIN
control R24 to audio power amplifier Z17.
The
crystal oscillator
output
is also divided by 2
in
216
and
then
by
1706 in
the
divider chainconsisting
of
Z9,
210,
ZI
1,
and
Z8 to produce the 960
Hz
tone.
When
pin 9
of
28
is held
at
logic 1 by
the
control circuitry,
the
960
Hz
tone is delivered through low-pass
filterZl
9,
level
control R20,
and
GAIN
control R24 to
amp
lifier Z17.
Transformer
Tl
provides a 600
ohm
balanced
output
which
is
delivered to
AUDIO
OUT
terminals
J3-7
and
J3-8
when relay
Kl
is
energized.
Pin
10
offlip-flop Z3 is normally
at
logic
1.
This
resets decadecounters
26,
Z7, ZS,
and
Z4 to0,
and
holds
them
at
this count.
When
COMMAND
toggle switches
S3
and
S4
are
activatedsimultaneously
in
oppositedirec-
tions,
or
when switch
Sl
is placed
in
the
TEST
position, a
logicO
is applied topin 7
or
Z3.
This
drivespin
10of23
to
logic0, enablingthe four decadecounters, whichproceed
to divide the 853
Hz
tone from pin 8
of
213
by
100,000.
The
frequency is furtherdivided by2 in
23
toproduce
the
required 23.4 second time pulse
at
pin
15
of
Z3. Flip-flop
23
is soconnected
that
the
pin10
output
returnstologic
t
at
the
end
of
the 23.4 second pulse
and
remains thereun-
til
the
next operation
of
the
COMMAND
or
TEST
switch.
The
23.4 second negative-going pulse
at
pin 10
of
Z3 turns
on
gate Z2-3 by means
of
Z2-6 to enable
the
853
Hz tone,
and
also the 960
Hz
tone
through
gateZ2-3
and
flip-flop Z-8.
When
the
Command
switches
are
activated (or
REMOTE
COMMAND
terminal
J3-t
is grounded),
latch
Zl-11/21-8
is set to
turn
on
Ql
and
thus light
COMMAND
LED
CR2
and
energizes relay
Kl
. When
Kl
is de-energized, its contacts feed the normal
program
audio to
AUDIO
OUT
terminals
J3-7
and
J3-8.
When
the relay is energized, the tones (or
the
announcement
input
form
J3-10
)
supply
the
audio
output.
Once
energized, the relay will remain in
that
condition until a
logic
O
is
applied to the reset
input
of
the latch from
switch
S1
or
from remote
RESET
terminal J3-2. Note
that
placing
SI
in
the
TEST
position does not energize
relay K1.
Placing S2 in the 853
Hz
position gates
the
853
Hz
tone
through
to
TEST
OUTPUT
J3-4,
so
that
this
tone
can
be
tested independently. Similarly,
the
960
Hz
tone
can
be delivered
to
the
TEST
OUTPUT
term
inal
by
placing S2 in
the
960
Hz
position.
Power for
the
Two
Tone
Generator
is normally
supplied
fr
om
the
Tone Decoder through connec
tor
J1.
When
the Generator is used without
the
Decoder,
the
power supply shown
in
Fugure 6-4 is used, with
AC
power
input
supplied from
the
cabinet
-mounted
12
vol
t
transformer through connector
J4.
4.6 Dual
Purpose
Decoder Model 760-5
(Schematic diagram Figure 6-6)
These
instructions apply to
the
EBS operating

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before April 16, 1976.
For
the
EBS
operating
after
that
date, refer
to
Section 4.4.
This
Module
detects
the
presence
of
a
Ca
r
rier
Break/
1
kHz
emergency signal from
the
transmitter
being monitored.
When
such a signal is detected,
the
Tone
Decoder demutes its speaker circuit so
that
the
receiver
audio
can
be
heard;
it also energizes a relay
whose contacts
can
be
connected
to
an
external
alarm
circuit.
The
Dual-Purpose
Decoder
detects
the
emergency signal consisting
of
the
following sequence:
Transmitter
carrier
off
5
seconds.
Transmitter
carrier
on
5
seconds.
Transmitter
carrier
off 5 seconds.
Transmitter
carrier
on
with 1-
KHz
tone
modulation.
The
audio
input
from
the
AM
or
FM
Receiver is
applied
to
tone
decoder
Z2
through
buffer amplifier
Zl-5.
The
decoder
output
at
pin
8 ofZ2
is
logic O
when a 1
kHz
tone
is
present,
and
logic1when it is not. R41
and
Cl
9 provide
a time delay
of
approximately 10 seconds, so
that
the
1
kHz
signal
must
be
present for
at
least
that
length
of
time
before
an
alarm
is
indicated. After
amp
lifi
cation
by
Q9,
QI
0, Q11,
the
received
tone
will
produce
a logic
1
at
pin
2
ofZ3.
When a
carrier
is being received,
the
Receiver
will deliver
+10
volts
to
the
Decoder
CARRIER
FAIL
terminal 9.
When
the
carrier
goes off,
the
voltage
at
terminal 9 drops
to
approximately Ovolts, which causes
integrator
24-5
to
develop a positive-going
ramp
voltage,
producing
an
abrupt
drop
from +Svolts
to
O
volts
in
the
output
of
comparator
Z4-4 when
the
threshold voltage is
reached.
When
the
carrier
comes
back
on
,
24-5
develops
a negative-going
ramp
voltage, causing the
output
of
Z4-
4
to
return
again
to
5 volts.
Th
us
,
the
emergency signal
4-3
will
produce
two positive-going pulses
at
the
clock
input
(pin 6)
of
ZS.
The
Qoutputs
of
the
two ZS flip-flops
are
normally
at
logic 0,
but
the
two pulses
of
the
emergency
signal cause
the
Q
output
of
the
secondflip-flop (pin 15)
to
go
to logic
1.
The
two logic 1
's
at
the
input
of
23
-3
thus
deliver a logic
1
to
the
gate
of
SCR
Q6
when
an
EBS
signal is received.
Gate
23-8, integrator
24-10
,
and
comparator
24-9
constitute
an
error
detector
which resets
the
ZS
flip-
flops
to
O
when
carrier
interruptions
are
received
that
do
not
meet
the
specifications
of
an
EBS emergencysignal.
Operation
of
the front-panel
or
remote
RESET
switch
will also reset
the
flip-flops
to
0.
When
SCR
Q6
is fired by
the
EBS signal, itener-
gizes relay
Kl
and
turns
off
CR8
to
demute
the
speaker
audio
, which
is
normally
muted
as
described below.
To
reset
the
realy
and
speaker,
RESET
switch S2
is
oper-
ated
to
either
position,
or
RESET
terminal
J2
-4 is
grounded.
This
turns
off
Q7
and
therefore
Q6
.
The
unbalanced
audio
input
from
the
Receiver
is also
appli
ed to the speaker amplifier (Z4)
through
volume control RS
and
muting
circuit
CR8.
With
switch
S1
in
the
OPERATE
position,
CR8
is
normally
on
and
furnishes
an
offset bias
to
pin
2
of
Z6,
thus
muting
it.
The
speaker
audio
can
be
demuted
by placing
Sl
in
the
LI
STEN
position.
The
audio
output
of
buffer
Zl
is also fed
to
LEVEL
terminal
J2-2
.
Gain
control RS
is
factory
set
so
that
at
100-percent
modulation
,
the
voltage
at
the
LEVEL
terminal is
10
volts peak-to-peak.
The
power
supply
for
the
entire
EBS
System is
contained
in
the
Tone
Decoder
module,
with
the
exception
of
the
12-volt transformerwhich is
mounted
on
the
cabinet. Power connections
to
the
Receiver
and
the
Two-Tone
Generator
are
made
throu.'(h
.J
1
and
J3.
-

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--
Sectian
5
Maintenance
5
.1
General.
Since the Model 760 is a solid-state instrument
and
its power requirements
are
low, no maintenance
problems
due
to
high
temperature
should
be
encountered, provided the instrument is installed well
away from vacuum-tube
and
other heat-generating
equipment. Likewise, because the operating voltages
are
low, excessive dust accumulation associates with high-
voltage devices should not occur.
5.2
Periodic
Maintenance.
The
only periodic maintenance required is
cleaning.
Once
a
year
,
or
more often
in
dusty locations,
take off the top cover
and
blow off the
dust
with com-
pressed
air
.
5.
.3
Performance
Checks.
Th
e following
procedures
will
enable
the
technician to determine whether
the
instrument is oper-
ating properly.
If
the tests indicate
substandard
oper-
ation, itis recommended
that
the instrumentbe
returned
to
the
factory
for
adjustment
or
repair. Internal adjust-
ments
are
not recommended to be
made
in
the field.
5.3. 7
AM
Receiver, Model 760-07
a.
Sensitivity
1.
Connect a Signal Generator (HP8640B
or
equivalent) to the
ANTENNA
input
on
the rearpanelwith its frequency
at
540kHz
and
AM
modulationset to
50%
, lkl-Jz. Set
output
level
at
I0µV.
2.
Connect a general purposeoscilloscope
to
the
UNBAL
and
GND
terminals
on
the
rear
panel.
3.
Dial
in
540kHz
on
thumb
wheel
switches
of
760-01
and
tune
the
pre-
selector
for
maximum
signal
on
the
oscilloscope.
4.
Slowly increase
the
level
of
the
Signal
Generator
until
the
CARR
LED
comes
on
-this should occur
at
approximately
30µV. At the time the
CARR
LED
comes
on
thevoltage
at
the
CARR
FAIL
terminal
on
the rear panel should change from 0
volts to 10V DC.
b.
AGC Range
1.
Increase the Signal Generator level
to
30m
V
and
the
1
kHz
sinewave
on
the
oscilloscope should remain undistorted.
2.
Repeat
steps
for
1030kHz
and
1600kHz
input
signal.
5.3
.2
FM
Re
cei
v
er,
Model 7@02
a.
Sensitivity
1.
Connect a Signal Generator (HP8640B
5
-1
or
equivalent) to
the
ANTENNA
input
on
the rear panel with its frequency
at
the
receiver's channel frequency
and
its fre-
quen
cy deviation set for 7SkHz
at
a 1
kHz
rate. Set
output
level
at
1
µV.
2.
Connecta general purposeoscilloscope
to the UNBAL
and
GND
terminals on the
rear panel.
3.
Slowly increase the level
of
the Signal
Generator until the
CARR
LED
comes
on
-this should occur
at
approximately
2µV. At the time the
CARR
LED
comes
on
the voltage
at
CARR
FAIL
terminal on
the
rear panel
should
change from
O
volts
to
l0V
DC.
b.
AGC
Range
1.
Increase
the
Signal Generator level
to
20mV
and
the
lkHz
sinewave
on
the
oscilloscope should remain undistorted.
2.
If receiver
is
a dual-channel version,
repeat procedure for alternate channel.
5.3.3 Tone Dec
oder,
Mod
el 760-03
a.
Connect a
jumper
wire between
rear
panel
terminals
TEST
INPUT
on
the Decoder
and
TEST
OUT
on
the
Generator. Ifa receiver is
available connect its UNBAL
output
to
the
AUDIO
INPUT
terminal
and
tune
the receiver
to
a
local
channel.
With
the
LISTEN
/
OPERATE
switch
on
the
Decoder
i~
the
LISTEN
position audio should be
heard
on the
speaker. Switch to the
OPERATE
position
and
the audio should no longer be audible.
b.
Activate
the
COMMAND
switch
on
the
Generator
and
check
that
LED's
CR3
and
CR4
go out, indicating
that
the two tones
are
being
received. 8 to
12
secondsafterthe initiation
of
the
COMMAND
switch
,
the
speaker
should
demute
and
the
two tones should be audible for
another
12
to 16 seconds. When demuting the
speaker the Decoder
RELAY
contacts should
switch.
The
speaker will remain in the
demuted
mode
and
the relaywill stayswitched until reset
by the Decoder
RESET
switch.
5.3.4 Two-Tone
Gen
erator,
Mod
el 760-04
a.
Conn
ec
t a voltmeter
and
a counter
at
the
TEST
OUT terminal
at
the
rear
panel
of
the
Two-Tone Generator.
b.
Activate the 853Hz tone by placing the
853
Hz
/O
PE
RATE
/960
Hz
switch
in
the85
3Hz
position.
The
voltage (unloaded) should
be
approximately
4V
r.m.s. (This voltage
may
be
adjusted with the front panel
GAIN
control).

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The
frequency should be 853Hz ± 0.5 Hz.
Repeat the procedure for
the
960
Hz
tone.
c. Activate
the
TEST
switch
and
two tones
shculd
be present for 23.4 seconds.
d.
Activate
the
COMMAND
switch
and
the
two tonesshould
be
presentfor 23.4 seconds
and
the
AU
DIO
#1
relay should switch
and
stay
switched until
RESET
is
activated
on
the
front
panel.
5.3.5
Dual
Purp
ose
De
code
r,
Mod
e[
760-05
a.
Connect a
jumper
wire between
rear
panel
terminals
TEST
INPUT
on
the Decoder
and
TEST
OUT
on
the
Ge
n
erator.
Connect
a
jumper
wire between the
AUD
IO UNBAL
and
--
5-2
AUD
IO
INPUT
terminals
of
the
Receiver
and
Decoder, respectfully.
Tune
the
Receiver to a
local channel so the
CARR
LED
on
its Receiver
front panel is on.
b.
With
LISTEN/OPERATE
switch
in
the
OPERATE
position
perform
the
following
Carrier-Break
simulation.
Disconnect
the
ANTENNA
for 5
seconds
,
reconne
ct
for 5
seconds, disconnect for 5 seconds
and
simul-
taneously
reconnect
the
ANTENNA
and
activate the 960Hz switch
on
the Generator.
After 8 to 12 seconds,
the
audio
should demute.
c.
Refer to 5.3.3 for check
out
of
the
Two-Tone
operational
mode
of the Decoder.

www.SteamPoweredRadio.Com
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