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Automatic Z-Match Greg P. Le Sage N6LYU May 2010
Outline What is a Z-Match? How does it compare to other tuners?Why automate? What's next? Demonstration
Harvey Wells Z-Match QST 1955Reputation for very broad matching range Best for open-wire feedlines No balun Only 2 knobs No variable inductor
Original circuit used two coilsSimilar to L-Network Parallel LC tuned near resonance
Single coil version Extensive theoretical and experimental work over the years Very elegant circuit I skipped the series inductor
No automatic Z-match foundTypical autotuner is an L-network with discrete components Opportunity to do something new Recycled my robot
Started with basic manual circuitZ-match is good candidate for automation: 2 knobs Followed on-line prescription for coil Used receiver type variable capacitors Test load is a 1k resistor
An ADC Senses Vr Tried to implement VSWR calculationAmplified microstrip signals Large frequency variation Adjacent channels bleed over
Control of capacitors Stepper motors were a challengeTried optical encoding Settled on standard version Backlash
Many control inputs Using Parallax “Board of Education”Added daughter board for many input channels
RF shielding was requiredApplication of TX level output sent computer and LCD into convulsions Even at low power, frequency near processor clock (20 MHz and harmonics) is still a problem
Capacitor Arcing Experience was that rcvr caps are fineTuning circuit is a resonator Arcing occurs on 80m Changing feedline length will hopefully avoid this problem
Parallax Basic Stamp Stepper motors Variable Capacitors Air wound coil Microstrip coupler
Added user configurationSelect band: sets series capacitor Sweep through parallel capacitor values
What's Next? Use toroid instead of air coil – compactDiscrete capacitors Sense frequency Remote to feedpoint – use coaxial line
Many examples on-line Most toroid Z-match units used for QRPNo automatic versions found
N6LYU Automatic Z-MatchRead details here: Source code, images, etc. Featured on The DXZone match-antenna-tuner.html Featured on Parallax.com hAntennaTuner/tabid/835/Default.aspx
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