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