BELL SYSTEM PRACTCES Plnt Series SECTON 362-4- 1 2 1 ssue 2, December 1969 AT&TCo Stndrd TYPE N AND ON CARRER REPEATERS-REPEATERED HGH-FREQUENCY LNE DESCRPTON-TYPE NA HGH-LOW TRANSSTORZED REPEATER CONTENTS PAGE 1. GENERAL 1.1 This section describes the physicl nd 1. GENERAL........... 1 functionl chrcteristics of the N1A high-low repeter used in the high-frequency line of Type 2. EQUPMENT DESCRPTON..... 2 N nd ON Crrier Systems. t is one of two similr repeter circuits nd is designted High-Low A. Overll Repeter....... 2 (H-L) Trnsistorized Repeter. Section 362-4-12 describes the N1A low-high repeter. B. E-W nd W-E Subssemblies... 2 1.2 This section is reissued to include the use C. OscilltorSubssembly..... 2 of the 63A bet suppression filter for H-L repeters nd other new developments such s 3. FUNCTONAL DESCRlPTlON..... 2 silicon diode modultors tht provide improved performnce for trnsistorized repeters. Miscellneous A. Repeter nput Coil...... 2 dditions nd chnges re lso included. Modultor Filter....... 2 Modultor Pd....... 2 Modultor......... 2 Modultor Repeting Coil.... 6 34-kHz Crrier Oscilltor.... 6 Amplifier......... 6 Flt-Gin Adjustments..... 6 Repeter Gin nd Regultion.. 9 Slope Adjustment....... 1 Power Arrngement...... 11 Lightning Protection...... 11 1.3 The N1A repeter is used on $-wire bsis to trnsmit the 12-chnnel N1 or N2 signls, the 24-chnnel ON2 or N3 signls, or the 2-chnnel ON1 signls. The input signls from the line pss through n input filter to remove unwnted frequencies. They re then modulted by 34-kHz crrier to chnge bnds from the high group to the low group. The sme oscilltor is used to supply the 34-kHz crrier for both directions of trnsmission, s shown in Fig. 1. The ction whereby the repeter trnsmits different frequency bnd thn it receives is termed frequency frogging. t is lso the bsis for the repeter nomenclture High-Low (H-L). The modultor output is pssed through the second filter to suppress crrier lek nd the unwnted sidebnd. The output of this filter is pplied to the input of the regulting feedbck mplifier. This mplifier utomticlly djusts the gin by thermistor regultor to mintin n output power tht is lmost constnt over the operting rnge of the input power. M. Testing Fcilities....... 11 1.4 Only smll mount of equliztion is ccomplished by the repeter. Most of the 4. DRAWNG REFERENCES...... 13 equliztion depends upon hving pproximtely @ Americn Telephone nd Telegrph Compny, 1969 Printed in U.S.A. Pge 1
SECTON 362-4-1 2 1 equl cble lengths between repeters nd the use of frequency frogging t ech repeter. The residul slope equliztion is djusted by the SLOPE ADJ control in the mplifier. 2. EQUPMENT DESCRPTON A. Overll Repeter 2.1 The N1 Trnsistorized High-Low Repeter Circuit consists of three mjor prts, the E-W (est-west) subssembly, the W-E (west-est) subssembly, nd the oscilltor subssembly. Test jcks nd the slope djust switches re mounted on the repeter fceplte for esy ccess. The subssemblies re enclosed in n luminum housing which plugs into N1A mounting shelf, s shown in Fig. 2. B. E-W nd W-E Subssemblies 2.2 The E-W nd W-E subssemblies re identicl, except the W-E subssembly contins voltge-regulting diode power supply. n ddition both subssemblies contin: (1) A modultor with input nd output filters plus ssocited trnsformers. (2) A 3-stge trnsistor mplifier with regulting thermistor, slope djustment, nd flt-gin djustment. C. Oscilltor Subssembly 2.3 The oscilltor subssembly consists of: (1) A 1-trnsistor crystl-controlled oscilltor with n output level djustment, plus 1-trnsistor buffer mplifier nd for those units equipped with copper oxide vristors in the modultor circuits, second hrmonic rejection filter. (2) A bis djustment for the E-W nd W-E mplifiers. (3) A current djustment for the heters of the two thermistors. 3. FUNCTONAL DESCRPTON ( Fig. 1) A. Repeter nput Coil 3.1 The repeter input coil (T) serves to mtch the impednce of the incoming line to tht of the 3-ohm filters. This input coil provides the simplex connection to the line for the purpose of obtining or supplying power over the line. t lso ids in mintining n dequte longitudinl blnce to the line to suppress longitudinl noise. B. Modultor Filter 3.2 The modultor filters used t the input nd output of the modultor select the desired frequency groups. These filters re designted FL1, FL2, FL3, FL4, )nd FL5.4 3.3 Modultor input filters FL1 nd FL2 )or FL54 pss signls of the incoming high-group frequencies on to the modultor nd reject the unwnted low-group signls tht re present t the repeter input becuse of crosstlk between the cble pirs. )FL5, which replces the older FL1 nd FL2 for trnsmission improvement, lso rejects the imge bnd tht is present s modultion product of the previous repeter nd is trnsmitted with little ttenution. The imge bnd if llowed to pss through the modultor produces interference, which hs been termed bets, in the outgoing low-group frequency bnd. The bndpss chrcteristic of this filter ttenutes both the low-group signls, s before, nd the imge bnd, thus eliminting this source of bets. The filter configurtion for FL1, 2, or 5 nd chrcteristics (mesured between 3-ohm resistnces) re shown in Fig. 3 (A) nd (B1.4 C. Modultor Pd 3.4 A 4dB pd is used between the modultor input coil nd the modultor input filter. This pd improves the impednce mtch between the filter nd modultor, mterilly improves the trnsmission chrcteristic, nd stbilizes the chnges with temperture. D. Modultor 3.5 The modultor receives the high-frequency group nd modultes it with the group crrier (34 khz) to produce the low-frequency group. Of the modultion products produced by the modultor, Pge 2
SS 2, SECTON 362-4-1 21 _ jt HlGH GR NPUT WEST 4 u PWR N FL5 FEEDBACK, NETWORK AND SLOPE ADJ RT THERMSTOR 1 '5 LOW GR OUTPUT PWR OUT WEST TO EAST SUBASSEMBLY - - - - 4-4- - - - - - OSCLLATOR AND POWER ASSEMBLY 4- KHz RYSTAL SCLLATOR 4,Y4.41 DSTRBUTON AND REGULATON PWR WEST THERMSTOR SLOPE ADJ 7. -.! - MODULATOR CR,A 7 8, PWR N.ld+ HGH GR < NPUT EAST EAST TO WEST SUBASSEMBLY Fig. 1 -Type Nl A Repeter-Block Schemtic Pge 3/4
SS 2, SECTON 362-4-121 3.7 The modultor ction my be considered s double-pole, double-throw switch inserted in the signl pth between the input nd output coils of T2 nd T3, respectively. This switch ction is ctivted by the plus nd minus voltges of the crrier pplied longitudinlly through trnsformers T2 nd T3. When the crrier voltge is positive t A nd negtive t B, the crrier current flows through the two outer rectifying elements, mking their impednce low. A signl present in the input will then flow directly through the modultor to the output trnsformer. During the next hlf cycle of crrier, the crrier potentil is reversed nd the current flows through the inner rectifying units, mking their impednce low. This is equivlent to reversing the pth for signl voltges from the input to the output trnsformer. 3.8 This double-pole, double-throw switch ction of the blnced modultor hs the inherent function tht mny of the modultion products formed do not pper t the output terminls of the circuit. f the symbol v represents the incoming group of signls nd c represents the 34-kHz crrier, the modultion products formed within the modultor my be considered in four sets. These sets re: Fig. 2-N1A H-L Repeter Unit (J9873LB) only the lower sidebnd is desired. The modultor is of the double-blnced type (input signl nd crrier both blnced from the output). t consists of copper-oxide vristor, or silicon diode qud (CRl), connected between two repeting coils (T2 nd T3). where ne represents even integers nd no represents odd integers. Of these modultion products only the odd order set, noc+nov, ppers t the output terminls of the modultors; ll the other sets of modultion products re theoreticlly blnced out. Of the odd order set, the simple difference (c-v) is the modultion products desired. 3.6 Modultor output filters FL3 nd FL4 (Fig. 4) select the lower sidebnd creted by the modultor for trnsmission to the mplifier nd reject the upper sidebnd, ll other modultion products, nd the signls of the frequency group pplied t the input of the modultor. This output filter lso includes pek section to reject the 34-kHz crrier tht is present becuse of imperfect modultor blnce. The other components of this order re rejected by the filters following the modultor. When perfect modultor blnce is not chieved, some energy from the other sets of modultion products does pper t the output terminls. This is composed principlly of the input signls v, which re suppressed bout 2 db, nd the 34-kHz crrier which is suppressed bout 4 db. Pge 5
SECTON 362-4- 12 1 E. Modultor Repeting Coil 3.9 A high-group sidebnd coil (T2) is used t the input to the modultor nd low-group sidebnd coil (T3) t the output of the modultor. These coils hve n impednce rtio of 3:13 ohms nd serve to mtch the impednce of the filters to tht of the modultor nd to chnge from n unblnced filter circuit to blnced modultor circuit. To mintin the proper blnce in this circuit, it is importnt tht the only c ground connection to this modultor circuit be 't T3 s indicted. F. 34-kHz Crrier Oscilltor 3.1 The crrier frequency used t ech repeter is supplied by the 34-kHz crystl oscilltor. This oscilltor employs trnsistor nd qurtz crystl to form the oscillting circuit. A buffer mplifier consisting of one trnsistor drives the two modultor circuits in prllel. This mplifier is necessry in order to obtin sufficient crrier power; it lso serves to isolte the oscilltor from the nonliner modultor lod. A rejection filter t the oscilltor output (for use only with the copper oxide vristor modultor) suppresses the second hrmonic of 34 khz. The filter is not in circuit when the silicon diode qud is used in the modultor circuit in plce of the copper oxide vristor. The nonliner chrcteristic of the silicon cretes squring effect on the driving signl which results in rejection of ll even hrmonics of the 34-kHz signl, so tht the second hrmonic t the modultor output is comprble in level to tht of the copper oxide modultor. A resistor t the output of the oscilltor circuit is connected in prllel with the silicon diode lod so tht the combined terminting impednce becomes more resistive. The ddition of this resistor enbles the crrier oscilltors to function in ll repeters upon ppliction of power. 3.1 1 The frequency of oscilltion is stbilized by crystl Y4 to 34 khz with mximum devition of pproximtely h2 Hz over temperture rnge of -4 C to +6"C. The output voltge is.55 volt +.2 volt nd the second hrmonic level is t lest 55 db below the fundmentl. G. Amplifier 3.12 A low-group mplifier is used in the H-L repeter. The mplifier uses three trnsistor stges with hybrid feedbck connections t both the input nd the output. The mplifier contins thermistor-regulted output, flt-gin djustment, nd slope control djustment. 3.13 The input to the mplifier is coupled to the modultor output filter by hybrid trnsformer T4. The input impednce of the first trnsistor (Ql), in conjunction with the feedbck, provides the proper termintion for T4, thereby ssuring tht the input impednce of the trnsformer is 3 ohms which mtches the modultor output filter. 3.14 The mplifier output is coupled to the line by hybrid trnsformer T5. The output impednce of the lst stge (Q3), in conjunction with the feedbck, provides the proper termintion for T5, thereby ssuring tht the output impednce of the trnsformer is 125 ohms, which mtches the line impednce. 3.15 The three trnsistor stges re direct coupled to conserve bis current. Temperture stbility nd stbility with respect to component vritions re chieved by minimizing the dc gin per stge nd judiciously plcing diodes so tht the temperture effects of diodes nd trnsistors tend to cncel. The emitter voltge of the trnsistor in the lst stge (Q3) is the most criticl point in the circuit becuse it sets the current in this trnsistor nd therefore sets the clipping level. This voltge is fctory set to 3. volts by djusting the potentiometer in the collector of the second stge. After this voltge is fctory set, it becomes good indiction of the condition of ll trnsistors nd diodes. H. Flt-Gin Adjustments 3.16 The gin of the mplifier is determined by the loss in the feedbck network nd thermistor RT1 between the input nd output hybrid tps of trnsformers T4 nd T5. The slope-djust network includes ldb gin djustment steps for use in mnufcture to compenste for the ccumulted vritions due to ll the circuit components. 3.17 When the repeter is used s n lternte repeter in the trnsistorized repeter switching set, fixed gin without regultion is desired. This condition is obtined by using 2,-ohm resistor in plce of the thermistor regultor. This resistor Pge 6
SS 2, SECTON 362-4-121 FL -167U FL2-167A 44 48 52 56 6 9 FREOUENCY KHZ - i A. FL AND FL2 FLTERS. FL5 F TER 1 FREOUENCY KHZ - Fig. 3-Schemtic nd nsertion Loss Chrcteristics of FLl, FL2, nd FL5 Filters Pge 7/8
SS 2, SECTON 362-4-121-1 t 6 $ +5 = +4 z +3 'c N + +2 5' - + m W n - 5-2 - 5-3 g -4-2 -5 L -6-12-1-8 -6-4 -2 +2 t 4 +6 +8+1+12+14 CHANGE N REPEATER NPUT DB Fig. 4- LOW-GROUP SDE BAND FREQUENCY N KHz HGH-GROUP SDE BAND 4 f RPTR GROUP CAR R E,R Schemtic nd nsertion Loss Chrcteristics of FL3 nd FL4 Filters provides 6-dB more repeter gin thn tht provided by the thermistor t its men operting vlue. The resistor is lso used for mnufcturing nd repir testing. t is normlly replced by the thermistor for field instlltion.. Repeter Gin nd Regultion 3.18 The repeter gin is controlled by the loss of the feedbck circuit. The fixed gin condition is provided by use of fixed resistor. The regulted gin condition is provided by use of thermistor regultor RT1 which functions to hold the repeter output nerly constnt for considerble rnge of inputs. This regulted gin is essentilly flt with frequency. The thermistor is ctivted in proportion to the totl power t the output of the repeter. This power is nominlly ++2.5 dbmc nd the thermistor holds this output power to within +1.5 db for chnge in input level of h8 db. This regultion performnce in terms of chnge of output from men condition versus chnge in input is shown in Fig. 5. Fig. 5-Regultion Chrcteristic of High-Low Trnsistorized Repeter 3.19 The thermistor regultor rection time is plotted in Fig. 6 in terms of the time required for the regultor to ttin given percentge of its ultimte chnge fter trnsmission ltertion. This rection time is different in the two directions of regultor chnge. The regultor decreses output three to five times s fst s it increses it. This rection time mterilly influences field use in tht, fter ny trnsmission chnge, witing period is required before the circuit will stbilize within ny desired mesuring ccurcy. This witing period is plotted in Fig. 7 in terms of stbiliztion within 114 db nd lso 1/1 db. The OUTPUT NCREASED curves pply for chnges which hve incresed the output bove norml nd which the regultor restores to norml by decresing the repeter gin, while the OUTPUT DECREASED curves pply for decresed chnges in output which the regultor restores to norml by incresing the repeter gin. Thus n increse in input of 2 db would require wit of bout 4 minutes for 111-dB mesuring ccurcy, wheres decrese in input of 2 db would require wit of bout 14 minutes. A cold repeter when inserted is t high gin nd for norml input will hve high output. To obtin 1/4dB ccurcy of stbiliztion output requires bout 6-minute wit. Accurcy within 1/1 db requires wit of 15 to 2 minutes. 3.2 Thermistor unit RT1 consists of thermistor pellet nd the ssocited mbient temperture control for this pellet. The thermistor pellet is Pge 9
SECTON 362-4-1 2 1 1 Hence heter is built round the pellet nd the pellet is mintined t temperture bove norml 9 mbients. The temperture t which it is held by 8 the het from this mbient compenstion heter is z 2 djusted in mnufcture so tht with e~2.5 dbm4 7 k output from the repeter, the pellet resistnce is 5 6 9 ohms. This thermostted temperture in E 5 5 generl is between 135 F nd 185 F. The temperture 3 compenstion is obtined by disc thermistor in 4 the heter network which vries the power dissipted - z 3 W in the pellet heter with the mbient temperture. U LT W 2 J This mbient temperture control permits the regulting thermistor to be used t operting 1 tempertures between -2 F nd +13"F without 1 2 3456 2 3 4 567891 2 pprecible chnge in its operting performnce. SECONDS 4 MNUTES Beyond these temperture extremes the regulting level will vry with incresing temperture, producing decresing repeter output level. However, this Fig. 6-Thermistor Regultor Rection Time chnge is not cumultive from one repeter to the next nd so in generl is not vitl to operting performnce. 1 9 8! 7 5 6 w 5 5 g 4 3 2 2 3 4 567891 15 2 5 1 TME N MNUTES Fig. 7-Stbiliztion Time (Within.25 DB nd.1 DB of Finl Vlue) negtive temperture coefficient resistnce unit tht normlly vries from bout 1 ohms to bout 2, ohms. Under bnorml trnsmission conditions, it my vry from few hundred ohms to 4, ohms. For repeter hving the nominl gin, the thermistor resistnce wil be bout 9 ohms. This vlue is referred to s the design vlue. 3.21 Becuse the thermistor chnges its resistnce with temperture, chnges in the mbient temperture would ffect the resistnce vlue. J. Slope Adjustment 3.22 The mplifier slope djustment provides the mnul control of the mplifier frequency chrcteristic to obtin the desired slope cross the bnd. The slope chnges re produced by vrying the mplifier feedbck s shown in Fig. 8. The djustment is in three steps designted A, B, nd C, providing slopes of pproximtely 2 db, db, nd -2 db of gin, respectively, for chnnel 12 with respect to chnnel 1 )nd 1.7 db, db, nd -2 db of gin, respectively, for chnnel 13 with respect to chnnel 24. These djustments re so rrnged tht for ech setting the repeter hs the sme power output. Thus chnge in slope setting my be mde on n operting system without ffecting the thermistor regulting ction. The slope djustment network is shunt cross the feedbck circuit. n position A the network consists of prllel resonnt circuit C2, L3, nd R28 in series with resistor R27. n position B the shunt consists of resistors R27 nd R28 nd does not provide shping. n position C the shunt consists of series resonnt circuit C2, L3, )or in lter models L64 nd R26 in prllel with the series combintion of resistors R27 nd R29. The networks ssocited with positions A nd C re designed to give the proper in-bnd slope while hving negligible effect on the out-of-bnd feedbck. The ltter ensures mplifier stbility for ll slope positions. Pge 1
SS 2, SECTON 362-4-121 SLOPE A SLOPE B SLOPE C Fig. 8-High-Low Trnsistorized Repeter Slope Adjustment Networks K. Power Arrngement 3.23 The power connections to the cble pirs re mde t the center tp of the pproprite repeter input nd output trnsformers. 3.24 The power used by repeter is pplied t jcks PA9 nd PA11 nd is. distributed to the severl components s shown in Fig. 9. The voltge pplied to the mplifiers, oscilltor, nd thermistor heter circuit is regulted by 22-volt regultion diode CR2. This diode is locted in the W-E subssembly. Cpcitor C26 is power supply filter which prevents crosstlk nd 34-kHz crrier lek. 3.25 The two thermistor heters re powered in series through potentiometer R54 nd resistor R55. The current through the thermistor heters is fctory set to 18 ma by djusting potentiometer R54 nd setting the voltge cross resistor R55 to 3 volts. The voltge cross ech thermistor heter is controlled by n internl 8.2-volt diode. 3.26 The oscilltor circuit is supplied through decoupling network consisting of resistor R5 nd cpcitor C48. This network is necessry to reduce the 34-kHz crrier lek. 3.27 The voltge t the bse of the first stge (Ql) of ech mplifier is regulted to bout 3. volts. The voltge regulting network for the W-E mplifier consists of components RT1 (W-E), R52, R3 (W-E), nd )RV1 (W-E) nd in lter models RVlO (W-E) nd RVll (W-E).C A cpcitor, C24, together with this network provides decoupling from the power supply to prevent crosstlk nd 34-kHz crrier lek. The internl diode in RT1 (E-W) nd diodes RVlO (W-E) )nd RVll (W-E)C re lso used to enhnce the temperture stbility. The regulting network for the E-W mplifier consists of components (RT1, E-W), (R56), (R3, E-W), nd )(RV1, E-W) nd in the lter models (RV1, E-W) nd (RVll, E-W).C The collector supplies of ll three stges re tken directly from the 22-volt diode without dditionl decoupling. The collector of the second stge is supplied through potentiometer R53 for the W-E mplifier nd R57 for the E-W mplifier. These potentiometers re used to fctory djust the emitter of trnsistor Q3 to 3. volts in ech mplifier. 1. Lightning Protection 3.28 The repeter is prtilly protected from lightning surges induced in the trnsmission lines by crbon lightning protection blocks exterior to the repeter. These blocks re plced from ech conductor to ground t both the input nd output of the repeter nd limit surge voltges to pproximtely 5 volts. f the blocks brek down t the fr side of the repeter from lightning surge, lrge longitudinl currents my flow through the power supply diode CR2 (W-E). Resistor R48 limits this current to sfe vlue. f the blocks t the ner side of the repeter brek down, trnsverse currents my flow through the input or output trnsformers. The input of the repeter is protected from trnsverse surges by the bnd limiting filters nd the modultor. The output of the repeter is protected from trnsverse surges by vristors which shunt the output trnsformer (7'5). M. Testing Fcilities 3.29 n order to fcilitte the in-service detection of component vritions, test points re provided on ech subssembly. n the E-W nd W-E subssemblies, the test points re locted t the emitters of Q1 nd Q3 nd t circuit ground. The test points in the oscilltor subssembly re locted t the emitter of Q4, in the emitter circuit of Q41, t both terminls of diode CR2 (one of which is the oscilltor circuit ground), t true ground, nd on both sides of resistor R55 in the Pge 11
SECTON 362-4-1 2 1 R48 PA9 + (+ ).,A,.,,TO COLLECTOR Q2 W-E TO OSC ' R5O R57,TO COLLECTOR 82 E-W TO COLLECTORS Q AND 93,W-E AND E-W - 41 OSC * CR2 GRD = RT 1 w-i R56 Q E-W, TO BASE RV " W-E la RV l l E-W - - *- A - CKT GRD E-W AND W-E Fig. 9-Power Distribution High-Low Trnsistorized Repeter thermistor heter circuit. The voltge mesured from n emitter test point to the pproprite circuit ground effectively mesures the emitter current of tht trnsistor. Any chnge in n emitter current indictes chnge in current gin of tht trnsistor or chnge in other bising component vlues due to ging or temperture chnge. The voltge from the emitter of Q3 to mplifier circuit ground is especilly sensitive to component degrdtion in the mplifier circuit. t is fctory set to exctly 3 volts t room temperture nd therefore is not ffected by initil component tolernces. ts vlue will be ffected only by component degrdtion, repeter temperture, nd cble temperture. The voltge cross the 22-volt diode indictes the condition of the diode nd the dc current in the cble. f this voltge drops below 2 volts, trouble condition exists. The voltge cross resistor R55 indictes the current in the heter circuit. f this voltge drops below 2.2 volts, trouble condition exists. All these voltges my be mesured with 2,-ohms-per-volt meter while the repeter is in service. (These voltges re intended to indicte trouble condition, not to specify the defective component.) 3.3 The test points re tbulted s follows: Pge 12
SS 2, SECTON 362-4-121 4. DRAWNG REFERENCES 4.1 The following listed schemtics show detiled informtion on the N1A High-Low Trnsistorized Repeter. SD-96124-2 SD4529-1 Appliction Schemtic for N1 Trnsistorized Repeter High-Low Trnsistorized Repeter Circuit oscilltor circuit Red Blck TP1 TP2 cross resistor (R55) Pge 13 13 Pges