PSK31 Audio Beacon Kit - Njqrp.club
PSK31 Audio Beacon KitBuild this programmable single-chip generatorof PSK31-encoded audio data streams anduse it as a signal generator, a beacon input toyour SSB rig — or as the start of a single-chipPSK31 controller!Version 2, July 2001Created by the New Jersey QRP ClubThe NJQRP “PSK31 Audio Beacon Kit”1
PSK31 Audio Beacon KitThank you for purchasing the PSK31Zudio Beacon from the New Jersey QRPClub! We think you’ll have fun assembling and operating this inexpensive-yetflexible audio modulator as PSK31-encoded data streams.This project was first introduced as a kitat the Atlanticon QRP Forum in March2001, and then published in a feature article of QST magazine in its August 2001issue. Since these initial public exposures,several new capabilities have been addedin “version 2” of the microcontroller software. This kit embodies this new software and describes how to use the newfeatures.And lastly, there were a few typographical errors in the QST article that have beencorrected in this kit. Most notably, thegraphics depicting the PSK31 waveformencoding now properly indicate waveformphase relationships at bit transitions, andthe schematic has been augmented withhelpful notations.For the very latest information, softwareupdates, and kit assembly & usage tips,please be sure to see the PSK31 Beaconwebsite at http://www.njqrp.org/psk31beacon/psk31beacon.html . Visitsoon and often, as it’s guaranteed to behelpful!We really hope you find this Manhattanstyle Homebrewing Starter Kit useful ingetting started in your first copper-cladboard project. It’s a fun, quick and flexible way to bring your favorite designs tolife!George Heron, N2APBemail: n2apb@amsat.orgfor the NJQRP Clubat http://www.njqrp.orgPARTS LISTU1SX28AC/DP Scenix microcontroller, 50 MHzU2LM386 amplifierU3MAX232CPE Dual RS232 transceiverY150 MHz ceramic resonator, Murata 250-05060SKT-128-pin IC socketSKT-28-pin IC socketSKT-316-pin IC socketVR17805V voltage regulator, 1AC30.1 uF ceramic (“104”)C4,C5,C6,C24,C26.01 uF ceramic (“103”)C20,C21,C22,C23,C25 1 uF electrolytic, 25V (longer lead is positive)C710 uF electrolytic, 25V (longer lead is positive)C847 uF electrolytic, 25V (longer lead is positive)C9100 uf electrolytic, 25V (longer lead is positive)R1,R210-ohmR410K J19V battery terminal clipJ29-pin RS232 D-style serial connectorPC Board2The NJQRP “PSK31 Audio Beacon Kit”OVERVIEWHere’s an easy, fun and intriguingly useful project that has evolved from an ongoing design effort to reduce the complexity of a PSK31 controller.A conventional PC typically providesthe relatively intensive computing powerrequired for PSK31 modulation and demodulation.With this Beacon project, however, thePSK31 modulation computations havebeen designed to fit into a small PIC-likemicrocontroller that can serve as the basis for the transmit half of a standalonePSK31 controller.A fast and inexpensive microcontrollerhas been programmed to generate an audio data stream using the PSK31 algorithms. The data-driven audio waveformis fed to an amplifier IC that drives aspeaker - and voila, the familiar and melodious PSK31 warble is able to be heard!When presented as input to a PSK31 receiving system such as DigiPan, thesemodulated audio tones are decoded andthe programmed beacon string is displayed.A keyboard or data terminal may alsoserve as the input of real-time textual datato the PSK31 Audio Beacon. A standardRS-232 serial interface is provided in thehardware and software to allow a moredynamic “signal generator” use of theproject.The project can be electrically connected to the input of an SSB transmitterto create an RF PSK31 beacon.This project is also ideally suited forgroups wishing to have some “audio beacon” fun during meetings. A number ofclub members would operate their audiobeacons while someone attempts successful copy of the beacon strings while sit-ting at a laptop equipped with DigiPansoftware.Construction is simple and straightforward and you’ll have immediate feedbackon how your Beacon works when youplug in a 9V battery and speaker.Beacon FeaturesnSingle-chip implementation ofPSK31 encoding and audio waveform generation.nAudio PSK31 tones presented to anaudio amp for use with a user-suppliedspeaker for use in group activities.nLower level signal available from chipsuitable for input to an SSB transmitterfor operation as an RF beacon.nScenix SX28 RISC microcontrolleroperating at 50 MHz with 20ns instruction cycle time provides computing powernecessary for accurate implementation ofthe PSK31 modulation algorithm. The SXchip is similar to Microchip’s popular PICmicrocontroller, containing the same software instruction set but operating over40 times faster.nSX28 microcontroller is programmedwith a unique beacon string, or acceptsreal-time text input from an RS-232 serialinterface.nConfiguration jumpers provide for selection of three base carrier frequencies(500 Hz, 1 KHz, or 2 KHz), and choiceof 8 sub-variations around the selectedbase frequency. This allows the user tooperate the Beacon on any of 24 distinctaudio frequencies.nConfiguration jumper provides forBeacon operation in a continuous loop oras a single pass when a pushbutton isThe NJQRP “PSK31 Audio Beacon Kit”3
actuated.nSource code and inexpensive development tools allow custom modificationof the beacon string and/or software operation.nConstruction may be done Manhattan-style (a form of ugly-style construction) for freedom of desired implementation. A printed circuit board is also available for this project when purchased as akit from the NJQRP Club.“What Can I Do with a PSK31Audio Beacon?As mentioned, the Beacon may be usedas the basis for a fun group “contest” activity for your club. All contestants wouldturn their beacons on and gather around alaptop running the DigiPan application.Laptops generally have built-in microphones that would be used to decode theaudio PSK31 tones “in the air” . andwith over 100 beacons warbling simultaneously, there will certainly be audio tonesin the air!RecallthateachBeacon’smicrocontroller is customized with acallsign and is run on slightly differentfrequencies. One Beacon may have itstones centered at 978 Hz, while anothermay have it’s tones at 1050 Hz. Thisspreading out of Beacon signals will helpwhen multiple beacons are placed in service at the same time within close geographic proximity.Okay, so you’ve got the picture of awhole bunch of club members amassedaround a table with an operator sitting atthe laptop running DigiPan, right? Withina specified period of time, the idea is tosee how many of the Beacons can be copied (callsign & code word), as capturedby DigiPan. Factors involved in successful reception include the settings of theaudio amp, the type of speaker, the dis4tance between the Beacon and the laptop,adjacent QRM (other Beaconers), etc.“Points” are awarded to all Beacons forthe degree of solid copy captured to theDigiPan log during that 15 minute period.(You can see a photo of this excitement inthe “Up Front” section of July QST. Thephoto was taken at the Atlanticon QRPForum held last spring.)This all may may sound complex, butit’s really quite simple — build the Beacon, turn it on and see how well it can becopied by DigiPan. Each contestant couldactually do this during the test phase athome prior to the club event.Putting the Beacon on the AirProjects can be fun in a group activity,but the PSK31 Audio Beacon has lastingvalue for the PSK31 enthusiast. The audio tones generated by the Beacon can bepresented as input to any SSB transmitter — a Warbler, PSK-20, PSK-40, or evena Yaesu FT-1000MP. Thus, a PSKer caneasily put a beacon signal on the air for allthe same reasons that CW beacons areused (e.g., studies of propagation, powerlevels, antenna characteristics, etc.)Special care must be exercised on twocounts, however.First, the audio level driving an SSBtransmitter needs to be extremely lowcompared to the output levels providedby the Beacon Kit. Most certainly, theLM386 audio amplifier output that drivesthe Beacon’s speaker should not be usedwhen feeding a transmitter. One shouldtake the output of the R-2R DAC andput it through a voltage divider pad (orpotentiometer) to bring the 0-to-4.5V sinewave signals down to the millivolt rangerequired by an SSB transmitter. The lowerthe better! If the transmitter is overdriven, all sorts of problems occur withthe transmitted RF spectrum – terribleIMD, distortion, and interference to otherThe NJQRP “PSK31 Audio Beacon Kit”signals up and down the band. You willquickly learn the wrath of others seeingyour callsign and email address transmitted over and over.Secondly, even in the case of perfectsignal quality, very careful attended operation needs to be done when using thisBeacon project with an RF transmitter.There should be no interference whatsoever to any other communication on theband, and even while in the CONTINUOUS mode of operation, the Beaconshould be stopped periodically to determine if other signals are present.Never leave the beacon on for continuous, unattended operation! Unattendedbeacon operation is illegal in the FCC’seyes, and you would not be able to determine if other signals are present in thearea of you transmissions.CIRCUIT DESCRIPTIONRefer to the Schematic at the center ofthis manual for the following discussion.DC Power InputThe kit provides a standard battery clipwith which the user can connect a 9V battery. Any DC voltage from about 9-12Vmay be used, as the 3-pin regulator VR1drops the input voltage down to the required 5V for the microcontroller.Current consumption of the Beaconcircuitry is nominally about 80ma, so theregulator will naturally get a little warmNote: If an SX-Key programmer is connected to the Beacon (allowingreprogrammability of the microcontroller)a TO220-packaged 1A voltage regulatorsuch as the LM7805 should be used dueto the overall higher current demands ofthe programmer.Scenix SX28 microcontrollerThe Scenix SX28 microcontroller usedin the beacon operates at 50 MHz clockrate, providing an instruction cycle timeof 20 nanoseconds. This fast operationenables precise control of signal generation and phase reversals to produce stableand accurate carrier modulation at the audio baseband frequencies. A 50 MHz ceramic resonator is used with the on-boardoscillator to provide a fast and simplecontroller solution to the generation ofPSK31 encoding.Carrier Generation: “R-2R DAC”There are numerous ways to generate asine wave suitable for use in communications systems, and each has advantagesand trade-offs. A discrete chip sine wavegenerator or a separate digital to analogconverter (DAC) could have been used,but it was desired to keep both hardwarecomplexity and cost to a minimum.Another popular method used in generating a sine wave is to pulse width modulate (PWM) a square wave on an outputbit of the microcontroller and then lowpass filter the signal with an R/C network.This method requires too much use ofprecious interrupt time in the processor.A simple technique was ultimately chosen to generate the carrier - the “R-2RDAC”. This digital to analog converterincorporates a ladder network of 15 resistors whose nodes are fed by an 8-bitparallel output port of the microcontroller.The values of the resistors in the networkare 10K- and 20K-ohms, hence the R-2Rnomenclature. The cumulative weightingof these R-2R resistors in the ladder ultimately produces an output voltage at thetop of the ladder corresponding to thedesired analog voltage. Thus all the software needs to do is present the desiredsine wave values in sequence to the output port at precise time intervals. Whensmoothed with a capacitor, the resultantwaveform at the top of the resistive lad-The NJQRP “PSK31 Audio Beacon Kit”5
der is a clean sine wave.Audio AmplifierThe output of the R-2R DAC is accoupled to the input of a common LM386audio amplifier through a potentiometerto provide continuous adjustability of theaudio volume.This amplifier provides significant gainand quite nicely drives a small speaker.Configuration JumpersFive user-installable configurationjumpers (X2-X6) instruct the softwareto produce one of 24 distinct carrier frequencies that will ultimately be phasemodulated at 31 baud. Input pins of theSX microcontroller are used to read thestatus of these configuration jumpers.These input pins have weak internal pullup resistors and float “high” when unconnected. However, when grounded byputting a jumper in place, the pin reads“low” and signals the software to takespecific action in configuring the Beacon’sfrequency.Another jumper (X1) instructs the software to set a specific interrupt timing thatpermits the software UART in the SXchip to communicate over the RS232 serial line with an external computer. Thismode is used for custom beacon stringentry or character-by-character sendingof data.Carrier Frequency Selectiona) Base Carrier Selection Jumpers - Twojumpers allow user to configure beaconcarrier signal to any of three frequencies:500 Hz, 1 KHz, or 2 KHz.b) Carrier Offset Jumpers - Three additional jumpers allow user to select oneof 8 closely-spaced frequencies aroundthe chosen base carrierTransmission Mode: Continuousor One-TimeThe Beacon may operate in either Con6tinuous transmit mode, or in One-Timetransmit mode.a) Continuous transmit is selected byinstalling configuration jumper X7, thusinstructing the beacon software to automatically restart the beacon transmit sequence (idle and pre-programmed datastring),b) One-Time transmit is selected byremoving the configuration jumper fromX7. The transmit sequence is initiatedby manual actuation of theSTARTpushbutton, upon which the idlestream and pre-programmed data stringare sent. The beacon stops transmittingat the end of the data string and awaitseither another STARTpushbutton actuation.Serial Input ModeJumper X1 instructs the software touse a fixed-time interrupt loop, thus allowing the UART routine send and receive serial data with the external terminal/computer. It may be convenient to usea SPST toggle switch for this configuration line, as it would only be used wheninputting a custom beacon string or whentransmitting keyboard data character-bycharacter. The switch would be open othertimes during automatic Beacon transmission.Custom String Entry ModeThe way to initiate entry of a customtext string is by having the X7 (CONTINUOUS) jumper in place and holdingdown the START pushbutton while applying power to the board. (You also musthave the X0 jumper in place to signifyuse of the serial COM port, as describedabove). A convenient way to switch theBeacon into this serial-entry mode is towire the X7 and START lines to a DPDTtoggle switch that would ground the respective input lines when this mode isdesired.The NJQRP “PSK31 Audio Beacon Kit”SOFTWARE DESCRIPTIONBeacon String ConstructThe Beacon software is programmedto transmit two types of data in sequence:1) Idle Stream - Upon transmit initiation, the Beacon sends a series of 64 zeros to allow the PSK31 receiving systemand decoder to synchronize for the datareception that follows. In some PSK31applications this idle stream time allowsthe decoding software to measure signal“IMD”, an indication of energy presentin adjacent sidebands and somewhat of afigure of merit for the received signal.2) Data String - Immediately followingthe idle stream of zeros, the Beacon begins sending the data string that will ultimately be displayed on the receiving sideof the communications channel. This isthe custom-programmed sequence ofASCII characters. The data string may beof any length, and is limited only by available memory.The SX chip provided in this kit comespre-programmed wih the informationspecified in the inital ordering process.This beacon string is “burned” into theprogram memory and is tranferred to internal RAM memory when power is applied. Whenever the START pushbuttonis actuated or the CONTINUOUS jumperput in place, the string in RAM memoryis encoded and audibly transmitted.Entering Custom Beacon StringsOne may alternatively enter a differenttext string directly to RAM memory overthe RS-232C serial COM port providedon the Beacon board. A separate computer would typically be used to sendthis new text string to the Beacon. Thenew text is entered character-by-character into RAM data memory, effectivelyoverwriting the pre-programmed textstring that was put there initially atpower-up time. But since RAM datamemory is volitile (i.e., contents are lostwhen board power is removed), the custom-entered text string is only presentwhile the power is applied. If power iscycled, the custom text string must beapplied again to overwrite the pre-programmed string.The way to initiate the entry of a custom text string is by having the X7 (CONTINUOUS) jumper in place and holdingdown the START pushbutton when applying power to the board. You also musthave the X0 jumper in place to signifyuse of the serial COM port. A convenientway to switch the Beacon into this serialentry mode is to wire the X7 and STARTlines to a DPDT toggle switch that wouldground the respective input lines whenthis mode is desired. The X0 input linecould also be put to a SPDT switch to begrounded for use of the serial port. (Twoseparate switches are recommended forreasons explained in the section concerning Direct Character Transmission mode.)Interrupt TimingFor this part of the discussion, it willbe assumed that the configuration jumpers are set to produce a 500 Hz carrierfrequency, with a nominal interrupt variability of 4 (X2 jumper in place for anRTCC reload value of 197.)The PSK31 Audio Beacon software iscompletely interrupt-driven, based on thetimeout settings of the real time clock(RTCC). The default setting of the RTCCcounter produces an interrupt every3.94us and the Interrupt Service Routine(ISR) counts two of these interrupts andthen signals the presence of a 7.88us interval by setting the SYNC7US softwareflag. This flag is inspected in a tight loopat the MAIN starting point of the program, and when detected as being set, theThe NJQRP “PSK31 Audio Beacon Kit”7
whole program sequence begins.much more spectrally clean.Creating the Carrier Sine WaveEvery 4th time the 7.88us windowstarts (i.e., at the 31.25us boundaries),the software gets the next 8-bit value fromthe sine wave look-up table and outputsit to the DAC output port RB. Whenthis process happens 64 times (i.e., when64 instances of the 31.25us windows haveoccurred) a single sine wave will have beenconstructed within a 2ms time period,creating a 500 Hz carrier.A cosine wave look-up table is used tomodulate (or “scale”) the carrier wave,sample by sample at the 31.25us rate.The cosine table pointer is advanced aseach cycle of the carrier is generated.The software keeps track of how manycarrier cycles have been generated, andwhen the count reaches 15 (i.e., at the31ms interval), the PSK bit window ispresent and the PSK bit processing begins.Actually, the recurring 31ms windowstarts at mid-position of one bit cycle andgoes to mid-position of the next bit cycle.It’s done this way so the software caninspect the current / next bit relationshipand command a zero-power phase reversal condition at the next end-bit time period, if required.Creating the Phase ReversalsThe bits constituting the Varicode character being sequentially presented formodulation are inspected on a bit-by-bitbasis at each 31ms bit processing window. When a “1” is encountered, nothingis done in that window. The sine waveconstruction continuesHowever when a “0” is encountered,the rules of PSK31 modulation state thata phase reversal must be forced in thecarrier.The processing gets a little more complicated at this point because we want toreduce the power of the carrier at the timeof phase reversals. This action greatlyreduces the “glitch” energy at the time ofthe reversals and makes the resultant tones8If the “next bit” of the varicode character to be processed is a “0”, the scalingprocess is turned on at mid-bit positionand the remaining 7 carrier cycles of waveform construction occurring in the bitprocessing window get scaled per the cosine look-up table. This effectively bringsthe amplitude of those seven sine wavesprogressively down to zero, at whichpoint the phase of the carrier is reversed(by changing to a different sine wave lookup table — one that is 180-degrees out ofphase from the other one.)After the phase reversal, the carriercontinues to be constructed at every31.25us interval, and the cosine scaling isstill engaged in sync with the carriercycles. For the next seven cycles, the cosine look-up table routines scale up thecarrier such that the carrier is back to fullpower (no scaling) by mid-bit position.All this can be more easily understoodby considering the oscilloscope screenphoto in Figure 1 on the next page.Here we see 15 cycles of the 500 Hzcarrier constituting a 31ms bit-processing window. The sequence of charactersprocessed were two sequential zeros –the first being encoded in the phase reversal seen zt the zero-power point on theleft, and the second on the right. Thesepoints are where the sine wave look-uptables are changed, resulting in the obvious phase reversals. It can also be seenthat the cosine “scaling” of the carrierstarts at mid position in the bit-processing window and proceeds to zero at theend of the cycle where the reversals oc-The NJQRP “PSK31 Audio Beacon Kit”Figure 1: Oscilloscope trace of 31.25 ms timing window (square wave onchannel 1) superimposed on the modulated 500 Hz carrier wave on channel 2.Note phase shifts at the zero-crossings, indicating two successive logical 0’s inthe digital bitstream.cur. The power is then raised in the following 7 cycles of the next window.oscilloscope properly synchronized at thestart of the character sequence.Encoding a “T”Using the PSK31 encoding algorithmfor phase reversals (i.e., insert a phasereversal whenever encountering a “0” inthe bit stream), we can begin to considerwhat a composite sequence of bits willlook like for an entire character.It’s useful at this point to mention thattwo (or more) consecutive “zeros” constitute a letter gap, thus instructing thedecoding engine on the receiving side tostart another character processing cycle.In this example, we’ll look at the letter“T”, which has a Varicode equivalent bitpattern of 1101101. The sketch in Figure2 illustrates what one would see with anIn the diagram below, a letter gap of 00 starts off the “T” sequence of bits.Upon encountering each “0”, the powerlevel is brought down to zero and thephase is reversed. The power level is thenFigure 2: Varicode “T” waveformThe NJQRP “PSK31 Audio Beacon Kit”9
raised back up to 100% by mid-next position, whereupon the “next bit” is inspected to see if another reversal will beneeded.Upon encountering the first “1”, thealgorithm dictates that no phase reversaloccurs, so the power level remains at 100 (no cosine scaling).The same happens again upon encountering the second “1”, but the next bitafter that is a “0” and the power level isreduced in anticipation of the comingphase reversal.One can easily see these principles inaction in the oscillosope trace in figure 3.The phase reversals can be seen at thepoint where the power is reduced to zero,which is at the bit-processing intervals(31ms). The square wave superimposedabove and below the carrier is the 31mssync signal present on the Test Point ofthe processor (bit 3 of port RA.) It canbe clearly seen how the current/next bitprocessing is actually done at the mid-bitposition, halfway through the 31ms period windowProducing Different FrequencyCarriersThe preceding discussion assumed a500 Hz carrier and a core interrupt timeof 3.94us. With a little software magic,some variability was placed into the program in order to produce two more basecarrier frequencies, and 16 sub-variationsaround each base frequency.The interrupt structure and timing isactually designed to produce a 2 KHzcarrier as the highest base frequency, using a 7.88us sine wave construction. Then,based on the state of the configurationjumpers, we’re able to sample at half-ratesto get the 15.75us rate for 1 KHz carriergeneration, and 31.25us rate for 500 Hzcarrier generation.10Achieving the 16 frequency variationsaround each of the three base carrier frequencies is achieved by slightly varyingthe basic underlying interrupt timingmechanism.The Real Time Clock Counter (RTCC)is clocked by the master 50 MHz oscillator internal to the microntroller. Interruptsare generated when the RTCC “rolls over”upon a countdown from a preset value,and the governing mechanism for interrupt timing is to preset the RTCC counterat the end of each interrupt cycle. Thenominal value of the RTCC preset is“200”, and we can go as much as /- 8counts before receiving systems lose synchronization with the master 31 baudsystem timing in the Beacon.Therefore, RTCCvariable is set to avalue between 194 and 209 within thesetRTCC routine based on the state ofthe configuration jumpers X0-throughX3. These four bits give 16 differentRTCC preset values that modify the basic system timing of the beacon, whichresults in an ability to more preciselyposition the base carriers within about /- 60 Hz around their nominal values.The last comment about the software design is that I make extensive use of thelook-up table (LUT) capabilities of theSX microcontroller. Using the LUTs, weare able to easily generate two 64-pointsine waves — a positive-going oneSINETBP and a negative going one(SINETBN) – and a 64 point half cosinewaveform (COSTBL). Using a pointer totravel through each table allows easy retrieval of the waveform values which represent a 0-to-1 percentage of the 5 bitvalues represented in the tables.The NJQRP “PSK31 Audio Beacon Kit”BASIC ASSEMBLYThere’s really not too much to assembling this project – it’s really just a coupleof IC’s and a handful of resistors and capacitors mounted on a printed circuit card.All you’ll need to do is to assemble thecircuits according to the Schematic andParts Layout diagrams, plug the chips intothe sockets, connect a DC power sourceand a speaker, and the Beacon shouldwork. No dreaded toroids to wind, noalignment no muss, no fuss!The top of the actual pc board is noted“Component Side”. Start by inserting theIC sockets into their respective holes.Carefully solder all pins in pace on thebottom side of the pcb.Next solder the J2 DB-9 connector inplace.Be sure to solder the heavy tabsthat will protrude through the two largeholes in the pcb, as this will give the connector strength.Next install the resistors. All resistorswill be mounted in the “upright” position, as noted in the sketch on the Layoutdiagram. Although there is no silkscreenon the pcb to denote precise location ofcomponents, carefully matching up thehole patters to the Layout diagram shouldallow an easy install of the resistors.Install the 3-terminal voltage regulator,VR1. This component should bemnounted so it can be bent over parallelto the pcb and about 1/8” off the board.Although it will get a little warm duringoperation, no heatsink will be required.Install all remaining components: capacitors, the 3-terminal resonator Y1, andthe potentioment R4.Carefully wire all off-board components to their respective pads, followingthe Layout diagram. This includes thespeaker, the START pushbutton, the J1battery clip,Before inserting the IC’s to their sockets, apply power to the circuit and ensure that the “O” (output) pin of VR1reads 5V DC.Turn off power and insert the ICs totheir respective sockets. Ensure that pin1 of each IC corresponds to the Layoutdiagram.With all off board components connected, you can apply DC power againand depress the START pushbutton (orplace the CONTINUOUS jumper inplace). You should hear a relatively loudPSK31 warble tone coming from thespeaker for the duration of the beacontransmission. Adjust R4 for an acceptable volume level.The “acid test” of your success will beto power up a computer running DigiPanor other PSK31 program and present theBeacon audio as input to the computer.Many computers and most laptops havea built-in speaker that allow the tones tobe “heard” by the program. Your beacon’swarble should be visible on-or-around oneof the base frequencies on the waterfalldisplay: 500 Hz, 1 KHz or 2 KHz. Placethe cursor on that displayed signal andyou should see your Beacon’s programmed sequence displayed in the textportion of the display. Experiment withthe jumpers to see and hear the flexibilityavailable in your Beacon’s frequency settings.In Case of TroubleIf you had any problems in the Checkout step, you should first re-check forproper voltages, proper IC orientationsin the sockets, and good solder joints.When the Beacon is running, the TestPoint will be a continuous 15 Hz squarewave (31ms high, 31ms low) that can beseen as a voltage bouncing around betweenThe NJQRP “PSK31 Audio Beacon Kit”11
2-to-3 volts on a DC voltmeter. If youhave an oscilloscope, you should see thePSK31 waveforms at the output of theDAC, as indicated on the schematic. Youwill also see a relatively constant 2.4Vreading at this same point when using aDC voltmeter. The PTT pad will be at 5Vduring transmission and at 0V when theBeacon is stopped. Current consumptionof the Beacon is nominally about 80ma.Using the Serial COM Line forCustom Beacon String EntryYou can next check out the capabilityof entering a custom beacon string.The serial channel is set for 19,200 bps,no parity, 8 bits of data, and 1 stop bit(“N-8-1”). Your external computer terminal should be set in this way also.As described previously, put the X1jumper in place to signal Serial Mode.Put the X7 (CONTINUOUS) jumperim place and hold down the STARTpushbutton while turning on the powerto the board.The terminal program running on thecomputer will display a “:” (colon) character to prompt you to begin string dataentry.You may enter up to 64 characters fromthe key
4 The NJQRP “PSK31 Audio Beacon Kit” The NJQRP “PSK31 Audio Beacon Kit” 5 actuated. nSource code and inexpensive devel- opment tools allow custom modification of the beacon string and/or software op-eration. nConstruction may be done Manhat- tan-style (a form of ugly-style construc- tion) for freedom of desired implementa-
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A rotating beacon is located at point A next to a long wall. The beacon is 9 m from the wall. The distance a is given by at 2 , where t is time measured in seconds since the beacon started rotating. (When t R 0, the beacon is aimed at point .) Find a for t 0.45 24. dA rotating beacon is located 3 m south of point R on an east-west wall .
The PSK signal will run at 50% duty cycle when in IDLE, and up to 90% when transmitting data. The transceiver audio path must stay linear (no or little ALC or Compression). Aggressive Method Use an IMD monitoring device such as the PSK Meter or the IMD Meter Tunr o ffCompoersnis Set the rig output control to 50% Transmit .
May 04, 2015 · MicroHAMS Digital Conference 2008 NUE-PSK31 Modem Details in March 2008 QST and QEX Portable Operation Low Power, Sunlight Readable Display Low Cost 200 Ready-to-Operate or 150 Kit Open Source Hardware and Software for DIY Produced by AmQRP George Heron, N2APB and Milt Cram, W8NUE
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