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Inovonics 708, Инструкция по эксплуатации и техническому обслуживанию

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Digital synthesis of the composite waveform is similar to the 

generation of the Stereo Pilot previously discussed, but with sinusoidal 

commutation

 between the left and the right stereo program channels at 

a 38kHz rate. 
Up/down counter IC26 is clocked at the 608kHz sampling rate.  The 

output is decoded by IC25.  With gating provided by IC20C and CR19, 

IC26 counts continuously from zero to 8, back to zero, etc.  A Pulse 

from IC16C presets the counter to its center position (count of 4) each 

time the pilot reaches the proper phase relationship.  This ensures 

proper and constant synchronization between pilot and subcarrier. 
IC35 and IC28C also decode the count, sequentially sampling each tap 

of the resistor divider string which bridges the left and right program 

audio signals.  Sampled program audio is buffered by IC29B, center-

sampled by IC28D, and held between samples by C38 and buffer 

IC29A.  The stereo multiplex signal consists of 16 discrete, 

sinusoidally-weighted steps. 
When the front-panel 

MODE

 switch, S3, is set to 

MONO

, the counting 

sequence is halted with the counter preset at the center position (count 

of 4).  This stops the subcarrier generation, and L+R audio appears at 

the 708 output.  In the 

MONO

 position, S3 also stops the stereo pilot, 

regardless of how S4 is switched. 

Composite 

Processor 

The emitters of transistors Q5 and Q6 are biased to the same 100%-

modulation level as the clipper diodes in the overshoot compensation 

circuit.  The transistor base/emitter junctions comprise the composite 

clipping network.  The buffered composite signal, less the stereo pilot, 

is presented to this clipper through front-panel 

COMPOSITE 

PROCESSING

 control R57.  When R57 is set to its fully- 

counterclockwise 

OUT

 position, the clipper is essentially a “safety” 

clipper, catching only those occasional program peaks which somehow 

have evaded the earlier overshoot protection circuitry.  As R57 is 

cautiously turned clockwise, program peaks at the 100%-modulation 

value may be subjected to as much as 3dB of clipping. 
Even though the composite waveform is clipped prior to pilot injection, 

good broadcasting practice demands judicious use of this feature.  (See 

Page 17.) 
Q5 and Q6 also function in the common-collector mode to flash the 

indicator adjacent to the 

COMPOSITE PROCESSING

 control.  

Additional gain is provided by IC14 to light the LED, which gives a 

visual indication of circuit action. 

Combining 

Amplifier 

IC22B is a combining stage for the main/sub portion of the composite 

signal, the stereo pilot, and any optional RDS or SCA subcarriers 

applied to the rear-panel 

SUBCARRIER INPUT

 connectors.  Adjustment 

over the composite level delivered to the exciter is afforded by R58, the 

front-panel 

OUTPUT LEVEL

 control in the feedback path of IC22A. 

 

Содержание 708

Страница 1: ...OPERATING AND MAINTENANCE INSTRUCTION MANUAL MODEL 708 FM STEREO GENERATOR __________ ...

Страница 2: ... No _______ Date Purchased _____________ Warranty Card Mailed OPERATING AND MAINTENANCE INSTRUCTION MANUAL MODEL 708 FM STEREO PROCESSOR GENERATOR September 1995 1305 Fair Avenue Santa Cruz CA 95060 TEL 408 458 0552 FAX 408 458 0554 ...

Страница 3: ...pation AC Mains Power 7 As Delivered Voltage Selector Power Cord Radio Frequency Interference RFI 8 Location Ground Loops Line Input and Input Range Selection 8 Input Connections Balanced Inputs Unbalanced Inputs Input Gain Range Gain Jumpers Pre Emphasis Selection 9 Subcarrier Inputs 10 Composite Output 11 Output Ground Loops Section III Setup and Operation Panel Controls and Indicators 12 All Co...

Страница 4: ...lter Matching Crosstalk Trim Input Level Calibration Output Level Calibration Stereo Pilot Distortion Null Subcarrier Calibration Separation Trim Section V Circuit Descriptions Circuit Descriptions 25 Component Annotation Input Circuitry Filter Overshoot Compensator Low Pass Filter Pilot and Subcarrier Generation Bargraph Meter Power Supply Section VI Appendix Parts Lists Schematics Warranty 33 ...

Страница 5: ...sis of pilot and subcarrier for unexcelled performance and freedom from drift and routine adjustment Built in adjustable Composite Processor AUDIO PRE PROCESSING REQUIREMENTS The Inovonics 708 Stereo Generator incorporates two separate circuits to safeguard against carrier overmodulation over deviation Nonetheless it is anticipate that the 708 will be preceded by some form of audio processing syst...

Страница 6: ...rating as a dual band device a broadband section to cope with normal program peaks and an independent high frequency limiter with proportionally faster time constants to deal with those program components accentuated by the transmission pre emphasis characteristic A limiter of this type now common in both FM and AM broadcasting systems has negligible audible effect on most program material while p...

Страница 7: ...DS subcarriers at 0dBu or greater levels for nominal 5 to 10 subcarrier injection relative to 100 modulation Pre emphasis May be jumpered for 75µs or 50µs characteristic may be switched OFF at front panel Composite Processor Adjustable between 0dB and 3dB clipping of the 100 modulated multiplex waveform prior to 19kHz pilot insertion Composite Multiplex Output Adjustable between 2V p p and 8V p p ...

Страница 8: ... 6 Figure 1 Block Diagram Model 708 FM Stereo Generator ...

Страница 9: ...ION INSTRUCTIONS should they be issued by Inovonics MOUNTING Rack Requirement Inovonics Model 708 is packaged to mount in a standard 19 inch equipment rack and requires only 1 inches 1U of vertical rack space The use of plastic finishing washers is recommended to protect the painted finish around the mounting holes Heat Dissipation Consuming no more power than a bedside clock radio heat generated ...

Страница 10: ...r our apologies cord vendors vary and advise that U S color coding applies BLACK AC HOT WHITE AC NEUTRAL GREEN GROUND RADIO FREQUENCY INTERFERENCE R F I Location Although we have anticipated that the 708 will be operated in close proximity to high power transmitters you should exercise care in locating the unit away from abnormally high RF fields Ground Loops In some installations a mains frequenc...

Страница 11: ... shield to G In addition a jumper wire should be installed between the terminal and G Input Gain Range The 708 can accommodate line level program inputs with a nominal Zero VU value between 10dBu and 20dBu This 30dB range is divided into two 15dB ranges by internal jumpering As shipped the generator is jumpered for professional input levels between 5dBu and 20dBu corresponding to 100 modulation Mo...

Страница 12: ...ons 75 MICROSECOND 50 MICROSECOND Figure 3 Pre emphasis Jumpering SUBCARRIER INPUTS Internal combining is provided for two auxiliary subcarriers for SCA and or RDS services The rear panel SUBCARRIER INPUT connectors are unbalanced inputs with a load impedance in the neighborhood of 10K ohms An RDS subcarrier normally accounts for 5 or less of the total composite multiplex output signal making it 2...

Страница 13: ...n 75 ohms at the far end A Stereo Generator must always be connected to an exciter or link STL input specifically intended for multiplex stereo This is a flat input rather than a monaural program input with signal pre emphasis Program signal pre emphasis is imparted by the 708 Output Ground Loops Because the Stereo Generator output and the exciter input are both unbalanced it is best to locate the...

Страница 14: ...PUT GAIN controls are adjusted so that the 100 modulation ceiling imposed by Model 708 internal circuitry coincides with the input program peak level which corresponds to 100 modulation PRE EMPHASIS System pre emphasis is imparted by the Stereo Generator in most situations With the front panel PRE EMPHASIS switch IN the selected characteristic see Page 10 is enabled and the attendant green LED wil...

Страница 15: ...ally applied SCA or RDS subcarrier s The OUTPUT LEVEL control varies the overall composite output level delivered to the exciter or STL OUTPUT LEVEL is a master adjustment and does not affect the relationships level ratios between the stereo program pilot and RDS SCA subcarrier MPX EQUAL is a composite multiplex equalization trimmer in the output stage of the 708 This has been factory set for best...

Страница 16: ...entify the function monitored The metered values are L Left program input channel R Right program input channel L R The sum of the left and right channels L R The difference of the left and right channels MPX The composite multiplex output PILOT The 19kHz stereo pilot SUB 1 Subcarrier 1 SUB 2 Subcarrier 2 POWER Sorry the function of this switch is classified BARGRAPH METERING The front panel bargr...

Страница 17: ...essor left channel input only with a 500Hz sinewave test signal which yields 6dB to 10dB of indicated signal limiting This should drive the processor left channel line output to its ceiling value and present the left channel input of the 708 with a signal representing 100 modulation of that channel NOTE Good engineering practice prescribes a standardized audio line level at any equipment interface...

Страница 18: ...typical program audio applied check bargraph metering of the composite multiplex output MPX Peak modulation should remain within the limits shown Stereo program modulation only 100 Stereo program and RDS only 105 Stereo program and one SCA only 110 Stereo program RDS and SCA 115 Stereo program and two SCAs 120 NOTE MPX metering relates to the total composite output voltage peak excursion before th...

Страница 19: ...linear gain reduction techniques cannot easily be applied to the interleaved multiplex stereo signal The historic justification for composite clipping reflects the need to control the overshoots of uncorrected low pass filters in early stereo generators Despite refinements in filter technology which all but eliminate overshoot as a potential overmodulation problem it seems that a small gain in per...

Страница 20: ...one or two dB of clipping distortion products will probably be tolerable Much more clipping than this will not only compromise subcarrier services but can interfere with adjacent stations as well Figures 4a through 4d reveal out of band components generated by composite clipping These worst case examples were created by feeding a stereo generator from a CD player No overmod protection audio proces...

Страница 21: ... 19 Figure 4c 2dB Clipping Figure 4d 3dB Clipping ...

Страница 22: ...t from 1kHz to 2Mhz Precision FM Stereo Demodulator station Mod Monitor with input for composite baseband signal Spectrum Analyzer optional must have good resolution in the 100Hz to 100kHz FM composite baseband display range The Spectrum Analyzer is not required if the Precision FM Stereo Demodulator is capable of resolving crosstalk stereo separation and 38kHz residual measurements to a value of ...

Страница 23: ...t channel waveform slightly above the right to keep track of which is which Low Pass Filter Matching The low pass filter for the right program channel is not adjustable rather it employs close tolerance components to meet design requirements Since close frequency and phase response matching between stereo channels is essential to good Stereo Generator crosstalk performance trim controls have been ...

Страница 24: ...he Mod Monitor 2 Next re apply the Audio Generator test signal to the left and right PROGRAM LINE INPUTS of the 708 as described under the Input Level Set section at the beginning of this Procedure The Audio Generator frequency should be 400Hz but the level should be reduced for a peak to peak waveform amplitude of 6 volts on the right hand ends of R128 and R135 3 Monitor the sub channel This is t...

Страница 25: ...ightness indication of the 0dB LED 5 Step the meter to monitor the right channel input R and adjust R46 for a half brightness indication of the 0dB LED 6 Verify that L R metering indicates 0dB with the LED at full brightness and that nothing shows in the L R position Output Level Calibration NOTE This portion of 708 calibration must follow the preceding Input Level Calibration procedure directly 1...

Страница 26: ...t of the Audio Generator to SUBCARRIER INPUT 1 of the 708 Reset the Audio Generator frequency to 80kHz output level to 0dBu 4 Adjust the 708 front panel SUB 1 INJ control for a Mod Monitor indication of 10 Total Modulation 5 Switch the 708 metering to SUB 1 and adjust R49 for a 0dB reading 6 Disconnect the Audio Generator from SUBCARRIER INPUT 1 and connect it to SUBCARRIER INPUT 2 7 Adjust the SU...

Страница 27: ...UT only Set the signal level for a 0dB indication on the 708 meter in the L position 2 Check the Mod Monitor reading of Total Peak Modulation It should read between 90 and 100 3 Also check the Mod Monitor indication of Pilot Injection Level If necessary adjust the 708 PILOT INJ control for a 10 reading 4 Switch the Mod Monitor to display left and right channel levels The left channel should measur...

Страница 28: ... is an active balancing stage for the left channel program line input affording rejection of unwanted common mode signals When jumper JMP3 connects R202 into the network H the Line Input accepts High program levels between 5dBu and 20dBu With R202 jumpered out L Low program levels from 10dBu to 5dBu are accommodated Input range setup is described on Page 9 The left channel INPUT GAIN control R198 ...

Страница 29: ... waveform amplitude CR20 and CR21 also biased to the 100 modulation level strip these displaced and added components from the program signal IC39A compares the stripper input and output recovering the stripped off components As these contain much of the program harmonic high frequency information we cannot afford simply to throw them away By recombining these stripped off program components with t...

Страница 30: ...esistor string with sine weighted values This generates one half a sinewave for each counting cycle IC15B reverses the DC polarity applied to the top of the resistor string for every other up down count forming the complete 19kHz pilot sinewave from 32 discrete steps R85 introduces an offset to compensate for any difference between the power supply rails and is adjusted to null the 38kHz second ha...

Страница 31: ...4 is switched Composite Processor The emitters of transistors Q5 and Q6 are biased to the same 100 modulation level as the clipper diodes in the overshoot compensation circuit The transistor base emitter junctions comprise the composite clipping network The buffered composite signal less the stereo pilot is presented to this clipper through front panel COMPOSITE PROCESSING control R57 When R57 is ...

Страница 32: ...eft and right channel program signals taken just after pre emphasis amplifier IC45 are presented independently to two inputs of multiplexer IC11 Left and right audio is also matrixed IC6A derives the L R stereo sum IC6A the L R stereo difference Sum and difference signals are scaled to give a reading of 0dB when both channels are driven to the 0dB point in and out of phase respectively The combine...

Страница 33: ...their associated driver ICs use a separate 12 volt supply taken prior to the 9 volt regulators POWER SUPPLY Stereo Generator circuitry operates from a bipolar 9 volt supply The two supplies are regulated by linear three terminal IC voltage regulators IC2 for the 9 volt supply IC3 for the 9 volt supply The power transformer has dual primary windings which may be switched in parallel or in series fo...

Страница 34: ... 32 ...

Страница 35: ...tion VI APPENDIX The following section of this Manual contains Parts Lists for the Inovonics 708 Stereo Generator Schematic Dia grams of all electronic circuitry and an explanation of Inovonics Warranty Policy ...

Страница 36: ...5 military series size designation P value is picofarads 5 200VDC open mfgr b 100pF to 0 47µF are of the metalized mylar or polyester variety whole number P values are picofarads decimal values are microfarads 5 50VDC or better The style used in the 708 is the minibox package with lead spacing of 0 2 inch Preferred mfgr Wima MKS 2 or FKC 2 series Alternates CSF Thompson IRD series or Roederstein K...

Страница 37: ...quires two 14 pin and two 16 pin Circuit Assembly Corp CA 14SE 10RAC3 01 14 pin CA 16SE 10RAC3 01 16 pin Pin strip sockets for BAR1 3 E CAM 250 1 2510 1208 708 requires three broken into two strips of 30 IC1 11 23 35 Integrated Cct open mfgr CMOS 4051B IC2 Integrated Cct open mfgr LM317 T Uses Aavid 574602 B03700 Heat Fin IC3 Integrated Cct open mfgr LM337 T Uses Aavid 574602 B03700 Heat Fin IC4 5...

Страница 38: ...plying a 1 tolerance example 3 01K 10 0K 15 0K 332K are watt 1 metal film type b Fixed resistors with values typical of 5 tolerance example 220 3 3k 10K 270K are watt 5 carbon film type c Multi Turn Trimming Potentiometers front panel adjustable are Beckman 89PR series Tokos RJC097P series or equivalent cermet types d Single Turn Trimmers circuit board are Beckman 91AR series or Tokos GF06U1 serie...

Страница 39: ...uantities of parts Any semiconductor IC capacitor resistor or connector used in the Model 708 is probably available from one or more of these firms Each supplier publishes a full line catalog available free for the asking Mouser Electronics Call 800 346 6873 Digi Key Corporation Call 800 344 4539 ACTIVE div of Future Electronics Call 800 677 8899 ...

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