Optimizing Your PSK31 Optimization PSK31 Signal

Optimizing YourPSK31 SignalClint Hurd - kk7uqPresented at SEAPACSeaside OregonJune 19, 2004Typical Station Setupfor Sound Card ModesBPSK Signal Envelope00100PSK31 Optimization The PSK Signal Setting Audio Level - Conservative andAggressive Methods Interfacing Software - Features & Tools Operating - Receiving, Transmitting, IMDRST Other ModesBinary Phase Shift Keying - BPSK31 Phase modulates an audio “carrier” at 31.25baud Reverses phase 180 degrees (BPSK) Reduces signal level at phase shift time toreduce spurious frequencies Uses variable length encoding - most usedcharacters are encoded into small wordlengthsIMD -32 dB Good Signal0Varicode “Space” character 1where 0 is a Phase Reversal and 1 is no reversalmust have at least two 0 between characters1

IMD -18dB Poor SignalIMD -11dB Very Bad SignalPSK SIGNAL BASICSStay Within Your TransmitAudio PassbandPegasus Tx Filter @ 2.25 kHz0500100015002000250030000.0-1.0-2.0dB A clean signal has unwantedsidebands at -24 dB or better Overdriving the signal mayimcrease power output, butdoes NOT improve copy.-3.0-4.0-5.0-6.0Stay Within Your TransmitAudio PassbandSystem Passband FT 8178Power / Dots765Pw r Watts4Display Dots321001000Freq Hz20003000F HzSetting the Audio Drive Level Adjusting the audio drive level is theproper way to set power output. You do NOT improve the signalquality by reducing the power levelsetting on the transceiver - you onlyreduce the power of an improperlyadjusted signal2

Setting the Audio Drive Level Adjusting the audio drive level can bedone at the:– PC using the WAVE control slider– Interface if you have a level controlpot– Transceiver Mic GainInterface Level Control If your interface has a level controlpotentiometer, use this for fineadjustments rather than the PC panel If your interface has an internal levelcontrol potentiometer, use the PCWAVE slider for audio level controlHow Much Power? Protect your transceiver finals normally run at no more than 50% ofrated CW output (peak) Turn off Compression Run with minimum ALCPC Output Audio Control- The WAVE output isthe one used togenerate the PSK signal- The WAVE andVolume work together- Mute all other sourcesTransceiver Mic Gain The transceiver Mic gain can also beused to control audio drive level. Normally this is set for proper phoneaudio level and left alone when usingpsk.Convervative Method Pick a waterfall frequency in the middle ofyour rig output filter - typically 1200 Hz Set your rig power control to 100% Turn off Compression Transmit an IDLE signal (no typing, bufferempty) Adjust audio drive level to produce anoutput of 25% (ave) or 50% (peak) of ratedCW output. ALC should be at low or zero level3

Why Derate Power So Much? The PSK signal will run at 50% dutycycle when in IDLE, and up to 90%when transmitting data. The transceiver audio path must staylinear (no or little ALC orCompression).Basic Hardware InterfaceHam RigComputer1 V p-pSC Mic InSC Spkr OutSerial Out (RTS)1 V p-pSpkr Out10 mV p-pAttenuator - 12VLevel ShifterMic InClosure to GndPTTSound Card Modes - Interface Block DiagramAggressive Method Use an IMD monitoring device such asthe PSK Meter or the IMD Meter Turn off Compression Set the rig output control to 50% Transmit an IDLE signal Adjust the audio drive level to producean IMD of -24 dB or better - typicallyrun at -30 dBOptimizingSound Card Interface Provide audio drive potentiometercontrol on the interface Provide waterfall drive potentiometercontrol on the interface Provide audio monitor on the interface Incorporate CAT control with soundcard interface to use single Serial PortSound Card Interface3.5mm StereoReceptaclew/ switches1:1 600 ohmAudio TransformerToSound CardLine InJ2X12Tip343.5mm StereoReceptacle3C1R4 100Tip51DTR4Ring RTSGnd75TipSleeveExternal Cable w/ DB9female serial portconn shown for ref.R102 megC3 10 uFR9 4.7 kR22.2kU2Tip1.0 uF5J5AT 20 AudioTransducer6C5 .0047uF12LED 1RetFrom XcvrTo XcvrBluWht3SW1PTT Control(SPDT Ctr Off)2D454Up AutoCtr - PTT OffDown - PTT OnAll resistors1/4W 5%kk7uq Interface Model II - Schematic DiagramTo XcvrGrnRet WhtPTT OrgTo Xcvr1N41484N33Photo DarlingtonOpto-IsolatorFSK Grn1N4148544N33U1RedBrnWhtQ12N3904D3Dual ColorT 1 3/4 LEDRed - PTTYel - FSKRet4 Mic BluSP 1 Yel2.5mmStereoReceptacle3R1210 kC4 10 uF12R12.2kRingC22R112.2 kD1 1N4148J11R84D2 1N4148Note: Return path foraudio to monitor amplifieris made through the cableshields to the groundpoint at the PC.7R5 516Primary2.0047uF8 Aud.BrnOutR6 51Tx Drive1k potAudio TaperX23.5mm StereoReceptacleJ3 RingFrom XcvrSpkr Out(Alternate)Ring11:1 600 ohmAudio TransformerR3 1.0 kFromSound CardSpkr terfall Drive1k potAudio Taper1RetOrgWhtRig cable matingconnector and wirecolors shown forref.Combined CAT &Sound CardControl4

VOX for rig control?Software Features HelpOptimize PSK Operation VOX could be used to “key” the rig insteadof a serial port control line Difficult to do in practise: – Audio drive level to trigger VOX reliably may exceedlevel which gives a clean signal– Any PC audio keys the rig Positive PTT control is more reliable Exception: the Signal Link interface builtin “VOX” does key reliably with outoverdriving the rig audioExample: MixW SoftwareMacrosLogSound HistoryMultiple modesTransceiver control using CATMultiple receive windowsMacros Single click creates full typing function Example Macro “CQ” TX CQ CQ CQ CQ DE KK7UQ KK7UQ KK7UQCQ CQ CQ CQ DE KK7UQ KK7UQ KK7UQCQ CQ CQ CQ DE KK7UQ KK7UQ KK7UQ PSE K RX Optimized Macro “CQ” CLEARTXWINDOW TX cq cq cq cq de kk7uq kk7uq kk7uq pse -k RXANDCLEAR Macro “Start QSO” Basic Macro “Start QSO” TX CALL CALL CALL DE MYCALL MYCALL MYCALL Optimized Macro “Start QSO CLEARTXWINDOW TX CALL CALL (NAME) de kk7uq (Clint) fb NAME .Macro “73” Basic Macro “73”73 CALL CALL DE MYCALL MYCALL QSO LOGGED AT SAVEQSO TIME DATE SK RX Optimized Macro “73”73 NAME CALL de kk7uq sk SAVEQSO RXANDCLEAR 5

Waterfall or Spectrum DisplaySpectrum Display Use waterfall when looking for CQ– Can see entire band and history– Easy to spot CQ’s Use Spectrum when in QSO– Can see quality of signal– Can estimate RST better– Can determine S/N of signalSound History Feature of some sound card software Stores 20 seconds (or more) of soundcard output Activated by holding down SHIFT keyand clicking on signal Plays back last 20 seconds to receivewindow Great for searching for CQsMixW Log EntriesAbove spectrum shows S/N about 35 dB, harmonic isabout -33dBBuilt in Log Logs QSO data from screen Name / QTH of previous contact pop intofields on new contact Tracks actual frequency if using CAT Mode automatically entered Can export to other logs or CabrilloTransceiver Control Using CAT Software controls & monitorstransceiver frequency and mode Logged frequency is accurate In some cases, can activate PTT viaCAT6

Operating Methods ReceivingTransmittingUpper vs lower caseRST reportingIMD measurementWorking DXReceiving Looking for CQ - use sound history Use LOCK to hold frequency on newstation Put AFC ONTransmittingTransmitting Calling CQ– Keep length short, repeat about every 8 seconds– Use lower case to speed it up– cq cq cq de kk7uq kk7uq kk7uq cq pse k– Use Auto CQ Calling a station– Keep length short, use his call once– W7WJK de kk7uq kk7uq pse kRST - “R” R readability 5 95 - 100% copyR4 90 - 95% copyR3 75 - 90% copyR2 50 - 75% copyR1 under 50% Compact macros– Keep length short– Use lower case wherever possible UPPER vs lower Case– lower case is faster because of variablelength encodingRST - “S” StrengthUse Spectrum Display - estimate S/N@ S/N of 6 dB per S unitS9 54 dBS6 36 dBS3 18 dBS8 48 dBS5 30 dBS2 12 dBS7 42 dBS4 24 dBS1 6 dB7

“T” - Signal Quality T9T8T7T4IMD -24 dB or betterIMD -20 dB to -24 dBIMD -15 dB to -20 dBIMD worse than -15dBWhat is IMD? IMD - Intermodulation Distortion Measures “linearity” of audio path ofthe PSK signal through the transmitterand the receiver A software tool built into most PSKsoftwareIMD What is IMD?Giving an IMD ReportThings to look out forTake the IMD with a grain of saltLet your eye be your guideIMD MeasurementThe strength of the primary signal compared tothe 3rd harmonic above is -19 dB hence IMD is-19 dBGiving an IMD ReportThings to look out for Monitor the IMD measurement at thebottom of the screen Signal must be in IDLE (no typing,buffer empty) Check the S/N of the signal - it shouldbe above 36 dB to get an accuratereport If S/N is too low, the IMD will bereported low If S/N is too high, the IMD will bereported low - because the receiver isclipping the signal - adjust the RF gain8

Take an IMD measurementwith a grain of salt If you are given a low IMD (say -19dB) : Have them use the spectrum displayand check the S/NLet Your Eye Be Your Guide If the signal you are monitoring hasS/N about -20 dB and IMD is about thesame number: If the signal looks clean i.e. straightsides, no apparent side bands, then thereal IMD is probably -24 or better.Working DX Split operation using LOCK on yourTX signal and RX on the DX station Strong signals - poor copy - look attuning indicator to see if wide phasedistortion - probably multi path Use short callsOther Modes QPSK vs BPSKBPSK63MFSKRTTYHellschreiber9

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 .