1. Antenna Tuners Do Not Tune Antennas
Hap Griffin
SARA
August 2016

2. But First, What is Reactance?
What is Impedance?
Impedance: The effective resistance of an electric circuit or component to alternating current, arising from the combined effects of ohmic resistance and reactance.
But First, What is Reactance?
Reactance: Opposition of a circuit element to change in current or voltage due to that element's inductance or capacitance. It is frequency dependent.

3. Back to Impedance
Impedance: The effective resistance of an electric circuit or component to alternating current, arising from the combined effects of ohmic resistance and reactance.
Impedance (Z) can be used interchangeably with R in Ohm’s Law to calculate the magnitude of voltages, current and power.

4. What is Resonance?
Resonance: In an electrical circuit, the condition that exists when the inductive reactance and the capacitive reactance are of equal magnitude, causing electrical energy to oscillate between the magnetic field of the inductor and the electric field of the capacitor.

5. Resonance
At a circuit’s resonant frequency, its inductive reactance and capacitive reactance cancels (equal in magnitude, opposite in phase) and we are left with only resistance.

6. Concept of Impedance Matching – Why?
To minimize signal reflections and preserve the frequency response (etc) of a filter by providing the source and load impedances for which it was designed. Example: tuning a repeater duplexer.
To provide for maximum power transfer from source to load.

7. Impedance Matching (Minimum Loss Pad)

8. Impedance Matching for Maximum Power Transfer

9. Impedance Matching for Maximum Power Transfer
Source Voltage = 10 volts
Source Impedance = 50 ohms
If Load Z = 30 ohms, then voltage at load = 10* 30/(30+50) = 3.75 v
Load Power = (3.75)(3.75)/30 = watts
If Load Z = 70 ohms, then voltage at load = 10* 70/(70+50) = 5.83 v
Load Power = (5.83)(5.83)/70 = watts
If Load Z = 50 ohms, then voltage at load = 10* 50/(50+50) = 5.00 v
Load Power = (5.00)(5.00)/50 = watts

10. Impedance Matching for Maximum Power Transfer

11. Impedance Matching for Maximum Power Transfer

12. RF Impedance Matching With L-Networks

13. Impedance Matching for Maximum Power Transfer

14. Basic Radio Installation

15. Unmatched Impedances Cause Reflections and VSWR (Voltage Standing Wave Ratio)

16. What is Antenna Impedance?

17. Common ½ Wavelength Dipole Antenna

18. Antenna Impedance (Dipole) vs Length

19. Common ½ Wavelength Inverted Vee Dipole Antenna

20. Antenna Impedance (Quarter Wavelength Vertical)

21. Transmission Line Impedance – Parallel (Balanced) Line

22. Transmission Line Impedance – Coaxial Line

23. Transmission Line Impedance – Coaxial Line

24. Transmission Line Loss

25. Transmission Line Loss Increase With VSWR

26. Transmission Line Loss vs VSWR Measured at Transmitter

27. Transmatch Design – L Networks
Z<Xmtr
Z>Xmtr
Good for single purpose
For use with wide range of output impedance, requires switching
Can simply reverse input/output to change impedance range
Examples: MFJ 16010

28. Transmatch Design – T Networks
Covers broad frequency and impedance range
Can be mis-tuned to show low input VSWR, but be very lossy
Most popular for inexpensive units
Examples: Dentron Super Tuner, most MFJ’s with two capacitance knobs

29. Transmatch Design – Differential T Networks
Covers broad frequency and impedance range (though generally not as wide as basic T-match because of the physical size constraints of the diff variable cap
Only one optimal setting…best input VSWR also equals best efficiency
Examples: MFJ 986, Palstar AT-500, Palstar AT2KD

30. Transmatch Design – Pi Network
Broad impedance range
Can work over wide frequency range with switched input caps
Very efficient
Uses relatively low and high value components – expensive to produce

31. Transmatch Design – Pi Network
Tube based transmitters/transceivers already have a transmatch built in
If final amp can be tuned for a proper plate current dip and a maximum power output with the “load” control, then no further transmatch is required

32. Line Length Matters

33. Line Length Matters

35. Impedance Matching – 1/4 Wavelength Transmission Line

36. Automatic “Antenna Tuners”

37. Internal “Antenna Tuners”

38. Balanced Transmatch Design – MFJ 949B

39. Balanced Transmatch Design – EF Johnson “Matchbox”

40. Remote Antenna Tuners