FMT633S STEREO SYNTHESIZER MODULATOR INSTRUCTION BOOK IB

Transcription

1 FMT633S STEREO SYNTHESIZER MODULATOR INSTRUCTION BOOK IB

2 TABLE OF CONTENTS GENERAL DESCRIPTION: 1 SPECIFICATIONS: 2 FUNCTIONAL DESCRIPTION: 3 INSTALLATION & OPERATING INSTRUCTIONS: 3-4 CAUTION: 5-6 SEPARATE 4.5MHz TV MODULATOR CONNECTIONS: 7 MAINTENANCE: 8 CENTERING THE 4.5MHz LOCK RANGE: 8

3 GENERAL DESCRIPTION: The FMT633S is a synthesized stereo TV audio modulator to be used at a cable of SMATV head-end in conjunction with a TV video modulator. This unit replaces the monaural 4.5MHz TV audio modulator in the TV modulator to convert a monaural television audio signal into a synthesized stereo signal for reception by MTS standard stereo TV sets. The input signal may be either a base-band stereo (Left and Right channel), or a monaural base-band signal. A wide range of input levels can be accommodated. The audio input level can be adjusted to create the correct audio carrier deviation and a front panel VU meter is used to set working audio levels. The input audio base-band signal is stereo multiplexed and frequency modulated onto a precision 4.5MHz carrier. The multiplexing process generates a stereo signal, which is added to the video signal in the TV modulator at the cable head-end. When this television and sound carrier is received by the subscriber s MTS standard stereo TV set, the multiplexed stereo signal is decoded. One FMT633S stereo TV audio modulator is required for each TV channel to be converted to stereo. This unit will work with all base-band satellite delivered programs. Microwave delivered TV programs can be converted to stereo at the cable head-end by demodulating the TV audio microwave sub-carrier with a FMR611S demodulator and filtering out the microwave sub-carrier with a BEF45 (band elimination filter) to block RF bars from the video signal. The audio output of the FMR611S is connected to the FMT633S to produce the stereo signal. Satellite signals carrying a stereo TV audio signal can be decoded with the FMR616S or FMR622S type of stereo demodulators then connected to the FMT633S stereo TV audio modulator. The FMT633S may also be used to convert Local Origination channels to stereo TV audio. The unit also provides a connector for injection of a Second Audio Program (SAP) input. An SAP channel modulator may be retrofitted to this input connected when a SAP channel is to be modulated onto the TV sound channel. FMT633Sisb page 1 of 8

4 SPECIFICATIONS: INPUT Monaural Stereo (L&R) Level (APL) Level (100%) Bandwidth SAP Channel SPECIFICATION 200K Bridging, Balanced 200K Bridging Balanced - 10 to +8 dbm (APL) +10 to +18 dbm (PPL) 40Hz 15KHz Input Combiner Connector PROCESSING Audio Compandor MTS Compatible 2:1/3:1 Stereo Synthesis L-R Phase Rotation MULTIPLEXING Pilot Multiplex Carrier L-R Modulation KHz KHz Double Sideband Suppressed Carrier RF OUTPUT Frequency Power (Adjustable) 4.5MHz +/- 200Hz +10 to +45 dbmv MECHANICAL Mainframe Power PMS610 One of Three Spaces mA CONNECTORS Audio Input RF Output Video Sync (in/out) SAP Channel Combiner 6 Position Screw Terminal F Type (female) Connector 2 BNC (female) Connectors RCA Connector FMT633Sisb page 2 of 8

5 FUNCTIONAL DESCRIPTION: The audio processor consists of U1, U2, U3, U4, U5 and U7. The input balance, audio low pass filter and pilot notch filtering is provided by U1. Companding and stereo generation is provided by U2, U5, U7, U8, and U9. Wherein U8 and U9 generate the precision 15734Hz and 31468Hz pilot and difference channel modulating frequency. Companding and combining of all components of the stereo signal takes place in U2 and U4. The horizontal sync separator consists of Q6 Q10, which drives the sync phase-lock-loop U11 to keep the pilot phase locked to the video horizontal rate. Loss of video will cause the pilot to squelch and prevent transmission of unlocked stereo. The system reverts to monaural audio modulation automatically if the source to video synchronization is removed. The VU mete drive circuit U6 provides both an average program level (APL) indication with the VU meter and also a 100% peak flasher to help set correct levels to prevent over modulation. The 4.5MHz modulator consists of a Variable Frequency Oscillator (VCO, Q3) a precision reference oscillator and a Phase-Lock-Loop frequency control system U10. The RF output stages consist of the buffer Q4 and the variable level output stage Q5. The -18 volt regulator U12, the -12 volt regulator Q1, and the -5 volt regulator Q2 stabilize the circuits to prevent power line variation from effecting the performance of the FMT63S. INSTALLATION & OPERATING INSTRUCTIONS: Select which of the three positions in the mainframe that will be occupied by the new circuit board module. Remove the mainframe from the rack and disconnect the power. Remove the bottom cover, and the #4-40 x ¼ mounting studs adjacent to the new modules location from the mainframe. Remove the appropriate rear panel connector cover (blank) from the mainframe. Then remove the appropriate front panel nameplate blank from the mainframe. FMT633Sisb page 3 of 8

6 Install the new circuit board module with the components toward the top cover. Take care to avoid moving any of the pre-set controls (just a slight change can cause the unit to malfunction). Slip the connectors through the holes in the rear panel and drop the front edge of the circuit board onto the brackets attached to the front panel. Install two 3/8 lock washers and two 3/8-32 nuts on the outermost F connector barrels. Gently tighten the nuts while holding the circuit board against the front mounting brackets. Next install two #4-40 x ¼ studs (less lock washers) to secure the front of the board to the mounting brackets. Remove the top over from the mainframe. Connect the negative DC supply to the new circuit board from the PMS610 power distribution wire square connector pins are used, usually connected to a multiple jumper (provided) with mating female connectors which connect from one circuit board to the next. Power supply return is through the chassis. Push any LED's (Light Emitting Diodes) straight into the appropriate mounting holes. (See instructions for the particular module being installed). Insert only until the dark collar around the colored LED is flush with the front panel, the collar must not protrude, in order to avoid interfering with the new nameplate. Mount the new front panel nameplate (Furnished with the circuit board module being installed). Temporarily set the new nameplate in place and check that all necessary cutouts are clear. Remove the paper peel coat from the adhesive baking of the nameplate. Then slide the nameplate down around the LED's onto the panel. Press gently to set the adhesive. Mount any additional panel components (switches, meters, potentiometer, etc.) with the hardware supplied. Gently tighten the fastener to secure the components, do not over tighten the hardware. Mount the new rear panel connector identification strips as illustrated in the instruction book for the particular module being installed. Connect input, output, and power cables. The green POWER ON indicator should be illuminated. Set any internal controls as required. FMT633Sisb page 4 of 8

7 CAUTION: Most circuit board modules have several adjustments which are carefully factory set with precision instruments for optimum performance. Change only those which must be adjusted, some control when mis-adjusted produce little change under normal operating conditions, but can seriously reduce the ability of the unit to function correctly under other conditions which may be encountered. Therefore, if you must adjust a control, place a mark on it before moving it, so that it may e returned to its original setting with reasonable accuracy. Disconnect power. Replace top and bottom covers and mount mainframe to rack. Reconnect power and check for normal operation of each module. One PMS610 mainframe may contain one, two, or three FMT633S steeo TV audio modulators. Mount the mainframe in the rack as near as possible to the TV modulators they will be associated with to reduce the length of video cable runs. There will be two or three coaxial cables according to the type of TV modulator used. Connect the mainframe power cord to a 120 volt AC 60Hz power source. Observe that the green POWER ON L.E.D. lights and that the Red OFF FREQ L.E.D. on each FMT633S lights briefly just as power is applied ad then goes out. The momentary lighting of the red L.E.D. shows that the circuit is functioning correctly and when the L.E.D. goes out, that indicates that the 4.5MHz carrier is Phase-Locked exactly on frequency. Connect the audio input to the FMT633S according to the type of audio source. There is a left and right input and each input is balanced with a high impedance termination so that this unit can be bridged across existing out of band stereo configurations without altering or loading down existing levels. Where this is the only audio connection to the program source, place a 600 Ohm termination at the terminal strip for each input. The equipment is shipped with external 600 Ohm terminations that can be removed for bridging applications. Video connections for SA6350 and similar TV modulators that do not have a separate 4.5MHz audio channel input require a BEF45MTS filter combining network to combine the 4.5MHz output of the FMT633S with the video ahead of the video input connector to the TV modulator. The BEF45MTS filters out video components at 4.5MHz so that these components will not cause sync buzz in the sound channel. FMT633Sisb page 5 of 8

8 Connect the video source to the right-hand BNC connector marked VIDEO SYNC. Using a short coax cable connect from the FMT633S Left-hand VIDEO SYNC connector to the VIDEO INPUT of the BEF45MTS. Using the other short coaxial cable, connect from the FMT633S FM CHAN OUTPUT to the 4.5MHz INPUT of the BEF45MTS. The OUTPUT of the BEF45MTS is connected to the VIDEO INPUT of the TV modulator. This completes the coaxial cable hook-up. The BEF45MTS incorporates a 6dB impedance improvement pad needed to prevent the very sharp 45MHz notch filters from distorting the stereo signal. To bring the video level back up to 1Vpp, remove the 75 Ohm termination oat the video input of the TV modulator, or adjust the video modulator to set video to the correct modulating level. The internal 4.5MHz modulator must be turned off so that only the stereo signal of the FMT633S will be present. On the SA6350 this switch over is accomplished by grounding pin #13 on the rear barrier strip. This does not turn off the actual internal 4.5Mhz modulator, but activates a diode switch, which is quite leaky, therefore the RF output level of the FMT633S must be at maximum output (full clockwise). The SA6350 has a switched 4.5MHz notch filter in the video modulator section. This control is inside of the modulator case and must be turned on (switch handle up). Not all SA6350 notch filters are set to maximum notch depth. By passing the 4.5MHz stereo signal through a de-tuned notch filter can interfere with the stereo signal, so it may be desirable to set this notch filter to optimum null with the signal from the FMT633S. To optimize the notch filter in the SA6350, observe the TV sound channel at a head-end cable tap. Pull out the audio modulator module and place the video modulator module on an extender card. Turn the notch filter switch up observing the drop in the TV audio RF level. Now tune the coil next to the switch for minimum TV audio RF level. After the filter adjustment is completed, plug the audio and video card back into frame. Set the RF OUTPUT of the FMT633S fully clockwise (maximum output). Adjust the RF level of the TV audio with controls on the SA6350. FMT633Sisb page 6 of 8

9 SEPARATE 4.5MHz TV MODULATOR CONNECTIONS: This hook-up does not require a BEF45MTS filter network. Connect the video source to the right hand "BNC" connector marked "VIDEO SYNC". Then connect the left hand "VIDEO SYNC" connector to the Video Input of the TV modulator. Next connect the "FM CHAN OUTPUT" of the FMT633S to the separate 4.5MHz TV audio input connector on the TV modulator. Adjust the "RF OUTPUT" of the FMT633S and/or the RF TV audio level control of the TV modulator to obtain the desired RF output level for the TV audio carrier. Observe the VU meter and 100% LED flasher during periods of maximum program level. Adjust the AUDIO INPUT LEVEL control so that the VU meter touches "0" during program peaks (occasional excursions into the red zone above "0" are acceptable, but the needle should not be in the red zone most of the time and particularly should not ever "pin" the meter). The 100% peak reading LED may flash on even when the VU meter is well below "0" VU. This is not a problem, it means that the wave shape of the program material is such that 100% peaks are being recorded even while the average power under the curve of the wave form is below the average power. Other music content may register "0" VU without lighting the peak reading LED. It may require observation of program level for some minutes to assure that 100% modulation level has transpired and that the correct level has been set. Note that a stereo signal (and associated pilot) will not appear unless the video signal is connected to the SYNC input. An input connecter on the rear panel makes provision for a Second Audio Program (SAP) channel. This connector is used to combine the SAP signal with the multiplex signal before modulating at 4.5MHz. The system is now operating. Now field test the system with your set-top converters in use in the cable system. Certain types of converters (especially some sine wave sync scrambling types) may react poorly to the higher audio deviations employed by MTS stereo TV audio. It may be necessary to reduce audio deviation slightly. The fault actually lies with the set-top descrambler, since the MTS stereo system requires wider deviation than monaural TV audio, but slightly reduced audio deviation may permit the descrambler to operate O.K. without impairing the stereo signal significantly. This problem does not occur on channels not being scrambled. FMT633Sisb page 7 of 8

10 MAINTENANCE: There are no routine periodic maintenance procedures required. Other than setting audio carrier level and audio modulation level, there are no user accessible controls. Internal control setting shave been made at the factory and should not be altered in the field. If the red LED lights and stays lit, that indicates that the 4.5MHz Phase-lockloop (PLL) has is out of lock for some reason. Failure of a component that shuts off the 4.5MHz carrier will light the red LED. Signal tracing may uncover the failed component. Another, more likely reason for the red LED to stay lit is that some component value in the oscillator resonant circuit has drifted enough to pull the PLL out of lock. If this is the case, the oscillator may easily be locked back on frequency by the procedure in the next paragraph. CENTERING THE 4.5 MHz LOCK RANGE: When the PLL lock is lost due to component value drift, lock may be reestablished in the following way. Remove the top cover of the PMS610. Locate the tuning transformer witch is a shiny metal can on the right hand side of the card as seen from the front panel, about 1/3 of the way from the rear panel. It is the only such metal can on the board. Using a special non-metal tuning tool, adjust the coil slug while holding down the momentary contact switch located near the coil. The light will dim and go out when the PLL lock is achieved. Center the slug in the middle of the "light out" condition, then release the switch. The light must remain out. Replace cover. ALIGNMENT PROCEDURES: Alignment of internal controls should not be attempted in the field. If there is reason to believe that some alignment is needed, contact the factory. The only exception it this rule is centering the lock range of the 4.5MHz PLL, which is explained in a previous paragraph. FMT633Sisb page 8 of 8