Experimenter's Project Incorporating AD9850 Complete-DDS Device Digita

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AN-557 APPLICATION NOTE
Experimenter's Project Incorporating AD9850 Complete-DDS Device Digital Function Amateur Radio Transceiver*
DIGITAL INJECTION SYSTEM
Peter Rhodes, BSc, G3XJP (email pirrhodes@aol.com) PART
This construction project brings together number themes which have been kicking around some time. first, MIX? ESSENTIAL TERMS PIC-A range microcontrollers produced Arizona Microchip Inc. this application, PIC16C84. DDS-Direct Digital Synthesis. technique digitally generating output frequency directly opposed typically mixing output with crystal oscillator-or employing phase-locked loop techniques). this application Analog Devices AD9850 "complete synthesizer" chip used. BRIEF provides controlled direct generation required injection frequencies into signal frequency mixer your transceiver. also sense that pick choose which functional elements build; sense that there design number different mechanical configurations best suit your circumstances. also presented with radical choice using software have designed-or writing your own. microcontroller (and about hours software development) provides control operational flexibility while chip used synthesize output giving stability low-phase noise. CONVERGING THEMES Discounting value your time, would argue that years been viable build multiband transceivers which outperform their commercial counterparts point price versus performance graph-from cheap cheerful through truly exotic. Except, that critical element-the injection oscillator. have been building VFOs years that practical purposes didn't drift. Almost were based Vackar running somewhere between MHz-10 MHz. Besides some time consuming temperature compensation, never gave them second thought. they need about eight x'tals, mixer switched bandpass filters before they feed both signal frequency mixer-and frequency counter which gives natural display exactly quite frequency made work, only substantial cost time, money space. only incremental feature easily obtained IRT. Then February 1996, Technical Topics reported results some phase noise measurements made Colin Horrabin, G3SBI Jack Hardcastle, G3JIR stable Vackar "rather disappointing." This thinking. Most ignore oscillator phase noise because can't measure Myself included. Does really matter practice? ARRL handbook excellent section subject which concludes far-out phase noise significantly reduce dynamic range receiver. Farout phase noise performance effects just critical blocking dynamic range two-tone dynamic range performance receivers." Yes, does really matter practice? mean, truly going fail copy real signals significant number occasions because poor phase noise performance?
*This five-part article reprinted entirety permission RadCom Magazine, radio magazine publication U.K.(website www.rsgb.com), author. international copyrights reserved.
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determined find adopting simple expedient fitting changeover switch between traditional phase-quiet alternative same power output. Then, under variety practical conditions, could tell difference? problem, course, find this alternative without spending impracticable sums money. Technical Topics came rescue again first bringing notice Analog Devices AD9850 chip. minutes Internet produced data sheet- looked good true. about designing some traditional control actually building some boards before giving Because although have doubt would have worked, chips control chip-and provide modest range useful features-was ignoring reasonable definition practice" imperative. obvious from outset that some form microcontroller would provide solution control problem same time offering ability provide range operational features. What months costs acquiring development environment hardware program chip. glance larger catalogues suggested little change from investment development-totally unacceptable. bottom line this. Arizona Microchip provide their website their complete development environment cost-as well copious application material. there numerous circuits Programmers published Internet which build less than project born. CONCLUSION? Phase noise does matter practice. substantial number occasions makes difference between signals. example, home-brew convenes daily around lunch time just down from SSTV calling frequency just from prominent French coastal station. convenient source large adjacent channel signals. band flat quiet, makes difference. conditions lively-using source-then often copy EI9GQ only just Switch over readability instantly degrades near hopeless only there significant adjacent channel activity. effect insidious. that Ed's signal goes down. that base level band background noise appears doesn't course. What happening that noise sidebands mixing with adjacent signals produce incremental noise passband. very salutary experience because this noise totally indistinguishable from band noise could operate years without realizing what happening. would seem that there basic conflict design. traditional view that drive oscillator gently keep heat (and, therefore, drift) down follow with appropriate buffer power required level. This approach also maximizes phase noise. Conversely, drive hard then becomes increasingly difficult experience, next impossible) maintain acceptable frequency stability. With approach, phase noise drift intrinsically small. topic covered shortly. SUMMARY Before covering essential theory these features offer should adopt software: GENERAL SUMMARY replaces functions crystal oscillator bank, VFO, mixer, bandpass filters, power driver frequency counter associated with conventional transceiver with significantly enhanced features lower cost. merely VFO! Alternatively, acts programmable and/or tunable signal source with output from audio steps. functions controlled either multifunction tuning knob-or simple telephone keypad with discrete combinations recognized software. large six-digit seven-segment display with autoranging gives resolution independent VFOs provide IRT, crossband operation. variety tuning scanning modes provides operational flexibility. desired frequency entered directly from keypad. switch-on frequency nine band initialization frequencies user programmable. frequency memories. three offsets (USB, separately) range entered. USB/LSB/CW selection outputs-and band switching outputs host transceiver provided hardware option.
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Front panel LEDs provide status information double bar-graph show tuning rate. Finally, there number possible physical layouts providing flexible outboard integrated configurations. ADMINISTRATIVE FEATURES frequency accuracy determined reference oscillator range. crystal range MHz-125 program actual frequency into software yourself. Final calibration subsequent correction crystal ageing achieved using tuning knob drive trimmer software. physical trimmer which would inevitably introduce drift phase noise neither required provided. offsets entered from keypad and/or trimmed zero beat with host transceiver carrier crystals. injection oscillator, output frequency selected frequency plus minus desired frequency. choice high-side low-side injection made fly" with sideband selection outputs host being switched correspond. OPERATIONAL FEATURES Intelligent tuning continuously monitors speed duration tuning knob rotation vary tuning rate dynamically. Thus longer faster turn knob, greater tuning increments. software flywheel engages automatically high tuning speeds rapid and/or large frequency excursions-and disengaged slightest turn knob opposite direction. opposed traditional tuning where rotation knob alters frequency, tuning rate option provided whereby rotation knob alters rate frequency change-from zero very fast. This particularly useful casually scanning around band without having continuously turn knob. Guard channel operation provides normal tuning, with brief switch another chosen spot frequency about every seconds. memories programmed with frequency. opposed merely providing spot frequencies, they also jumping points further tuning. Memory scanning mode cycles between memory frequencies speed determined tuning knob. Spot scanning switches between chosen spot frequencies speed determined tuning knob. Range scanning tunes down between chosen limits with frequency increments determined tuning knob. AD9850 Throughout this article, have used nomenclature used Analog Devices their data sheet only mentioned features configuration chip used this project. There others. There little need know about internal workings this device. most significant consideration that contains DAC-necessary convert digitally generated sine wave analogue form-on chip. neither have worry about specifying suitable interfacing
CLKIN
REFERENCE CLOCK
AD9850
FOUT
32-BIT TIMING WORD (GENERATED PIC)
Figure Block Diagram
basic block diagram shown Figure There simple relationship between output frequency FOUT, reference clock frequency CLKIN, 32bit tuning word Phase:
FOUT (Phase CLKIN)/232
Using clock, highest frequency permitted, this gives tuning increments 0.0291 orders magnitude better than needed this application. practice this means that using tuning increments error 0.0291 significantly smaller than, example, drift your carrier x'tal. Stability system same parts million) that reference clock x'tal oscillator. example, clock drifts then with 12.5 injection, will drift Phase noise output better than that reference clock-which contributes most system phase noise. improvement (CLKIN/FOUT) that simple? Unfortunately, quite, well generating required frequency, aliased image outputs also present. This inherent sampled signal output observes Nyquist's theorem. aliased images multiples reference clock, CLKIN output frequency FOUT. Thus with clock frequency wanted output MHz, images will (first image),
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(second image), (third image), (fourth image)
AD9850 14-PIN
Another consequence Nyquist's theorem that maximum theoretical output frequency half reference clock frequency-but practice, third usually taken rule-of-thumb limit-to provide reasonable separation between wanted signal significant images. amplitude images follows sine envelope shown Figure low-pass filter therefore inserted output reduce image outputs; highest bands using high Tx/Rx signal frequency tuned circuits offer further protection. Using highest possible reference clock frequency obviously helps.
Figure AD9850's 28-Lead Shrink Small Outline Package Compared 14-Lead Package
tried double-sided board, both surface mounted into slot that thickness PCB. great problems hand-etching boards- found substantial difficulty soldering chip pads. best managed with medium-sized iron length sharpened copper wire bound bit- very fine solder. propensity bridge adjacent leads enormous. Worst, seemed impossible maintain clean power ground plane layouts- which ultimately prejudices phase-noise performance. After obtaining batch unmarked devices same packaging rally having destroyed many quest, settled dead-bug approach with continuous power ground planes-mounted subassembly socket with input/output leads taken socket fine wires. This method reproducible have average eyesight good magnifier) short-term steady hand. process described detail Part this article. WORLD PICS 16C84 large growing range 8-bit microcontrollers. devices vary according speed, amount memory, built devices (including converters) other features. latest detail, consult Arizona Microchip website. 16C84 specifically is-in brief-an electrically reprogrammable device with program memory (i.e., room 1024 instructions), bytes working data bytes data EEPROM which survives power down; input/output pins. Also website will find integrated development environment MPLAB which used exclusively developing software. includes editor, assembler simulator. latter particularly useful since progressively build test code with your target chip simulated PC-no real hardware needed. want download MPLAB, watch your phone bill because about when unzipped! elements software under DOS, used exclusively under Windows. first under Windows latterly under Windows 486. Both were entirely satisfactory. compilers also available, haven't tried them, work being assembler.
SIN(X)/X ENVELOPE WHERE FOUT/CLKIN
AMPLITUDE
FIRST IMAGE
SECOND THIRD IMAGE IMAGE
FOURTH FIFTH IMAGE IMAGE
REFERENCE CLOCK CLKIN FREQUENCY 125MHz
Figure Output Spectrum
There other discrete spurious outputs result limitations technology. significant ones number appear from user's perspective random frequencies. Analog Devices specify them better than down practical consequence these occasional birdie. remaining spurs form continuous noise floor about down these give rise greatest concern. typical double balanced mixer will furnish about further suppression-so mixer injected dBm, weak birdies will heard band noise less than mixer port. bands with most receivers this will academic say, typical will need preamp with some gain both retain adequate sensitivity mask noise floor. This topic will much less issue when 12-bit available affordable prices meanwhile this 10-bit suitable home-brew topologies, particularly reluctant alter your gain distribution. final challenge with AD9850 size, Figure Designed surface mounting, truly microscopic. Much effort gone into finding repeatable amateur methods mounting which compromise performance. Analog Devices recommend 4-layer board with dedicated power ground planes.
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various programmers available, built TOPIC David Tait6 which runs parallel port. also build ones serial port operation some even need power supply, deriving their power from port. Having conducted intellectual exercise "designing" some aspect software, mechanics easy enough. After typing code using editor, assemble then simulator-if necessary instruction time-looking intermediate results works. also check execution times. When happy, then download software onto using programmer (say, seconds) your code real world. careful, programmed situ target environment which speeds process enormously. assembler language itself easy learn with only instructions. art, turns out, usually whether write something that works rather, find efficient enough doing squeeze into space without unduly compromising features, performance ultimately maintainability? Eric Morecombe once said "Composing good music same composing music. just matter putting notes different order." with software! have never written software before have with least temporary access Internet, have with incremental cost. could suitable secondhand about most Internet service providers offer free trial period.) Think range applications-self-tuning ATUs, intelligent generators, keyers readers; fact application involving control logic potential candidate where 18-pin coupled with your intellect replace acres conventional hardwired logic trivial cost. says computers amateur radio don't mix? view these microcontrollers going dominate many aspects home-brew construction before long. INPUT/OUTPUT CHALLENGE JUST MENTIONED 16C84 input/output (I/O) pins controlling environment. many actually needed? following first-pass answer: Inputs-total follows: Line Monitoring Keypad Shaft Encoder Outputs-Total follows: Digits Segments Decimal Status LEDs Band Switch Outputs AD9850 Control Giving grand total (apparently) Clearly something give some supplemental hardware needed. There however, mitigating feature. pins used either inputs outputs-and change them fly" midprogram with cunning they both! Firstly, keypad switches aren't individually monitored. Each tested turn looking each column turn presses. This needs only seven lines. Next, rather than drive each display separately, each driven turn-in rapid succession; i.e., they multiplexed. low-cost decoder chips added this gets count display segments down seven. these, three outputs fact same lines used three inputs keypad columns; other four outputs also multiplexed drive keypad rows. Then three serial parallel latches added handle status band switching. These have three unique data lines, common clock line (with four again multiplexed with display)-and latch line shared with AD9850. final touch drive decimal point output same line shaft encoder direction input. have kept with this, then will agree that total count down Figure shows what looks like-and good measure lines also shared with situ programming. only other viable approach would multi-PIC solution. turns marginally more expensive significantly more intellectually demanding. There remains question. multiplex this multiplexing fast enough software that user sees "instant" response smooth "continuous" operation? answer, transpires, that even difficult! BUDGETS Cost-If were electronic components from new, should allow about Time-Construction time obviously very variable, good estimate would each make PCBs one-half days assemble them. will need about hours build subassembly. this "weekend project," probably won't exceed two! design your software, times impossible estimate. write some software some useful thing-say, generate fixed output frequency-very quickly. integration whole which takes time. Power-you need smoothed necessarily regulated. From V-13 acceptable.
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BOARD DISPLAY BOARD
3-TO-8 DECODER
REGULATORS
LOGIC
REFERENCE OSCILLATOR
BUFFER ENABLE
COMMON ANODE
PIC16C84
DIRECTION PULSES OSC1 4MHz OSC2
7-SEG DECODER
110MHz REFERENCE CLOCK OSCILLATOR LINE
AD9850
CLOCK BUFFER DATA W_CLOCK FQ_UD
8-BIT LATCH DATA CLOCK DISPLAY BOARD LATCH
BROADBAND [SPARE] 1.8MHz 3.5MHz 7.0MHz
8-BIT LATCH DATA CLOCK LATCH
10MHz 14MHz 15MHz 18MHz 21MHz 24MHz 28MHz 29MHz
SWITCH OUTPUTS HOST Tx/Rx
Rate
Scan
8-BIT LATCH DATA CLOCK LATCH
Freq
Save
Split
MODE
Figure block diagram, illustrating input/output allocations physical partitioning. Besides power supply distribution decoupling, functional elements shown.
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PART
this issue alternatives techniques mechanical construction explored. These include process making one-off PCBs-and mounting chip socket carrier. OVERALL STRATEGY When comes gross layout hardware, flexibility design objective. When comes mounting chip itself, successful outcome likely only absolutely follow rules allow adopt somewhat dictatorial style. Your first decision revolves around whether building external injection source integrating mechanically with your Tx/Rx. either case, self-evidently, tuning knob keypad need front panel with display board immediately behind board same size display board. designed mounting parallel behind display board, right-angles completely remotely from connected ribbon cable. last choice relevant self-contained external source. tuning knob mounted either side display, choice being governed simply whether right left-handed. keypad should mounted same side display tuning knob. Should mount opposite side display, although give some appearance better aesthetic balance, courting ergonomic disaster. Visual feedback your presses given display status LEDs your forearm will inevitably obscure view. photographs, will note that keypad mounted contrary these recommendations. This layout peculiar requirements since unusual being mostly ambidextrous, preferring twisting
3.25" NOMINAL HEIGHT FRONT PANEL
motions (e.g., screw drivers) with right hand pushing motions (e.g., sawing) with left hand. practice, therefore, both hands, most people would find this uncomfortable. second decision whether build shaft encoder integral part mounted display boards-or split them. choice yours governed mostly where starting from. separation between presents performance issues. want take this approach, simply both boards, separate them reconnect them using four flying leads some ribbon cable. four leads pulses direction. Obviously could build them like this first place. final consideration housing stand-alone unit. Those have built have found need screened enclosure would obviously represent good practice. event, will need consider weighting securing since Newton's Second applies when press keys-and last thing want skidding around. DISPLAY BOARD MOUNTING display board mounts immediately behind front panel. will need aperture 3/4" view frequency readout. Having aperture, need back hole with some optical filter material which either corresponds color your display (typically red/green) or-and preferably-is circularly polarized. latter gives much superior performance bright natural light some reason become expensive recent years. Figure suggested front panel template which also shows have accommodated status LEDs. Three holes drilled these, LEDs inserted board soldered. front panel mounted into position, LEDs adjusted their
DISPLAY BOARD 6.1"
2.75"
0.75" DISPLAY CUT-OUT
Figure Drilling template front panel. position tuning knob shown assumes mounting shaft encoder display boards. could much further right opposite side display.
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holes equal protrusion. They then tacked finally soldered display board when fully aligned. like deprecate idea screw-heads showing front panel, then will need glue some nuts threaded pillars back front panel mount display board. find rivets ideal this since they have large surface area which makes strong permanent adhesion using super glue. BOARD MOUNTING Figure shows configuration right angle mounting Figure illustrates parallel mounting. ensure full access during commissioning would strongly recommend that avoid parallel mounting configuration start with. this your target configuration, join boards with short length 0.1" pitch ribbon cable. This allows access both sides both boards testing. mounting boards right angles close proximity, then best approach permanently solder boards together shown Figure Butt boards form small junction (not "L"), tack them lightly together, check angle then beads solder along full length both
DISPLAY BOARD ACETATE DISC DISC MOUNTING KNOB FLYWHEEL FRONT BEARING
REAR BEARING
DETECTOR
DIODE
TUNING KNOB BOARD
Figure board mounted right angles integral with display board. Also illustrates suggested mounting method (not scale) shaft encoder disc, diode detector. Note long lead lengths latter give simple adjustment diode detector positions relative disc. disc needs mounted near enough display board clear x'tal oscillator enclosure described later. rear bearing mounted piece soldered board and/or rear x'tal oscillator enclosure.
DISPLAY BOARD
FLYWHEEL
BEARINGS
DIODE
DETECTOR BOARD
TUNING KNOB
Figure Alternative mounting method (not-to-scale) where board mounted parallel display board spacers (not shown). small hole drilled board pass infrared, rear bearings fitted board. leads detector pass through board tracks-which avoid interference with rear bearing. detail will become apparent when described later.
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sides intimately join ground planes. Join edge-connectors with small solder bridge test shorts. further advantage taking this approach that display board need secured front panel. Mounting board horizontal base with display touching rear optical filter provides effective location. MAKING PCBs article Third Method Transceiver, described approach constructing boards without etching which proved very popular. would perfectly viable this technique display board this project, wholly inappropriate board. what follows technique have used many years making one-off PCBs without expense exposure techniques. must emphasize that this approach viable only one-offs hopeless need greater quantities. would also very surprised these particular boards made using etch-resist pen, since some tracking very fine. technique revolves around removal material where want remove copper-rather than applying resist where want retain copper. board firstly size then drilled. surface mounting areas, board gently punched drilled. idea give yourself guides draw artwork directly onto board. With board clean polished, sprayed both sides with aerosol paint. Matt black best contrast color against copper. important light enough coat just cover substantial build paint thickness. Then, only after paint truly dry, paint removed between tracks using scribing tool. holes, punch marks master artwork guide. only need remove fine line paint. fact stand feet back from finished board, looks substantially like continuous copper. Note that example, have parallel tracks, would need three scribed lines implement technique takes little getting used should make mistake, simply repaint affected area with small brush again-differently! There some important tips: Tape board down reasonable block wood stop skidding around prevent scratching paint reverse side. also square against edge wood want posh lines- square needs transparent want avoid frustration. piece Vero board guide need scribe edge connectors. Scribe board good room temperature-certainly never cold. heat from desk light makes even easier helps prevent paint chipping. Finally, scribing tool itself important. needs pointed incredibly also wants retain point. find best tool take masonry nail- which hard steel-cut head grip draughtsman's clutch-pencil. Failing that, long masonry nail through cork pretty comfortable. Sharpen point with rotate drag motion piece emery when have sharp can, blunt ever slightly piece fine dry. piece scrap, holding scribe about 45°, should clean fine line. Resist gouging copper. only trying remove paint! Repeat sharpening process every minutes will feel when cutting paint cleanly. way, really fine work (you won't need here) sewing needle excellent gramophone needle. When have scribed both sides board checked meticulously, etch board conventional manner with ferric chloride. will find will through very little FeCl because total amount copper removed very small. Observe usual safety precautions. Keep board FeCl solution gently move time even etch have courage overetch slightly anything. Make sure both sides fully etched before removal. Wash board thoroughly cold water, inspect etch further necessary. Finally wash board with water then clean paint using cellulose thinners. small paint brush helps paint holes, being good insulator, this critical. Polish board with fine (used wet) polishing block. important stage. Using continuity tester check isolation between each every adjacent track. find shorts that obvious, clear then with sharp blade. they obvious, practice which hesitate publicize connect test probes battery then blow short. careful! result individual piece craftsmanship- produced with greater effort time than needed draw artwork onto film first place. home-brew! with much more ground plane than typical with other approaches-which only good. there critical processes sense that what happening time avoid moving until have right. commend you.
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PROCEDURE FITTING AD9850 CHIP CARRIER CAUTION: Analog Devices recommend taking proper antistatic precautions when handling AD9850. would folly ignore this advice with chip this value. Take 28-pin, 0.6" wide turned-pin socket piece PCB, copper side into recess between pins. needs snug fit. Most sockets have small moulding pimples adjacent Pins These should removed with sharp knife allow flat. When correct size fitting, clean copper surface handle only edges thereafter. Secure socket soldering some tinned copper wires between Pins 28-and Pins Solder wire also. This secures place socket establishes earth connection point each corner. Take socket secure something heavy enough allow work without sliding around. small block wood with some antistatic foam stuck it-and press legs socket into foam secure Take AD9850 chip, turn over mark underside with paint similar. This ensures that even when chip upside down, still sure which thus preventing from connecting rotated 180°. Place chip centrally right angles socket between Pins Mark position chip moulding under pins-on PCB, using sharp pencil. Remove chip. evenly strips about wide under where chip pins will be-up under marked moulding position. This facilitate soldering earthy pins chip later. Secure chip upside down with trace super glue PCB. Make absolutely certain that chip same corner socket. Check again! Please follow rest this process without creativity. result illustrated Figure have hand mounted about chips optimize process carefully observed others deviate practice chips!) wrong. source error always operating wrong pin. Although this seem surprising, when have tried yourself will understand why. From work only full natural daylight. idea work down side chip, never taking your eyes job. Should have start recounting pins, this proved single largest source errors. only chance right must some help dictate following sequence you-so stay focused job. best tool bending pins Stanley knife blade. Push with point blade required direction. this stage; just enough sure intended direction later. this sequence, "down" means bend towards PCB. "Up" means bend away from board, approximately vertically upwards. "Leave" means nothing. down down down leave leave leave down leave leave leave
focus infinity walk around several minutes before addressing other side. leave leave leave down leave leave down down leave down down down
That completes tricky bit! Bend down Pins within about tinned surface then solder them PCB. solder pins copper, best technique place iron board about back from pin(s) hold there couple seconds heat mass PCB. Then form small blob solder push towards pins. contact, remove iron almost immediately.
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COPPER FOIL POWER PLANE
FQ_UD FQ_CLK CLKIN GROUND PLANE
100R
COPPER FOIL POWER PLANE
GROUND PLANE REFOUT
Figure assembly. chip mounted upside down (dead-bug) ground plane. strip copper foil provides impedance power plane. shown decoupling capacitor connected between ground power planes adjacent chip.
Repeat this process Pins 26-28, that order. Make very sure operating correct legs. bend them down perhaps once before risking amputation worth risk. Obtain small strip copper foil. Copper brass shim stock would suffice. worst case, suitable strip removed from piece scrap with sharp knife stripped from some foil braided coax. needs long enough solder Pins socket, pass over chip down other side solder Pins width needs same anything, whisker more than) chip moulding width. trimmed size trial fitted width with pair scissors. Excess length removed later. foil chip moulding using trace super glue. When set, bend ends down, trim length solder pins socket 22), making sure that does touch ground plane. Bend completely pins chip, namely then quickly solder each foil. There remains only attach seven signal pins ease process, some pins bent down little near horizontal some degrees. This gives more clearance soldering iron Bend Pins little Pins down little. Trim three resistors size solder down their earthy ends with just touching target pin, bending resistors leads necessary touch pins. Quickly solder resistors pins. Take some enamelled copper wire, very thin critically Vero wire ideal. Make wire socket first then trim wire length. With wire both pretinned, clean tinned iron, solder wire (and case, resistor lead). best order Pins 13-17 connected.
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PART
this issue circuit diagram layout display board described together with some construction notes complete project components list. DISPLAY BOARD DESCRIPTION Referring Figure display element itself comprises three double-digit seven-segment common anode displays. They were chosen because they large make comfortable viewing. Their segments wired parallel. tempted substitute different seven-segment decoder chip, since software relies behavior `LS47 values greater than nine achieve leading zero suppression. Data clocked into latch IC13 8-bit serial word -and outputs updated latch pulse RB5. These bits drive current LEDs (D4-D11) directly current limiting resistors R41-R48. green LEDs, others red. This gives strong visual clue when operating "split." seven lines keypad routed through display board convenience. They could equally taken directly from board provided some means found mount series resistors R49-R55. resistors there prevent potential shortcircuiting lines event that more keys pressed simultaneously. KEYPAD keypad cost four-row three-column switch matrix designed push-button phones. software polls keypad periodically looking presses. does this driving each turn. each row, then tests each column looking found, column/row intersection defines which pressed. press de-bounced software since contacts rapidly make break ms-and without this facility, average press would otherwise interpreted about successive identical presses. keypad needs overlay give better feel alternative meaning keys this application. Figure copied size glued over keys, digits having been first with sharp knife. keypad connected display board some seven-way ribbon cable. need cable routing which brings lead from display board most right-hand connector keypad.
Rate
Scan
Freq
Save
Split
Figure Keypad Overlay Reproduction, Wide 57.5 High
traditional drive character backlit displays this sort application. cost would comparable (for one-off), power consumption noticeably less software complexity about same, albeit totally different nature. preferred approach since find character size just little small comfortable viewing. display digits multiplexed; that only digit time, turn (rapidly frequently) provide flicker-free viewing. software controls multiplexing process devotes much time repainting display circumstances permit. operation, IC12 decodes RA0, determine which digit being addressed-driving switches Tr5-Tr10 handle digit current. same time, IC11 decodes input RB0, determine which segments light; addition pulled decimal point. rushing round each digit turn executing entire sequence often enough, human sees continuous sixdigit display.
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Figure shows best achieve this. cable routed across front display board beneath frequency display LEDs. then passes behind keypad somewhat beyond cable then folded back itself-i.e., through 180°-and then folded downwards through 90°. then made onto seven right-most pads keypad. This process produces neat cable with correct connections. DISPLAY BOARD CONSTRUCTION NOTES layout shown Figure rear tracking somewhat complex around display sockets. perfectly acceptable less purist approach would bring these pins those IC11 onto small pads then hand wire segments sevensegment decoder using Vero wire. Other common anode devices, including single-digit those with pins vertical edges could easily substituted with simple changes PCB-or again, using Vero wire. status LEDs tacked onto board without shortening their leads commissioning purposes. When inserting sockets onto board with this form construction, insert them only enough give useful tail back board. Specifically, avoid bridging tracks earthling pins component side board shoulders pins.
DISPLAY BOARD
KEYPAD
Figure Display board keypad ribbon cable routing viewed from front. Note that eight connectors keypad, extreme left connected.
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(FROM BOARD) 2.2k 2.2k 10nF 10nF 10nF 10nF 10nF 10nF
BC327 BC327 2.2k 2.2k BC327 BC327 2.2k 2.2k
IC12 74LS138
3-TO-8 DECODER
CONNECTED
BC327 TR10 BC327
ANODE1
ANODE2
ANODE1
ANODE2
ANODE1
ANODE2
DIGITS
DIGITS
IC10
DIGITS
FROM BOARD
7-SEG DECODER/ DRIVER CONNECTED
IC11 74LS47
1N4148
3.3k 3.3k 3.3k 3.3k 3.3k 3.3k 3.3k 3.3k MODE
KEYPAD 7-WAY RIBBON CABLE
IC13 4094
SERIAL PARALLEL SHIFT REGISTER LATCH LATCH DATA CLOCK CONNECTED
Figure Display board circuit diagram. Note that segments display wired parallel except some decimal points which never used which connected. eight status LEDs, D4-D11 soldered display board, physically mounted holes front panel.
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COMPONENTS LIST Resistors 1/8-1/4 5%-10% except R17, R27-31 100R 330R R14, R20, R21, 220R 200R 180R R12, R13, R49-55 470R 560R R24-26 270k 10R, R35-40 R41-48 Capacitors TC1, 2-22p film dielectric trimmer feedthrough C11-14, C17, disc ceramic radial electrolytic C24, ceramic plate ceramic plate C40, axial electrolytic C10, C16, C19-23, C34-39 disc ceramic axial electrolytic ceramic plate ceramic plate ceramic plate C29, ceramic plate C31, ceramic plate 100p ceramic plate Semiconductors LD271 diode 1N4148 current (green) D6-D11 current (red) 78L08 7805 16C84-04/P socket) AD9850BRS HLC2705 IC6, IC7, IC13 4094 sockets) IC8-IC10 2-digit common anode 7-seg LED, Maplin FA01B (green) BY66W (red) IC11 74LS47 (socket optional) IC12 74LS138 socket) .2N2222A J310 2N3866 with small heat sink BC108 Tr5-10 BC327 Inductors turns 1/4" dia, 1/2" long, turn from earthy turns 22swg 1/4" dia, 1/2" long, centretap axial choke 0.68 axial choke bifilar turns FT37-43 Miscellaneous 2-sided dimensions text Keypad Maplin JM09K 7-way 0.1" pitch ribbon cable above 1-off 32-pin turned socket (0.6") 1-off 28-pin turned socket (0.6") Mount display above unused pins Display optical filter, 3.5"x1" approx. 1-off 28-pin turned socket (0.6") assy 1-off 28-pin turned socket (0.6") mount assy mother board 1-off 18-pin turned socket (0.3") 16C84 1-off turned socket (0.3") 74LS47 (optional) Shaft encoder disc text Knob mount encoder disc, approx skirt dia, drill right Tuning knob, flywheel, shaft bushes/bearings Your choice! 18-way ribbon cable Tx/Rx (optional) 16-way inter-board ribbon cable (optional) input connector (optional) output connector (optional) 18-way host connector (optional) approx (see text) SUPPLIERS MAJORITY above components were purchased from Electronic Components, 5774, Great Barr, Birmingham, 8PJ. 0121 6827045. They offer excellent service. significant exceptions keypad, IC8-IC10, D6-D11, which available from Maplins. 16C84 (IC3) also obtained from Maplin 1-off price want write your software. will happy supply ready programmed with features described this article, acetate disc shaft encoder paper overlay keypad receipt SAE. bushes bearings, much recovered from scrap potentiometers variable capacitors. Failing that, model shops good source. AD9850BRS chip purchased through Analog Devices distributor will sell small quantities. There long lead time. price will depend delivery payment methods. used Kudos Thame Ltd., Suttons Business Park, Reading, Berks 1AZ. 0118 1010.
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REAR VIEW (NONCOMPONENT SIDE) SHOWING REAR TRACK SOLDERING POINTS
FRONT VIEW (COMPONENT SIDE) SHOWING FRONT TRACK SOLDERING POINTS
RFOUT
ASSY COMPRISING IC4, R10, R18,
DETECTOR
SLOTTED DISC 51MM DIODE ANODE
DIRECTION
MCLR
6.1" 2.75"
18MHz 15MHz 14MHz 29MHz 28MHz 24MHz 21MHz 10MHz 7MHz 3.5MHz 1.8MHz BROADBAND [SPARE] (PTT LINE)
SHAFT CENTER LINE TUNING KNOB (NOMINALLY 1.75" DIA)
TRACKS MARKED CONNECTED GROUND PLANE
LOGIC INTERFACE Tx/Rx
VIEW SHOWING COMPONENT LOCATION DRILLING TEMPLATE
Figure Display board drawn production described text. ground plane shown since board (both sides) ground plane copper except where removed tracking. Holes front rear track views shown soldered that side board. They should lightly countersunk. Holes shown soldered either track ground plane. holes dia. front panel LEDs (D4-D11) shown. They solder ground plane pairs horizontal line about half rear view. Nine short wire links shown pecked lines rear view.
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PULSE
PROGRAMMER INTERFACE ONLY
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PART
this issue circuit diagram layout provided board together with some construction notes details building shaft encoder. BOARD DESCRIPTION Referring Figure functional blocks comprise x'tal oscillator (the reference clock) feeding assembly, followed low-pass filter buffer. There output latches least, which controls operations. input side, monitoring shaft encoder, line keypad. conventional x'tal oscillator followed Tr2, common gate buffer. crystal value range MHz-125 MHz, higher better. exact achieved frequency trimmed into software using calibration process described next month. entire oscillator surrounded enclosure formed board, four sides top. latter braid hinges access-and holes drilled allow adjustment TC2. bias AD9850 reference clock input half rail. IC4, AD9850, operated serial control mode. That pulse stream 32-data bits eight control bits clocked serially line corresponding clock pulses W_CLK. That sequence then actioned pulsing FQ_UD high. resulting synthesized sine wave appears complimentary current outputs IOUT IOUTB, terminated R10. sets on-chip full-scale output current accordance with manufacturer's recommendations. C24-28 form MHz, elliptic low-pass filter taken from AD9850 data sheet. R11, form terminate filter match into base driver Tr3. This turn delivers into important that feeds nonreactive load about ensure effective termination LPF. injection port say, SBL-1 mixer ideal. Being double balanced also reduces noise floor. Data clocked into latches serially sequence eight clock pulses followed latch pulse. Pulses other purposes appear data clock lines effectively ignored since there following latch pulse. These latches well IC13 display board AD9850 updated simultaneously pulsing high which reserved exclusively this purpose. latch outputs when true, interface these with transistor switches etc. drive band switches your Tx/Rx, switch antennas etc. "broad band" output goes true displayed frequency explicitly specified ones. precise, digits compared). this switch relays which short-circuit front-end remove selectivity. This allows listen frequency. Obviously performance seriously compromised under these circumstances, ability listen broadcast stations, frequency standards etc., price well worth paying. Equally, your does have front-end explicit band could diode-OR that band with broad band bit. IC3, been covered previously. hardware configuration entirely conventional. three lines shown "Programmer interface" together with omitted never have intention programming situ. cheap emitter designed remote control applications. IC6, detector designed computer mouse position encoding. merit producing decoded outputs which very easy (and fast) handle software. "pulses" output goes briefly every dark/light transition. This used interrupt handle consequences. "direction" output steady level which reflects last direction rotation. software can, therefore, test this line time pretty well leisure determine tuning direction. This cheaper program size than decoding gray code outputs produced many commercial shaft encoders. isolates host transceiver line. logic line either polarity since software assumes initial level switch-on corresponds receive. This allows your connecting line running only. running Tx/Rx this line must connected since software needs know state order allow split operation; safety reasons, cancel scanning operations when appropriate.
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Construction Notes There preferred order building commissioning board ensure access progressive testing. layout shown Figure Build crystal oscillator first. That components within screening enclosure (but enclosure itself) omitting oscillator components surface mounted islands copper plane. leads must short practicable, consistent with being able iron Mount coils last. also C15, insert temporary jumper from track junction provide power oscillator. Loosely couple passive detector) your crystal frequency. Adjust oscillation peak maximum output specified frequency. Repeat several times check that oscillator fires from cold. Next interplane wire links (i.e., some component leads) which either under socket between edge connector. solder board. C8-C10, R33. This completes rail distribution. Check shorts, apply verify available track busbar under shaft encoder detector-second track from left. getting this far, several crosses from bottom track verified. Fit, order, C29, C30, Tr4, R22, R32, R26, R25, Check again links under socket (IC3), your last chance, socket. R24, surface mount components low-pass filter buffer amplifier. transistor last heat sink last all. Temporarily track shown, other forming centre Solder board without shortening their leads adjust them that they about apart. socket ready Assembly insert assembly itself this stage. Mount other components except Insert socket. Build display board link board. Check interboard leads shorts earth shorts every other such lead. Apply your display should initialize "A,"' LEDs should light. This verifies that working-as well Display board. this stage there course, actual output. screwdriver passed between from left right should produce decrease indicated frequency- vice versa right left. Wire keypad check that keys work-as well status LEDs. Verify Assembly socket check shorts bridges connected pins. Finally, only everything else working, insert Assembly, monitor output from board apply power. Look around MHz-13 MHz. there output, peaking TC2. being well, "83" give signal generator mode. output should change status indicator LEDs should correspond. screened compartment around oscillator, drilling holes leads pass through. This compartment must made from two-sided fiberglass board, since both screening thermal conductivity properties needed. top, drilling holes adjustment TC2. Secure using some internal braid hinges. Repeak clean stable output some known frequency-and specifically ensure output multiple submultiple that frequency. shaft encoder. Adjust disc, that disc runs just touching IC5. position less critical (actually, none very critical). needs about away from disc. Note that bright incident light, shaft encoder will work reliably produce apparently random pulses. easy-but less than useful- with device which produces output frequency proportional number passing clouds! last since their operation independent rest board. need line connected testing purposes, should before starting serious operational use. there evidence multiplex noise your receiver, 1000 electrolytic from junction earth. Multiplex noise characterized disappearing completely sleep mode [73].
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there occasional musical tones, these reduced fitting three further decoupling capacitors well C14), each corner assembly from power plane ground plane. further with shortest possible leads. SHAFT ENCODER shaft encoder assembly comprises tuning knob, length shafting, some bearings, flywheel encoder disc. will also need some means taking end-float shaft. fortunate that Jack, G3XKF turned some beautiful brass fittings Don't skimp mechanics here "feel" tuning knob important pleasurable operation. very least, assembly must spin freely with binding. borrowed flywheel from cassette recorder drilled take shaft. Because software flywheel, don't need much physical mass here, some inertia needed smooth turning rate. heavy tuning knob sufficient. Mine loaded with lead caps wine bottles, thereby doubling pleasure. While subject tuning knobs, with finger hole turning (tram) handle best. software been tuned encoder disc with spokes. Since detector emits pulse every dark/light transition, this gives natural tuning rate rev, rate which speeded slowed down software appropriate. Figure shows Disc used which reproduced size onto acetate film your local copy shop). Ensure "spokes" reproduce black with much contrast "slots" possible. Glue carefully onto knob with toner side away from detector avoid scratching. Drill knob right through first ensure disc properly centered spinning (slowly!) shaft before glue fully set. Long parallel tracks provided board give flexibility mounting position. actual configuration will depend whether board mounted parallel right angles display board. Next Month This article concludes with calibration process details user operation.
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100nF 7805 10nF J310 4.7k IOUTB 3.9k MCLR OSC1 [SPARE] W_CLK IOUT 3.3p 8.2p 0.68 10nF AVCC CLKIN 4.7k 200V 28-PIN SOCKET 10nF RFOUT 100nF 10nF 10nF 10nF 470nF 10nF
AN-557
78L08
100p
2N2222A
2N3866 10nF
110MHz
DISPLAY KEYPAD
AD9850
PROGRAM INTERFACE
MCLR
LD271
FQ_UD CONNECTED AGND RESET DGND
Figure board circuit diagram. associated components mounted 28-pin socket form assembly. This plugs into 28-pin socket main board.
4094
LATCH CONNECTED OSC2 LATCH 270k 10MHz Tx/Rx DIGITAL INTERFACE (OPTIONAL) BROADBAND 1.8MHz 3.5MHz 7.0MHz
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16C84
IN4148 BC108
HLC2705 DIRECTION DETECTOR PULSES SLOTTED DISK
4.7k
SERIAL PARALLEL MUST DATA SHIFT REGISTER CLOCK LATCH
LINE FROM Tx/Rx
4.7k
270k
270k
4094
CONNECTED
21MHz 24MHz 28MHz 29MHz 14MHz 15MHz 18MHz
DISPLAY KEYPAD
SERIAL PARALLEL MUST DATA SHIFT REGISTER CLOCK LATCH
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BOTTOM VIEW (NON-COMPONENT SIDE) SHOWING BOTTOM TRACK SOLDERING POINTS
VIEW (COMPONENT SIDE) SHOWING TRACK SOLDERING POINTS
RFOUT
ASSY COMPRISING IC4, R10, R18,
DETECTOR
SLOTTED DISC 51MM DIODE ANODE
DIRECTION
MCLR
6.1" 2.75"
18MHz 15MHz 14MHz 29MHz 28MHz 24MHz 21MHz 10MHz 7MHz 3.5MHz 1.8MHz BROADBAND [SPARE] (PTT LINE)
SHAFT CENTER LINE TUNING KNOB (NOMINALLY 1.75" DIA)
TRACKS MARKED CONNECTED GROUND PLANE
LOGIC INTERFACE Tx/Rx
VIEW SHOWING COMPONENT LOCATION DRILLING TEMPLATE
Figure board drawn production using same conventions Figure holes except three leads from which oscillator screened enclosure. uses leads connect from hold enclosure track. connected track short jumpers. detector/diode disc shown mounting degrees display track. connected track short jumpers. detector/diode disc shown mounting degrees display board.
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PULSE
PROGRAMMER INTERFACE ONLY
AN-557
PART
this concluding article, process calibration covered. Suggestions operational also offered together with complete definition keypad sequences resulting system behavior. CALIBRATION PROCESS Because software been explicitly written handle range different reference oscillator crystal frequencies; range (including direct conversion) there calibration process which stores details your installation long term memory. will need follow this process first use, time change your Tx/Rx installation then periodically, thereafter, compensate crystal ageing. There separate procedures, namely first calibrating reference oscillator; then calibrating three offsets (USB, LSB, CW). They both conducted with synthesizer connected mixer target Tx/Rx with everything warmed with reasonable ambient room temperature. first use, general idea calibration roughly right (i.e., within kHz) against crude definition frequency available you; then good against some known (and typically off-air) standard. WORD CAUTION time enter calibration modes pressing "Cal" key) must explicitly exit calibration mode before resuming normal use. There only ways this. save calibration setting (931, 934, 933) other "999" complete restart. latter doubt. REFERENCE OSCILLATOR CALIBRATION This process gives best results when carried highest possible frequency. practice easiest roughly right some frequency finalize against some standard such MHz. first use, software reference oscillator. This lowest permitted frequency chosen make easy percentage arithmetic. example, using crystal, will actually generate frequencies roughly higher than that indicated. Roughly, because crystals oscillators will same frequency. will need separate receiver tuned station known frequency. aide getting started, memory locations preloaded with World Service frequencies. These frequency standards found reliably throughout Europe simple domestic radio with short-wave band will provide basic calibration. Proceed follows: synthesizer indicate target calibration frequency. "83" enter signal generator mode. This mode ignores offsets (and therefore offset calibration errors) generates indicated frequency plus minus only calibration error. Locate generated frequency your receiver. need small antenna attached synthesizer output. first worth calculating where expected frequency will come error substantial +20%). "83" again exit signal generator mode. "33" enter reference clock calibration mode. This same signal generator mode except that turn tuning knob displayed frequency remains fixed while software reference oscillator trimmer varied -thus altering emitted frequency. Turn tuning knob check other receiver that moving right direction. Then keep turning until chosen calibration frequency. tuning very fine, will turning long time error large. Zero beat with frequency standard initially "933" [Save Cal] retain this coarse calibration. repeat refine calibration highest possible frequency against some known standard. Here little trick help. Since tuning zero beat arbitrary, useful above calibration frequency other below When hold down key, will alternate between two-and easily judge beat notes same-to within Just take second opinion, because significant percentage population tone deaf-and don't know same trick extrapolated fine tuning offset calibration. OFFSET CALIBRATION There point doing this until reference oscillator immaculately calibrated. rather, time alter reference oscillator calibration, must repeat this offset calibration.
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This procedure lets synthesizer know exact frequencies your offsets LSB, fitted). Remember allow modest time crystal warm-up switching between carrier crystals host. using direct conversion, either ignore this procedure simply synthesizer signal generator mode-or follow this procedure enter offsets. This applies equally using make life easy first use, offset loaded with 10.7 MHz, offset with offset with representing three common choices. This seem obtuse none these correct anyone. does provide quickest right most. first only then, choose that nearest yours copy across other follows: followed "1," "7," selecting your desired offset from choice three. "93" followed "1," thereby overwriting unwanted offset. Repeat overwrite other offset. this stage offsets identical least right part spectrum. proceed follows: Select your crystal Tx/Rx. This lower frequency sideband crystals. "31" [Cal USB] turn tuning knob zero beat. this point frequency display will show your offset frequency. When happy, "931" [Save USB] save result-and reboot synthesizer. Select your crystal Tx/Rx. This higher frequency sideband crystals. "37" [Cal LSB] turn tuning knob zero beat followed "937" [Save LSB] above. Repeat process your crystal have one, otherwise leave centre passband. offsets calibrated want fussy, actually trim carrier crystals themselves maximum exact. This will have absolutely effect performance. This completes calibration process. OPERATIONAL have relied simple now, then range features provided seem daunting first sight. There indeed some which turn useful your particular operational circumstances. That simply ignore them. general advice them start with, while contemplating circumstances under which would them. day, have keys tuning knob does take long become familiar with using them right order! KEYPAD SEQUENCES Substantial effort gone into ergonomic design keypad sequences make them easy safe use. brief review design thinking will hopefully make them more memorable. sequences listed Table easy reference. sequences executed immediately. visual confirmation, sequence displayed held briefly frequency readout. invalid sequence simply effect. Every attempt been made combine legends into crude meaningful sentences. Obvious examples already discussed (enter calibrate mode) Save (save this frequency calibration). critical operational functions achieved with press. Most normal functions require presses with most commonly used functions being achieved with presses same key. sequences also have up/down directional theme. example above keypad which turn above LSB. sequences three keys begin with [Save]. This acts qualifier sequence which follows. example, "10" means Conversely "910" means save present frequency default. word "save" always used here mean retain even while powered off. SWITCH-ON system will initialize until change store retain switch-on frequency, first desired frequency means, later) enter "990" [Save, Save, Zero]. This will save startup frequency with full resolution. sideband save time stored; system will initialize "normal" that frequency. BAND SWITCHING CHANGE BANDS, first digits nine bands meters. (e.g. "80" "10" "nonexception" Band (alas, longer Top) where "16" above rule. synthesizer will immediately initialization frequency that band automatically select "normal" sideband. fitted, band switching sideband selection outputs host will change automatically correspond.
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band switch time, band will initialize "normal" sideband that frequency. band will initialize change initialization frequency band, first desired frequency means, later) enter [Save] followed 2-digit band sequence. This will save frequency rounded down nearest kHz. fact, save arbitrary frequency against each 2-digit band code. example, never some bands, save useful frequency their 2-digit allocations. change them will. Specifically, sideband band switching outputs computed from digits actual frequency from 2-digit sequence. MANAGING VFOs Because this most useful critical feature set, functions achieved immediately with press. There three them bottom keypad, from left right: Pronounced full "VFO This swaps between VFOs. Whichever will switch other. fact, both frequency mode associated with swapped over. this context, mode sideband (i.e., USB/LSB/CW), display resolution injection either high side IF). Since VFOs nearby vastly different frequencies, this gives full range facilities from through cross-band capability. Sets both VFOs same frequency mode, namely ones using moment entry. This system initialized power-on-with both VFOs same. This used establish known situation before tuning around should want able revert quickly original frequency pressing "A/B")- want split working IRT, etc. Split This toggles between split pure transceive operation. state this setting immediately apparent from indicators. operating "split" then will different color (red/green) LED. Conversely, pure transceive, they same color. event, frequency readout always applies current transmit/receive state. receive, receive frequency shown; transmit, transmit frequency. DISPLAY RESOLUTION default, 6-digit display starts with most significant digit left with leading zero, then fills rest digits right. Decimal points placed after digits. consequence this autoranging that right hand digit gives resolution frequencies below resolution above MHz. want suppress digit below show above then "78" toggle back forth-per VFO. whole display moves along appropriate direction, complete with decimal points necessary, suppresses leading zero. USB/LSB/CW "NORMAL' SIDEBAND selected automatically function displayed frequency when switch bands memory frequency. want override this time choose press USB, respectively, twice. front panel LEDs will confirm change, generated frequency will change; course displayed frequency itself will change. have included optional selection outputs your host Tx/Rx, will have select appropriate offset there manually. chosen offset retained associated with each when swapping VFOs. NORMAL TUNING TUNING AROUND achieved-self evidently-by turning tuning knob. Clockwise increase frequency, anticlockwise decrease This simple statement belies number intelligent tuning algorithms which seek establish your intent help. With specified shaft encoder disk, natural tuning rate rev. This little fast easy netting slow rapid frequency excursions. Accordingly, software monitors fast turning knob-and long-and smoothly alters tuning rate between extremes through rev. want monitor this effect, especially while getting used "70" toggle LEDs bar-graph rate tune indicator. extreme turning rates (typically, quick flick wrist) software flywheel engages automatically tuning continues rapid steps chosen direction with further turning knob. LEDs light when flywheel engaged.
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slightest turn knob opposite direction immediately cancels outstanding frequency changes, resets tuning rate minimum cancels flywheel. Equally, transmit/receive switching press achieves same effect instantly. Operation flywheel toggled between enabled inhibited keying "26." enabled switch-on. Since synthesizer continuously tunable over whole range, could, theory frequency continuously turning knob. This realistic modest excursions flywheel engaged practice, large MHz) excursions best achieved using rate tuning starting from nearest band memory frequency; entering frequency keypad. this reason maintain performance, band switch outputs host recomputed normal tuning mode unless flywheel engaged. Should find yourself tuning slowly across band-edge boundary want update switching outputs, simply force this selecting reselecting) desired sideband. DOWN want quickly tune nearest point, "47" round frequency down nearest "41" round nearest kHz. RATE TUNING this mode tuning knob controls frequency rather rate change frequency. Thus, more turn knob clockwise, faster frequency will increase. more turn knob anticlockwise, faster frequency will decrease. change direction will freeze frequency instantly. this mode, LEDs provide bar-graph display show tuning rate. enter this mode, "22" [Rate Rate]. decimal point pulsed denote nonnormal tuning. exit, press switch between transmit receive. KEYPAD FREQUENCY ENTRY frequency entered from keypad nearest kHz. this mode, "88" [Freq Freq]. frequency display will blank, showing only decimal points. this point must enter FIVE digits. This implies entering leading zero frequencies below MHz. example, 1.812 entered "01812." Conversely, 18.123 entered "18123" entered "00181." Immediately fifth digit entered, display auto-ranges, output frequency generated, "normal" sideband selected, front panel LEDs updated band select sideband select outputs host. make mistake part through, either abort sequence start again. MEMORY OPERATION memories provided, accessed from keys 60-69 [Mem 0-Mem These visualized simply quick jumps frequency-much like band switching. Having switched memory frequency, tuning proceeds normal from that frequency without altering original stored frequency. change stored frequency, desired frequency means [Save] followed two-digit memory code. example, store current frequency memory location five, "Save Memory locations stored with full resolution. SCANNING GENERAL There several scanning modes which share following features common: entered two-key sequence, first being [Scan]. exited normal tuning mode pressing key. Scanning stops immediately transmit/receive switching. scanning operating "Split," then system reverts pure transceive transmit/receive change. While scan mode engaged, decimal point pulsed visual reminder. These scanning modes useful only monitoring activity number different operational situations, invaluable adjusting band/high/low-pass filters signal generator mode. SPOT FREQUENCY SCANNING switch continuously between frequencies, first place each frequency. Then "5*" [Scan A/B]. Turn tuning knob clockwise increase switching delay anticlockwise decrease amount delay shown bargraph. MEMORY SCANNING cycle between memory locations, "56" [Scan Mem]. Again, tuning knob controls switching delay.
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RANGE SCANNING scan across range frequencies, each range then "58" [Scan Freq]. will then tune from high limit, switch back limit-and repeat continuously. switch time, line "RxA" pulsed briefly used synchronize "scope, etc. tuning knob controls frequency increments hence tuning speed-as shown graph. display dimmed this mode improve performance. GUARD CHANNEL SCANNING monitor fixed frequency activity-or lack while tuning elsewhere, first tune fixed frequency guard channel). Then switch VFOs [A/B] tune around even switch bands), leaving other guard channel. Obviously, manually switch back forth guard channel time [A/B], automatically "55" [Scan Scan]. still tune main VFO, approximately every seconds software will switch guard channel about second then switch back again. performance reasons, flywheel disabled main VFO, otherwise full normal tuning available. SELECT BROAD BAND display frequency does coincide with nine amateur bands, band selection logic automatically selects "broad band" output. This that have choice using some different front-end your want force this output, then "72" toggle this output off. SIGNAL GENERATOR MODE signal generator mode, displayed frequency generated with offsets. "83" toggle signal generator mode off. "Sig Gen" provides visual confirmation. tune, switch bands scan while still signal generator mode. theoretical frequency range chip control logic from audio half reference clock frequency. practice, buffer amplifier limit this response both ends spectrum, need extremes, capacitively couple output from subassembly output (Pin 19). HI/LO SIDE INJECTION default, synthesizer generates hi-side injection. That wanted frequency plus intermediate frequency offset. have high higher bands, injection frequency getting close limit adequately suppressing unwanted birdies. force lo-side injection time keying "87' hi-side injection keying "81." This choice retained with currently use, option have both VFOs same frequency, each hi/lo side injection. sideband selection outputs switched correspond, setup calibrated properly, should hear perceptible shift frequency. This feature also useful have asymmetric filter since arrange always same sideband. facility retained flexibility since possible synthesizer with lo-side injection into high IF-or with transceivers using up-conversion architectures. Neither these possibilities been tried. SLEEP MODE This mode included development determine and/or multiplexed display coupling noise into output. Sleep mode, stops executing program displays keypad effectively switched continues generate last commanded output. installation there perceptible difference noise output frequency. facility retained because substantial power saving useful some environments-and noise insidious beast prone appear unsolicited time. enter Sleep mode "73." exit Sleep mode, simply turn tuning knob. CONCLUSION Hopefully this article will have inspired upgrade conventional injection system. intention writing remove some mystique surrounding "computers" showing their place real-world useful application. look forward reading about fruits your labors near future. ACKNOWLEDGMENTS thanks Jack, G3XKF built first production prototype suffered some early software. Jack also responsible photography good enough turn bushes shaft encoder. thanks also Keith, G3OHN independently designed built something similar Third Method transceiver Much useful mutual learning occurred over air. Also David, G3LUB help with spurious measurements. lastly, wife Fran reliably advised seen last project withthe third method transceiver.
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Table Summary Two-Key Entries First Second Scan VFOs Flywheel Disable Down Offset Scan Freq Select Tune Rate Mode Clock Offset Select Guard Channel Scan Memories Rate offset Scan Select Shift Display Side Injection Keypad Freq Entry Broad Band Sleep Mode Mode Graph Tune Freq Side Injection
E3732-.5-4/00 (rev. PRINTED U.S.A.
Note that ergonomic beauty entries only visualized when looking keypad layout with overlay legends. Entries shown preceded with save current frequency that location when two-key entry preceded "Save" key. Other combinations "990" which saves power-on frequency "999" which restarts software.
Figure slot encoder disc, reproduction acetate film.
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Experimenter's Project Incorporating AD9850 Complete-DDS Device Digita

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