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Automatic Z-Match
Greg P. Le SageN6LYU
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/AutomaticZMatchAntennaTuner/tabid/835/Default.aspx