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Inovonics 708 Operating And Maintenance Instruction Manual

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OPERATING AND MAINTENANCE
INSTRUCTION MANUAL
MODEL 708
FM-STEREO GENERATOR
__________

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Summary of Contents for Inovonics 708

  • Page 1 OPERATING AND MAINTENANCE INSTRUCTION MANUAL MODEL 708 FM-STEREO GENERATOR __________...
  • Page 2 —– USER’S RECORD —– Model 708 - Serial 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...

  • Page 3: Table Of Contents

    TABLE OF CONTENTS Section I - INTRODUCTION Model 708 Product Description ................... General - Features Audio Pre-Processing Requirements ................... Pre-emphasized Transmission - Split-Spectrum Peak Control - Internal Overmod Protection Model 708 Technical Specifications..................Patent Notice ........................Block Diagram ........................Section II - Installation Unpacking and Inspection ....................
  • Page 4 Implications of Composite Processing ................Pilot Modulation - Out-of-Band Components Section IV - Calibration Calibration .......................... Equipment Required - Power Supply Check - Clock Set - Input Level Set - Low-Pass Filter Matching - Crosstalk Trim - Input Level Calibration - Output Level Calibration - Stereo Pilot Distortion Null - Subcarrier Calibration - Separation Trim Section V - Circuit Descriptions...

  • Page 5: Section I - Introduction

    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” system which places a ceiling on program peaks with specific allowances for protection of the pre-emphasis characteristic.
  • Page 6 Because of its unique mode of operation, a Protection good deal more peak clipping may be tolerated than with more simple audio clipping circuits. The 708 may, in fact, even be used “barefoot,” or with minimal audio pre-processing, yet still yield acceptable performance.

  • Page 7: Model 708 Technical Specifications

    –10dBu and +20dBu, equivalent to 100% modulation. BLOCK DIAGRAM A simplified Block Diagram of the Model 708 is shown on the following page. Generator circuitry is explained in detail under Circuit Descriptions, Section V, which references Schematic Diagrams found in the Appendix, Section VI.
  • Page 8 Figure 1 - Block Diagram, Model 708 FM-Stereo Generator — —...

  • Page 9: Section Ii - Installation

    Consuming no more power than a bedside clock radio, heat generated Heat Dissipation by the 708 is insignificant. The unit is specified for operation within an ambient temperature range from freezing to 120°F/ 50°C. Because adjacent, less efficient equipment may radiate substantial heat, be sure that the equipment rack has sufficient ventilation to keep the temperature below the stated maximum.

  • Page 10: Radio Frequency Interference (Rfi)

    BE SURE that the mains voltage selector setting and pri- mary fuse value are appropriate for the mains supply before plugging the 708 into the wall outlet. The detachable power cord supplied with the 708 is fitted with a Power Cord North-American-standard male plug. The individual cord conductors are supposed to be color-coded in accordance with CEE standards: BROWN = AC “HOT”...
  • Page 11 A balanced program audio feed to the 708 will use both the + and the – Balanced Inputs terminals, plus the associated G (ground) terminal for each of the two stereo channels. Since these are “bridging” (high impedance) inputs, they provide no termination for an audio processor or other equipment which feeds the 708.

  • Page 12: Pre-Emphasis Selection

    PRE-EMPHASIS SELECTION The Model 708 Stereo Generator supports the 75-microsecond FM broadcasting pre-emphasis standard common to the Western Hemisphere and parts of the Orient, and the 50-microsecond standard used in Europe and Asia. Pre-emphasis appropriate to the shipping destination is jumpered at the factory, but this is easily changed if necessary.

  • Page 13: Composite Output

    Because the Stereo Generator output and the exciter input are both Output Ground unbalanced, it is best to locate the 708 near the exciter and power both Loops from a common AC mains circuit. This will help avoid ground loops and mains-related hum in the transmitted signal.

  • Page 14: Section Iii - Setup And Operation

    (see Page 10) is enabled and the attendant green LED will light. If, on the other hand, pre-emphasized audio is applied to the 708, the switch should be set to the OUT position to avoid “double” pre-emphasis. This alternate mode is indicated by the red LED.
  • Page 15 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 stereo separation into a resistive load, but can be used to compensate for frequency response deficiencies in a composite STL or in the input section of the exciter.
  • Page 16 POWER BARGRAPH METERING The front-panel bargraph meter is useful in initial level-setting and to verify proper operation of the 708 Stereo Generator. The up/down switch to the right of the display cycles the meter through its various measurement functions. The meter is peak-responding, and is scaled both in percent-modulation and in dB, with 0dB corresponding to 100% modulation.

  • Page 17: Normal Setup Procedure

    COMPOSITE OUTPUT to the wideband input of an exciter/transmitter. Variations from these conditions, such as an intermediate STL or other link, analog or digital, in either the input or the output path of the 708, may call for considerations not addressed here.
  • Page 18 COMPOSITE OUTPUT to the input of the exciter. 2. Turn off or disconnect any subcarrier inputs to the 708. With only the stereo programming applied, advance the OUTPUT LEVEL control for a Mod-Monitor indication of frequent 100%-modulation peaks.

  • Page 19: Implications Of Composite Processing

    INJ. control, if necessary, then re-confirm 100% carrier deviation. 5. If an RDS or an SCA subcarrier is to be broadcast, re-connect it to the 708 at this time. Using the Mod-Monitor, or other means of reading the auxiliary subcarrier injection level, verify proper injection.
  • Page 20 Simple clipping of a symmetrical waveform will invariably generate Out-of-Band odd-order harmonics of the fundamental frequency. The level of, and Components signal degradation by, these harmonics will depend in large part on the depth of the clipping action. Because of its complementary pre- and de- emphasis, FM broadcasting can forgive a surprising amount of baseband clipping, insofar as audible distortion is concerned.
  • Page 21 Figure 4c - 2dB Clipping Figure 4d - 3dB Clipping — —...

  • Page 22: Calibration

    Section IV CALIBRATION “Routine” calibration of the Model 708 Stereo Generator is never required, its digital-synthesis circuitry is simple and stable. The only justification for confirming any of the internal adjustments is out-of- specification operation, and only after all other possible faults have been considered and eliminated.
  • Page 23 1. Preset the 708 front-panel switches as follows: Input Level Set POWER — ON MODE — MONO PILOT — OFF O’SHOOT COMP. — OUT PRE-EMPHASIS — OUT 1. The input gain range should be jumpered for high-level inputs; this is the H position on jumpers strips JMP2 and JMP3. Apply the output of the Audio Generator to both the right- and the left- channel PROGRAM LINE INPUTS.
  • Page 24 Procedure. If a Mod-Monitor of insufficient precision is used, final Calibration (and performance!) of the 708 will reflect the inaccuracy. 1. Connect the COMPOSITE OUTPUT of the 708 to the input of the Spectrum Analyzer (or directly to the Composite Input of the Mod- Monitor).
  • Page 25 Procedure. 2. Turn the O’SHOOT COMP. switch to the IN position. 3. Make no changes to the 708 INPUT GAIN controls. Note that as the output level of the Audio Generator is increased, the 9-volt p-p waveforms will clip, or flatten, top and bottom. Carefully, adjust the output level of the Audio Generator to a point where the flattening is scarcely visible.

  • Page 26: Separation Trim

    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.
  • Page 27 “composite” STL, or even in a long run of coax cable. The following procedure leaves the 708 adjusted for its own best stereo separation. Nevertheless, the front-panel MPX EQUAL. control will give a user the option of optimizing the entire transmission system, though he should keep in mind that a chain is only as strong as its weakest link.

  • Page 28: Circuit Descriptions

    Section V CIRCUIT DESCRIPTIONS This section details the circuitry of the Inovonics Model 708 FM Stereo Generator. Circuit descriptions refer to the three pages of Schematic Diagrams contained in the Appendix, Section VI, Pages 38, 39 and 40. The schematics may appear to be annotated in a somewhat haphazard Component manner, insofar as component reference designations are concerned.
  • Page 29 L-C designs worked-out in Germany during the late 1940s (probably with a slide rule!). The particular active configuration used in the 708 is sometimes called the “FDNR” because each of the legs to ground simulates a Frequency-Dependent Negative Resistance.
  • Page 30 Components in the right channel filter have fixed values. The resonant frequency of each of the left channel legs is variable over a small range so that the two channels may be precisely matched in amplitude and phase response. A great “cookbook,” with this and other filter circuits which might prove valuable to the broadcaster, is the Electronic Filter Design Handbook by Arthur B.
  • Page 31 (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.
  • Page 32 Each of the LED drivers contains ten voltage comparators and a resistive voltage-divider reference. When the three are “stacked,” this creates a 30-step voltage-linear readout, though only 29 segments comprise the Model 708 display. The front-panel meter is scaled both — —...

  • Page 33: Power Supply

    Model 708 display. The front-panel meter is scaled both in percent-modulation and in dB. This is similar to a standard VU meter except for the peak-response ballistics. Each of the three LED bargraph modules is series-connected. This is a power-saving technique since each module, rather than each individual segment, draws only 5 milliamps.
  • Page 34 — —...

  • Page 35: Section Vi - Appendix

    Section 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. — —...

  • Page 36: Parts List

    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.
  • Page 37 10-Segment LED-bar display module, green; Kingbright DC-10GWA BAR3 10-segment LED-bar display module, yellow; Kingbright DC-10YWA — Right-angle socket for BAR1-3 (708 requires 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...
  • Page 38 Switch, 2-position SPDT Miniature Toggle; C&K 7101-M-D9-A-B-E Switch, 3-position SPDT “Center Off” Miniatue Toggle; C&K 7105-S-D9-A-B-E S501 Switch, Power Rocker; Carling RA 911-RB-O-N Power Transformer, PC-mounting; Signal LP-20-600 or direct cross- reference Crystal 1.216MHz; SPECIAL - Inovonics Part No. 1242 — —...
  • Page 39 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.

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