1. Automatic Z-Match
Greg P. Le Sage
N6LYU
May 2010

2. Outline What is a Z-Match? How does it compare to other tuners?
Why automate?
What's next?
Demonstration

3. 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

4. Original circuit used two coils
Similar to L-Network
Parallel LC tuned near resonance

5. Single coil version
Extensive theoretical and experimental work over the years
Very elegant circuit
I skipped the series inductor

6. No automatic Z-match found
Typical autotuner is an L-network with discrete components
Opportunity to do something new
Recycled my robot

7. 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

8. An ADC Senses Vr Tried to implement VSWR calculation
Amplified microstrip signals
Large frequency variation
Adjacent channels bleed over

9. Control of capacitors Stepper motors were a challenge
Tried optical encoding
Settled on standard version
Backlash

10. Many control inputs Using Parallax “Board of Education”
Added daughter board for many input channels

11. 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

12. 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

13. Parallax Basic Stamp
Stepper motors
Variable Capacitors
Air wound coil
Microstrip coupler

14. Added user configuration
Select band: sets series capacitor
Sweep through parallel capacitor values

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

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

17. N6LYU Automatic Z-Match
Read details here: Source code, images, etc.
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