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 1955 Reputation for very broad matching range Best for open-wire feedlines No balun Only 2 knobs No variable inductor

Original circuit used two coils Similar 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 found Typical autotuner is an L-network with discrete components Opportunity to do something new Recycled my robot

Started with basic manual circuit Z-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 calculation Amplified microstrip signals Large frequency variation Adjacent channels bleed over

Control of capacitors Stepper motors were a challenge Tried 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 required Application 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 fine Tuning 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 configuration Select band: sets series capacitor Sweep through parallel capacitor values

What's Next? Use toroid instead of air coil – compact Discrete capacitors Sense frequency Remote to feedpoint – use coaxial line

Many examples on-line Most toroid Z-match units used for QRP No automatic versions found

N6LYU Automatic Z-Match Read details here: Source code, images, etc. http://www.greglesage.com/Ham/ZMatch.html Featured on The DXZone http://www.dxzone.com/dx22685/automatic-z- match-antenna-tuner.html Featured on Parallax.com http://www.parallax.com/Hobby/AutomaticZMatc hAntennaTuner/tabid/835/Default.aspx