1. Antenna Basics

2. Antenna Basics Antennas Feed lines Monitoring station performance
Types
Patterns
Gain
Feed lines
Coax
Open or Ladder Line
Monitoring station performance
Antenna tuners
SWR

3. Basic Antenna Types Horizontal Vertical Random Directional
Gain
Single band and Multi-band

4. Some General Rules The bigger the better (well most of the time)
The higher the better (well most of the time)
The lower the SWR the better (well most of the time)
Coax is better than twin-lead (well some of the time)
Antenna tuners do not change the performance of a bad antenna
Tuners just fool the transmitter into thinking everything is okay
Improve antennas first – then improve power (all of the time)
Improves hearing as well as sending

5. Some Vocabulary Antennas are used to send and receive radio waves.
The wave includes both electrical and magnetic fields.
The orientation of the fields when compared to the earth’s surface determines the antenna’s polarization.
Antenna polarization can be horizontal, vertical or circular.
Polarization is based on the orientation of the electric field.
Generally, polarization can be determined by looking at the orientation of the antenna conductors.

6. Antenna Components Radiator – Radiates and receives the radio wave
Feed line – Feeds energy from transmitter to radiator and energy from the antenna to the receiver
Matching Network – Matches impedance of the transmitter (i.e., 50 Ω to 75 Ω) to the radiator and/or feed line.

7. Simple Dipole Antenna

8. Half- Wavelength Dipole
Basic building block of most antennas.
Has two poles – di-pole.
Length is a physical ½ wavelength of frequency.
A 20-meter half-wave dipole would be about 10 meters long.
An 80-meter half-wave dipole would be about 40 meters long.

9. Length of a ½ Wave Dipole
Calculate the following dipole dimensions:
MHz
3550 kHz
MHz
10.05 MHz
7.150 MHz
440 MHz

10. Dipole Configurations

11. Inverted Vee Trap Dipole
Dipole Detail
Inverted Vee Trap Dipole

12. Dipole Kit

13. Dipole Height Above Ground
For best performance, a dipole should be mounted at least a half wavelength above the ground.
½ wavelength high

14. Dipoles in Free Space Elevation Plot
Looking into wire end

15. Dipoles in Free Space Azimuth Plot

16. Horizontal Dipoles Over Real Ground

17. Effect of Height Above Ground
45 feet
15 feet
30 feet
60 feet

18. Vertical Antennas
Good choice when you do not have room for a dipole or beam.
Vertical polarization.
Used extensively for mobile operations (whip).
Omni-directional pattern.
¼ wavelength long (some ½ waves available).
Low angle of radiation, good for DX.

19. Radials for Verticals
For a vertical to work effectively, it needs artificial ground wires since the ground acts as the other half of the antenna.
These wires are called radials. Lots of radials are sometimes needed.
Radials should be placed on the surface of the ground or buried a few inches below the ground.

20. Ground Radials

21. Vertical Antennas
If the radials are changed from horizontal to downward sloping, it increases the feed point closer to 50 ohms (to match the transmitter’s impedance).
This type of antenna is called a ground plane.

22. Length of a Vertical Calculate the following dipole dimensions:
MHz
3550 kHz
MHz
10.05 MHz
7.150 MHz
440 MHz

23. Vertical Antennas

24. Dipole vs. Vertical
Takeoff Angle = 34o
Takeoff Angle = 25o

25. Directional (Beam) Antennas
Take available power and focus the power in desired direction.
When power is focused, it appears that the signal strength has increased.
This apparent increase in strength or power is called gain.

26. Yagi Antennas Multi-element (at least two).
Properly called a Yagi-Uda Antenna.
Can be for one band (monobander) or multiple bands (tribander).
Produces gain over a dipole in specific direction.

27. Yagi Antennas
The driven element is usually about ½ wavelength long – just like a dipole.
The direction of maximum radiated field strength is called a lobe. The “main lobe” is the direction of maximum strength from the antenna.
Adding more directors and increasing the boom length increases the gain of the antenna.

28. Yagi Gain Antenna

29. How is Gain Produced? Driven Element

30. How is Gain Produced? Reflector Element Added

31. How is Gain Produced? Director Element Added

32. Other (some specialized) Antennas
Random wire
Multiband
Loops
Quads
Log Periodic
Beverage
NVIS

33. Feed Line

34. Feed Line Types

35. Feed Line – Flat-Ribbon TV Twin Lead
Typical Impedance = 300 ohms
There can be air space or dielectric space between conductors.
The impedance depends on the distance between the conductors and the radius of the conductors.

36. Feed Line - Coaxial (Coax) Cable
Typical impedance 50 and 75 ohms.
Used in most modern amateur antenna systems.

37. Feed Line Losses
The higher the frequency, the greater the feed line loss.
This is caused by “skin effect.”
Feed line losses are measured in dB/100 ft.
A cable would have a much higher loss on 2 meters (145 MHz) than on 160 meters (1.8 MHz).

38. Standing Wave Ratio (SWR)
If the impedances within the antenna system are not matched, the power fed into the antenna is not all radiated into space.
The non-radiated power needs to go someplace.
It is reflected back to the source (the transmitter).
It is dissipated as heat or spurious radiation.
This reflected power is measured by SWR.

39. SWR Definition
The ratio of maximum voltage to minimum voltage along a feed line.
Also the ratio of antenna impedance to feed line impedance when the antenna is a purely resistive load.
1:1 (one to one) is the optimum SWR.

40. SWR Meters

41. SWR
SWR is optimum when feed line and antenna impedances are matched. All the power from the transmitter goes to the antenna. None is reflected back.
Up to an SWR or 2:1, you’re okay.
Above an SWR of 2:1, modern transceivers start to reduce transmitter power output for protection.
Above an SWR of 3:1, you need to take corrective action.

42. SWR Calculation
A dedicated SWR meter will have a direct readout of the SWR.
Some meters will read the actual forward and reflected power (watts), voltage, or impedance.
This data can be used to calculate the SWR.

43. SWR Calculations
Impedances (ohms):
Feed line
Load 50 25
300

44. Antenna Tuners More accurately: impedance matching transformers.
Transform the input impedance to match the output impedance.
Do not change the actual impedance of the feed line, the impedance of the antenna, nor the impedance of the transmitter.
If the feed line SWR is 5:1, it is still 5:1 even with an antenna tuner in line! (But the tuner allows the transmitter to operate under those conditions.)