Manual / Guide
HAL ST-5000 FSK demodulator keyer manual
HAL ST-5000 FSK demodulator/keyer manual (175 V 60 mA loop; 2N5655 high-voltage keyer; ±15 V FSK output)
Manual / Guide
HAL ST-5000 FSK demodulator/keyer manual (175 V 60 mA loop; 2N5655 high-voltage keyer; ±15 V FSK output)
: HAL ST-5OOO FSK DEI'4ODULATOR / KEYER TrcHN I cAL llnnuAL ***************************************lt********** CopyrightOlgTT by HAL Communications CorP., Urbana, lllinois. Printed in the United States of America. Al I rights reserved. Contents of this publication may not be reproduced in any form without the rvritten permission of the copyright owner. February, 19Bq Printing HAL sT-5000 I]EI{OD U LATO R CONTENTS l. INTRoDUCTI0N 2. SPECIFICATIONS 3. INSTALLATIoN . 3.1 3.2 3.3 3.\ . o .......... o. l-l .. 2-1 3- t . lnitial lnspection Audio Connections Loop Connect i ons 3- l FSK Connections STANDBY Connect i ons 3.5 3.6 CW lD Key Cable Connection 3.7 AC Porver Cord Connection 3.8 Hotor Por.,e r Connect ion 3.9 Ground Connection 3.10 External 0scilloscope Connect i ons 4. \.2 \.3 3-7 3-7 I{- I OPERATION 4. t 5. . 3-r 3-z 3-2 3-2 3-6 3-6 3-6 Front Panel Control s and I nd icators Simpl i fied 0peration Procedu re Reception of Radio Teleprint er Signals 4.3.1 Receiver for FSK Rece ption \. 1.2 Rece i ve r fo r AFS K Rec ept ion 4- t \-2 \-2 \-z q-t{ \.3.\ Tuning a RTTY Signal l+. \ Use of the SENSE Srvitch \.5 Use of the PRINT Srvitch \.6 Use of the Autostart Ci rcui try \.7 Tone Keyer Circuit l{. I Transmi t t ing Rad io Teleprinter Signals I{.8.1 Transmitting FSK Signals \.8.2 Transmitting AFSK Signals \-7 \-7 \-7 \-9 ST-5OOO C I RCUI T DESCRI PT I ON 5-1 5. I 5.2 5.3 lnput Lirniter Stage Discriminator Fi lters Di scrimi nator Detectors 5. tl Heter Amplif ier and Detectors 5.5 Active Lovr-pass Fi I ter 5.6 Slicer Amplifier and Keyer Stages 5.7 Autostart Stage 5-1 5-1 5- l 5.8 Tone Keyer Stages 5.9 Por,.,er Supply 5. l0 User Adj us tments 5-2 5-2 5-2 5-2 5-3 5-3 N0TE: See ADDENDUI.l 1 on pages 5-4a. and 5-4b. operation. Lt- E \-5 \-6 I{- 5 5-l for jumper requirements before I LLUSTRAT I ONS Figure 3. r Figure 3.2 Figure 3.3 Connector Preparation Loop Connections to the ST-5000 FSK Connec t i ons to the ST- 5OOO 3-3 l-l{ . -5 Figure 5. I ST-5OOO Block Diagram . . 5-5 Figure 5.2 SI-5OOO Schematic Diagram Conventions . . 5-6 Figure 5.3 ST-5000 Receive Section . . . . 5-7 Figure 5.\ SI-5OOO Transmit Section and Porver Supply . . . . . . 5-8 Figure 5.5 ST-5OOO Circuit Board Layout 5-9 Figure 5.5 ST-5000 Cabinet Layout . . . . 5-10 I, IrurnoDUCTIoN The Hal Communications Hodel ST-5000 is a high performance FSK dernodulator and tone keyer designed for use with radio teleprinter systems. The ST-5OOO incorporates the features and performance characteristics of previous HAL demodulators as wel I as of f ering some features previous ly not available. The ST-5000 is an audio tone type of demodulator and keyer. Audio tones from the receiver, r€presenting the "mark" and "space" teleprinter code states, are converted into keying pulses by the demodulator section. Active discriminator filters are used in the ST-5000 so that a wide range of input frequencies can be accomodated. Two standard audio tone sets are normally stocked by the factory. The standard tone sets are based on a mark frequency of 1275 Hz ("low-tone" set) or a mark frequency of 2125 Hz ("high-tone" set) for frequency shifts of 170 Hz and 850 Hz. The tone keyer section of the ST-5OOO generates the same set of tones for transmitting in addition to a narrow-shif t tone for Horse code identif ication. The demodulator uses a wide bandvridth Iimiter and active detector circuit to give outstanding performance for a wide range of input signal amplitudes. A three pole active lowpass filter follows the detector stages to reduce the post-detection noise bandrvidth. The ST-5000 autostart circuit senses the presence (or absence) of a valid teleprinter signal. lf the input signal is not recognized as a tele- printer signal, the printer is held in the "mark-hold" condition. lf rnore than twenty seconds pass without recognition of a valid signal, the po\{er to the printer motor is removed. As mentioned earlier, the tone keyer generates the same tone set as is used in the demodulator section to assure true "transceive" conditions. The tone keyer rvill also generate an additional narrow-shift tone that can be connected to an external keyer circuit for Morse code identif ication. AII tones of the tone keyer are derived from a type 555 lC oscillator. The output signal is a low distortion siner.,ave generated in a digital-to- analog converter and then f iltered in an active low-pass f ilter. A rvide range of output amplitude (into 500 ohms) is available f rom 'the ST-5000, adjustab'l e with an internal control. The shift of the tone keyer is controlled by the f ront panel SHIFT swirches. The SENSE switch (ruOnm - REV) controls only the demodulator, not the tone keyer. The audio input to the demodulator and the audio output f rom the tone keyer are both 500 ohnrs unbalanced vrith respect to ground. The oscilloscope signals for a crossed-ellipse oscilloscope display are connected to a rear panel connection. The ST-5OOO is furnished with a front panel tuning meter" lnternal, €lectronically regulated + 12 vo'l t power supplies provide operating voltages for the demodulator, .ontrol, and tone keyer sections of the ST-5000; a 175 volt, 60 ma. loop povrer supply is also included. The main power transformer of the ST-5000 can be connected for operation vrith either 105 to 125 VAC or 210 to 250 VAC, 50 or 60 l1z po\{er sources. The power Iine fuse is accessable from the rear panel of the unit. The ST-5000 requires approximately 1B watts of AC power and is housed in an attractive l- I blue and beige cabinet that matches the HAL Communications DS-3000 and DS- 4OOO KSR and R0 Video Display Terminals. A complete set of connectors are f urnished with the ST-5000 to simpl ify the initial installation. lf you are anxious to try your ST-5000, it is suggested that you skip to sections 3,1 and 3.2 of the installation chapter and then read sections 4.t and \.2 of the operation chapter before turning the equipment on. The balance of this manual should then be studied before attempting any t'customrr connections. 1-2 't. I SprcrFIcATIoNS nput Sect i on: Data: I I I nput Amp I i tude: nput lmpedance: nput Frequenc i es : Serial, tone-encoded data, UP to ll0 baud - 60 to +20 d Bm ("pp rox. I mV to 0V rms ) 500 ohms , uoba I anced 1 " Low- tonesrl Hark = 1275 Hz "High-tones'l Mark = 2125 Hz Space = 2295 Hz (tZO Hz shift = "NARRO\^/" ) ,'WtDE") Space = 2975 Hz (850 Hz shi ft = Discriminator Fi lter Bandwidth: Space = ll{l{5 Hz (tZO Hz shif t = "NARROW") Space = 2125 Hz (850 Hz shi ft = "WIDE") 190 Hz Tone Keyer Sect i on: Da Serial data from loop circuit, uP to 110 ta: ba ud 0utput Amplitude: Variable f rom -40 to O dBm ("pprox. 1OmV 0utput lmpedance: 0utput Frequenci es: 500 ohms , urba I anced CW- I D: to 1.00V) Same as those given above for input sec- tion plus: 1175 Hz ("Low-tones"), key down 2025 Hz ("High-tones"), key doln Autos ta rt Sect i on : Pri nt-control resPonse: Motor turn-off time: Motor control: funing lndicator: 2 to 4 seconds 20 to 40 seconds Relay svritched power line voltage to accessory socket;'up to-8.0 amperes (1 /\ HP). 0-l ma front panel meter; rear Panel connections to an external osci I Ioscope are p rov i ded. Mechanical Speci fications: Size: Weight: Finish: 12 1/B" u, x 7 7/8" D x 2 13/16" H 30.8 x 20.0 x 7.t cm 5.75 lbs Q.e kg), NET 7.00 lbs (l.z kg), shippins Two-tone, blue toP over beige bottom, ffidtches ST-5000, DS-3000 KSR and other current HAL Products. Power Requi remen ts : 105-125 VAC (ZtO-Z5O VAC optional), 50-50 Hz, I U Watts 2-1 3, IrusrnLLATroN 3. r lnitial lnspection Upon receipt of the ST-5000, uopack and inspect it carefully for shipping damage. lf evidence of shipping damage is found, contact the carrier immediately. Before discarding the packing material , check that al I parts and accessories are accounted for. lf any are missing, please notify the factory or distributor in writing so that replacements can be supplied. The following parts and accessories are furnished with the ST-5000. Accessory parts: I 1 4 2 2\ 2 5 fr Non-captive AC power cord 6 ft. Audio cable, phono connectors each end 3 pin female connector shells (Ol-09-2031) 6 pln female connector shells (Ol-09-2061) male cable pins (oz-09-2rq3) 0.5 ampere, slow-blorv fuses 2-conductor shielded cable ************.r+*n********lr***Jrnr+.rr**itls***r+it**J+*****tt*ifit********** * ** **X It + * *** It cAUTtoN! A SERIOUS SHOCK HAZARD MAY EXIST WHEN CONNECTING THE sT-5000 T0 oTHER EqUTPMENT. BEFoRE MAKING ANY CoNNECTIONS, BE SURE TO DISCONNECT THE ST.5OOO AND OTHER EQU I PHENT FRoM THE AC PoWER L I NE. Jt{t*lt.^q*lt*lf*****lt,{'**tt************lt*.,f.r+*******Jtlf*****t**.,+J+*l+***rt*** *** *It * *** ** **It 3.2 Audio Connections Audio tones from the receiver as r.rell as ST-5000 tones to the tFansmitter are both connected via the three pin AUDI0 jack on the rear panel. lt is highly recommended that the ST-5000 input be connected to a 500 ohm audio output from the receiver. Although the demodulator r".lill vrork when driven f rom a lovrer impedance source (l{-B ohms, for instan."), the voltage level from most receivers is insuff icient to take full adrrantage of the wide synamic range of the ST-5000 input circuitry. Use of a \ ohm output instead of a 500 ohm output causes a loss of 22 dB in the audio signal strength, y,rhich may impair the vreak signal capabilities of the RTTY receiving system. lf the receiver does not have a 500 ohm output, a h to 500 ohm transformer is highly recommended. The tone keyer orjtput is a Iso connected to the AUD l0 connector. This output has a nomina I source inrpedance of 600 olrms, but may be used to drive high impedance audio circuits as vrell. The output level of tlre tones is adjustable over the range of 0 to -l{0 dBm (t.O V to l0 r,rV rms) as is described later in section 14.1. 3-l Connections between the receiver and transmitter and ST-5OOO can be made using the 6 ft. phono cable supplied. Cut the cable in half; connect one section between pins I and 2 (shield) for the receiver audio connection. Connect the other half between pins 3 and 2 (shield) for the transmitter audio input connection. Preparation of the plastic connector snd pins is illustrated in Figure 3.1; connections to the AUDI0 connector are shorvn in Figure 3.2. 3.3 Loop Connections The station RTTY equipment can be connected to the ST-5000 internal loop circuit through pins t (+) and t{ (-) of the l/0 C0NTR0L rear panel connector. The internal loop supply generates a 60 ma dc current florv for mark condition from a 175 volt dc power supply. lf a polarity sensitive device such as a solid state keyboard or display generator is connected in the loop ci rcui t, be sure to observe proper polari ty connections. Preparation of the plastic connector and pins is shown in Figure 3.1; some common loop connections are shown in Figure 3.3. CAUTION THE 175 VOLT LOOP POI{ER SUPPLY CAN CAUSE A LETHAL ELECTR ICAL SHOCK IF c0NTACTED. BE EXTREHELY CAREFUL l{HEN CoNNECTTNG EQUtPHENT tN THE L00p CIRCUIT TO BE SURE THAT POWER TO THE ST-5OOO IS DISCONNECTED. BE SURE T0 GRoUND THE CABINETRY 0F ALL EQUIPHENT CoNNECTED tN THE L00P CIRCUtT AND PROV I DE PROTECT I VE I NSULAT I ON FOR ALL LOOP CONNECT I ON PO I NTS. 3.\ FSK Connections A low-voltage data output is also available on the l/0 - CONTR0L connector at pin 3, labeled rrFSK." This signal is derived f rom the loop circuit and will provide approximately -15 volts on mark condition and +15 volts on space condition. This signal is compatible with a RS-232C data standard and can be used to directly drive solid state display systems such as the HAL RVD-'l 005 or the DS-3000 KSR units. - This signal can also be used to drive saturated diode FSK keying circuits. Preparation of the connector is shown in Figure 3.1 and typical FSK connections are shor^,n in Figure 3.U. 3.5 STANDBY Connections As explained in section \.5, the ST-5000 can be locked into a markhold condition where the loop (and FSK) data outputs do NOT respond to an audio input signal. This feature allovrs "local loop" operations suclr as preparing tape and transmitting whi le sti I I using the loop supply of the ST-5000. This mode can be activated by either using the L0CAL position of the f ront panel L INE switch or by grounding the STANDBY pin (no. 2) of the l/0 - C0NTR0L rear panel connector. The REHOTE feature is generally connected to a pole of the transmit-receive switch or relay so that the demodulator is disabled while transmitting. As before, refer to Figure 3"1 vrhen prepa r i ng the connector p i ns. 3-2 .- MALE PIN \ FEMALE wlRE --;.\= .- SOLDER INSERT PIN CON N ECTOR LOCKED' BLOCK Figure 3.1 Connector Preparat ion 3-3a DS2OOO KSR sr 50 00 I rroP + +t 4 LOOP 5 GND 2 STANDBY 6 CW-ID 2 +3 4 UO GND 5 t/o CON T ROL BLK KOS 6 coNNECT TO EITHER CATHODE (+) CATHODE 7 OR GRID BLOCK (_), DEPENDING UPON TRANSMITTER REOUIREMENTS. GND 8 sHELL:323-9206t PtNS:320- 2t430 (sre rExr) GRID BLOCK 9 > SHELL: 323-9lO9l PINS:322-91143 3 OUT 2 GND IIN MORSE AUDIO / oru\ \unzooo/ [^ SHEL 9203 I PINS: 430 sHELt: 323 - 92031 PrNS:320- 21430 GND GND PLUG: 3ro-ooolo CABL E : 355 - t3072 BLK WHT GND PTT MIC GND AUD IO AUDIO KEY OUT PUT TRANSCEIVER DS2000 and ST5000 System Connection Schematic 3-3 b MON ITOR ( ES M - 9I4 ) DSzOOO KSR MORSE IN (0N MR2000) vlDEo @ OUT PUT S = SHIELD sT5000 E r< fo \_!, o-) ILK E SCOP AUDIO wH' MICROPHONE CONN. TRANSCEIVER @* ANrO@ XEY @ OTiO DS2000 and sr5000 sys tem connect i on p i ctor i a I 3-3c AUOIO OUT PUT wHr (+ ) DKB- 20rO PIN 4 PIN 6 VI DEO BLK(-) PIN4 MON I TOR RVD - tOOs LOOP CONN ECTION OF DKB - ?O IO AN D RVD - IOO5 DS-3OOO KSR wHT (+) BLK (-) prru + SHIELD LOOP CONNECTION OF DS-3OOO KSR .l ro AS ELECTRON IC EQUI PMENT -) LOOP CABLE SHOWN ABOV E wnr (+) TTY MACH INE BLr( (-) SHIELD SHIELD TO ALL TAPE EQUIPMENT GROUNDS TRANSMITTER TAP E RE PERFORATOR LOOP CONNECTION OF ELECTRONIC AND MECHANICAL EQUIPMENT Figure 3.2 Loop Connections to the ST-5000 3- tl VI DEO MON ITOR RVD - |OOS SH I ELD USE OF FS K OUTPUT TO DRIVE THE RVD - IOO5 I DS.3OOO KSR 2 FSK CABLE 3 WHT SH I ELD SHI ELD GND USE OF FSK OUTPUT TO DRIVE THE DS-3OOO KSR FSK DIODE KEYER CIRCUIT (AOO TO TRANSMITTER ) RFC 1.5-15 pl- FSK CABLE SHIELD t__ USE OF FSK OUTPUT TO DRIVE DIODE FSK CIRCU Fi oure 3.3 FSK Connect ions to the ST-5000 3-5 3.6 C\.l lD Key Cable Connection is labeled "CW-lD." Connect the keyer between this Pin and ground or electronic station Morse code hand key (pin 5) to provide narrow-shift Cl,J identification of the transmitted signal. When an electronic keyer is used, the outPut circuit for ca!!oc!g keying should be used, instead of the giid-block keying circui t. I" "o case should the keyer reflect any negative voltage or positive voltages greater than +12 to the ST-5000. Pin 6 of the I/O CONTROL connector 3.7 AC Power Cord Connection The ST-5OOO can be internally connected to operate from power sources in rwo voltage ranges: 105 to 125 VAC or 210 to 250 VAC, 50 or 50 Hz. The rear panel power cord connector is of the "universal" USA/European type and mating power cords can be obtained for most common wall connectors. The ST-5OOO is normally factory wired for operation from 105 to 125 VAC, 5O to 50 Hz power lines. Upon request at the time of the order, the ST-5000 can also be supplied for 210 to 250 VAC, 5O to 50 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-5000. lf this tag is NOT on the rear panel, do NOT connect the ST-5000 to a 2\O volt line without first checking the internal wiring of the power transformer. Particular attention should be given to the precautionary notes of section 3.8 rvhen connecting to the M0T0R recep- tacle. 3. B Motor Power Connection The power for the teleprinter motor can be supplied by the M0T0R connector of the ST-5000. The power to this connector is controlled by the autostart relay. The T0TAL current suppl ied by this receptacle should not exceed '10.0 amperes. The following precautions should be observed when us i ng t he l'10T0R recep tac I e : l. 2. The power to the HOT0R receptacle is NOT fused in the ST-5000. The user should be sure that any device attached to this connector has its own f use protection. The AC voltage furnished on the M0T0R receptacle is the SAHE as the AC po\{er line voliage supplied to the ST-5000; if the ST-5000 is operated from a nominal 2\0 VAC power line, the M0T0R receptacle also furnishes 240 VAC. The proper power transformer primary connect ions are: 105 to 125 VAC, 5O/60 Hz: j umper termina I power line to terminals I and q. 210 to 250 VAC, 5O/6A Hz: j umper termina I to terminals I and 4. 3-6 to 3 and 2 to \, connect 3 to 2, connect por{er line 3.9 Ground Connection The ST-5OOO cabinet should AL\JAYS be connected to an adequate ground system. A three-prong grounding type AC power plug is furnished for connection to a grounded-outlet povJer system (105-l25VAC connection). lf the wiring of the building is correct, use of the grounding AC plug should provide an adequate SAFETY ground return for the instrument. However, it is a good idea to first check the outlet wiring with a multimeter before plugging in the unit. lf a three-prong AC outlet is not available, use a three to two-prong adapter at the wall socket and connect a separate ground lead between the adapter ground lead or ST-5000 cabinet and a good ground. When using 210 to 250 VAC power mains, be sure to connect the cabinet to a good safety ground. OPERATI0N OF THIS EQUIPHENT WITH0UT AN ADEQUATE SAFETY GROUND I NVAL I DATES THE WARRANTY. When the ST-5000 is used in a radio communications system that includes a high-powered transmitter, a short length of low-inductance wire (+" r^ride shield braid is recommended) should be used to interconnect all equipment cabinets, including the ST-5000 and all teleprinters, etc. Lack of a good RF ground connection may cause false triggering of the logic in the control sections or other improper operations. Open-wi re antenna feedl ine systems with high standing-r.,ave-ratios can be particularly troublesome to solid state equipment. ln such cases, changing the antenna, ffistching syster,r, and/ or feedline to a matched coaxial I ine system rvill usually clear-up RF interference. When good RF grounds and low SWR feed-lines are used, the ST-5000 wil I work rvith even very high por,vered transmi tter systems. 0bviously, a great many other l/0 and control connections can be made The user should thoroughly study section 5 and understand how the various sections of the ST-5000 operate and interact before these connections are made. 3.10 External 0sci I loscope Connections The MARK and SPACE AC signals f rom the discriminator f ilters are available on the rear panel SC0PE connector. The s ignal s -are approximately 2.0 volts peak-to-peak amplitude into a recommended 100 k ohm minimum load impedance. The HARK signal is available on pin 3, the SPACE on pin 1, and signal ground on pin 2. 3-7 q, 0prRAT I oN The ST-5000 contains many advanced features designed to assure convenient operation. The operating instructions presented in this section r^rill help you to take full advantage of the demodulator's capabilities. Please read all sections carefully. q.1 Front Panel Controls and lndicators The ST-5000 f ront panel has a total of f ive push-button srvitches that al low operator control of the demodulator. Normal operation of the demodulator with ALL automatic features active is obtained by depressing the four right-hand sr^ritches and selecting the desired shif t with the f ar-lef t si'ritch" These functions will be discussed in greater detail later in this section and in section 5. Table q.1 describes the front panel sr^ritches. Table 4. t ST-5000 Front Panel Control s SW I TCH POSITION FUNCT I ON POWE R ON - Controls AC potder to sr- 5000 OFF AUTOSTART lorrs rece i ved da ta to drive printer L INE AI LOCAL Locks printer in mark for "local- Ioop" operation ON. OFF Turns autostart ci rcui t on or off NORI,l Normal signal polarity; mark = Iorver tone REV Reverse signal polarity; mark = higher tone NARROW Se I ects 170 Hz shif t WIDE Se I ects BSO Hz slf i f t PR INT SENSE SH IFT The rear panel connectors have been discussed in detai I in section 3 and internal adjustments will be discussed in detail later in thi s manual. \.2 Simpl ified 0peration Procedure The fol lovring procedure is suggested for those operators tvho are anxious the ST-5OOO rvithout reading the rest of this manual. try to Prepare audio input and printer cables as described in sections 3.2 E 3.3 and connect the unit to a receiver and printer or display. Do NOT connect a transmitter rvithout reading the rest of section l{ of this manua l. 4-l 2. 3. AFTER C0NNECTIONS ARE I'{ADE, plug-in the ST-5OOO and other equipment and turn on the AC po\{er to each. Set the ST-5000 switches as follows: POWER PRINT ON IINE AUTOSTART OFF SENSE SH I FT 5. 6. 7. \.3 - NORH sel ect des i red sh i ft Set the receiver to LSB mode and tune to a FSK RTTY signal. (Approximately 3500 kHz at night and 1!,100 kHz during the day are good frequencies to look for 170 Hz shift radio amateur RTTY signals at 50 wPH). Tune the receiver dial until the tuning meter def lects up-scale to approximately 0.5 to 0.7 and has minimum fluxuation as the signal changes from mark-to-space. ( I f an osci I loscope i s connected, tune for perpendicular ellipses on the screen). The printer should now print the received signal. lf it doesn't, try reversing the SENSE srvitch or selecting dif ferent speeds on the printer or display. NOW, read the rest of this manual ! Reception of Radio Teleprinter Signals Radio teleprinter signals are usually generated in two forms: direct shifting of the transmitter carrier frequency by the mark and space teleprinter data (called "FSK") or by shif ting the f requency of audio tones rvith the data and using the audio tones as modulation in either an A,'1 or FM transmitter (called t'AFSK"). FSK transmissions are usually used in the HF f requency range, below 3O MHz and AFSK is the normal technique for VHF transmissions, above 30 MHz. A currently popular method used to transmit FsK signals is to apply the frequency-shifted tones as modulation to a single side-band (SSg) transmitter. Since a properly idjustqd SSB transmitter signal is the same as that by direct FSK, a separate RF frequency for mark and space data conditions. Reception of such signals is therefore exactly the same as if direct FSK had been used. Use of this technique rvi ll be discussed in greater detail in section I{.8. \.1. I Receiver for FSK Reception The performance of the ST-5000 depends to a great extent upon the characteristics of the receiver used and the care taken in tuning the FSK signal. 0bviously, the better suited the receiver, the better the qua I i ty of the printed displayed output. some of the desi rable recei ver characteristics and fea tu res a re : l. The recei ver should preferably be of the SSB type wi th se lectab le sideband. Standard convention is to use LSB mode for FSK reception. \-z 2. 3. lr. 5. 5. 7. The frequency stability of the receiver should be very good - a small amount of drift when receiving a 170 Hz shift signal can cause poor pr i nt from even very s trong s i gna I s. The tuning ratio of the main tuning knob should be slow to allow precise adjustment of the FSK signal into the receiver. The selectivi ty of the receiver should be sl ightly greater than the shift to be received: for 850 Hz shift, a bandwidth of 1200 to 2l0O Hz is adequate; for 170 Hz shift, a bandwidth as narrow as 4OO Hz can be used. Two I imitations should be kept in mind, however; the narrower the bandwidth, the greater the frequency stability requirements on the receiver, and wider bandwidths permit more interference and noise to be processed with the FSK signal A "slow" agc with fast attack and slow decay is very desirable when receiving FSK signals. As mentioned in section 3.2, a 500 ohm audio output connection or speaker to 500 ohm transformer are highly recommended for connect i on to the ST- 5000 i nput. An adjustable BFO frequency or adjustable pass-band tuning are very desirable features for reception of FSK signals. Proper positioning of the receiver's BFO with respect to the lF pass-band and the FSK signal is particularly important. The standard convention t^rhen transmitting HF FSK signals is to transmit mark data at the higher RF frequency and space at the lorver. The separate mark and space RF frequencies are both received nithin the receiver lF pass-band and mixed in the product detector with the BFO to produce audio tone beat signals which then drive the ST-5000. Since the audio filters of the ST-5OOO 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. However, if the signal is inadvertantly tuned-in using USB (upper side-band) mode, the sense can be corrected with the SENSE switch on the ST-5000 front pane I . The receiver BFO frequency posi tioning qlso determines the RANGE of audio frequencies that can be detected and used to drive the ST-5000. The normal SSB receiver has generally been designed for optimum performance with voice signals with ; typical audio f requency pass-band of 300 to 2!00 Hz. However, the so-called rrstandard'r demodulator audio tones have been 2125 Hz for mark with the space tone higher in frequency by the amount of the shift received. For 170 Hz, both the mark (2125 Hz) and space (2295 Hz) tones fall within the 300 Hz to 2\00 Hz pass-band, although they are not centered. However, the B5O Hz shift space tone at 2975 Hz is not detected for all but the strongest FSK signals. Obviously, the 8SO Hz shif t FSK signals are NOT compatible with the usuaI SSB receiver if the "standard" demodulator tones are used. There are trro solutions commonly applied to this problem, both of which are usable with the ST-5000. One sol ution i s to simply change the receiver BF0 frequency so that the audio pass-band of the receiver is changed to, say 1500 Hz to 3500 Hz, which will pass all of the "standard" demodulator toneS, centering the passband on the 850 Hz shift signal. ln this case, the BF0 frequency should be changed so that it is FARTHER AWAY FR0M THE CTNTER 0F THE lF PASS-BAND bv \-3 approximately'l 000 to 1l{00 Hz. lf the receiver BF0 is adjustable, this is a simple solution. However, many modern SSB receivers do NOT have adjustable BF0's; rather, the BFO may be crystal controlled. ln such cases, the BFO crystal should be changed for one of the correct frequency as determined above. Alternately, the second solution, oUtlined below, ffiEy be used. The receiver audio pass-band problem can also be solved by changing the tones used by the demodulator for detection of mark and space. This technique, commonly referred to as "low-tones" allows direct use of a voice SSB receiver with no internal modifications to the receiver. The ST-5OOO can be furnished with filters designed to accept a mark frequency of 1275 Hz and therefore space frequencies of: 1\\5 Hz (tZO Hz shift) or Z1Z5 Hz (850 Hz shift). ln some cases, this can be the best solution. However, as discussed in the next section, it can lead to a basic incompatibility when receiving AFSK VHF s ignals as wel I as presenting some transmi tter problems. The ST-5000 can also be adjusted for special sets of input tones between 1200 and 3000 Hz on special order. \.1.2 Recei ver for AFSK Recept ion The receiver requirements for AFSK reception are not as exacting as those for FSK reception.'Since the teleprinter data is an AFSK modulation of the transmitter, receiver stabi I ity is not genera I Iy critical . Hor.rever, since the data is in the form of audio frequency modulation, the frequency of the tones is determined at the transmitter and cannot be changed at the receiver by simply adjusting a BFO or similar control. The current VHF-AFSK standards in use by radio amateurs in the United States use the highe r'-f requency "standard" tones of 2125 llz for rnark and 2295 or 2975 Hz for space, depending upon the shift used. Therefc.rre, a demodulator with "low-tone't input f ilters will NOT be compatible with reception of current VHF-AFSK signals. As in the case of the FSK receiver, a 500 ohm audio output is certainly desirable, but may not be as important to performancy, particularly if strong-signal VHF-FM signals are used. \.3.3 Tuning a RTTY Signal Tuning of the radio receiver for optimum rdcovery of the teleprinter signal is an operation which may require some practice'. Two alternate tuning aids are usable r^rith the ST-5000; the standard tuning meter and a user supplied external tuning oscilloscope. The tuning objective is to adjust the receiver tuning so that the output audio tones r"natch the center frlquencies of the ST-5000 fi I ter ci rcui ts. The tuning meter functions in exactly the same manner as that used on previous models ST-5 and ST-5 demodulators. Portions of the signals th" both theHAL from mark and space discriminator fi lters are positive rectified, fi ltered and summed. The resulting "plrs-plus" voltage is used to drive both the tuning meter and the autostart circuit. The amplitude of the,'plusplus" volt3g€, therefore, depends upon hor,,r vrell the mark or space tones are centered in the discriminator f ilters. Correct tuning of the receiver is indicated by an up-scale meter deflection that fluxuates very little as the RTTY signal changes betvreen mark and space. The ST-5000 circuits are adjusted so that proper tuning is indicated by a non-varying reading of 0.5 to 0.7 on the meter. I'lote that the meter may give widely varying readings \- tl when noise, interfering signals, or incorrectly tuned RTTY signals are received. However, it will 0NLY give the non-varying, up-scale indication when the RTTY signal is properly tuned. An external osci lloscope can also be connected to the ST-5000. The osci lloscope presents the standard crossed-ell ipse display r^rith the mark signal on the horizontal axis and the space signal on the vertical axis. Because the d i scr iminator f i I ters in the ST-5000 (t i t<e those of the ST-5 and ST-5) are relatively broad-band, the mark ald space scope displays are NOT lines, but ellipses. The ellipses are fairly narrow when 850 Hz shift i s rece ived and wider when 170 Hz i s se Iected. I,/hen the RTTY s igna I i s correctly tuned, the el lipses will have maximum length and be essentially perpendicular. The major axis of the ellipse is ALWAYS the parameter to observe and maximize. When the signal is incorrectly tuned, the ampl i tude of the major axis will be reduced and the two traces may be rotated and/or no longer perpendicular. After using the tuning osci I loscope, the user will discover that, in many cases, the trace positions and amplitudes can be used to determine which direction the receiver dial should be adjusted for correct tun i ng. Proper tuning adjustment of the receiver is much more critical when the autostart circuits of the ST-5OOO 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 f ilters. However, if the autostart is not active, the relatively broad bandwidths of the discriminator f ilters themselves will allorv good reception of even poorly tuned RTTY signals. A good operating procedure, then, is to turn the autostart 0FF (wi th the f ront panel switch) whi le tuning a signal. When the signal is correctly tuned, the autostart can be activated, if desired. This technique is hishly recommended for operators rvho are unfamiliar with the ST-6 and ST-5000 autostart circuits although, with practice, you r,nay prefer to tune with the autostart circuit on to avoid the garbled print whi le tuning. Tuning when the autostart is active requires experience and faith in the tuning indicators since there is a delay of 1.5 to 3.5 seconds after correct tuning is achieved before the printer is act i vated. The above tuning procedures in general only to the reception of "pptV FSK RTTY signals. Receiver tuning of AFSK-AH or FM signals will obviously tl not affect the frequency of the tones. Therefore, tuning of the receiver is not at all critical for AFSK signals. The tuning meter or oscilloscope wi I I indicate the match between the transmitted audio tones and the SI-5000 discriminator filter rather than correct receiver tuning. 0bviously, the frequencies of the transmitted tones must match the discriminator fi lters fairly well for satisfactory autostart operation. Host problems with AFSK autostart systems can be traced to ei ther off- frequency transmi tter tones or mi s-a I i gnment of the demodu I ator. 4.4 Use of the SENSE Switch The SENSE srvitch allows the ST-5000 to receive signals rvith either the normal polarity of mark=lower f requency or the reversed sense where mark= h igher f requency tone. ALL f eatures of the ST-5000 f unct ion equa I ly r^re I I for either signal polarity. This reverse position is convenient if the signal has been inadvertently tuned-in using USB rather than LSB receiver \-5 mode. 0NLY the discriminator f ilter f requencies are controlled by this switch; the tone generator sense is NOT switchable. \.5 Use of the PRINT Switch There are many occasions in which it is desirable to turn-off the received data to the teleprinter Ioop circuit and just use the internal loop supply to operate the RTTY machines at the station. Operations such as local testing of equipment or preparation of punched paper tape are typical examples. I{hen the PRINT switch is in LINE position, data from the receiver is allowed to key the loop cir:cuit. When the switch is in LOCAL position, the loop keyer stage is held in mark condition and received data will NOT drive the loop. The demodulator can also be held in LOCAL position by grounding the STANDBY line on pin 2 of the l/0 CONTROL connector. \.6 Use of the Autostart Circuitry The ST-5OOO autostart circuit operates in a manner very similar to that of the ST-5000, ST-5 and earlier TI/L and TTlL-l I demodulators. The autostart provides a trvo-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 "plrs-plus" Iine, r.vhich is, as described previously, proportional to the f requency match betvreen the signal tones and the discriminator f ilters. If both mark and space tones are not sensed in the discriminator, the "pIusplus" voltage remains at a low average value and the autostart circuit wil I be in the standby condition, giving a continuous mark output. After the autostart has remained in the standby or mark-hold condition for 20 seconds (nominal), the power to the H0T0R AC socket on the rear panel is turned off with an internal relay. lf valid mark and space tones are now sensed in the discriminator, the "plus-plusrr voltage wi ll increase and activate the autostart after a delay of 3.5 seconds. The AC power to the M0T0R connector is now srvitched on and the data is allowed to drive the loop. lmmediately after the tones turn-off at the end of a transmission, the autostart returns the data to mark hold, completing the cycle. Because of the turn-on del ay inherrent in the autostart, it is recommended that tuning of the RTTY s igna I be done wi th the AUT0START srvi tch in the OFF position during initial testing of the ST-5000. After the operator has some pract i ce i n tun i ng the receiver, he may then wish to Ieave the autostart ci rcui t 0N, rememberi ng to account for the time delay of the autostart. The autostart trigger voltage level on the "plrs-plus" I ine is adjustable with a potentiometer mounted on the control circuit board inside the ST-5000 cabinet. The potentiometer is located almost in the exact middle the circuit board and can be identified as a 25Ok pot near the letters ,of rrASrr on the circuit board. This control is normally set at the factory to trigger the autostart on all signals giving a tuning meter reading of 0.5 and higher. The user may adjust this control to fit his own requirements. lf the autostart sensitivity is set too close to the noise level, false printing may occur on noise or interfering signals; if set to too high a level , the autostart may not trigger on al I but the strongest s ignals with exact ly correct shif t. Experience vrill determine the optimum setting for a particular system. Notice that the "plus-plus'r voltage and therefore \-6 autostart sensitivity are directly proportional to the degree of match between the signal tone frequencies and the center frequencies of the discriminator fi lteis. lt may therefore be difficult to set the autostart sensitivity and receiver tuning to respond to signals with improper f requency shif t. Also, if the transmitter 0R receiver should drif t, the signal tones wil I soon no longer match the discriminator filters, ctsusing the autostart to rrshut-down." lf drifting is a problem, the receiver should either be monitored often and manually retuned as required or the autostart should be swi tched oFF. \.7 Tone Keyer C i rcu i t The ST-5000 includes a tone keyer that is very similar in design to previous HAL model XTK-100 tone keyer board. All mark' space' and the are digitally synthesized from a type 555 lC oscillator. Unlike CW-lD tones previous tone keyers, the ST-5000 CW- tD tone is generated at 100 Hz BELO\'I the mark tone instead of above. This further reduces the chances of falsely triggering the autostart of the receiving demodulator, even when 170 Hz shift is used. The tone keyer is driven from the loop derived FSK output signal. The tone output amplitude can be adjusted over the range of 0 to -40 dBm (approximately l.O V to 1O mV across 500 ohms) with an internal potentiometer. The amplitude is adj usted with the rt0Lil potentiometer, located on the rear of the circuit board. Although the output impedance of the tone keyer is 500 ohms, Virtually any load impedance from 500 ohms to several megohms can be driven by the ST-5000. lt is NOT necessary to terminate the audio output connector in a 500 ohm load 4.8 Transmitting Radio Teleprinter Signals As mentioned previously in section \.3, radio teleprinter signals are generated by either shifting the transmitter RF frequency rvith the data (FSK) or by modulating the transmitter carrier with audio tones whose frequencies are shif ted by the data (nfSf) . Usually, FSK transmission is used for radio frequencies lower than 3O tllHz and AFSK above 30 HHz. The ST-5000 can be used to receive AND transmit both FSK and AFSK types of signals. 4.8. 1 Transmi tti ng FSK Signal s There are two dif ferent techniques that are normally used to generate an FSK teleprinter signal. The simplest method involves direct shif ting of the frequency of an osci I lator stage in the transmi tter. Typical ly, the data signal is used to turn on or off a diode switching circuit that effectively increases the osci llator tuned circuit capacitance on sPace, thus lowering the transmitter frequency for space condition of the data. A typical diode keyer circuit is shown in Figure 3.3. Note that the FSK data output is ideally conditioned for this application. Further information on this type of circuit can be found in a current edition of the Radio Amateur's Handbook (RRRL, Newington, Conn.) or in the Radio Handbog! (0re, Howard W. Sams, lnc., lndianapolis, lnd. ), or other text on raaio tran