Transmitter and Receiver Transmitter and Receiver Architecture Optimized for Architecture Optimized for

QRP OperationQRP OperationBy: David Turner By: David Turner AI5EEAI5EE

““Knowledge unencumbered by experience.Knowledge unencumbered by experience.””

What is QRPWhat is QRP

Low power ham radio operationLow power ham radio operationDerived from Derived from ““Please reduce your power.Please reduce your power.””or or ““Shall I reduce my power?Shall I reduce my power?””TX power less than 5W CW, 10W SSBTX power less than 5W CW, 10W SSBWhy use 2KW when 1W will do?Why use 2KW when 1W will do?FCC rules require it.FCC rules require it.

Optimization CriteriaOptimization Criteria

Possible ConsiderationsPossible Considerations–– Portable / battery powerPortable / battery power–– Small / light weightSmall / light weight–– SimpleSimple–– HomebrewHomebrew--ableable–– Easily repaired / adjustedEasily repaired / adjusted–– Multi band / frequency agileMulti band / frequency agile

Optimization CriteriaOptimization Criteria

The communication system The communication system must have the features must have the features

necessary to permit necessary to permit effective communication.effective communication.

Everything else is gravy.Everything else is gravy.

Proposed QRP Transmitter Proposed QRP Transmitter FeaturesFeatures

CW onlyCW onlyClean signal (no chirp, drift, warble or click)Clean signal (no chirp, drift, warble or click)Unwanted harmonics as low as reasonable Unwanted harmonics as low as reasonable (30dB below fundamental for <5W transmitter)(30dB below fundamental for <5W transmitter)Power output sufficient to be copied (in China)Power output sufficient to be copied (in China)GravyGravy

–– Efficient (for battery power operation)Efficient (for battery power operation)–– Adjustable power outputAdjustable power output–– Full break inFull break in–– built in keyerbuilt in keyer

CW Transmitter BasicsCW Transmitter Basics

Oscillator Amplifier Low Pass Filter

Key

Antenna

Oscillator TypesOscillator TypesCrystalCrystal–– small bandwidthsmall bandwidth–– very stablevery stable–– easy to buildeasy to build

LC ResonatorLC Resonator–– drift (must be temperature compensated)drift (must be temperature compensated)–– large bandwidthlarge bandwidth–– easy to buildeasy to build

Oscillator TypesOscillator Types

Direct Digital SynthesisDirect Digital Synthesis–– Stable (crystal controlled)Stable (crystal controlled)–– Controllable phaseControllable phase–– Must interface to a microprocessorMust interface to a microprocessor–– Output contains many spurious outputsOutput contains many spurious outputs–– Larger power drainLarger power drain–– Limited output frequency (12 MHz easily, 33 Limited output frequency (12 MHz easily, 33

MHz not so easilyMHz not so easily

Amplifier TypesAmplifier Types

Amplifier type (generally) designated by Amplifier type (generally) designated by how long the transistor conducts during the how long the transistor conducts during the RF periodRF periodClass A (100% of RF period)Class A (100% of RF period)–– very linearvery linear–– very inefficient (30very inefficient (30--50%)50%)

Class AB (~75% of RF period)Class AB (~75% of RF period)–– worse linearityworse linearity–– better efficiencybetter efficiency

Amplifier TypesAmplifier Types

Class C (<50% of RF period)Class C (<50% of RF period)–– Not linear (not usable for SSB communication)Not linear (not usable for SSB communication)–– Fine for CW (with a filter)Fine for CW (with a filter)–– More efficientMore efficient

Class DClass D–– Uses pushUses push--pull transistors in a pull transistors in a ““digitaldigital”” mode mode

(think pulse width modulation)(think pulse width modulation)–– More Efficient (transistor either fully on or fully More Efficient (transistor either fully on or fully

off).off).

Amplifier TypesAmplifier Types

Class EClass E–– Most efficient (can be 90% or better)Most efficient (can be 90% or better)–– Transistor either fully on or fully offTransistor either fully on or fully off–– Tuned output prevents the simultaneous Tuned output prevents the simultaneous

application of high voltage and high current to application of high voltage and high current to transistortransistor

–– Tuned output allows power greater than Vdd Tuned output allows power greater than Vdd into 50 ohmsinto 50 ohms

–– Not linearNot linear

Receiver OptimizationReceiver Optimization

Low noise floorLow noise floorLow power drawLow power drawMinimal LO driftMinimal LO driftReject AM interferenceReject AM interferenceSensitivity <.1 microvoltSensitivity <.1 microvolt

Receiver OptimizationReceiver Optimization

Single sideband?Single sideband?Tuning range?Tuning range?RIT?RIT?Frequency Readout? Audio / Visual?Frequency Readout? Audio / Visual?Volume Control?Volume Control?Automatic Gain Control?Automatic Gain Control?

Receiver ArchitectureReceiver Architecture

General typesGeneral types–– Direct ConversionDirect Conversion–– RegenerativeRegenerative–– SuperheterodyneSuperheterodyne–– PhasingPhasing

HartleyHartleyWeaverWeaver

Direct ConversionDirect Conversion

SimpleSimpleLow parts countLow parts countEasy to buildEasy to buildClean audio (no birdies)Clean audio (no birdies)Dual sideband onlyDual sideband only

RegenerativeRegenerative

SimpleSimpleLow parts countLow parts countDual sideband Dual sideband onlyonlySensitive to Sensitive to ““Hand Hand CapacitanceCapacitance””

http://web.telia.com/~u43200663/rx/bipol_regen_rx.htm

SuperheterodyneSuperheterodyne

Single SidebandSingle SidebandMore complexMore complexRequires sharp, narrow band filterRequires sharp, narrow band filterRequires 2 frequency conversionsRequires 2 frequency conversions

Hartley Phasing ReceiverHartley Phasing ReceiverSee Rick Campbell KK7B's work.See Rick Campbell KK7B's work.

Single SidebandSingle SidebandRequires precise phase shift networkRequires precise phase shift networkRequires two mixersRequires two mixers

Sin

Cos

90 deg.

Weaver Phasing ReceiverWeaver Phasing Receiver

Sin

Cos

Sin

Cos

RF AF

Weaver Phasing ReceiverWeaver Phasing Receiver

Single sideband receptionSingle sideband receptionNo sharp RF filter or phase shift networkNo sharp RF filter or phase shift networkSame architecture can be used for SSB Same architecture can be used for SSB generationgenerationAF oscillator is fixed frequency (center of AF oscillator is fixed frequency (center of audio passband)audio passband)Requires 4 mixersRequires 4 mixers

Quadrature Mixer (Tayloe Style)Quadrature Mixer (Tayloe Style)

0 deg.

90 deg.

180 deg.

270 deg.

RF

counter4*LO

Audio Frequency

Quadrature LOQuadrature LO

2*LO

0 deg.

180 deg.

Q

QD

>

Q

QD

>

LO(0 deg.)

LO(90 deg.)

Quadrature LO TimingQuadrature LO Timing

2*LO

0

180

QQD>QQD

>

LO(0 deg.)

LO(90 deg.)

2*LO

0 DEG

180 DEG

LO(0)

LO(90)

Weaver Receiver with Weaver Receiver with Tayloe DetectorTayloe Detector

RF

Quad LO2*LO

0

90

180

270

Sin

Cos

AF

0

90

Hartley Receiver with Hartley Receiver with Tayloe DetectorTayloe Detector

Polyphase 90 degree phase shifterPolyphase 90 degree phase shifter

http://home.planet.nl/~niess153/Polyphase_networks/Understanding_and_designing_Polyphase_networks_V3.5.pdf