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Transcription

1 WABCC '----MA_N_UAL_5_ J STYLE FST FREQUENCY SHFT CARRER EQUPMENT CONTENTS Section No. Title Page V NTRODUCTON Purpose DESCRPTON AND OPERATON General Application Circuit Description A. Transmitter. B. Receiver... C. Voltage Regulator D. Repeater Amplifiers E. Squelch NSTALLATON General Frequencies and Power Levels 3. 3 Line Connections and Equipment Adjustments OPERA TNG CHARACTERSTCS FST Carrier Equipment A. Frequency Range, 7-26 KC.... B. Receiver and Repeater nput mpedances. C. Transmitting Level. D. Receiver Sensitivity E. Receiver Output "'" UNON SWTCH & SGNAL DVSON PRNTED N U.S.A. A Westinghouse Air Brake Company February, 1967 PTSBURGH, PA

2 WABCO Section No. v V V CONTENTS (CONT) Title F. Repeater Gain G. Frequency Shift H. Operating Power.. Keying Speed. J. Mounting K. External Connections L. Delayed Squelch Board M. Standard Squelch Board FELD-SERVCE TESTS General Field-Service Tests and Level Adjustments. A. Power Supply Voltage... B. Voltage Regulator - All Units C. Transmitter. D. Receiver. E. Repeater Amplifier F. Squelch Recommended Field-Service Test Equipment, SHOP TESTNG 6. 1 General. 6, 2 Shop Service Testing and Adjustments. A. Preliminary Connections B. Voltage Regulator C. Transmitter D. Receiver... 6, 3 Recommended Shop Testing Equipment for Transmitters and Receivers... 6, 4 DC Test Voltage for Style H Transmitter- Receiver.... 6, 5 Shop Testing of FST Repeaters. A. Preliminary Connections B. Voltage Regulator.... C. Amplifier.. 6, 6 Recommended Shop Testing Equipment for FST Repeaters..... NSTRUMENTS FOR MANTENANCE OF FST CARRER SYSTEMS...., 7. 1 General..... A. B. Field-Service Testing.. Shop Testing..... Page ii

3 WRBCC LST OF LLUSTRATONS Figure Transmitter - Block Diagram... Receiver - Block Diagram.... Repeater Amplifier - Block Diagram. Normal Squelch Circuit.... Delayed Squelch Circuit... Open Line Wire Attenuation Data. Cable Attenuation Data Arrangement of Test nstruments for Measuring Carrier Levels and Frequencies on a Line Circuit. Shop Test Arrangement for Checking FST Receiver Shop Test Arrangement for Checking FST Repeaters. D A D A Page /38 39/40 iii

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5 WRBCC SECTON NTRODUCTON 1.1 PURPOSE This manual presents a detailed outline for maintaining the "Frequency Shift Carrier, Style FST" system. t contains general features, circuit description, operation, installation, operating characteristics, and maintenance testing. The manual is primarily designed for maintenance purposes. t points out step-by-step procedures to be followed in placing a carrier section in service and adjusting the various units to obtain proper operation of the system. t also recommends test maintenance and trouble-shooting procedures for the field and shop personnel. Some of its contents will serve well for general instruction, however, it is assumed that personnel who become involved in maintaining the FST equipment are familiar with the operation of its basic components and the test equipment that is recommended for testing such equipment. The requirements for communication facilities are ever increasing on the railroads. The consolidation of CTC territories increases the required transmission distances. Line wire is becoming increasingly costly to construct and maintain so carrier circuits which can operate independently of the physical DC and voice circuits are superimposed on existing line pairs. Large numbers of independent carrier circuits can be added to a line pair SECTON DESCRPTON AND OPERATON 2.1 GENERAL The Union FST carrier is tone equipment designed primarily for use with Union CTC codes systems, for teleprinter service, and multi-channel code systems. t is completely transistorized and is available in the frequency range of 7 to 26 kilocycles in 500-cycle increments. Carrier equipment will generally fall into one of two categories: broad band type, which is used to transmit voice circuits; and tone type, which is used to transmit CTC codes, and teleprinter codes or telegraph codes. The equipment is packaged in panel form suitable for mounting on 19-inch communication racks. The Style H Transmitter-Receiver Panel provides a fullduplex terminal and requires 3 rack spaces or 5-1/4 inches. ndividual transmitter and receiver panels are also available. Each one requires 3 rack spaces. The transmitter-receiver panel and one receiver panel are frequently operated in Manual 543, p. 1

6 WRBCC connection with a Relay Panel which also requires 3 rack spaces. The Style M Repeater Panel contains two independent amplifiers which are normally used to amplify a single channel in each direction. This panel requires 6 rack spaces or 10-1/2 inches. The FST carrier operates from a 16-volt battery. A voltage regulator is incorporated in each panel which maintains the DC operating voltage essentially constant over the full voltage range of the various types of storage batteries. The power required to operate the Style H Transmitter-Receiver Panel is 5. 6 watts, and the Style M Repeater requires approximately 2 watts. The complete Transmitter-Receiver is made up of a basic panel which is the same for all applications regardless of the operating frequencies. The associated plug-in units include the tuned circuits which establish the operating frequencies. The Repeater is similarly made up of a standard repeater panel and plug-in units APPLCATON One transmitter panel, or the transmitter portion of the Transmitter-Recei ver panel with its associated plug-in units, is a complete assembly and no additional material is required. t includes a plug-in keying relay. This relay is available as a biased type or stick type. One Receiver panel or the Receiver portion of the Transmitter-Receiver panel with its plug-in units, is complete except for the receiving relay. For CTC time code applications, a Style A relay panel is available which contains a KP receiving relay. This is a 20/20 ohm magnetic stick relay. With this relay, the maximum keying speed which can be used is approximately 30 cycles per second. A Style B relay panel is available for teleprinter operation. This panel contains a mercury-wetted contact receiving relay which allows the maximum keying speed of 60 cycles per second. The panel is suitable for connecting directly to a teleprinter loop for either full-duplex or half-duplex operation. When either the Style A or Style B relay panel is used, connections between the carrier panel and the relay panel are made through a standard plug-connected cable. External connection to the equipment is made through a plug-connector on the relay panel. The Style A panel uses standard A. A. R. terminal posts; whereas, the Style B employs #6-32 terminal posts with nuts and solder lugs. f desired, the receiver can work directly into some other type of relay or electronic circuit. Two output circuits exist in the unit. One circuit or the other is energized depending upon which character is being received by the receiver. Either circuit will provide 125 ma at 10 volts. The Style M Repeater panel contains two independent single channel amplifiers. These are normally connected so one will function in each direction to provide a repeating station for a duplex carrier circuit. External connections are made through a standard A. A. R. terminal board which is plug-connected to the panel. Manual 543, p. 2

7 When it is not convenient to mount the panels on a communication rack, a small individual rack can be supplied which is designed for shelf mounting. Each of these individual racks can hold one repeater panel, or one Transmitter-Recei ver panel and one relay panel. WABCC 2. 3 CRCUT DESCRPTON A. Transmitter The transmitter section of the Transmitter-Receiver is comprised of an Oscillator Stage, a Keying Relay, two Amplifier Stages, and an Output Filter. A block diagram for the transmitter is shown in Figure 1. OUTPUT CONTROL OSCLLATOR DR VER AMPLFER OUTPUT AMPLFER OUTPUT FLTER TO LNE KEYNG RELAY Figure 1. Transmitter - Block Diagram The carrier frequency is generated in the oscillator stage and boosted in the two amplifier stages for application to the line. The Output Control, shown between the oscillator and first amplifier stage, is a manual adjustment for setting the carrier level applied to the line to the desired value. The function of the Output Filter located between the output amplifier stage and the line is to block harmonics generated in the transmitter from reaching the line. t will also present a high impedance to DC and other carriers which may be operated over the same line. The Keying Relay serves to shift the oscillator frequency between the two values representing the two different characters that are transmitted. The schematic for the Transmitter-Receiver is shown on drawing D65026, Sh. la. Referring to the schematic, the transmitter oscillator, which is a Hartley type unit, is made up of: transistor SCl; resistors R, R2 and R5; capacitors Cl and C2; and the plug-in unit, designated as the Transmitter Oscillator Unit, The Transmitter Oscillator Unit contains the oscillator tank circuit which determines the frequency generated in the oscillator stage. Shifting of the frequency is accomplished by changing the value of capacity in the tank circuit. The change in capacity is effected by the keying relay. When the keying relay is in the position Manual 543, p. 3

8 WABCO shown with its front contacts open, the total capacity in the tank circuit is that presented by the combination of the bottom capacitor in series with the two top ones in multiple. This value of capacity together with the circuit inductance results in the oscillator generating the higher of the two shift frequencies. When the keying relay is operated in the energized position to transmit the other character, the bottom capacitor shown in the tank circuit is shorted out by the front contacts of the relay. Shorting out this capacitor, which is very large in capacity as compared to that of the other two in multiple, increases the net capacity in the tank circuit by a small amount that the generated frequency is sufficiently decreased by 150 cycles. Output from the oscillator is obtained from a winding in the tank coil. This is the winding which is connected to pins 1 and 2 of the Transmitter-Oscillator Unit plug connector. That portion of the oscillator output appearing across the Output Control (R4) is applied to the input circuit of the driver amplifier which is a Class A type unit. Transistor SC2; resistors R3, R6, and R7; capacitors C3 and C4; and transformer Tl make up the driver amplifier (see D65026, Sh. A). The output of the first amplifier is coupled to the Output Amplifier stage through transformer Tl. The Output Amplifier is a Class B, push-pull type made up of transistors SC3 and SC4; resistors R8, R40 and R41, and transformer T2. The signal is boosted in the Output Amplifier and fed through transformer T2 to the Output Filter and then to the line. Output transformer T2 is tapped for matching to line impedances of 600, 300 or 100 ohms. The taps are terminated on a 3-way terminal strip mounted on the back of the Transmitter-Receiver panel with the impedance match provided by each terminal being designated on the white tag alongside the strip, To change the tap, the white wire that runs between the 3-way strip and pin 3 of the Output Filter socket is shifted to the proper terminal on the strip. The unit, as shipped from the factory, is wired for the 600 ohm connection. B. Receiver The Receiver is a superheterodyne type unit consisting of the following: nput Filter, Oscillator Stage, Mixer Stage, F Filter, F Amplifier Stage, F Limiter Stage, Discriminator Stage, Trigger Stage, nverter Stage, and two Relay Drive Stages. A block diagram illustrates the operation of the Receiver (see figure 2). The heterodyne principle, using a relatively low F and with a considerable portion of the selectivity being provided by filtering in the F stage, is employed because filtering is more easily accomplished at the low F than at the higher frequencies. Manual 543, p. 4

9 WABCC RECEVER SENSTVTY CONTROL TO LNE NPUT Fl LTER MXER F FLTER F AMPLFER F LMTER OSCLLATOR SQUELCH RECEVE RELAY RECEVED FREQUENCY SELECTOR SWTCH _-r- -1-+, r r----t + - f1---..l : L -+--_J L.l.._ RELAY DRVE B RELAY DRVE A NVERTER TRGGER DSCRM NATOR Figure 2. Receiver - Block Diagram The nput Filter isolates the receiver circuits from the line and provides a part of the frequency selectivity of the receiver. t is a band pass type with relatively narrow band pass characteristics. The line or input side of the filter is connected directly to the line over which the carrier is operated, Output from the filter is applied to the Receiver Sensitivity control. This is a manually adjustable voltage divider which establishes the amount of output signal from the input filter that is fed into the succeeding stage of the receiver and thus establishes what minimum received signal on the line that will affect operation of the receiver. Signal received from the line, after passing through the nput Filter and the Receiver Sensitivity Control, is applied to the Mixer and there is heterodyned with the receiver oscillator signal to produce an F signal which effects operation of succeeding stages of the receiver. The F is the difference product of the received and receiver oscillator frequencies and is 5050 cycles for one shift frequency and 5200 cycles for the other shift frequency. The F Filter following the Mixer readily passes the band of frequencies in the F range (5050 to 5200 cycles) but sharply attenuates frequencies outside this band and hence provides additional selectivity over and above that provided by the nput Filter. Output signal from the F Filter is fed to the F Amplifier where its level is boosted and applied to the F Limiter. Manual 543, p. 5

10 WABCO The F Limiter functions to maintain the signal applied to the succeeding or Discriminator stage at a nearly constant level over a wide range of received signal input levels. This limiting action provides automatic compensation for variations in line attenuation. The function of the Discriminator is to distinguish between the two shift frequencies on the basis of which F is applied to it and to deliver to the succeeding or Trigger stage a DC signal whose polarity is opposite for the two shift frequencies. n other words, with one shift frequency applied to the Receiver, the Discriminator Output is positive and, with the other shift frequency applied to it, the output is negative with respect to the common connection of the output windings. The Trigger stage is a Schmitt Trigger circuit which is operated by the Discriminator Output and functions to cut one relay drive circuit OFF and the other ON in accordance with the particular shift frequency applied to the Receiver. The Trigger is operated to one position by a positive input and to the other by a negative input. Once the circuit is operated to a given position, it will remain in that position even though the signal applied to it from the Discriminator is removed and will operate to the other position only when the polarity of the input signal is reversed. Output from the Trigger, which is fed directly to Relay Drive A and to Relay Drive B through the nverter, is positive in one position and negative in the other. The nverter ahead of Relay Drive B inverts the signal applied to it from the Trigger so that the signals to Drives A and B are always of opposite polarity. Relay Drives A and B are electronic switches. One controls energy applied to one coil of the polar stick type receiving relay to position it to normal; the other controls energy applied to the other relay coil to position the relay reverse. Relay Drive A is operated to the ON or conducting state by a negative output from the Trigger; whereas, Relay Drive B, because of the intervening inverter, is operated to the OFF or non-conducting state. Similarly, when the Trigger output is positive, Drive A is OFF and Drive B is ON. The Received Frequency Selector switch, located between the relay drive stages and the Receiving Relay operating coils, is a pole changer. This is incorporated so that the direction of operation of the Receiving Relay for a given direction of shift of the carrier frequency can be maintained the same for all operating frequencies without the necessity for wiring changes. Pole changing is necessary to provide the same operation above KC as it is obtained below KC, because there is a difference in the polarity of the discriminator output for a given direction of frequency shift in the two ranges. This is due to the fact that the receiver oscillator frequency is above the received frequency in the range below KC, whereas the receiver oscillator frequency is below the received frequency in the range above KC. The signal for operating the receiver is received from the line through the nput Filter and applied across the Sensitivity Control (R12) (see D65026, Sh. la). Depending on the position of the Sensitivity Control, a portion of the signal is applied through the winding (pins 4 and 2) of the coil in the Receiver Oscillator Unit to the nput of the Mixer Stage which consists of transistor SC7 and the associated resistors and capacitors. The signal from the Receiver Oscillator is also fed to the Mixer Stage through this same coil in the Receiver Oscillator Unit. Manual 543, p. 6

11 The Receiver Oscillator Stage tank circuit contained in the Receiver Oscillator Units is comprised of transistor SC8 and the associated resistors and capacitors. The oscillator is a Hartley type similar to that contained in the transmitter section. The products produced by heterodyning the received and receiver oscillator frequencies in the Mixer Stage are applied to the F Filter. The F Filter blocks all signal components in the mixer output except the difference products (5050 cycles for one shift frequency and 5200 cycles for the other) which it applies to the F Amplifier Stage. The F Amplifier, which is made up of transistor SC9 and the associated resistors and capacitors, is a tuned output transformer coupled amplifier which operates Class A with low level input and Class AB with high level input. The output of the F Amplifier is the transformer coupled (transformer T3) to the Limiter which is comprised of transistor SCO and the associated resistors. The Limiter operates Class B and a portion of its output is applied to the series primary windings of the two discriminator coils which are contained in the Discriminator Unit. The discriminator coil on the right in the schematic D65026, Sh. A is tuned to parallel resonance at 5200 cycles by the capacitor connected across a second winding and the discriminator coil on the left is in a like manner tuned to parallel resonance at 5050 cycles. Each of the discriminator coils have a third winding. The output is rectified by a diode (D2 and D3), and applied to an integrating network consisting of resistors R25, and R26 and capacitor C5 for operation of the Trigger. To illustrate operation of the Discriminator, let us assume that the frequency of the receiver input signal is such that the F produced is 5200 cycles. Under this condition, a certain amount of the 5200 cycle signal will be present across the output winding of the discriminator coil that is tuned to 5050 cycles, but a considerably greater amount will be present across the output winding of the discriminator coil tuned to 5200 cycles. Since the output from the coil tuned to 5200 is the larger, the DC voltage developed across resistor R25 will be greater than that developed across resistor R26. Being opposite in polarity, it will cancel it out entirely so that the net discriminator output appearing across capacitor C5 will be of such polarity as to make the base of the Trigger transistor SCH more positive with respect to the emitter. n the other condition, whereas the received signal frequency is such as to produce an F of 5050 cycles, the voltage developed across resistor R26 is larger than that developed across R25. Therefore, the net discriminator output is of the opposite polarity to that when the F is 5200 cycles. Consequently, it makes the base of Trigger transistor sen more negative with respect to the emitter. The Trigger stage is comprised of transistors sen and SC2 and the associated resistors. These constitute a Schmitt Trigger. n one state SCll is ON and is conducting heavily and SC2 is CUT OFF and is non-conducting. The other state is when SCH is CUT OFF and is non-conducting and SC2 is ON and is conducting heavily. The Trigger is activated to the first mentioned state when the discriminator output is of the polarity which makes the base of SCH more negative with respect to the emitter (F of 5050 cycles). t is activated to the other state when the WA.BCC Manual 543, p. 7

12 WABCC discriminator output is such as to make the base of sen more positive with respect to the emitter (F of 5200 cycles). Once the Trigger has been operated to a particular position, it will remain in that position even though the activating signal is removed. t will operate to the other position when an activating signal of the opposite polarity is applied. To illustrate the operation of the Trigger stage, assume that it is in the state wherein transistor sen is conducting and that the signal which activated it has been removed and no signal is being applied from the discriminator. Under this condition, with the activating signal removed, sen will continue to conduct because the voltage drop across resistor R28 in the base biasing network of SCH is greater than that produced across resistor R29 in the emitter circuit of SCll. Therefore, the base of sen is negative with respect to the emitter. With transistor sen conducting, transistor SC12 is CUT OFF because the base is slightly positive with respect to the emitter. With sen conducting, the drop across resistor R29, which is in the emitter circuit of both sen and SC12, is slightly greater than the drop across resistor R32 in the base biasing network of SC12. Hence, the emitter of SC12 is slightly negative with respect to the base. Now, if a signal is applied to the input of the receiver to produce a positive output from the discriminator, sen will be CUT OFF and SC12 will conduct. The positive output from the discriminator applied to the base of sen makes the base positive with respect to the emitter. Hence, sen ceases to conduct. When sen ceases to conduct, the current in resistor R32 in the base biasing network of SC12 increases. The base then becomes negative with respect to the emitter and SC12 conducts. With SC12 conducting, the value of the emitter current is such as to permit sufficient drop across resistor R29 to keep SCll CUT OFF even if the signal applied to the receiver is removed. The application of the other shift frequency to the input of the receiver produces a negative output from the discriminator. This negative signal causes the base of SCll to become negative with respect to the emitter. Hence, SCll is switched to the conducting state (previously explained) effecting the CUTOFF of SC12. The two relay drive stages are electronic switching circuits which respond to the output from the Trigger stage to effect operation of the Receiving Relay. One drive stage is composed of transistor SC14 and associated resistors; the other of transistor SC15 and associated resistors. With the Received Frequency Selector Switch in the position shown on D65026, Sh. la, SC14 controls the flow of current through the bottom coil of the Receiving Relay for positioning the relay reverse. Transistor SC15 controls current flow in the top coil for positioning the relay normal A phase inverter stage consisting of transistor SC13 and associated resistors is located between one of the relay drive stages (SC14) and the Trigger to provide a polarity differential between the signals applied to the two driver stages. Thus, when the signal applied to one of the drive stages is such as to switch it ON (which causes the transistor to conduct), the signal applied to the other is such as to cut it OFF (this makes the transistor non-conducting). Manual 543, p. 8

13 To illustrate the operation of the drive stages, assume that the Trigger is in the state wherein transistor SC12 is conducting and transistor SC11 is CUT OFF. Under this condition, the voltage drop across resistor R33, produced by the flow of current in SC12, is such that the base of both SC13 and SC15 are positive with respect to the emitter. Hence, both SC13 and SC15 are CUT OFF. Thus, no current is flowing in the normaling (top) coil of the Receiving Relay. However, with SC13 CUT OFF, the voltage drop across resistor R39 in the base biasing network of SC14 is such that the base is negative with respect to the emitter. Hence, SC14 is conductive and current flows through the reversing (bottom) coil of the Receiving Relay. When the Trigger is actuated to the other state wherein transistor SCll is conducting and SC12 is CUT OFF, the base of both SC13 and SC15 become negative with respect to the emitter so that both transistors become conductive and the collector current of SC15 flows through the normaling (top) coil of the Receiving Relay. Simultaneously, current ceases to flow in the reversing coil because, when SC13 is switched on, the voltage drop across R39 is reduced so that the base of SC14 becomes positive with respect to the emitter. Hence, SC14 is CUT OFF. C. Voltage Regulator The Voltage Regulator circuit contains a voltage regulator (Zener) diode Dl, two transistors with associated resistors, and capacitor. The voltage regulator diode is connected in series with resistor R9 across the supply voltage. When the operating battery voltage is above 13 volts, the diode breaks down and conducts sufficient current in the reverse direction to maintain a 13-volt drop. This establishes a fixed bias on the base of transistor SC5. Since the emitter and the base of a transistor must operate at nearly the same voltage, the emitter voltage of SC5 will be near 13 volts. This establishes a bias on the base of transistor SC6. Since the emitter must assume near the same voltage as the base, the N connection is held at 13 volts below B16. All the current drawn by the Transmitter and Receiver flows through the network of transistor SC6 (emitter to collector) in multiple with resistor RlO. Transistor SC6 acts like a variable resistor increasing in resistance as the supply voltage increases, thus, holding the current to a fixed value. D. Repeater Amplifiers Each repeater amplifier is comprised of four stages of amplification and a Limiter-Clipper stage. Four plug-in units provide the frequency selectivity. See figure 3 (block diagram for one direction). WABCC Manual 543, p. 9

14 WABCO r -...: - - L_., - - TO LNE WEST w_ FLTER - NPUT <- - W-E GAN CONTROL NTER- AMPLFER - STAGE - FLTER SQUELCH ' AMPLFER LMTER- - CLPPER,. fv W-E OUTPUT CONTROL 1/2 TRANS. - COUPLNG - AMPLFER - UNT! ' 1/2 TRANS. - OUTPUT COUPLNG - AMPLFER UNT - OUTPUT - FLTER --+. TO LNE EAS T Figure 3. Repeater Amplifier - Block Diagram The nput Filter isolates the repeater circuits from the line and provides a part of the frequency selectivity of the receiver. t is a band pass type filter with relatively narrow band pass characteristics. The line or input side of the filter is connected directly to the line over which the carrier is operated, Output from the filter is applied to the gain control. This is a manually adjustable voltage divider which establishes the amount of output signal from the input filter that is fed into the succeeding stage of the repeater and thus, establishes the gain of the repeater, Signal received from the line, after passing through the input filter and the gain control, is amplified and fed into the nterstage Filter which provides additional frequency selectivity. Manual 543, p. 10

15 From the nterstage Filter, the signal is amplified and fed to the Limiter Clipper stage through one-half of the Transformer Coupling unit which also provides frequency selectivity. The Limiter-Clipper stage determines the maximum signal which can be transmitted from the repeater. When the incoming signal is small, no limiting action takes place. When the incoming signal is of sufficiently high level, limiting action begins so that the output level is controlled at a predetermined value. The signal level at which limiting begins is determined by the output control. Following the Limiter-Clipper stage, the signal is amplified and fed to the push-pull output amplifier through one-half of the Transformer Coupling unit which is tuned for additional frequency selectivity. From the Output Amplifier, the signal is fed through the Output Filter to the line. The primary functions of the Output Filter is to block harmonics generated in the amplifier from reaching the line and also to prevent a high impedance to DC and other carriers which may be operated over the same line. The schematic for the repeater is shown on drawing D65026, Sh. 2A. Referring to this drawing, a signal is received from the line west. t passes through the nput Filter of the West to East Amplifier and appears across potentiometer R3B, the W-E Gain Control. The signal is amplified by transistor SC and is fed to the second amplifier (SC2) through the nterstage Filter. The output of the second amplifier is fed to the Limiter-Clipper stage through one-half the Transformer Coupling Unit. The Limiter-Clipper stage is comprised of transistor SC3, diode D2, potentiometer R22B with associated capacitors and resistors. This circuit controls the maximum output signal from the repeater by limiting action. The level at which limiting occurs is determined by the position of the Output Control, R22B. When a very low level output is desired, the limiting action is not adequate. Thus, a clipper, diode D2, is provided to clip the incoming signal to this stage. The Output Control is a part of a voltage divider network made up of Rl5, R22B, and R25. As the control is varied, the DC voltage on the collector of SC3 changes, thus, varying the level of signal this transistor can handle before limiting. A second voltage divider network consisting of R20 and R21 connects to the Output Control. As the control is varied, the voltage across this divider changes and this controls the bias across diode D2. f the incoming signal is higher than the bias, the diode conducts causing the signal to be clipped. Output from the Limiter-Clipper stage is amplified by SC4. The output transistors SC5 and SC6 are connected as a push-pull amplifier and feed to the line east through the Output Filter. E. Squelch The normal squelch circuit, hereafter referred to as No. 1, consists of a signal amplifier (SCl), signal rectifier diodes (Dl and D2), squelch switch (SC2 and SC3), relay drives (SC4), and relay (SQ) (see figure 4). WABCC Manual 543, p. 11

16 WABCC The delayed squelch circuit, hereafter referred to as No. 2, consists of a signal amplifier (Ql), signal rectifier diodes (Dl and D2), time delay components (D4, R5 and C5), squelch switch (Q2 and Q3), relay driver (Q4), and relay (SQ) (see figure 5). The squelch sensitivity is controlled by potentiometer R2, which attenuates the input signal. Depending on circuit application, this signal is obtained from either the Style H Receiver or the Style M Repeater. When obtained from the receiver, the input signal is at the F level which has a frequency of 5. 2 or KC. Specifically, this signal is from the collector of F amplifier transistor SC9 (see drawing D65026, Sh. A). When obtained from the repeater, the signal is at the carrier level which has a frequency somewhere between 7 KC and 30 KC. This signal is specifically obtained via the collector or second amplifier transistor SC2 (see drawing D65026, Sh. 2A). Transistor SC, No. 1 squelch circuit, amplifies the input signal. The amplified signal is fed to a voltage doubler circuit (Dl and D2) which produces a DC voltage proportional to the signal input. n the quiescent state, whenever the input signal is absent, SC is conducting, SC2 is cut off, SC3 is conducting, SC4 is cut off, and relay SQ is de-energized. Transistor SC2 and SC3 are in a switching circuit similar to that of a Schmitt Trigger. SC2 is held in cutoff due to the current of conducting transistor SC3 which passes through common emitter resistor RS and diode D4. SC3 is forward biased by the high collector voltage of SC2, through resistor divider network R9 and RO. Transistor SC4 is cut off due to the low collector voltage of saturated transistor SC3. Whenever an input signal is applied, a negative voltage proportional to the signal is present at the base of transistor SC2. Ultimately, the rising voltage becomes sufficiently negative to overcome the reverse emitter bias and drives transistor SC2 into condunction. At this instant, the collector voltage decreases the forward bias applied through the resistor network R9 and RO, to the base of SC3. This in turn develops less voltage across common emitter resistor RS and drives SC2 further into conduction. This is a regenerative charge since conduction in either transistor is enhanced by the alternate transistor. SC2 is ON and SC3 is cut off. Any further increase of the input signal only reinforces the conduction state. The rising negative voltage on the collector of SC3, when it is being cut off, causes relay driver SC4 to conduct and energize relay SQ. A similar but opposite conduction occurs whenever the input carrier signal is removed. The No. 2 squelch circuit is similar in operation to the No. 1 circuit, except for minor differences, and will not be repeated here. The relay driver Q3 is a NPN instead of a PNP transistor. This will make Q3 (in the quiescent state without an input signal) normally conducting and relay SQ normally energized. Time delay components D4, R15, R5 and C5 are connected to the base of transistor Q2. Manual 543, p. 12

17 ,,,-=--'-''',,,,,---,,.,,.,,,,,,,,,=,== SQUELCH N N r Cl 2 R 3 R6 R4./ R14 v--, f '-' ' W -...,.. "" '- -. ;> R7 Rl2.. r V\, SC2.-_L-..J Cr"""l SC4 SQ Dl D3 $::: e. c.n..,::.. co 'P... c..:i Rl R3 C4 C2 Rl3 RB RO Rll + L Figure 4. Normal Squelch Circuit D4 F :...,..1 n D

18 ============== - -,- -'' i::: e CJ] c.:> "d.... SQUELCH N N r-y _l Cl -12.5V ----, R6 R7 R9 -llv -11.5V -2.BV '\ Q2-2.2V Q3-12V SQ D3 RB RlO L Figure 5. Delayed Squelch Circuit ov.-----<!> F : J

19 Whenever an input signal is applied, a rising negative voltage proportional to input signal appears at the anode of D2. The DC path for the voltage (until capacitor CS charges) is through resistor R5, diode D4 and capacitor C5. The RC charge time is determined by the volume of R5 and C5. Diode D4 isolates the discharge components R15 and C5 from other circuit components and presents a delay when input signal is removed. After C5 charges, the DC path is to the base of transistor Q2. This voltage fires the Schmitt Trigger circuit which in turn causes Q4 to be cut off and relay SQ de-energizes. A similar, but opposite condition occurs when the carrier input signal is removed. The interfacing of SQ relay contacts depend entirely on circuit application and cannot be shown here. n general, these contacts will ultimately, directly or indirectly, disable the output of whichever unit the squelch is operating; i.e., (the Style H receiver or Style M repeater) whenever the input signal is too weak for reliable operation. WASCC SECTON NSTALLATON 3.1 GENERAL When installing a carrier installation it is first necessary to determine the proper frequencies to be used and the maximum allowable transmitted levels. (See section 3. 2 "Frequencies and Power Levels".) Often it is necessary to determine, on paper, the anticipated line loss to the carrier frequencies to be used. f, however, the line is in service, exact attenuation measurements may be made. From this data it can be determined whether or not carrier repeaters are necessary. f it is necessary to estimate the line attenuation over which the carrier must operate, data is readily available which shows the carrier attenuation at different frequencies for the various types of line wire. This data is usually used when working with "clean" lines. That is, lines with no drops or other shunts which affect the carrier. Generally, on CTC installations, it is necessary to install frequent drops from the line pairs. These drops increase the carrier attenuation. Figure 6 shows the attenuation of carrier based on one drop every two miles for #8-40% copperweld line wire. The FST carrier is designed to operate into 600 ohm open line wire. Short entrance cables do not affect this impedance matching. When cable is used for transmission of the carrier, (if cable lengths exceeding approximately 1500 feet are inserted in open line sections or are used for entrance purposes) impedance matching is required. Figure 7 shows the attenuation for #14 signal cable, rubber insulated. Carrier attenuation through cable remains nearly constant since weather does not affect it. Attenuation on open line wire, on the other hand, is greatly Manual 543, p. 15

20 ""''' ' '"' """'"''""-""- -'''""'' i;.:i ;:j... C11 *"" c.,.:i '? -' O") w.28 a:: ::::'..26 co Cl z.24 V' ' , ,000 FREQUENCY N CYCLES 100,000 Figure 6. Open Line Wire Attenuation Data

21 w... ::E w Cl. co Cl z V) V) FREQUENCY N KLOCYCLES e. Cl CA) "O -' -;i Figure 7. Cable Attenuation Data

22 WRBCC affected by weather. Open line carrier circuits used for communication purposes are often designed to operate with the twice normal line attenuation. For most signal applications, the carrier circuit is designed to operate with three or four times normal attenuation. On longer installations, the design may allow for only 50 miles of extremely high attenuation at one time. The remaining portion being able to operate over twice normal attenuation. These decisions, of course, are based upon the reliability of service needed FREQUENCES AND POWER LEVELS DC and voice circuits are so often used on open line wire pairs that it is usually necessary to use carrier frequencies above the voice range. The range of 7 KC to 30 KC is very common. Although, frequencies up to 150 KC are becoming increasingly popular. When new line wire is installed for communication purposes, it should be transposed to a 30 KC (or 150 KC pattern). This provides for coordination between voice and carrier circuits between the different line pairs. The direction of transmission of all carrier frequencies should be in accordance with the A. A. R. agreement which states that frequencies of 7 KC, to and including 17 KC, shall be transmitted from East to West or North to South and frequencies 1 7 to 30 KC shall be transmitted from West to East or South to North. The carrier power output levels normally employed are set in accordance with the A. A. R. specifications for tone equipment of six decibels above the one milliwatt base (+6 dbm). However, values higher than this may be used if interference to other carrier circuits does not occur. FST transmitter and repeater output levels are adjustable for output levels up to +18 dbm. The receivers are adjustable down to -40 dbm. The repeater has a maximum gain of 40 db LNE CONNECTONS AND EQUPMENT ADJUSTMENTS 1. When installing the equipment, it is advisable to make the line circuit connection to all equipment first. f repeaters are used, connect battery to the repeaters, one at a time, and connect the wave analyzer to the line circuit in accordance with figure Turn the output and gain controls to maximum (clockwise). f voltage exists at the frequency which the repeater is to operate, it indicates the repeater is self-oscillatory (singing). f this is the case, reduce the gain until no voltage reading exists. This "singing" condition is caused by the input and the output of the amplifier being connected together through capacitive and inductive coupling which exists in the outside plant wiring (pole line configuration and house wiring). This situation is sometimes very expensive to correct. 3. The gain dial potentiometer is linear. Therefore, if turned halfway between minimum gain and maximum gain it will reduce the voltage gain to half. t must be realized that this represents only 6 db. Therefore, with the dial in this position, the repeater is operating with about Manual 543, p. 18

23 34 db gain. There will be numerous installations where 30 db gain will be the maximum that can be obtained without "singing''. 4. f a + 18 dbm transmitted level is permissable, the output control may be left at maximum. f some other output level is desired, turn the output control to minimum and readjust later. 5. After all repeater gains have been set, apply battery to the transmitters and receivers. 6. Using the wave analyzer, adjust transmitter outputs to levels desired. 7. Measure received levels at repeaters or receivers. 8, Set repeater output levels. All levels, received and transmitted, should be recorded for future reference. These levels should also be checked against the originally estimated levels to determine that the overall system is operating properly. WABCC SECTON V OPERATNG CHARACTERSTCS 4. 1 FST CARRER EQUPMENT A..Frequency Range, 7-26 KC The operating frequency is determined by selection of the proper plug-in units which are available in 500 cycle steps. The same basic panels are used for all frequencies. B. Receiver and Repeater nput mpedances The input impedances are 600 ohms. The transmitter and repeater outputs can be adjusted for 600, 300 or 100 ohms. C. Transmitting Level Transmitter output level can be manually adjusted over a continuous range from -20 to +18 dbm by means of the "Output Control" adjustment on the front of the panel. The repeater output level can be manually adjusted over a continuous range from +3 dbm to +18 dbm providing a sufficient carrier level is being received. This adjustment is by means of an "Output Control" adjustment on the front of the panel. Manual 543, p. 19

24 WABCO D. Receiver Sensitivity The minimum received signal to which the receiver will respond is -40 dbm. The sensitivity can be continuously adjusted downward by means of the "Switch Control" on the front of the panel to the value desired. E. Receiver Output The receiver has two DC output circuits. One of which will be energized when one frequency is received, the second when the other frequency is received. Each output circuit will deliver 125 ma at 10 volts. F. Repeater Gain The maximum gain through the repeater is +40 db. The maximum gain through the repeater is continuously variable by means of the "Gain Control" adjustment on the front of the panel. G. Frequency Shift 150 cycles total (75 cycles either side of center frequency). H. Operating Power 16 volt battery (14. 4 to 24 volts). The voltage regulator employs a Zener diode for stability. The Style H transmitter-receiver requires approximately 5. 6 watts. The Style M repeater requires approximately 2 watts.. Keying Speed 60 cycles per second. J. Mounting The equipment is arranged for panel mounting on standard 19 inch communication racks. The Style H transmitter-receiver panel is 19 inches wide by 5-3/16 inches high. The Style M repeater panel is 19 inches wide by 10-3/8 inches high. The Style A and Style B relay panels are 19 inches wide by 5-3/16 inches high. Handles are provided on all panels to facilitate handling. Maximum projection from the surface is 5-1/8 inches and from the rear surface 5-3/8 inches. K. External Connections On the Style H transmitter-receiver panel these are made through a soldered connection type plug connector at the rear of the panel. When a transmitter-recei ver panel is used in conjunction with a Style A relay panel, a standard plugconnected cable connects the two panels together. The external connections are then made to the relay panel via A. A. R. terminals which are plugged connected to the panel. External connections to the repeater panel are made in this same way. Manual 543, p. 20

25 WABCC L. Delayed Squelch Board 6 volt RMS input at 5 KC, R2 set for maximum sensitivity. Under static zero signal conditions, relay SQ is energized. Monitor closure of contacts B and H of relay SQ. The drop time for the relay after signal is applied is 14 sec., ±0. 2 sec. The pick time for the relay after signal is removed is 14 millisec., ±2 millisec. M. Standard Squelch Board 1. 5 volt RMS input at 5 KC/R2 set for maximum sensitivity. Under static zero signal conditions, relay SQ is deenergized. Monitor closure of contacts F and H of relay SQ. The pick time for the relay after signal is applied is 14 millisec., ±0. 2 millisec. The drop time for the relay after signal is removed is 14 millisec., ±2 millisec. SECTON V FELD-SERVCE TESTS 5.1 GENERAL The basic instrument for field-service tests is one which will measure the level of any des ired frequency at any point on a line or circuit where many other frequencies may also be present. This instrument must be highly selective, sensitive and, also, immune to the effects of high-level interfering signals at frequencies near to that being measured. A very satisfactory instrument for this purpose is the Hewlitt-Packard Model 302-A Wave Analyzer. Laboratory tests show that this instrument will accurately read signals 60 db below an interfering signal 300 cycles away. Another important function of this instrument is to identify those frequencies which may be present at any point on a line or other circuit. The extremely high selectivity and narrow band-width of this instrument makes it suitable for this purpose. The Analyzer may be conveniently used for voltage and frequency readings anywhere in the field since the Analyzer may be operated from any 24 volt battery, such as four standard lantern batteries, as well as from a volt, cycle source. The Analyzer will also provide a variable-frequency output signal which may be used to test a receiver or filter for frequency response. Manual 543, p. 21

26 WABCO Since the internal frequency calibration of the 302-A Wave Analyzer is guaranteed to only ±1 % of the dial reading, we recommend the use of a Hewlitt Packard Model 521-C Counter in order to obtain more accurate frequency calibration. The 521-C Counter is a five-digit, crystal-time-base counter with which the frequency dial of the Analyzer can be accurately calibrated in the shop or at a central location. Also, the 521-C Counter could, if required, be carried to and used in the field where 110 volt-60 cycle energy is available since it is relatively portable compared to most electronic counters. The 302-A Wave Analyzer provides an output which can be fed directly into the counter to allow frequency identification to within 1 cycle with the counter in place. n order to make readings directly from a code line circuit, it will be necessary that a balanced input transformer, Hewlitt-Packard No. AC60B, be used with the 302-A Wave Analyzer. 5, 2 FELD-SERVCE TESTS AND LEVEL ADJUSTMENTS A. Power Supply Voltage The battery supply to all units is normally 16-volts. This voltage should measure from to volts for proper operation of the equipment. WARNNG Do not megger test the local battery to ground while FST equipment is connected to the battery. A high voltage between the battery leads and ground will damage the FST equipment. B. Voltage Regulator - All Units Connect a Voltmeter between B16 and N (see Sh. la). A reading of to volts should be obtained. B16 and N are available on test jacks on the repeater panel and on the relay panels when used with the terminal equipment. Transmitter and receiver panels that are used without the relay panels may be checked by connecting the meter between pins 7 and 2 on the plug connector. f the voltage regulator is not operating properly, remove the panel in question from service and repair. C. Transmitter Connect the Wave Analyzer with the balanced nput Transformer and the Electronic Counter to the line circuit in accordance with figure 8. Levels - The transmitted voltage from each transmitter should read within 10% of the output to which it was adjusted when installed. Manual 543, p. 22

27 WAECC NOTE A line fault or a rearrangement of the line circuit components can cause a variation in this reading. f there is any question, the transmitter output should be removed from the line and connected to a 600-ohms load and checked according to the shop testing specifications. f excessive variation is noted, the likely cause of trouble is in the panel itself, although the plug-in units can be responsible. f a variation in output between the high and low frequencies exceeds 1. 5 db at a transmittal level of +3 dbm, the output filter should be replaced, Frequency - The Transmitter on the high frequency should read from 60 to 90-cycles above the center frequency. The center frequency is that frequency marked on the unit name plate. Similarly the low frequency should read from 60 to 90-cycles below the center frequency. f the frequency is not within the values specified, the transmitter oscillator should be returned to the factory for repair. D. Receiver Connect the Wave Analyzer and Electronic Counter as shown in figure 8. Check the input signal to the receiver. f the signal is above - 40 dbm and within the frequency limits outlined above under "Frequency", the receiver should operate properly. f the high frequency is being received, a voltage output of about 11-volts will appear across a 180-ohm load between pin 3 and N (see 0_ la). When the low frequency is received, 11-volts should appear across a 180-ohm load connected between pin 11 and N. f the Receiver is not operating properly, it is recommended it be removed from service and shop tested in accordance with the shop testing procedure. E. Repeater Amplifier Connect the Wave Analyzer and Electronic Counter as shown in figure 8. Levels - Check the input signal to the amplifier. The received level should be similar to the received level when the equipment was installed. Line and weather conditions will cause the received level to vary but it should be of the same order of magnitude. Manual 543, p. 23