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Hal Communications ST-6000 Instruction Manual

Demodulator
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ST-6000
FSK
DEMODULATOR

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  • Page 1 ST-6000 DEMODULATOR...
  • Page 2 HAL ST-6000 FSK DEMODULATOR / KEYER Technical Manual ******************************************************************************** Copyright © 1976 by HAL Communications Corp., Urbana, Illinois. February, 1982 Printing Reprint January, 2019, DC7XJ...

  • Page 3: Table Of Contents

    Alternate Connection to the ST-6000 3-11 3.3.1 Use of External Loop Supplies and Multiple Loop Circuits 3-12 3.3.2 Separate Printer and Keyboard Connection 3-12 3.3.3 Full Duplex Operation of the ST-6000 3-12 3.3.4 External Data Processing Equipment 3-15 3.3.5 External Oscilloscope Connections 3-15 3.3.6 Tone Keyer Control Connections...
  • Page 4 ST-6000 CIRCUIT DESCRIPTION ST-6000 Analog Processing Circuits - Input Circuit Board 5.1.1 Input AGC Circuit 5.1.2 Input Bandpass Filters 5.1.3 Limiter Amplifier 5.1.4 Discriminator Filters 5.1.5 Discriminator Detectors 5.1.6 A/S Amplifier and Detectors 5.1.7 Active Lowpass Filter 5.1.8 ATC Circuit 5.1.9 Tone Keyer...
  • Page 5 Figure 5.1 ST-6000 Block Diagram 5-11 Figure 5.2 ST-6000 Schematic Diagram Conventions 5-12 Figure 5.3 Input AGC Circuit 5-13 Figure 5.4 Input Bandpass Filter 5-14 Figure 5.5 Limiter Amplifier 5-15 Figure 5.6 Discriminator Filters 5-16 Figure 5.7 Discriminator, Meter Amp., Lowpass Filter, ATC 5-17 Figure 5.8...

  • Page 6: Introduction

    2125 Hz ("high-tone" set) for frequency shifts of 170 Hz, 425 Hz, and 850 Hz. The tone keyer section of the ST-6000 generates the same set of tones for trans- mitting in addition to a narrow-shift tone for Morse code identification.
  • Page 7 A complete set of cables and connectors are furnished with the ST-6000 to simplify the initial in- stallation of the ST-6000. If you are anxious to try your ST-6000, it is suggested that you skip to sections 3.1 and 3.2 of the installation chapter and then read sections 4.1 and 4.2 of the operation chapter before turning the equipment on.

  • Page 8: Specifications

    SPECIFICATIONS Demodulator Section: Input data: Serial Data Data rate: Up to 110 baud Input Impedance: 500 Ohms, balanced and isolated from ground Input frequencies: "Low-tone" set: Mark = 1275 Hz Space = 1445 Hz (170 Hz shift) 1700 Hz (425 Hz shift) 2125 Hz (850 Hz shift) "High-tone"...
  • Page 9 Tone amplitude: Adjustable from -40 dBm to 0 dBm (approximately 10 mV to 1.0 V) Amplitude variation: Less than ±0.5 dB at 0 dBm output Output impedance: 500 Ohms, balanced to ground Distortion: All harmonics below the 9 are attenuated greater than 40 dB (Less than 1.0 % total harmonic distortion).
  • Page 10 Miscellaneous Data: Fuse protection: Main AC Power - 0.5 A, slow-blow Loop Power Supply - 0.1 A Accessible from rear Panel Power requirements: 105 to 125 or 210 to 250 VAC, 50 or 60 Hz, 20 Watts (excluding printer motor) Cabinet size: Width 17"...
  • Page 11 Balanced 500 ohm demodulator tone input. NOTE: All of the above specifications are nominal, design-center values and may vary in produc- tion units by as much as ±10 %. HAL Communications Corp. reserves the right to alter any specifications without prior notification.

  • Page 12: Installation

    A total of five factory prepared cable-plug combinations and two jumper-plugs are supplied with the ST-6000. These cables and plugs can be used to make most standard input and output con- nections to the ST-6000, particularly those connections in which an ST-6 or similar demodulator is being replaced by the ST-6000.

  • Page 13: Audio Output Connection

    10.0 Amperes. The following precautions should be observed when using the MOTOR receptacle: 1. The power to the MOTOR receptacle is NOT fused in the ST-6000. The user should be sure that any device attached to this connector has its own fuse protection.
  • Page 16 Note: The data connection between the DS-3100 and the ST-6000 is via a loop connection, not an RS-232 connection. The "RS-232" connector on the ST-6000 is only used to connect the CW-ID line to the demodulator.
  • Page 17 Figure 3.? DS-2000 and ST-6000 System Connection Schematic...

  • Page 18: Kos Cable Connection

    The ST-6000 and terminal will now operate in the half-duplex mode using RS-232 I/O interface connections. The RS-232 data from the terminal will both drive the ST-6000 Loop 1 circuit and op- erate the KOS circuitry. A teleprinter connected into the Loop 1 circuit will print data generated on the RS-232 terminal or data demodulated by the ST-6000.

  • Page 19: Figure 3.2 Loop Connections To The St-6000

    Figure 3.2 Loop Connections to the ST-6000...

  • Page 20: Figure 3.3 Rs-232 I/O Connections To The St-6000

    Figure 3.3 RS-232 I/O Connections to the ST-6000...

  • Page 21: Separate Keyboard Connection

    250 VAC, 50 to 60 Hz operation. When the 210 to 250 VAC connection is supplied, it is indicated by a small tag on the rear panel of the ST-6000. If this tag is NOT on the rear panel, do NOT con- nect the ST-6000 to a 240 Volt line without first checking the internal wiring of the power trans- former.

  • Page 22: Alternate Connection To The St-6000

    In such cases, changing the antenna, matching system, and/or feedline to a matched coaxial line system will usually clear-up RF interfer- ence. When good RF grounds and low SWR feed-lines are used, the ST-6000 will work with even very high powered transmitter systems.

  • Page 23: Use Of External Loop Supplies And Multiple Loop Circuits

    The general block diagram of the ST-6000 and a listing of the rear panel pin connections is shown in Figure 5.1. The connections made by the AUXILIARY jumper plug furnished are shown by the dotted lines. This figure, as well as the discussions of section 5, Theory of Operation, should be carefully studied before alternate connections to the ST-6000 are attempted.

  • Page 24: Figure 3.5 Alternate Loop Connections

    Figure 3.5 Alternate Loop Connections 3-13...
  • Page 25 Figure 3.6 Connections for the ST-6000 for Full-Duplex Operation 3-14...

  • Page 26: External Data Processing Equipment

    (for autostart recording, for instance) or to repeat the signal on another communications link. (Use of the ST-6000 in a TTY re- peater would be further enhanced if the received data is first coupled through a UART digital data regeneration circuit before driving the tone keyer section.).
  • Page 27 ON signal (pin 9, J3) can be connected to TONE ENABLE (pin 12, J3), taking care to first remove the jumper between pins 8 (ground) and 12 of the AUXILIARY connector (J3). In this case, the KOS circuit will actuate the tone keyer output. Figure 3.7 Connection to External Data Processing Devices 3-16...

  • Page 28: Operation

    Please read all sections carefully. Front Panel Controls and Indicators The ST-6000 front panel has a total of twelve push-button switches that allow operator control of the demodulator. Normal operation of the demodulator with ALL automatic features active is ob- tained by depressing all six of the right-hand bank of switches and the right-hand three switches of the left bank.

  • Page 29: Simplified Operating Procedure

    The following procedure is suggested for those operators who are anxious to try the ST-6000 without reading the rest of this manual. 1. Use the "standard" cables and jumper plugs supplied with the ST-6000 to connect the unit to a receiver and printer or display as described in section 3.2. DO NOT CONNECT A TRANSMITTER WITHOUT READING THE REST OF SECTION 4 OF THIS MANUAL.

  • Page 30: Reception Of Radio Teleprinter Signals

    IF pass-band and mixed in the product detector with the BFO to produce audio tone beat signals which then drive the ST-6000. Since the audio fil- ters of the ST-6000 follow the demodulator standard of mark being the lower frequency audio tone, it follows that the BFO of the receiver should be HIGHER in frequency than the FSK signal.

  • Page 31: Receiver For Afsk Reception

    Because the discriminator filters in the ST-6000 (like those of the ST-5 and ST-6) are relatively broad-band, the mark and space scope displays are NOT lines, but ellipses.

  • Page 32: Use Of The Atc Circuit

    Proper tuning adjustment of the receiver is much more critical when the autostart circuits of the ST-6000 are active than when they are not. This is because the autostart circuitry senses the "plus-plus" voltage which is quite sensitive to the centering of the signals in the discriminator fil- ters.

  • Page 33: Use Of The Limiter Switch Fm Vs. Am

    Although the ST-6000 performance in AM mode exceeds that of the previous model ST- 6 demodulator, the actual improvement in print may or may not be noticed, depending upon the receiving conditions.

  • Page 34: The Kos Circuit

    4.10 Use of the Autostart Circuitry The ST-6000 autostart circuit operates in a manner very similar to that of the ST-5 and earlier TT/L and TT/L-II demodulators. The autostart provides a two-step control of the printer mark-hold and control of the AC power to the printer motor. The autostart circuit senses the voltage on the...

  • Page 35: Antispace Circuitry

    RTTY signal be done with the AUTOSTART switch in the OFF position during initial testing of the ST-6000. After the operator has some practice in tuning the receiver, he may then wish to leave the autostart circuit ON, remembering to account for the time delay of the autostart.

  • Page 36: Transmitting Radio Teleprinter Signals

    Although the output impedance of the tone keyer is 500 Ohms, virtually any load impe- dance from 500 Ohms to several Megohms can be driven by the ST-6000. It is NOT necessary to terminate the audio output connector in a 500 Ohm load.
  • Page 37 typical voice is at best 50 % (less compressors, etc.) while a RTTY transmission has a 100 % duty cycle. SSB transmitter power amplifier stages are usually designed to take advantage of the re- duced duty cycle of a voice signal to produce relatively high output powers in small enclosures with proportionally smaller power supplies.

  • Page 38: Transmitting Afsk Signals

    VHF-FM transmitters are designed for intermittent duty and may NOT permit extended RTTY trans- missions without reducing the transmitter power. 4.13.3 Adjustment of the ST-6000 Tone Keyer The tone frequencies generated by the tone keyer are all derived from crystal oscillators and therefore do not require adjustment.

  • Page 39: St-6000 Circuit Description

    5.1.1 Input AGC Circuit (Figure 5.3) The audio input to the ST-6000 is first coupled through a 500 to 500 Ohm transformer to the in- put AGC amplifier. The transformer allows connection of the ST-6000 to either a balanced or un- balanced audio source and provides DC isolation of the input.

  • Page 40: Discriminator Filters

    Both sections of a MC 1458 IC are used in a three-pole active low-pass filter that follows the discriminator stage. The cut-off frequency of this filter is set to approximately 82 Hz to minimize noise on the signal while still allowing use of the ST-6000 at data rates up to 100 baud. 5.1.8 ATC Circuit (Figure 5.7) When using the ST-6000 in the "AM"...

  • Page 41: Tone Keyer

    5.1.9 Tone Keyer (Figure 5.8) The tone keyer section of the ST-6000 is very similar in design to that used in the HAL XTK-100 AFSK Oscillator. The circuit is made up of five basic sections: oscillators, keyer, divider, D/A con- verter, and lowpass filter.

  • Page 42: Antispace Circuit

    5.2.2 Antispace Circuit (Figure 5.9) If a signal at the space frequency is held for a long period of time, the teleprinter will "run- open", making an annoying, louder than normal noise. To prevent this problem, sections of inte- grated circuits 2 and 3 are connected in a timer circuit that senses the length of the space signal and places the post-autostart data signal in a mark-hold condition whenever the space exceeds 250 ms.

  • Page 43: Post-Autostart Data Output

    Both the pre- and post-autostart data signals are CMOS logic signals with mark = 0 Volts and space = +12 Volts. Part of the versatility of the ST-6000 lies in the fact that these signals are available for external connection and can be jumpered to suit individual requirements.

  • Page 44: Rs-232/Mil-188 Interfaces

    The operation of the front panel indicators (see Table 4.2) can now be explained in terms of the control circuitry of the ST-6000. The MARK, SPACE, and AUTO indicators are shown in Figure 5.9. The MARK indicator is driven directly from the output of the slicer stage. Thus, it ALWAYS indicates...

  • Page 45: Power Supply

    The power transformer, loop resistor, and fuses are mounted directly on the cabinet. The +12 and –12 voltages required by the ST-6000 are derived from a full-wave bridge rectifier. The +12 Volt supply is regulated with a type 7812 integrated circuit regulator, the –12 Volt by a type 7912 IC.

  • Page 46: Cabinet Wiring

    Cabinet Wiring The ST-6000 is constructed in semi-modular form with most of the circuitry on the two large cir- cuit boards, the input and control boards. The six LED indicators are mounted on a flexible circuit board which is attached directly to the switches on the control board.

  • Page 47: Troubleshooting Guide

    ATC off. 6) Use DTH only with high signal levels. 7) If you intend to run RS-232 or MIL-188 signals out of the ST-6000 to drive a printer, be sure to refer to sections 3 and 4 of the manual! 8) Cables are extremely important.
  • Page 48 4) Make sure that the passband of your transmitter is of sufficient width to pass both the Mark and Space tones you are using. THERE ARE THREE WAYS TO SET THE ST-6000 FOR TRANSMITTING: 1) KOS activated 2) Print switch in LOCAL position...
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  • Page 67: Appendix A: Rf-Induced Problems

    APPENDIX A RF-INDUCED PROBLEMS HAL Communications equipment is designed to operate in close proximity to radio frequency transmitting and receiving equipment. Particular attention has been paid to the shielding of circui- try through the use of all-metal enclosures and good common grounds. However, under certain conditions in an RF-saturated environment, HAL equipment may be susceptible to RF-induced in- terference.
  • Page 68 2A shows a common bypass-filter method used in many transmitters. The drawing in Fig. 2B de- picts a brute-force AC-line filter that can be added to transmitters or other equipment to eliminate the flow of RF on power lines. RF-induced problems that cannot be cured, or ones that appear not to be the fault of inade- quate transmitter filtering should be referred to HAL factory Customer-service personnel.

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