Technician License CourseChapter 4

Propagation, Antennas and Feed Lines

Lesson Plan Module 10:

Practical Antennas

Vertically Polarized Radio Wave

Signal Polarization

• Determined by the transmitting antenna polarization.

• For line-of-sight communications, differences in polarization can result in significantly weaker signals. – Vertical / Horizontal = up to 30 dB loss.

• Signals that refract in the ionosphere will have their polarization randomized. (Sky-wave or Skip)

Signal Polarization

• Vertical – Antenna perpendicular to the earth.– Electric field also perpendicularly oriented.

– Most natural and man-made radio noise is vertical

• Horizontal – Antenna parallel to the earth.– Electrical field has also parallel orientation.

– Used for weak signal modes at VHF, UHF, and above.

• Circular – Special antenna– Can be right hand or left hand circular.

Practical Antennas

• Rubber Duck – Flexible antenna supplied with HT’s

• Horizontal Dipoles

• Verticals

• Loops and Yagis

• Dummy Loads

The Dipole• Most basic antenna.

– Two conductive, equal length parts.– Feed line connected in the middle.

• Total length is ½ (electrical) wavelength (½ ).

• Antenna Length (in feet) = 468 / Frequency (in MHz).

• Signals are strongest in the directions broadside to the antenna.

The Dipole

The Dipole• When suspended about ½ high, it has a

nominal impedance of 50 Ohms.

• There are several variations:• The inverted V – Suspended from the center

with the legs sloping down.• The flat top – or T antenna

The Ground-Plane

• Simply a dipole that is oriented perpendicular to the Earth’s surface (vertical) .

• One half of the dipole is replaced by the ground-plane. (1/4 )– Earth– Car roof or trunk lid or other metal surface.– Radial wires.

• Length (in feet) = 234 / Frequency (in MHz).• Signals are omnidirectional.

The Ground-Plane

Loop Antennas – Variations

• Quad - Four Sided

• Delta – Three Sided

• Horizontal – Parallel With the Ground

• Full wavelength antennas

Quad AntennaThe Elements are One Wavelength – ¼ Wavelength per Side

Directional (Beam) Antennas

• Beam antennas focus or direct RF energy in a desired direction.– Gain– An apparent increase in power in the desired

direction (both transmit and receive).

• Yagi (rod-like elements – TV antennas).

• Quad (square shape, wire loop elements).

Directional (Beam) Antennas

Yagi Antenna

Delta Loop and Quad Antennas

Directional (Beam) Antennas

• All beam antennas have parts called elements.– Driven element is connected to the radio by the

feed line.– Reflector element is on the back side. Longer

than the driven element.– Director element is on the front side toward the

desired direction. Shorter than the driven element.

Other Antennas

• Rubber Duck Antenna– Not as good as a full sized antenna.

– When used inside a car, much of the signal is wasted.

• NVIS (Near Vertical Incidence Skywave) Antenna– Used for local communications.

– Directs signal upwards

• Dummy Load– Used for testing or adjusting transmitters where you do not

want to send out a signal.

Feed Line Devices

• Balun

• Duplexer

• Antenna switch

• SWR meter

• Antenna analyzer

• Antenna tuner

Feed Line Devices• Balun – Matches balanced antenna to an unbalanced

feed line. Can also match impedances. 1 to 1 4 to 1

• Duplexer – Combines / separates signals

• Antenna switch - Switch between feed lines

• SWR meter – Measures impedance match

• Antenna analyzer - Measures antenna resonant frequency

• Antenna tuner – Matches antenna system impedance to transmitter impedance.

Coax Feed Lines

• RG-58

• RG-8

• RG-213

• RG-174

• Hardline

Coax Feed Lines• RG-58 - Medium Diameter Cable, OK for HF

frequencies and medium power.

• RG-8 – Larger Diameter Cable, OK through VHF frequencies and high power.

• RG-213 - RG-8 type, with lower loss at VHF & UHF.

• RG-174 - Small flexible cable, OK for short lengths.

• Hardline - Low loss. Requires special procedures to keep out moisture on air core types.

Coax

• Most common feed line.• Easy to use.• Matches impedance of

modern radio equipment (50 ohms).

• Some loss of signal depending on coax quality (cost).

Coax

• Dielectric can be solid, foam, or air.• Air has lowest loss,

followed by foam and solid.

• Moisture in the cable will increase loss.

• UV resistant jacket (black) protects cable.

Coax Connectors

• SO-239/PL-259• BNC• N• SMA

Coax Connectors

• SO-239/PL-259 • Also called UHF

connectors

• Usable below 400MHz.

• BNC• Bayonet type

connector.

• Good to GHz range

Coax Connectors

• N• Commonly used at

VHF and above 400Mhz. Good to GHz.

• Can be water resistant

• SMA• Common on newer

hand held radios.

Nothing is Perfect• Although the goal is to get 100% of your radio

energy radiated into space, that is virtually impossible.

• What is an acceptable level of reflected power or SWR?– 1:1 SWR is perfect.– 2:1 SWR should be the max you should accept (as a

general rule).• Modern radios will start lowering transmitter output power

automatically when SWR is above 2:1.– 3:1 is when you need to do something to reduce SWR.

Test and Matching Equipment

• Proper impedance matching is important enough to deserve some simple test equipment as you develop your station repertoire.

• Basic test equipment: SWR meter.

• Matching equipment: Antenna tuner.

Test and Matching Equipment

• Matching device: Tuning Stub

• Test equipment: Directional Wattmeter

• Advanced test equipment: Antenna Analyzer

Standing Wave Ratio (SWR)• If the antenna and feed line impedances are

not perfectly matched, some RF energy is not radiated into space and is returned (reflected) back to the source.– Something has to happen to this reflected

energy – generally converted into heat or unwanted radio energy (bad).

SWR Meter

• Placed in the feedline between the transmitter and the antenna.

• Measures the impedance mis-match between the transmitter and the antenna. (Standing Wave Ratio)

• Dual needle types measure forward and reflected power simultaneously

SWR Meter

• The SWR meter is inserted in the feed line and indicates the mismatch that exists at that point.

• You make adjustments to the antenna to minimize the reflected energy (minimum SWR).

Antenna Tuner• One way to make antenna matching

adjustments is to use an antenna tuner.

• Antenna tuners are impedance transformers (they actually do not tune the antenna).– When used appropriately they are effective.– When used inappropriately all they do is make

a bad antenna look good to the transmitter…the antenna is still bad.

How to use an Antenna Tuner

• Monitor the SWR meter.

• Make adjustments on the tuner until the minimum SWR is achieved.– The impedance of the

antenna is transformed to more closely match the impedance of the transmitter.

Directional Wattmeter

• Inserted in the feedline between the transmitter and antenna.

• Measures forward or reflected power, depending on how the measuring element is turned.

• Can be used to determine feedline match (mismatch).

Bird Wattmeter with slugs

Antenna Supports

• Trees.• Towers or masts.• Covenants and

antenna restrictions must be considered.

Soldering

• Use rosin core solder for electrical connections.

• Surfaces must be clean for a proper bond.

• Good connections have a shiny appearance.

• Poor connections have a dull or grainy appearance. (Cold solder joint).

• Older equipment will have lead/tin solder, newer will have lead-free solder.

What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands?

(T3A03)

• A. Right-hand circular

• B. Left-hand circular

• C. Horizontal

• D. Vertical

What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands?

(T3A03)

• A. Right-hand circular

• B. Left-hand circular

• C. Horizontal

• D. Vertical

When using a directional antenna, how might your station be able to access a distant repeater if

buildings or obstructions are blocking the direct line of sight path? (T3A05)

• A. Change from vertical to horizontal polarization

• B. Try to find a path that reflects signals to the repeater

• C. Try the long path• D. Increase the antenna SWR

When using a directional antenna, how might your station be able to access a distant repeater if

buildings or obstructions are blocking the direct line of sight path? (T3A05)

• A. Change from vertical to horizontal polarization

• B. Try to find a path that reflects signals to the repeater

• C. Try the long path• D. Increase the antenna SWR

What is the primary purpose of a dummy load? (T7C01)

• A. To prevent the radiation of signals when making tests

• B. To prevent over-modulation of your transmitter

• C. To improve the radiation from your antenna• D. To improve the signal to noise ratio of your

receiver

What is the primary purpose of a dummy load? (T7C01)

• A. To prevent the radiation of signals when making tests

• B. To prevent over-modulation of your transmitter

• C. To improve the radiation from your antenna• D. To improve the signal to noise ratio of your

receiver

Which of the following instruments can be used to determine if an antenna is resonant

at the desired operating frequency? (T7C02)

• A. A VTVM

• B. An antenna analyzer

• C. A “Q” meter

• D. A frequency counter

Which of the following instruments can be used to determine if an antenna is resonant

at the desired operating frequency? (T7C02)

• A. A VTVM

• B. An antenna analyzer

• C. A “Q” meter

• D. A frequency counter

What instrument other than an SWR meter could you use to determine if a feedline and

antenna are properly matched? (T7C08)

• A. Voltmeter

• B. Ohmmeter

• C. Iambic pentameter

• D. Directional wattmeter

What instrument other than an SWR meter could you use to determine if a feedline and

antenna are properly matched? (T7C08)

• A. Voltmeter

• B. Ohmmeter

• C. Iambic pentameter

• D. Directional wattmeter

Which of the following is the most common cause for failure of coaxial cables? (T7C09)

• A. Moisture contamination

• B. Gamma rays

• C. The velocity factor exceeds 1.0

• D. Overloading

Which of the following is the most common cause for failure of coaxial cables? (T7C09)

• A. Moisture contamination

• B. Gamma rays

• C. The velocity factor exceeds 1.0

• D. Overloading

Why should the outer jacket of coaxial cable be resistant to ultraviolet light? (T7C10)

• A. Ultraviolet resistant jackets prevent harmonic radiation

• B. Ultraviolet light can increase losses in the cable’s jacket

• C. Ultraviolet and RF signals can mix together, causing interference

• D. Ultraviolet light can damage the jacket and allow water to enter the cable

Why should the outer jacket of coaxial cable be resistant to ultraviolet light? (T7C10)

• A. Ultraviolet resistant jackets prevent harmonic radiation

• B. Ultraviolet light can increase losses in the cable’s jacket

• C. Ultraviolet and RF signals can mix together, causing interferance

• D. Ultraviolet light can damage the jacket and allow water to enter the cable

What is a disadvantage of “air core” coaxial cable when compared to foam or solid dielectric types?

(T7C11)

• A. It has more loss per foot• B. It cannot be used for VHF or UHF antennas• C. It requires special techniques to prevent

water absorption• D. It cannot be used at below freezing

temperatures

What is a disadvantage of “air core” coaxial cable when compared to foam or solid dielectric types?

(T7C11)

• A. It has more loss per foot• B. It cannot be used for VHF or UHF antennas• C. It requires special techniques to prevent

water absorption• D. It cannot be used at below freezing

temperatures

Which of the following types of solder is best for radio and electronic use? (T7D08)

• A. Acid-core solder

• B. Silver solder

• C. Rosin-core solder

• D. Aluminum solder

Which of the following types of solder is best for radio and electronic use? (T7D08)

• A. Acid-core solder

• B. Silver solder

• C. Rosin-core solder

• D. Aluminum solder

What is the characteristic appearance of a “cold” solder joint? (T7D09)

• A. Dark black spots

• B. A bright or shiny surface

• C. A grainy or dull surface

• D. A greenish tint

What is the characteristic appearance of a “cold” solder joint? (T7D09)

• A. Dark black spots

• B. A bright or shiny surface

• C. A grainy or dull surface

• D. A greenish tint

What is a beam antenna? (T9A01)

• A. An antenna built from aluminum I-beams

• B. An omnidirectional antenna invented by Clarence Beam

• C. An antenna that concentrates signals in one direction

• D. An antenna that reverses the phase of received signals

What is a beam antenna? (T9A01)

• A. An antenna built from aluminum I-beams

• B. An omnidirectional antenna invented by Clarence Beam

• C. An antenna that concentrates signals in one direction

• D. An antenna that reverses the phase of received signals

Which of the following describes a simple dipole mounted so the conductor is parallel

to the earth’s surface? (T9A03)

• A. A ground wave antenna

• B. A horizontally polarized antenna

• C. A rhombic antenna

• D. A vertically polarized antenna

Which of the following describes a simple dipole mounted so the conductor is parallel

to the earth’s surface? (T9A03)

• A. A ground wave antenna

• B. A horizontally polarized antenna

• C. A rhombic antenna

• D. A vertically polarized antenna

What is a disadvantage of the “rubber duck” antenna supplied with most handheld radio

transceivers? (T9A04)

• A. It does not transmit or receive as effectively as a full-sized antenna

• B. It transmits a circularly polarized signal

• C. If the rubber end cap is lost it will unravel very quickly

• D. All of these choices are correct.

What is a disadvantage of the “rubber duck” antenna supplied with most handheld radio

transceivers? (T9A04)

• A. It does not transmit or receive as effectively as a full-sized antenna

• B. It transmits a circularly polarized signal

• C. If the rubber end cap is lost it will unravel very quickly

• D. All of these choices are correct.

How would you change a dipole to make it resonant on a higher frequency? (T9A05)

• A. Lengthen it

• B. Insert coils in series with radiating wires

• C. Shorten it

• D. Add capacity hats to the ends of the radiating wires

How would you change a dipole to make it resonant on a higher frequency? (T9A05)

• A. Lengthen it

• B. Insert coils in series with radiating wires

• C. Shorten it

• D. Add capacity hats to the ends of the radiating wires

What type of antennas are the quad, Yagi, and dish? (T9A06)

• A. Non-resonant antennas

• B. Loop antennas

• C. Directional antennas

• D. Isotropic antennas

What type of antennas are the quad, Yagi, and dish? (T9A06)

• A. Non-resonant antennas

• B. Loop antennas

• C. Directional antennas

• D. Isotropic antennas

What is a good reason not to use a “rubber duck” antenna inside of your car? (T9A07)

• A. Signals can be significantly weaker than when it is outside of the vehicle

• B. It might cause your radio to overheat

• C. The SWR might decrease, decreasing the signal strength

• D. All of these choices are correct

What is a good reason not to use a “rubber duck” antenna inside of your car? (T9A07)

• A. Signals can be significantly weaker than when it is outside of the vehicle

• B. It might cause your radio to overheat

• C. The SWR might decrease, decreasing the signal strength

• D. All of these choices are correct

What is the approximate length, in inches, of a quarter-wavelength vertical antenna for

146 MHz? (T9A08)

• A. 112

• B. 50

• C. 19

• D. 12

What is the approximate length, in inches, of a quarter-wavelength vertical antenna for

146 MHz? (T9A08)

• A. 112

• B. 50

• C. 19

• D. 12

What is the approximate length, in inches, of a 6 meter ½-wavelength wire dipole

antenna? (T9A09)

• A. 6

• B. 50

• C. 112

• D. 236

What is the approximate length, in inches, of a 6 meter ½-wavelength wire dipole

antenna? (T9A09)

• A. 6

• B. 50

• C. 112

• D. 236

In which direction is the radiation strongest for a half-wave dipole antenna in free

space? (T9A10)

• A. Equally in all directions

• B. Off the ends of the antenna

• C. Broadside to the antenna

• D. In the direction of the feedline

In which direction is the radiation strongest for a half-wave dipole antenna in free

space? (T9A10)

• A. Equally in all directions

• B. Off the ends of the antenna

• C. Broadside to the antenna

• D. In the direction of the feedline

What does an antenna tuner do? (T9B04)

• A. It matches the antenna system impedance to the transceiver’s output impedance

• B. It helps a receiver automatically tune in weak stations

• C. It allows the antenna to be used on both transmit and receive

• D. It automatically selects the proper antenna for the frequency band being used

What does an antenna tuner do? (T9B04)

• A. It matches the antenna system impedance to the transceiver’s output impedance

• B. It helps a receiver automatically tune in weak stations

• C. It allows the antenna to be used on both transmit and receive

• D. It automatically selects the proper antenna for the frequency band being used

Which of the following connectors is most suitable for frequencies above 400 MHz?

(T9B06)

• A. A UHF (PL-259/SO-239) connector

• B. A Type N connector

• C. An RS-213 connector

• D. A DB-23 connector

Which of the following connectors is most suitable for frequencies above 400 MHz?

(T9B06)

• A. A UHF (PL-259/SO-239) connector

• B. A Type N connector

• C. An RS-213 connector

• D. A DB-23 connector

Which of the following is true of PL-259 type coax connectors? (T9B07)

• A. They are good for UHF frequencies

• B. They are water tight

• C. They are commonly used at HF frequencies

• D. They are a bayonet type connector

Which of the following is true of PL-259 type coax connectors? (T9B07)

• A. They are good for UHF frequencies

• B. They are water tight

• C. They are commonly used at HF frequencies

• D. They are a bayonet type connector

Why should coax connectors exposed to the weather be sealed against water intrusion?

(T9B08)

• A. To prevent an increase in feedline loss

• B. To prevent interference to telephones

• C. To keep the jacket from becoming loose

• D. All of these choices are correct

Why should coax connectors exposed to the weather be sealed against water intrusion?

(T9B08)

• A. To prevent an increase in feedline loss

• B. To prevent interference to telephones

• C. To keep the jacket from becoming loose

• D. All of these choices are correct

What electrical difference exists between the smaller RG-58 and larger RG-8 coaxial

cables? (T9B10)

• A. There is no significant difference between the two types

• B. RG-58 cable has less loss at a given frequency

• C. RG-8 cable has less loss at a given frequency

• D. RG-58 cable can handle higher power levels

What electrical difference exists between the smaller RG-58 and larger RG-8 coaxial

cables? (T9B10)

• A. There is no significant difference between the two types

• B. RG-58 cable has less loss at a given frequency

• C. RG-8 cable has less loss at a given frequency

• D. RG-58 cable can handle higher power levels