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Combining

Amplifier

IC18A is a combining stage for the main/sub portion of the composite

signal, the stereo pilot, and an optional RDS or SCA subcarrier applied

to the rear-panel

SUBCARRIER INPUT

jack. The front-panel

OUTPUT

LEVEL

control, R13, is in the feedback path of IC18A, affording

adjustment over the composite level delivered to the exciter.

Output Filter

Since all components of the composite output are digitally synthesized

at a 608kHz rate, only a simple filter is required to eliminate the

sampling frequency from the

DAVID-II

output. L2, L1, C31 and C30

form a 4-pole filter with quasi-Butterworth response. This filter is

exceptionally flat to about 100kHz, but effectively attenuates higher-

order digital noise components in the

DAVID-II

output.

Output

Phase and

Equalization

Trimmers

The output amplifier consists of IC18B, IC19A, and transistors Q1 and

Q2. R57 affords variable high frequency tip-up, and R56 varies the

phase response. These two controls can be used together to optimize

stereo separation throughout the transmission system. As adjusted at

the factory, separation is maximized into a resistive load. Using a

precision stereo demodulator, the two pots may be re-tweaked to

compensate for response or phase irregularities in a composite STL or

exciter input circuitry.

POWER SUPPLY

DAVID-II

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, IC1 for the –9-volt supply. The power

transformer has dual primary windings which may be switched in

parallel or in series for 115V or 230V mains, respectively.

Содержание DAVID-II 716

Страница 1: ...OPERATING AND MAINTENANCE INSTRUCTION MANUAL DAVID II MODEL 716 FM STEREO PROCESSOR GENERATOR __________...

Страница 2: ..._______ Date Purchased _____________ Warranty Card Mailed OPERATING AND MAINTENANCE INSTRUCTION MANUAL DAVID II MODEL 716 FM STEREO PROCESSOR GENERATOR October 1995 1305 Fair Avenue Santa Cruz CA 9506...

Страница 3: ...nce RFI 7 Location Ground Loops Line Input and Input Range Selection 7 Input Connections Balanced Inputs Unbalanced Inputs Input Gain Range Gain Jumpers Pre Emphasis Selection 9 Bass Enhance Equalizat...

Страница 4: ...on V Circuit Descriptions Circuit Descriptions 23 Component Annotation A PWM Primer PWM Ramp Circuitry Signal Path Circuitry Input Stages AGC Stage Wideband Compression and Limiting High Frequency Lim...

Страница 5: ...iding AGC Wideband Compression and Peak Limiting Independent High Frequency Limiting Exclusive Bass Enhance equalizer defeatable Extended response low pass filtering with proprietary overshoot compens...

Страница 6: ...rm time constant to compress dynamic range with average value weighting Independent high frequency limiter conforms to selected pre emphasis characteristic Subsequent program signal clipping is relega...

Страница 7: ...5 Figure 1 Block Diagram DAVID II FM Stereo Processor Generator...

Страница 8: ...INSTRUCTIONS should they be issued by Inovonics MOUNTING Rack Requirement Inovonics DAVID II is packaged to mount in a standard 19 inch equipment rack and requires only 1 inches 1U of vertical rack sp...

Страница 9: ...GROUND RADIO FREQUENCY INTERFERENCE R F I Location Although we have anticipated that the DAVID II may be operated adjacent to high power transmitters you should exercise care in locating the unit away...

Страница 10: ...should be installed between the terminal and G Input Gain Range The DAVID II can accommodate line level program inputs with a nominal Zero VU value between 15dBu and 15dBu This 30dB range is divided...

Страница 11: ...umpering options 75 MICROSECOND 50 MICROSECOND Figure 3 Pre emphasis Jumpering BASS ENHANCE EQUALIZATION The DAVID II incorporates a unique bass boost equalizer which may be enabled at the user s opti...

Страница 12: ...ertical row of integrated circuits closest to the right hand side of the chassis the one just behind the PROGRAM LINE INPUT barrier strip Close to the front panel and just to the right of the two INPU...

Страница 13: ...e unbalanced COMPOSITE OUTPUT of the DAVID II has a resistive source impedance of 75 ohms This permits runs of moderate length about 50 feet maximum to the exciter or microwave link input If the cable...

Страница 14: ...PUT GAIN controls are adjusted to maintain AGC gain in the center of its operating region A G C GAIN This series of five LED indicators displays the amount of correction in effect for long term variat...

Страница 15: ...delay between adjusting this control and hearing any change COMPRESSOR GAIN These two LEDs display the gain state of the average level compression circuitry With a steady state tone or with no input...

Страница 16: ...d harmonic generation Use this feature sparingly COMPOSITE OUTPUT PILOT SUB The PILOT INJ and SUB INJ controls set the injection levels of the 19kHz stereo pilot and an externally applied SCA or RDS s...

Страница 17: ...nsist of L R the algebraic sum of the left and right program channels The MODE switch does not remove an RDS or an SCA subcarrier POWER Nuf said NORMAL SETUP PROCEDURE This setup procedure presupposes...

Страница 18: ...ave access to the station s Modulation Monitor An RDS or SCA subcarrier should not be connected until Step 6 Be sure that the COMPOSITE PROCESSING control is OUT that is fully counterclockwise PLEASE...

Страница 19: ...ssume responsibility for any adjustment which deviates from this procedure AVERAGE COMPRESSION ADJUSTMENT Once the OUTPUT LEVEL has been set for proper carrier peak deviation the user may determine a...

Страница 20: ...dio Generator 10Hz 1MHz 20dBm output capability Digital Multimeter Frequency Counter capable of accurate frequency measurement from 1kHz to 2Mhz Precision FM Stereo Demodulator station Mod Monitor wit...

Страница 21: ...enerator output to either G The input terminals may be left unconnected for test purposes 4 Set both scope attenuators at 2V div Position the left channel signal from R22 above the right 5 Adjust the...

Страница 22: ...um Analyzer should display the 38kHz component at the noise floor the Mod Monitor should indicate a 38kHz residual reading at the bottom of its most sensitive scale 70dB or better 5 Next re apply the...

Страница 23: ...is entirely feasible to trim the equalization and phase adjustments in the DAVID II output circuitry to correct for shortcomings elsewhere in the transmission system for instance in a composite STL o...

Страница 24: ...ween these two adjustments but there will be only one setting of each which will give best separation Null one then the other and back and forth etc until no further improvement can be had The final a...

Страница 25: ...r than voltage controlled amplifiers or FET attenuators in its three distinct processing sections This technology as applied to broadcast audio processing was pioneered by Inovonics in 1982 PWM is a s...

Страница 26: ...s this function X represents the circuit gain needed to hold the output at a constant 1 volt with a 1 volt to 10 volt input signal Y This technique becomes a bit precarious at small duty cycles attenu...

Страница 27: ...tion is in effect Figure 7 Ramp Waveform This ramp runs continuously at a 152kHz rate It is applied to one input of a comparator and a DC voltage derived from the input signal is fed to the other comp...

Страница 28: ...Q11 is an emitter follower buffer for the composite ramp waveform applying the ramp to the inputs of comparators IC42A and IC29A These generate the PWM squarewave switching waveform for the broadband...

Страница 29: ...y See Figure 4 on Page 10 The effect of this special equalization is to accentuate frequencies which are perceived as bottom end while attenuating sub audible program components which can compromise o...

Страница 30: ...with a DC level corresponding to 0dB AGC gain When the program level is too low the output of IC30A toggles positive When the program level is too high IC30A toggles negative Integrator IC30B translat...

Страница 31: ...400Hz WIDEBAND COMPRESSION AND LIMITING Compressor Limiter Timing As discussed in the description of the AGC circuitry the output of IC28C is the full wave rectified program signal CR17 passes the pea...

Страница 32: ...this equalized signal via R198 with flat program audio via R197 to impart proper pre emphasis to the program audio JMP1 may be jumpered for the 75 s American or 50 s CCIR pre emphasis standard Indepe...

Страница 33: ...ing of which is judged less obtrusive than a temporary reduction in overall broadband level Phase Lag and Recombining IC34B includes a phase lag network which time displaces the fast leading and trail...

Страница 34: ...ed in the PWM discussion IC8C is a crystal controlled oscillator at 1 216Mhz IC8D buffers the clock and IC7A the first binary divider furnishes the 608kHz digital synthesis sampling frequency Pilot Ge...

Страница 35: ...lot and subcarrier IC13 and IC16D 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 bu...

Страница 36: ...gital noise components in the DAVID II output Output Phase and Equalization Trimmers The output amplifier consists of IC18B IC19A and transistors Q1 and Q2 R57 affords variable high frequency tip up a...

Страница 37: ...5 Section VI APPENDIX The following section of this Manual contains Parts Lists for the Inovonics DAVID II Schematic Diagrams of all electronic circuitry and an explanation of Inovonics Warranty Polic...

Страница 38: ...r CM 05 military series size designation P value is picofarads 5 200VDC open mfgr b 100pF to 0 47 F are of the metalized mylar or polyester variety whole number P values are picofarads decimal values...

Страница 39: ...fgr LM337 T Uses Aavid 574602 B03700 Heat Fin IC2 Integrated Cct open mfgr LM317 T Uses Aavid 574602 B03700 Heat Fin IC3 5 7 Integrated Cct open mfgr CMOS 4013B IC4 6 Integrated Cct open mfgr CMOS 402...

Страница 40: ...series R64 Resistor Variable 5K Piher PT 15 YB 5K with Fig 3 spindle Uses Rogan 1R00A110BD001 PT 0 WL knob R145 Resistor Variable 10K Piher PT 15 YB 10K with Fig 3 spindle Uses Rogan 1R00A110BD001 PT...

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