INSTRUCTION MANUAL FOR CSG-10 COMPOSITE STEREO GENERATOR JT COMMUNICATIONS 579 N.E. 44TH AVE. OCALA, FLA. 34470 352-236-0744 fax 352-236-5130 email: jtcomm@atlantic.net TABLE OF CONTENTS: 1) INTRODUCTION 2) INSTALLATION 3) OPERATION/CALIBRATION 4) TROUBLESHOOTING 5) SCHEMATIC 6) PC BOARD LAYOUT 7) PARTS LIST 1) INTRODUCTION NOTE- PLEASE READ THE ENTIRE CONTENTS OF THIS INSTRUCTION MANUAL BEFORE INSTALLING THIS UNIT. IF YOU HAVE ANY QUESTIONS CONCERNING THE OPERATION OR INSTALLATION OF THIS UNIT, PLEASE CONTACT THE FACTORY. The CSG-10 Stereo Generator is a universal replacement for the FM broadcast services. The CSG-10 will retrofit older broadcast Stereo Generators that are either unreliable or unrepairable. Many early-model Generators are operating below current standards. The CSG- 10 can replace the older equipment, and will remain acceptable within F.C.C. broadcast specifications. The CSG-10 has been designed for the user to provide the power supply, enclosure, and audio connections. The CSG-10 is simple to install, and will provide prolonged life and performance. THEORY OF OPERATION (Refer to schematic) Audio inputs are routed into an active 75uS pre-emphasis network, determined by C1 and the 7.5k feedback resistor. This routes to a twin-tee 19 kHz notch filter. This anti-alias filter keeps audio frequencies from interfering with the pilot frequency. This is a deep (60 dB) notch, and produces an extremely narrow band-stop. The output is routed into a 6 pole active 15 kHz Butterworth low-pass filter. This filter attenuates and reduces the pre-emphasis' effects on frequencies above 15 kHz, and further reduces the 19kHz frequencies from affecting the Pilot. Active filters were chosen over passive due to the overshoot and ringing anomalies that occur with passive filter design. The filtered left and right signals are split into L+R (sum) and L-R (diff) components with a matrix circuit. The L+R component connects to an all-pass phase shift network. This network compensates for the increase in phase delay that occurs linearly in frequency of the L-R chain. The L-R signal is routed into U7, a CMOS switch; this switch electronically selects between the in-phase and out-of-phase L-R signal. The result is a double-balanced mixer, whose performance is independent upon temperature variations. The signal is switched at a 38kHz rate, from the output of U8, a preselectable divider. The divider contains a crystal oscillator operating at 9.728mHz, which is 256 times the switching rate. The 19kHz pilot signal is also derived from U8. The output of U7 is converted into a voltage with U4B. U4B connects to a phase-corrected low-pass 60 kHz filter, which removes switching components from the double balanced mixer. This output, and the L+R output are summed into U5, a variable-supply amp. The outputs of U4B & C are at D.C. potentials directly dependent upon the setting of R69 (clip level). Varying R69 adjusts the power rails of U5. By reducing the power rails, a hard limit sets the maximum output level of U5. This forms the composite clipper stage. The output of U5, and the filtered Pilot signal are summed into U6A. The output of U5 is adjustable through the Output Level pot, R66, and is buffered by line driver U6B. 2) INSTALLATION The CSG-10 has 1/2" long standoffs located 1/8 inch from each corner of the PC board. It is recommended that the PC board be mounted into a metallic enclosure for minimized RF interference. The use of feed-through low-pass filters for audio and power is recommended. POWER The CSG-10 is designed to connect to a bipolar 12 to 15VDC power source. The power supply should be regulated, clean and free from any noise or ripple. THIS IS DIRECTLY DEPENDENT ON THE PERFORMANCE OF THE CSG-10. The minimum current should be 0.2 amps. The Red wire is the +V connection, and the Violet wire is the -V connection. The Black wire is the +/- common (ground). If properly mounted on a metallic surface, the surface will be adequate for the return (ground) path. WARNING: IMPROPER CONNECTIONS TO THE POWER SUPPLY, OR FAILURE TO USE REGULATED SUPPLIES WITH +/- 15 VDC MAXIMUM WILL VOID WARRANTY. AUDIO CONNECTIONS The audio inputs are unbalanced 10K impedance. Any D.C. components present from the program source are blocked by the input capacitors. NOTE- THE CSG-10 IS CAPABLE OF OPERATION TO BELOW 10 HZ. PROPER INPUT HIGH-PASS FILTERING MAY BE NECESSARY TO AVOID MODULATION AT OR BELOW THESE FREQUENCIES. The audio inputs should be connected from a low-impedance source.The inputs are frequency sensitive and caution must be observed during excessive level changes. It is recommended that an appropriate audio processor be connected to the CSG-10. A nominal -30 dBv re. 0.77 Vrms is recommended for program material, and will provide 10 dB of headroom at 15kHz . REMEMBER: Higher input levels will cause distortion particularly at the higher frequencies, and should be avoided. If higher input levels are used, input attenuation will be necessary. The inputs are located near the 47 uF input blocking capacitors. EXTERNAL INPUT CONNECTIONS There are two unbalanced connections for additional multiplexing, such as SCA, etc. One input is before the clipped output, and the other is after it. Both inputs are 10K unbalanced. The input closer to the right (near output pot) is the post-clipper input. OUTPUT CONNECTION The CSG-10 should be connected to the COMPOSITE input of a conventional Exciter, such as the JT Communications' PLFM-100. The composite output is an unbalanced 600 ohm type, and care should be observed when driving excessively long lines. Ground loops should be avoided at all costs, as this will significantly reduce performance. 3) OPERATION ADJUSTMENTS- DESCRIPTION COMPOSITE CLIP LEVEL (R69) The purpose of this control is to stop the transient peaks that occur during multiplexing. These peaks cause over-modulation. Pre-generator clipping (processing) will not effectively reduce these transient products caused in the creation of the Stereo Generation process. This control should be used in moderation, as excessive clipping will produce harmonics which may fall outside the authorized bandwidth, as well as degrade the stereo image and separation. Some installations will use composite clipping aggressively; usually a protection low-pass filter should be installed at the output of the CSG-10 to reduce the harmonics that are produced by the clipping process. Once a desirable clip level is set, the program signal will hard-limit above the "clip-point". Increasing the frequency, level, or both will increase the amount of composite clipping on the multiplexed signal. The operation of the composite clipper in the CSG-10 will not affect the pilot signal performance, but will maintain effective transient control. Turning the control Counter- clockwise increases the amount of composite clipping, reducing max. output. CLIP OFFSET (R93) This control will adjust the ratio of Positive to Negative peak ratio in the composite clipping process. Some exciters have non-linear characteristics which may cause more clipping to develop on one side of the modulation envelope than the other. Adjustment of this control will reduce the peaks on one side, and increase the peaks on the other. This adjustment should be made if there are more peaks of a particular polarity than another, and the adjustment of this control should be performed with a calibrated modulation monitor, or an Oscilloscope connected to the demodulated composite output of a conventional FM tuner. PILOT LEVEL (R65) This control should be adjusted for -20dB (8-10%) of 100% modulation level, and set with a calibrated modulation monitor. If you reset the maximum output level for clipping, etc. , you should recheck the setting of the Pilot level. The pilot level setting is 10% of TOTAL MODULATION setting. There is a jumper on the CSG-10 which can be removed and connected to an external switch, so that you can manually turn the pilot on and off. The effect of this switch will change the demodulated signal from stereo to mono. Turning this control CW increases pilot level. NOTE ON PILOT PHASE Each CSG-10 is factory calibrated for optimum separation. Phase compensation for the pilot is not necessary, as the transmission chain will typically produce phase shifts beyond 19 kHz. Maximized separation is obtained by the proper adjustment of R59 & R94. (note- these controls are calibrated in a phase-free environment; you may need to readjust according to your requirements.) L-R GAIN (R59) This factory-calibrated control sets the gain of the 38kHz subcarrier. It is calibrated at a low frequency (100 Hz) for a flat baseline. This adjustment adversely affects overall separation, and caution should be observed when adjusting this control. See "CALIBRATION" section for proper alignment. L-R PHASE (R94) This factory-calibrated control sets the maximum separation at high frequencies (above 5 kHz). This control compensates for the phase delay that occurs in the generation and filtering of the 38 kHz subcarrier. For proper adjustment, see "CALIBRATION" section. L-R OFFSET (R92) This control adjusts the 38 kHz carrier null. The digital balanced modulator in the CSG-10 operates independent upon temperature, therefore the 38 kHz carrier is not subject to the usual changes that occur in linear balanced modulators. This carrier null is directly dependent upon the power supply voltages; adjustment should be made upon initial installation, and any time the power supply is changed. As your application may vary, you may want to readjust this control upon installation of the CSG-10. OUTPUT LEVEL (R66) This control adjusts the final composite output level. This adjustment should be set after the composite clipping level is established. The adjustment of this control should be set with a calibrated modulation monitor. NOTE: YOU CAN DEFEAT PRE-EMPHASIS BY REMOVING C1 & C2. MAXIMIZED HEADROOM IS OBTAINED USING +/- 15 V. SUPPLIES. GAIN CAN BE ADDED TO OUTPUT LINE DRIVER STAGE FOR ADDITIONAL OUTPUT LEVEL- CONTACT FACTORY FOR THIS MOD. ADJUSTMENTS- MANUAL The CSG-10 includes controls that are factory-set. Unless a complete recalibration is required, it is not absolutely necessart to adjust the following controls: Control Function R92 (L-R offset) Minimizes carrier null at various power supply fluctuations (you may need to readjust when connecting your power supply). R59 (L-R gain) Adjusts the L-R gain set below pre-emphasis. R94 (L+R phase) Compensates for L-R phase delay, maximizes HF separation. The function of the following controls are user-adjustable, and should be set with an Oscilloscope with a 10mHz bandwidth, or a modulation monitor. Control Function R66(output level) Sets composite output level R65(Pilot level) Sets pilot injection R69(Clip level) Sets composite clip level R93(Clip offset) Sets the positive to negative clip ratio The settings of the above user-adjustable controls are factory set to the following: R66 half-gain (-6dB below max. setting) R65 -20 db re .775 Vrms (0.8 V P-P) R69 full CW (least clipping) R93 even + and - clip levels CALIBRATION: recommended equipment: Oscilloscope 10 mHz B.W. min. Low-distortion audio generator Audio Spectrum Analyzer Audio RMS voltmeter V.O.M. well regulated & filtered power supply SET ALL CONTROLS AS FOLLOWS: R92- middle R69-least clipping R59-middle R65-minimum out R66- middle R93-middle JP1-in (shorted) R94-middle CONDUCT THE FOLLOWING TESTS: 1) Connect power supply. Disconnect L & R audio inputs, and short to ground. Connect RMS voltmeter, scope, and audio spectrum analyzer to composite output of CSG-10. 2) Observe 38 kHz component at output, and adjust R92 for minimum output of 38kHz sub- carrier injection (Typ -55 dB). 3) Remove short to audio input, and connect either L or R input (not both) to audio generator. Set generator to -10dBv, re. 0.775 Vrms out, and 500 Hz. Adjust R59 for flat baseline. Set generator to -20dBv, 10kHz, and adjust R94 for as flat a baseline as possible. 4) TROUBLESHOOTING IF A PROBLEM EXISTS IN THE OPERATION OF THIS UNIT, PLEASE REFER TO THIS CHART. PROBLEM SOLUTION(S) no output 1,4 not in stereo 2,3,4,6 no pilot on tuner 2,3 distortion 4,5,7 poor separation 8 excessive 38kHz component 9 SOLUTIONS: 1) check power supplies 2) pilot level not properly adjusted 3) pilot jumper removed 4) composite level not properly set 5) excessive input level 6) mono source 7) composite clipper set too high 8) L-R gain/phase not set, see CALIBRATION section 9) see CALIBRATION section --NOTICE-- IF YOU CAN NOT FIND SOLUTION TO PROBLEM, CONTACT FACTORY FOR TECHNICAL ASSISTANCE. IF THE PRODUCT FAILURE IS DUE TO A FACTORY DEFECT, THE PRODUCT WILL BE REPAIRED FREE WITHIN ONE (1) YEAR FROM DATE OF PURCHASE. YOU MUST CALL THE COMPANY DURING WORKING HOURS SO THAT A RETURN AUTHORIZATION CAN BE GENERATED. IN SOME CASES, A LOANER UNIT MAY BE AVAILABLE; REQUEST THIS WHEN CONTACTING FACTORY.