Rohde & Schwarz GC 003 User manual

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Table of Contents
Data sheet
2. Pregaration for Use and 02erating Instructions ............. ..... 5
2.1 Legend for Fig. l............................... ..... . ....... ... 5
2.2 Preparation for Use ............................................. 7
2.2.1 Adjusting to Local AC Supply ......................... ........ ... 7
2.2.2 Adjusting the Preemphasis (L and R) and
Deemphasis (M =LgR).......................................... 8
2.2.3 Input Resistance .................. ..... ........... .............. 8
2.2.4 Changing to Operating Mode MONO .... ...... ...... .............. ... 8
2.2.5 Synchronization to External Pilot Tone .............. .... ...... .. 8
2.2.6 Fitting the SCA Modulator (option) ............ ..... .... ......... 8
2.3 Brief Operating Instructions ..... ..... ... ............ ........... 9
2.4 Operation .. ....... .......... ...... .............................. 9
2.4.1 L and R input .... ..... .......... ........... .. ..... . .......... .. 9
2.4.2 MPX land MPX 2 Outputs ............. ......... ................... 10
2.4.} MOutput ..... ..... .............. ..... .... ..... .. ...... . ...... ... 11
2.4.4 Stereo/Mono Switchover ............. .................. ........... 11
2.4.5 Pilot Tone ........... ..................................... ...... 12
2.4.6 Auxiliary Inputs ................ ...... .................. ........ l3
3. Maintenance .................................................... 14
3.1 Routine Maintenance ................. ....... ... .................. 14
3.2 Checking the Rated Specifications ............................... 14
3.2.1 Required Measuring Equipment .......... ................. ... ...... 14
3.2.2 Measurements ......... ......................... ..... ............. l4
4. Circuit Descrigtion .. ..... .................. .................... 17
4.1 Land RChannels ......... . ...................................... 17
4.2 Coder ... ........................................................ 17
4.3 Summing Amplifier, MPX Lowpass Filter and Output
Amplifier ........ ........ ............... ....... . ....... . ...... .. 18
4.4 Pilot—frequeney Processing .................... .................. 19
4.5 AF Generator ............................................ ........ 20
4.6 Indication ... .................. .. ...... ...... ................... 21
4.7 Selection of L or RChannel for Mono ............................ 21
R38122 -3

4.8 Power Supply ...
5. Repairs ........
5.1 Required Measuring Equipment ...........
5.2 Trouble-shooting ........................
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nguo-nuoco-o:oo-nacoooo-n. .....
.....Ialoooloono
......
5.2.1 Power Supply ...................................................
5.2.2 AF Generator, Input Amplifier, L/R and L +R
Indication ....
5.2.3 Generation and Processing of Pilot Tone ........... .
5.2.4 -Coding and Output Amplifier ..
5.3 Adjustments .............................
5.3.1 Supply Voltages ..................
5.3.2 AF Generator ........................................
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IIIOIICDIDIOIIIIOIIIDIIIOIIO
5.3.3 Indication .....................................................
5.3.4 Channels Land R...-..c-no-ooooon-ooogno IJ-olouo
5.3.5 MPX Lowpass Filter and Output Amplifier .........
5.3.6 Pilot-tone Generation ..........................................
5.3.7 Crosstalk L/R ..................................................
5.3.8 Crosstalk M/S ..................................................
Interior view
Pin assignment
1
2
3
Fig. 4Preemphasis
5Level diagram
6
Front— and rear-panel controls
Oscillograms Pilot—tone generation
Fig. 7Oscillograms Coder circuitry
Translations for Drawings and Diagrams
Drawings and Diagrams
R38122 —4
noun.-
23
23
23
25
25
23
24
24
24
24
25
25
25
26
28
28

2. Pre aration for Use and Operati Instructions
2.1 Legend for Fig. 1
IW
L:
Kn
®L,R
O
R6dBn
Lf=500 Hz
L=—R
L=R
+6 +3 0-5 L/R
INP.
”1 ‘0‘ ‘1 LEVEL
(dEm)
A+O,4A +O,2A O
PRE—EMPH.
Input selector with the following
positions:
inputs L and Rswitched through
inputs switched off
the built—in generator feeds the
two inputs in the selected mode;
the frequency can be adjusted
internally.
LED ;_2_is on for Q-(off) and R,
L, L=-Ra_ndL=R.
Attenuator switches for common level
adjustment of the Land Rchannels
in steps of 3dB (2), 0.5 dB (2)
and 0.1 dB (5)
Pushbutton for switching on and off
the preemphasis (change soldered links
for 50 or 75 us).
LED 1g signals when preemphasis is
switched off.
Panel meter with the following two
scales (0 dEm =0.775 Vrms):
—15 to +8 dEm (for L, Rand MPX signals)
(nominal level marked at +6 dEm)
—17 to —8 dEm PILOT (nominal levels
marked at -9.5 dEm and —15 dEm)
sensitivity (+10 dB) can be changed
with switch E
R38122 —5

MPX2 MPXl PILOT
RL L&R
Selector for type of indication on
meter 6
§+10 dB Sensitivity switch for meter é
Position "0": direct reading
Position ”+10 dB": 10 dB must be
added to reading
2A—-- Level control for pilot tone
__
Phase control for pilot tone
Mode selector for pilot tone with the
following positions:
0- :no pilot tone in the MPX signal
(LED lg signals)
-— :pilot tone is adjustable with
g(amplitude) and $9 (phase)
(LED lg signals)
<:> :pilot tone with standard level
and standard phaSe available in
the MPX signal
LED; lights when pilot tone is missing or
not to specification, when the inputs or
the preemphasis are switched off.
13 MONO Pushbuttons with pilot lamps for
mode selection:
MONO =both channels linked and driven
from the input internally set with link
ERle
R38122 —6

IIIIIIIIIIiiiiEEHIIIIIIIIIIIIIIIIIIIII
STEREO =normal operation
These functions can be remote—con—
trolled and are maintained even in the
case of AC supply failure
0115
115 V/125 VT0.16 B
220 V/235 VT0.08 B
Power switch with pilot lamp
Power fuse, must match with AC supply
Sll voltage as shown
STlO 47 —63 Hz Power connector with label indicating
the selected AC supply voltage
Multiplex outputs, fed by separate
amplifiers
Mono- (centre) signal output
Left-channel input
Right—channel input
Male connector strip with pin assign—
ment according to Fig. 3
Terminals 1g to 22 are in parallel
with those on the male connector strip
2.2 Pregaration for Use
See Fig. 2.
2.2.1 Adjusting to Local AC Sugglx
The GC 003 is factory-adjusted for 220 V. When switching over to another
AC supply voltage, change the soldering connections of the corresponding
R58122 —7

terminal on the soldering—lug strip of the power transformer. This soldering-
lug strip is located below the cover, on which adiagram of the wiring is
printed, and is accessible from above after having removed the stereocoder
from the rack. Check the value of the fuse Sil (lg) and, if necessary, insert
the correct value. Change the voltage value on the label below the power
connector (g1) accordingly.
2.2.2 Adjusting the Preemphasis (L and R) and Deemphasis (M =L2R)
________________________———————-———————-—-
The capacitors C101, C115 and 0141, which determine the time constant, are
fitted on solder tenninals. Their value for 50 us is 10 nF (tl%) and for
75 us 15 nF (fl%)3 the value set in the factory is 50 us.
2.2.} Ingut Resistance
By changing the resistors R138 and R139 (solder terminals) the input resist—
ance Bin can be adjusted up to 4k9. For Rin =600 Q, R138 =R159 =700 9.
2.2.4 Chaggihg to Operating Mode MONO
For the transmission of monaural signals, the stereocoder can drive both
channels from one input.Eithatthe left or the right channel must be set by
alink; the channel will then feed both multiplex outputs in the mode "linked"
(a MONO).
Insert the link 2810} into L for the left channel and into Rfor the right
channel according to the silk-screening on the printed wiring board.
2.2.5 Synchronization to External Pilot Tone
The pilot-tone circuit can be adjusted to synchronization with an external
pilot tone.
Apply the pilot signal to Sthl.3a (50 =.L) with alevel of Vpp
z1V.
Insert the link E8104 into E(external).
In normal operation, ERlO4 must be set to I(internal).
2.2.6 Fitting the SCA Modulator (0 tion
See separate manual and specified codings.
Fit the modulator into StllO. Remove the link ERlO? to enable the output,
and insert ERlOb. The AF input Sthl.5c (60 =J.) is at the rear of the set.
R58122 -8
-
J

2.} Brief Operating Instructions
The following switch positions are required for generating astandard coded
signal:
0Input selector 1to (:>(on).
0Common level adjustment for Land Rchannels with g, 2and fl.
0PRE-EMPH. button 2pushed, i.e. preemphasis switched on.
oPILOT switch gto ®(on), i.e. standard pilot level.
0STEREO button A; pushed.
2.4 Ogeration
2.4.1 Land RInpgfis
Connections
The sound sources are applied to the female connectors or, if the stereocoder
is rack—mounted, to the connector strip 22 (contacts L=Oabc, R=9abc;
see Fig. 3). The inputs may be balanced or unbalanced. The input voltages must
be free from any DC component to avoid DC magnetization of the transformers.
Channel LEulO (gg) Sthl.Oab-c (23)
Channel REuEO (2;) Sthl.9ab-c "'
Input selection
Switch lpermits the above inputs to be switched on and off as well as the
signal from the built—in AF generator to be applied for checks and measurements.
Level adjustment
The attenuator switches g, 5and 5adjustable in steps of 5dB, 0.5 dB and
0.1 dB are effective on both the left and the right channels. The labelling
on the switches refers to the nominal input level.
Nominal levels 22fl
The nominal levels are adjustable between -4 and +8 dEm, resulting in avalue
R38122 -9

of +6 dEm without pilot tone at the MPX outputs.
AF generator
In the positions L, R, L=R and L=—R of switch 1, the built-in AF generator
is connected to the inputs corresponding to the switch labelling. The amplitude
is +6 dEm.
Preemphasis
The preemphasis can be switched on and off with pushbutton 5. In normal Opera-
tion the button is pushed in, i.e. the preemphasis is switched on. It can
also be changed over between 75 us and 50 us by changing capacitors. The mono
output (M =L2R
section cancels the preemphasis switched into circuit.
has always aflat frequency reSponse, since adeemphasis
Note for measurements with discrete frequencies
Apreemphasis of 50 us increases the voltage by 13.6 dB at 15 kHz. Thus the
maximum input voltage (AF) should be no more than —1 dEm, in order not to
exceed the overdrive limit of +l2.5 dEm. In the case of 75 us preemphasis,
the maximum input voltage is -4.5 dEm.
Signal indication
The level of the left or right channel can be observed on the upper scale of
meter 6with switch 7in position "L” or "R". The measurement range can be
extended by +10 dB with slide switch g.
2.4.2 MPX land MPX 2 OutEuts
Connections
The coded signal (MPX or multiplex signal) is available in unbalanced form
at two parallel-connected outputs via two buffers.
MPX 1Bum (lg) StiOl.7b-c
MPX2 BuSO (3;) StiOl.7a-c (25)
Level adjustment
The output voltage is fixed to anominal level of +6 dBm referred to the
nominal input level and the corresponding position of attenuator switches
g, Qand E. The pilot component is added during level measurement.
R38122 -lO

518%LEEQEEEEE‘BE
In positions ”MPX l” and ”MPX 2" of the indication selector switch 1, it is
possible to observe the output level on the upper scale of meter Q. The measure—
ment range can be extended by +10 dB with slide switch g. The meter indication
represents the peak value of the complete signal (MPX+pilot +SCA +additional
signals).
2.4.} MOutEut
Connections
LER(mono or centre signal) is floating and available at
The signal M=
the parallel—connected outputs Eujo (29) and Sthl.8ab-c (£2). The nominal
output level is fixed to +6 dEm; there is no preemphasis.
Signal indication
In position "L +R" of indication selector Z, the level may be observed on
the upper scale of meter é.
Note for measurements with discrete frequencies
The output voltage is obtained by adding the Land Rsignals after the pre-
emphasis sections. This causes an increase of 13.6 dB at 15 kHz when the
preemphasis is switched to 50 us and of about 17 dB with 75 us. Adeemphasis
section compensates for this increase so that aflat frequency response is
obtained. The overload limits, such as mentioned in section 2.4.1, have to
be taken into account.
2.4.4 Stereo/Mono Switchover
_____._______L_—_—-——————
For monaural transmissions, the signal on the left or right ohanneL depending
on the setting of link BRIO}, can be directly taken to the MPX outputs. The
changeover can be carried out either on the front panel or via remote-control
lines. All switch positions are stored and unaffected by AC supply failure.
For pin assignment of Sthl see Fig. 3.
R38122 -ll

Control Stereo
Pushbutton on front panel STEREO MONO
Momentary connection to ground Sthl.2a—2c Sthl.2b-20
Signalling Stereo Mono
Lamps on front panel STEREO MONO
External lamps (24 V/BO mA) Sthl.la—lc Sthl.lb—lc
Floating contacts Sthl.6a-6b Sthl.5a—5b
2.4.5 Pilot Tbne
Operating modes
Switch ll selects the following Operating modes:
"On” =(:> :19-kHz pilot tone with standard amplitude and phase
added to the multiplex signal
”Off" =<:>o:pilot tone switched off (available at sync output
St105.3bc with adjustable phase)
AU -A4) :pilot tone with adjustable amplitude (control 2
"AU”) and adjustable phase (control 19 ”aq)”) added
to the multiplex signal. Pilot amplitude adjustable
in the range -16 dBn to -5 dEm relative to the
+6 dEm level of the multiplex signal. Pilot phase
adjustable in the range -50 to +50 compared with
the standard phase with respect to the 38—kHz sub-
carrier.
Indication
If the indication selector 1is in position PILOT, the pilot level can be
read on the lower scale of meter §. The indicated value applies to an output
level of +6 dBn of the MPX signal (nominal value: —9.5 dEm).
Trigger output
Aconstant l9—kHz Squarewave voltage of approx. 1Vpeak-to—peak (Zout<100 Q)
is available at the rear connector 22 (contact Sthl.3b-c), the phase being
equal to that of the pilot tone in the multiplex signal.
R38122 —12

With the pilot-mode selector i; set to "on", the phase is internally coupled
to the 38—kHz subcarrier, whereas in the positions "off" and "fluP AM" the
phase of the squarewave voltage is adjustable with control 19 in position
"Aw H
§ynch€0niza229£19122293399?
The entire pilot-tone processing of the coder can be synchronized to an
external l9-kHz signal at the rear connector g2 (contact Sthl.5a—c), if
link ER104 is set to E (external).
Voltage requirement: approx. 1 V peak—to-peak; pull-in range: approx. f2 Hz
2.4.6 Auxiliary Inputs
The three auxiliary inputs can be used as follows:
Nominal level
SCA signal Sthl.50—6c 30 Hz to 7.5 kHz —10 to +12 dEm
Traffic radio signal Sthl.4a—4c 53 to 100 kHz -14 dEm
Additional signal Sthl.4b-4c 53 to 100 kHz -10 dEm
Contacts 4c and 60 =chassis (screen).
"I
The SCA channel can only be used when the SCA modulator is built in. ror
this purpose, BRIO? must be removed and E8106 fitted (see separate manual).
The inputs for the traffic radio signal and the additional signal can be
used without taking any particular measures. The gain between the input used
and the MPX output is 0dB :1 dB.
R38122 -l}

3. Maintenance
3.1 Routine Maintenance
______..____———————-——-————
Regular maintenance is not required. However, it is recommended that the
unit be checked occasionally against the specifications according to section
3.2.
3.2 Checking the Rated Specifications
3.2.1 Reguired Measuring Eguiggent
DC voltmeter
AF voltmeter 10 Hz to 100 kHz SUN 2/U
—70 to +12.5 dEm
Bin >1k9
AF generator 10 Hz to 100 kHz
+12.5 dEm, max.
Rout <30 Q
Oscilloscope bandwidth >10 MHZ TEKTRONIX
high overload capability
for measurements of cross-
talk in multiplex signal
AF analyzer or bandwidth <100 Hz FAT 2
selective AF volt— sensitivity better than
meter —70 dBn
Stereodecoder MSDC 2
Psophometer (contained in SUN 2/U)
Distortion meter e.g. LEA or HP
5.2.2 Measurements
Refer to the data sheet for the required results.
Checking the amolifier characteristics
Apply asignal to the L and Rinputs (EulO and EuEO) at f =30 Hz to
15 kHz and with the specified input levels. Measure at the decoder outputs
(DEC.), the MPX output (Bu40) and the Moutput (EujO) by means of an AF
voltmeter and the panel meter (J10).
R38122 -l4

Input Measure at Measured value Remarks
Coder circuit
500 Hz/+6 dEm
=R
=R
Pilot ”on”
Value with
ideal decoder!
wwfififif‘fit“
Referred to
500 Hz
Freguencz response
30 Hz to 15 kHz/+6 dEm
L=R
Preemph. "off”
(Deemph. in
LR
L=R
LRdecoder "off")
Referred to
500 Hz
Preemghasis
500 Hz/15 kHz/—6 dEm
L=RHH
+lj.6b dB (BOus Preemph. on
+17.07 dB (75¢s
(t0.2 dB)
(Deemph. in
decoder ”off"
Pilot level
L=o, R=oBu4O "MPX" Pilot "on" or
”Akp AU”
J10 "MPX" (32g§3_scale)
Indication
500 HZ/+6 dBm *)Pilot ”off”
L=R
L=R
L=R
L=Rupper scale
L=R
L=Rlower scale
R38122 —15

Checking the crosstalk
Measure at the MPX output with an oscilloscope with high overload capability
(for L/R crosstalk checks) and with aselective AF voltmeter (for M/S) according
to sections 5.3.7 and 5.3.8.
Checking the distortion
Apply asignal to the Lor Rinput with alevel of +6 dEm or +12.5 dBm at
frequencies of 30 Hz, 500 Hz and 5kHz. Measure the harmonics at the corres-
ponding output of the decoder.
Checking the intermodulation distortion to DIN 4540}
Apply asignal to the Lor Rinput'via two identical decoupling resistors
of about 18 k9 using two generators. Frequencies fl =13 kHz and f2 =14 kHz.
Adjust the same level on both generators to that the meter J1 indicates
"+6 dEm” or "+l2.5 dEm". Measure the amplitudes at the corresponding decoder
outputs:
fl: V1 (13 kHz) f2: V2 {14 kHz)
2fl -f2: 81 (12 kHz) 2f2 -f1: SE (15 kHz)
f2 -fl: D(1 kHz)
If the distortion is <10%, the intermodulation distortion components may be
calculated in accordance with DIN 45403 as follows:
D_51 +32
2‘V1 +V2 d
d3_Vl +V2
Checkigg the carrier suggression
Apply asignal to both inputs: L=R=+6 dEm at 500 Hz. Measure at the
MPXl output (Eu40) at 38 kHz.
Checking the weighted and unweighted noise voltages
Measure at the decoder output with the psophometer, the Land R inputs of
the GC 00} being short-circuited and with the preemphasis in the coder and
deemphasis in the decoder switched on.
R38122 —16

4. Circuit Descri ption
4.1 Land RChannels
See circuit diagram 230.8518 8, sheet 1.
The signals on the left and right channels are taken to two identical signal
paths either via BulO and Bull or via St101.0abc and .9abc. Switch 8101 per-
mits the inputs to be switched off or the internal sinewave generator to be
cut into circuit.
tors switchable in steps of 3dB and 0.5 dB and decoupled by buffer stages.
The preemphasis sections R122/C101 (R162/C115) are followed by further buffers
B101 (B105) whose feedback paths include attenuator sections switchable in
0.1-dB steps.
The Cauer-type lOWpass filter L101 to L104 (L105 to L108) suppresses frequen—
cies in the range above 15 kHz; it has notches at 38.8, 19.2, 18.1 and 25.1 kHz.
After inversion in B102 (B104), the signals are passed on to the resistor
chain of the coder (lines Dand G in circuit diagram). Correction signals for
improving the crosstalk are also required (lines A, B, E, F).
Link ERlO} selects the channel associated with mono operation.
The amplifier T111 to T116, which has atwo-stage feedback circuit, feeds the
L;Rm; 31.150 and St101.8abc by means of transformer TrlO}.
The deemphasis section R206/C141 in the feedback path.is switched with 8105
sum outputs M(=
and cancels the preemphasis in the left and right channels.
4.2 Coder
See circuit diagram 230.8518 8, sheet 2, and oscillograms Fig. 6a.
The coder operates on aprinciple which is based on the switching technique.
The "hard—switching" procedure at 38 kHz is replaced by graded switching in
14 steps. In this way unwanted sidebands only occur at the 13th harmonic and
can be filtered out by asimple lOWpaSS filter.
”Soft-switching" is performed by the resistor chain R231 to R262 between the
signal lines ”-L" (line Din circuit diagram) an ”-R” (line G) and by the field-
effect transistors T121 to T128 that are switched in one after another. The cor—
rection signals ”—L'" and ”-R'” (lines Eand F) improve the coding at the moment
of subcarrier zero crossing. The switching pulses for the field—effect transis—
tors are generated in the shift register BlO8/B109 and delivered in the correct
R38122 -l7

sequence by the AND gates 3106/8107 (see oscillograms Fig. 6a). The switching
sequence of the 38—kHz subcarrier frequency within each cycle starts with T124
towards T121, is reversed to T128 via T124 and terminates with T125.
4.} Summing Amglifier, MPX Lowgass Filter and Outgut Amplifier
See circuit diagram 230.8518, sheets 2and 3.
The summigg amglifier consists of the input stage designed as adifferential
amplifier comprising T151 and T132, and of the driver stage T133 whose collec-
tor resistor is the constant current source T135 to increase the open—loop
gain. The operating point of the complementary output stage T134/T135 is de-
termined by the emitter resistors R293 and R294 together with the diodes 01 121
and G1 122. The negative feedback is adjustable with R288. The following sig—
nals are summed at the amplifier input with the correct relative levels:
LgRand difference signal S=LgR
acarrier and delivered by the coder (see section 4.2).
a) Sum signal M=superimposed on
b) Pilot tone P(19 kHz) obtained from the pilot generator circuit
(see section 4.4).
c) Correction signals for reducing the crosstalk via R265 +0146 and R264 +
0147 (lines A and B).
Interfering switching spikes (532 kHz) from the coder are eliminated by the
sample &hold circuit T137/0155. The emitter follower T138, whose resistor
is designed as aconstant current source comprising T139, feeds the MPX low—
pass filter (Via line J).
The MPX lowpass filter using L111 and L112 is aCauer-type filter with two
attenuation peaks at 768 kHz and 498 kHz. The harmonics of the subcarrier —
which theoretically may be present —are sufficiently suppressed without de—
teriorating the phase and amplitude response up to 53 kHz.
A contact of the bipolar relay R5101 selects the MPX signal or the mono
signal (from ERlOE).
The outgut amElifier is made up of the summing circuit T151 to T154 and the
two output stages MPXl, T155 to T157 and MPX2, T158 to T160. The first stage
adds the following signals with the correct relative levels:
a) MPX signal (coded signal including the pilot tone).
b) SCA signal, if the option "SCA modulator" is used.
This signal from the input ST101.50 (.60 =) is frequency—modulated and has
acarrier in the range 60 to 74 kHz whose centre frequency is referenced
R38122 -l8

to the pilot tone.
0) Additional signal on input St101.4b (c).
d) Radio traffic signal on input St101.4a (c).
For the MPX signal the stage gain is +6 dB (R357 :R325); the other signals
are not amplified.
The two output stages MPXl and MPX2 are of identical design. The emitter follo-
wers T155 (T158) are equipped with the controlled current sources T156/T157
(T159/T160) acting as emitter resistors. The capacitors 0195/0196 (0198/C199),
which are connected back to back, couple out the MPX signal without the DC
component and feed the parallel—connected outputs Eu40 and St101.7bc (Bu50 and
St101.7ac) at the rear of the unit. The source impedance is basically the
resistance of R347 (R555).
4.4 Pilot-freguency Processing
See circuit diagram 230.8518 S, sheet 2, and oscillograms in Fig. 6b.
The crystal oscillator QlOl/Blll III delivers the 4.256-MHZ reference frequen—
cy (= 2x8x14 x58 kHz) via the inverters 3111 II and 1. After adivision
of 8:1 in B113 1, the 532-kHz clock frequency is available for the shift
register. From this frequency the monostable circuit consisting of T141/T142
obtains the slightly delayed sampling pulses for the sample &hold circuit
T137 in the summing amplifier.
The stages 1to 14 in the 16-digit shift register B108/BlO9 are connected Via
3109.12 —G1 107 —B108.7 so as to form aring. One bit continuously cycles
with the clock frequency and thus causes a"high" level at the output assigned
to the corresponding digit. All other outputs that are not activated are at
"low". If there is no hit circulating, it is fed in by G1 111 to G1 118 via
B111 IV and G1 106. The reset line B109.13 (13th digit) which is run to
B108.6 +.14 and B109.6 erases the contents of the stages 1to 12 before the
bit is transferred to the first stage, thus avoiding the circulation of two
or more bits.
Pilot-tone generation is carried out in two different ways, depending on the
pilot mode selected with switch 8107; the shift register acts as a14 :1
divider.
The signal from the 8th shift register stage (8108.2) is used for the pilot
tone with fixed phase. It is applied to the 2:1divider 3113 II which pro—
duces asymmetrical squarewave at 19 kHz.
R38122 —19

For the pilot tone with adjustable phase, the signal from the 6th shift register
stage (8108.12) triggers the monostable B112. Its delay can be adjusted between
2us and 4us, approximately, by means of R316 "bf", corresponding to aphase
shift of about 140 (> 100) referred to the pilot tone. The divider 3113 II is
again used to generate the l9-kHz squarewave signal.
The squarewave signal performs several functions. It synchronizes the phase
control loop in the SCA modulator option (see separate manual) via C170. After
limiting with G1 l25/Gl 126, the emitter follower T147 feeds the pilot output
Sthl.3b (c) at the rear of the stereoooder. The differential amplifier T145/
T146 delivers the sinewave pilot tone to the summing amplifier via the l9—kHz
bandpass filter (L113 to L114) and the emitter folTOWer T144. The pilot ampli—
tude is determined by the current flowing through T145/T146, depending on the
pilot mode selected with 8107. It is preset with R314 in the pilot mode ”on"
and adjustable by means of R312 "AU" on the front panel in the variable pilot—
tone mode; there is no output in the pilot mode "off".
The PLL IC B114 provides external synchronization of the pilot tone via the
input Sthl.3a. It compares the offset between the internal pilot frequency
at pin 3and the external pilot frequency at pin 14 and then delivers aDC
voltage which is proportional to the phase difference. With appropriate set-
ting of link BRTO4, this DC voltage is taken to the tuning circuit T143/0163/
0164 of the crystal oscillator instead of the internally generated DC voltage
(R317/3318)-
4.5 AF Generator
See circuit diagram 230.8518 S, sheet 1.
The AF generator is designed as a Wien bridge oscillator and operates when
input selector 5101 is in the positions L, R, L=R and L=—R.
The frequency-determining section is formed by the series—connected RC high—
pass and lowpass filters. The capacitors C132 and 0133 are fixed, whilst the
resistors R181 and R182 can be changed to set the desired frequency (see
section 5.3.2). The output voltage is +6 dEm.
The following operating modes can be obtained by turning input selector 8101:
L: asignal is only applied to the left channel, whereas the input
of the right channel is connected to O V (chassis).
R: asignal is only applied to the right channel.
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L=R: both channels are driven in phase with the same level.
L=-R: both channels are driven out of phase with the same level.
The amplitude is stabilized with the control loop 3105 II and T107.
After peak rectification with G1 101, R191 feeds amplifier BIOS II.
The reference is aconstant current flowing in the opposite direction Via
R192. G1 102 temperature-compensates G1 101. The field—effect transistor T109
in series with R185 is connected in parallel with R184. The output voltage of
B105 II acts on the feedback circuit R185/R184 until the nominal value of the
oscillator voltage is achieved.
4.6 Indication
See circuit diagram 230.8518, sheet 1.
The checkpoint selector 8106 selects the signal to be indicated and can be set
to the positions L and Rfor the AF input signal, L+R for the sum signal,
MPXl and MPX2 for the multiplex signal and PILOT for indication of the pilot
component in the multiplex signal. The indication sensitivity can be increased
by disconnecting the lO-dB attenuator R225/R226 with 820.
The halfwave peak rectifier circuit using T117 to T120 evaluates the negative
halfwaves of the input signals Lor R. The differential amplifier Tll9/T120
delivers the signal for the transistor T118 which operates as a rectifier.
Capacitor C143 is charged to the peak value. The FET impedance transformer
T117 delivers the indicating voltage for meter J10 while offering aminimal
load for the charging circuit. The feedback Via R216 adjusts the operating
point of the differential amplifier so that only the peaks exceed the ad-
justed level (for aconstant-level input it is exceeded for only short periods)
and recharge the capacitor immediately.The discharge time constant is fixed
by R219 and is around 10 seconds.
4.7 Selection of Lor RChannel for Mono
See circuit diagram 230.8518 S, sheet 3.
For monaural transmissions the signal on the left or right channel, depending
on the setting of link E8103, is switched through to the outputs instead of
the coded signal.
The selected mode is stored— irrespective of power failure —in the bipolar
relays R5101 and R5102 whose windings are connected in parallel. Acontact
of relay R5101 switches the signal path. A contact of relay R5102 feeds the
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