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FM Systems FMU622CA, Инструкция, Страница: 6 / 21

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LPF, U3: 
 
 

U3, with C126-128, L108 and R125-127, is a 15 KHz low pass filter with low 

output impedance to drive the following section. 
 
SLIDING DE-EMPHASIS, U4, U5, U6, AND Q5: 
 
 

U4 is a precision rectifier, used to control the output drive impedance of U5 into 

C141 such that the variable de-emphasis curve tracks the signal level appropriately. 
Adjustments for through level and de-emphasis provide precise tracking to 
accommodate production component tolerances. W5 provides a low impedance 
drive for negative feedback to stabilize the gain and operating point of U5 at low 
frequencies. U6 provides 10 dB of gain and buffers the high output impedance of U5 
and C141 to feed the following stages. 
 
AUDIO OUTPUT, ½ U7 & U8: 
 
One half of U8 provides the 75 microsecond de-emphasis for the base-band audio 
output, and is used to set the drive level to U8, a semi-floating fully balanced audio 
output stage. U8 provides approximately 10dB of voltage gain, and is capable of 
driving loads of 600 Ohms or more, either balanced or unbalanced. When running 
unbalanced loads, the unused output terminal must e grounded, just as with a 
floating transformer coupled output. 
 
 

STEREO PILOT & CARRIER, U9 & U10: 

 
 

The stereo pilot and carrier frequencies (19 and 38 KHz) are digitally 

synthesized with U10, which is driven by U9, and crystal-controlled oscillator with 
multiple frequency dividers. This provides stable frequency, amplitude, and phase 
relationships. The synthesized sine-wave output are filtered to very low distortion by 
C473-C475, R476, & VR471 (19 KHz) and C483-C486, R485, & VR472. 
 
STEREO MATRIX & MODULATOR, ½ U7 and U12: 
 
 

The second half of U7 is driven by U6 in a matrix to produce L+R and L-R 

channels. The L+R channel is applied to the FM oscillator, via level control VR401. 
The L-R channel is applied, via level control VR402, to one input of the stereo 
multiplex modulator U12. The other input is driven by the 38 KHz carrier generator, 
U10. The output of U12 is a conventional double sideband, suppressed carrier 
amplitude modulated signal centered on 38 KHz. This signal is added to the L+R 
signal at the input to the FM oscillator, along with the 19 KHz pilot signal, also from 
U10. 
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Содержание FMU622CA

Страница 1: ...FMU622CA STEREO AUDIO PROCESSOR NARROW BAND DUAL SUBCARRIER INPUT FM STEREO BAND OUTPUT INSTRUCTION BOOK IB 1222 02 ...

Страница 2: ...TABLE OF CONTENTS SECTION 1 0 INTRODUCTION 2 0 INSTALLATION OPERATING INSTRUCTIONS 3 0 SPECIFICATIONS 4 0 FUNCTIONAL DESCRIPTION 5 0 MAINTENANCE 6 0 TUNING PROCEDURES COMPONENET LOCATOR APPENDIX B ...

Страница 3: ...tput is also available as Base band Audio with separate balanced outputs for left and right channels 2 0 INSTALLATION AND OPERATING INSTRUCTIONS NOTE This section assumes that the FMU622CA is tuned to the desired sub carrier frequency and FM channel output frequency If not proceed to section 6 5 Tuning Procedures Remove the unit from its shipping container and inspect for shipping damage The FMU62...

Страница 4: ...t side to co ordinate with the RF Band levels standard for your cable system NOTE Reversal of the RF channel output IN OUT connections will result in a 20dB reduction of the output due to the directional coupler To connect he separate base band audio left and right output connect the low impedance output to any load of 600 Ohms resistive or higher preferably balanced although unbalanced loads will...

Страница 5: ... in the PMS610 does not require a separate module location as it is beside the three module locations 4 0 FUNCTIONAL DESCRIPTION INPUT Where the subsections are dual the description will be of the left channel only except where the right channel differs Adjustment of the controls is covered in Section 6 Tuning Procedures INPUT Q1 The sub carrier input band pass filter consists of C101 107 and L101...

Страница 6: ...ore either balanced or unbalanced When running unbalanced loads the unused output terminal must e grounded just as with a floating transformer coupled output STEREO PILOT CARRIER U9 U10 The stereo pilot and carrier frequencies 19 and 38 KHz are digitally synthesized with U10 which is driven by U9 and crystal controlled oscillator with multiple frequency dividers This provides stable frequency ampl...

Страница 7: ...ammed on frequency set switch SW501 The total division is down to 10 KHz which is also the frequency generated by the reference crystal oscillator after it is separately divided The two 10 KHz signals are applied to a phase comparator in U14 The output of the phase comparator is a control voltage proportional to any phase and frequency difference between the reference and the FM oscillator center ...

Страница 8: ...ING There is no requirement it touch up the tuning of the sub carrier input circuitry and the factory strongly suggest that no adjustments be made except when there is a need to tune new sub carrier input channel frequencies In this case we recommend that the unit be returned to the factory for retuning If circumstances require that the retuning be done in the field the following procedure may be ...

Страница 9: ...ed sub carrier frequency to the RF input of the modulation meter Connect the demodulated audio output of the modulation meter to the audio input of the distortion analyzer Connect the output of the distortion analyzer to the vertical input of the oscilloscope Connect the auxiliary output of the signal generator to the external trigger input of the oscilloscope Adjust the 1000Hz level to cause a su...

Страница 10: ...dulate the sub carrier 100 50 KHz with 50 Hz Measure signal level at U6 7 Adjust VR131 for 10 dBm output Switch the modulating frequency to 15 KHz verify that sub carrier deviation remains 50 KHz Adjust VR133 for 10 dBm output from U6 Verify that the circuit is functional by switching the modulating frequency to 2 KHz at 10 sub carrier deviation 5 KHz The output of U6 should drop to 21 dBm a 31 dB...

Страница 11: ...erator and re install U7 The stereo carrier and pilot frequencies are crystal controlled to better than 1 Hz accuracy The crystal frequency may be trimmed over a narrow range by adjusting C472 As this is an extremely stable circuit re adjustment is unnecessary unless the crystal is replaced by one not tuned for a 30 pf load In order to provide optimum stereo separation the 19 KHz pilot phase zero ...

Страница 12: ...to the center of its control range Small changes of L501 tuning may cause the red LED to light momentarily but is must be out when L501 is correctly set when illuminated the output frequency is not locked to the reference crystal frequency Connect a field strength meter to the FM channel output OUT and terminate the IN connector with 75 Ohms Tune C515 and C516 Multi turn piston capacitors for maxi...

Страница 13: ...nged considerably retune the output filter by adjusting C516 C515 the two variable capacitors nearest the output connectors for peak output level SWITCH SETTING FOR ANY FREQUENCY NOTE Although the frequency setting switches may be programmed over a very wide range the oscillator will only work within the range of frequencies originally specified attempts to operate far outside the specified range ...

Страница 14: ...onvenient way of determining the correct switch positions the example frequency is again 88 5 MHz as above FREQUENCY RUNNING SWITCH SWITCH INCREMENT TOTAL OPEN 1 NUMBER MHz MHz CLOSE 0 10 102 4 102 4 0 9 51 2 51 2 1 8 25 6 76 8 1 7 12 8 89 6 0 6 6 4 83 2 1 5 3 2 86 4 1 4 1 6 88 0 1 3 0 8 88 0 0 2 0 4 88 4 1 1 0 2 88 6 0 STRAP 0 1 88 5 1 Open the switch if the total is less than or equal to the des...

Страница 15: ... 89 4 0 1 1 0 1 1 1 1 1 1 0 89 5 0 1 1 0 1 1 1 1 1 1 1 89 6 0 1 1 1 0 0 0 0 0 0 0 89 7 0 1 1 1 0 0 0 0 0 0 1 89 8 0 1 1 1 0 0 0 0 0 1 0 89 9 0 1 1 1 0 0 0 0 0 1 1 90 0 0 1 1 1 0 0 0 0 1 0 0 90 1 0 1 1 1 0 0 0 0 1 0 1 90 2 0 1 1 1 0 0 0 0 1 1 0 90 3 0 1 1 1 0 0 0 0 1 1 1 90 4 0 1 1 1 0 0 0 1 0 0 0 90 5 0 1 1 1 0 0 0 1 0 0 1 90 6 0 1 1 1 0 0 0 1 0 1 0 90 7 0 1 1 1 0 0 0 1 0 1 1 90 8 0 1 1 1 0 0 0 1 ...

Страница 16: ... 93 4 0 1 1 1 0 1 0 0 1 1 0 93 5 0 1 1 1 0 1 0 0 1 1 1 93 6 0 1 1 1 0 1 0 1 0 0 0 93 7 0 1 1 1 0 1 0 1 0 0 1 93 8 0 1 1 1 0 1 0 1 0 1 0 93 9 0 1 1 1 0 1 0 1 0 1 1 94 0 0 1 1 1 0 1 0 1 1 0 0 94 1 0 1 1 1 0 1 0 1 1 0 1 94 2 0 1 1 1 0 1 0 1 1 1 0 94 3 0 1 1 1 0 1 0 1 1 1 1 94 4 0 1 1 1 0 1 1 0 0 0 0 94 5 0 1 1 1 0 1 1 0 0 0 1 94 6 0 1 1 1 0 1 1 0 0 1 0 94 7 0 1 1 1 0 1 1 0 0 1 1 94 8 0 1 1 1 0 1 1 0 ...

Страница 17: ... 97 4 0 1 1 1 1 0 0 1 1 1 0 97 5 0 1 1 1 1 0 0 1 1 1 1 97 6 0 1 1 1 1 0 1 0 0 0 0 97 7 0 1 1 1 1 0 1 0 0 0 1 97 8 0 1 1 1 1 0 1 0 0 1 0 97 9 0 1 1 1 1 0 1 0 0 1 1 98 0 0 1 1 1 1 0 1 0 1 0 0 98 1 0 1 1 1 1 0 1 0 1 0 1 98 2 0 1 1 1 1 0 1 0 1 1 0 98 3 0 1 1 1 1 0 1 0 1 1 1 98 4 0 1 1 1 1 0 1 1 0 0 0 98 5 0 1 1 1 1 0 1 1 0 0 1 98 6 0 1 1 1 1 0 1 1 0 1 0 98 7 0 1 1 1 1 0 1 1 0 1 1 98 8 0 1 1 1 1 0 1 1 ...

Страница 18: ... 0 1 1 1 1 1 1 0 1 1 0 101 5 0 1 1 1 1 1 1 0 1 1 1 101 6 0 1 1 1 1 1 1 1 0 0 0 101 7 0 1 1 1 1 1 1 1 0 0 1 101 8 0 1 1 1 1 1 1 1 0 1 0 101 9 0 1 1 1 1 1 1 1 0 1 1 102 0 0 1 1 1 1 1 1 1 1 0 0 102 1 0 1 1 1 1 1 1 1 1 0 1 102 2 0 1 1 1 1 1 1 1 1 1 0 102 3 0 1 1 1 1 1 1 1 1 1 1 102 4 1 0 0 0 0 0 0 0 0 0 0 102 5 1 0 0 0 0 0 0 0 0 0 1 102 6 1 0 0 0 0 0 0 0 0 1 0 102 7 1 0 0 0 0 0 0 0 0 1 1 102 8 1 0 0 0...

Страница 19: ...05 4 1 0 0 0 0 0 1 1 1 1 0 105 5 1 0 0 0 0 0 1 1 1 1 1 105 6 1 0 0 0 0 1 0 0 0 0 0 105 7 1 0 0 0 0 1 0 0 0 0 1 105 8 1 0 0 0 0 1 0 0 0 1 0 105 9 1 0 0 0 0 1 0 0 0 1 1 106 0 1 0 0 0 0 1 0 0 1 0 0 106 1 1 0 0 0 0 1 0 0 1 0 1 106 2 1 0 0 0 0 1 0 0 1 1 0 106 3 1 0 0 0 0 1 0 0 1 1 1 106 4 1 0 0 0 0 1 0 1 0 0 0 106 5 1 0 0 0 0 1 0 1 0 0 1 106 6 1 0 0 0 0 1 0 1 0 1 0 106 7 1 0 0 0 0 1 0 1 0 1 1 106 8 1 0...

Страница 20: ...ank from the mainframe Then remove the appropriate front panel nameplate blank from the mainframe 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 brack...

Страница 21: ...nts 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 CAUTION Most circuit board modules have several adjustments which are carefully factory set with p...

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