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Chapter 4Propagation, Antennas

and Feed Lines

Propagation• Black magic topic #1.

• How do radio waves get from point A to point B?

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Radio Wave Propagation• Normally radio waves travel in a straight

line, just like light.• Radio waves can be reflected.• Radio waves can be refracted (bent).

Radio Wave Propagation• Radio waves propagate by many

different mechanisms.• The science of radio wave propagation is

complex.• Deep, dark, & mysterious!

• We will discuss three basic mechanisms:• Line of sight.• Ground wave.• Sky wave.

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Line of Sight• If a source of radio energy can been

“seen” by the receiver, then the radio energy will travel in a straight line from transmitter to receiver.• There is some attenuation of the signal as

the radio wave travels.

• Primary propagation mechanism for VHF and UHF signals.

Line of Sight• Radio horizon.

• Distance at which radio signals are blocked by curvature of the earth.

• Slightly greater than optical horizon.• Refraction increases radio horizon by about 15%.

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Line of Sight• Penetration.

• Radio waves can penetrate openings in apparently solid objects.• Due to the shorter wavelengh UHF waves can

penetrate building more readily than VHF waves.

• Reflections.• Buildings may block line of sight, but

reflections may help get past obstructions.

Line of Sight• Knife-Edge Refraction.

• Radio waves can be refracted by an edge.

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Line of Sight• Multipath.

• Radio waves reflected off of many objects arrive at receive antenna at different times.• Picket fencing.

Ground Wave• Some radio frequency ranges (MF &

lower HF frequencies) will hug the earth’s surface as they travel.• These waves will travel beyond the range of

line-of-sight.• A few hundred miles.

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Sky Wave• Some radio frequency ranges (HF &

lower VHF frequencies) will reflect off of ionized layers in the upper atmosphere.• These waves will travel well beyond the

range of line-of-sight.• Several hundred to a few thousand miles.

Ionosphere• Radiation from the Sun momentarily will

strip electrons away from the parent atom in the upper reaches of the atmosphere.• Creates ions.

• The region where ionization occurs is called the ionosphere.

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Ionosphere

Sunspot Cycle

• The level of ionization depends on the radiation intensity of the Sun.

• Radiation from the Sun is connected to the number of sunspots on the Sun’s surface.• High number of sunspots, high ionizing

radiation emitted from the Sun.

• Sunspot activity follows an 11-year cycle.

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Levels of the Ionosphere

• Density of the atmosphere affects:• The intensity of the

radiation that can penetrate to that level.

• The amount of ionization that occurs.

• How quickly the electrons recombine with the nucleus.

The Ionosphere – An RF Mirror

• The ionized layers of the atmosphere actually act as an RF mirror that reflect certain frequencies back to earth.

• Sky-wave propagation is responsible for most long-range, over the horizon communication.

• Reflection depends on frequency and angle of incidence.

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Other Types of Propagation

• Sporadic-E.• 10m, 6m, & 2m.

• Tropospheric ducting.• VHF & UHF.• >300 miles.• Associated with weather front or

temperature inversion.

Other Types of Propagation

• Aurora.• Rapid changes in signal strength.• Often sounds distorted.

• Meteor scatter.• Best on 6m.• Short bursts of high-speed CW.

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T3A01 -- What should you do if another operator reports that your station’s 2 meter signals were strong just a moment ago, but now they are weak or distorted?

A. Change the batteries in your radio to a different type

B. Turn on the CTCSS toneC. Ask the other operator to adjust his

squelch controlD. Try moving a few feet, as random

reflections may be causing multi-path distortion

T3A02 -- Why are UHF signals often more effective from inside buildings than VHF signals?

A. VHF signals lose power faster over distance

B. The shorter wavelength allows them to more easily penetrate the structure of buildings

C. This is incorrect: VHF works better than UHF inside buildings

D. UHF antennas are more efficient than VHF antennas

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T3A06 -- What term is commonly used to describe the rapid fluttering sound sometimes heard from mobile stations that are moving while transmitting?

A. Flip-floppingB. Picket fencingC. Frequency shiftingD. Pulsing

T3A08 -- What is the cause of irregular fading of signals from distant stations during times of generally good reception?

A. Absorption of signals by the “D” layer of the ionosphere

B. Absorption of signals by the “E” layer of the ionosphere

C. Random combining of signals arriving via different path lengths

D. Intermodulation distortion in the local receiver

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T3A10 -- What may occur if VHF or UHF data signals propagate over multiple paths?

A. Transmission rates can be increased by a factor equal to the number of separate paths observed

B. Transmission rates must be decreased by a factor equal to the number of separate paths observed

C. No significant changes will occur if the signals are transmitting using FM

D. Error rates are likely to increase

T3A11 -- Which part of the atmosphere enables the propagation of radio signals around the world?

A. The stratosphereB. The troposphereC. The ionosphereD. The magnetosphere

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T3C01 -- Why are “direct” (not via a repeater) UHF signals rarely heard from stations outside your local coverage area?

A. They are too weak to go very farB. FCC regulations prohibit them from going

more than 50 milesC. UHF signals are usually not reflected by

the ionosphereD. They collide with trees and shrubbery and

fade out

T3C02 -- Which of the following might be happening when VHF signals are being received from long distances?

A. Signals are being reflected from outer space

B. Signals are arriving by sub-surface ducting

C. Signals are being reflected by lightning storms in your area

D. Signals are being refracted from a sporadic E layer

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T3C03 -- What is a characteristic of VHF signals received via auroral reflection?

A. Signals from distances of 10,000 or more miles are common

B. The signals exhibit rapid fluctuations of strength and often sound distorted

C. These types of signals occur only during winter nighttime hours

D. These types of signals are generally strongest when your antenna is aimed to the south (for stations in the Northern Hemisphere)

T3C04 -- Which of the following propagation types is most commonly associated with occasional strong over-the-horizon signals on the 10, 6, and 2 meter bands?

A. BackscatterB. Sporadic EC. D layer absorptionD. Gray-line propagation

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T3C05 -- What is meant by the term “knife-edge” propagation?

A. Signals are reflected back toward the originating station at acute angles

B. Signals are sliced into several discrete beams and arrive via different paths

C. Signals are partially refracted around solid objects exhibiting sharp edges

D. Signals are propagated close to the band edge exhibiting a sharp cutoff

T3C06 -- What mode is responsible for allowing over-the-horizon VHF and UHF communications to ranges of approximately 300 miles on a regular basis?

A. Tropospheric scatterB. D layer refractionC. F2 layer refractionD. Faraday rotation

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T3C07 -- What band is best suited to communicating via meteor scatter?

A. 10 metersB. 6 metersC. 2 metersD. 70 cm

T3C08 -- What causes “troposphericducting” ?

A. Discharges of lightning during electrical storms

B. Sunspots and solar flaresC. Updrafts from hurricanes and tornadosD. Temperature inversions in the atmosphere

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T3C09 -- What is generally the best time for long-distance 10 meter band propagation?

A. During daylight hoursB. During nighttime hoursC. When there are coronal mass ejectionsD. Whenever the solar flux is low

T3C10 -- What is the radio horizon?

A. The distance at which radio signals between two points are effectively blocked by the curvature of the earth

B. The distance from the ground to a horizontally mounted antenna

C. The farthest point you can see when standing at the base of your antenna tower

D. The shortest distance between two points on the Earth’s surface

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T3C11 -- Why do VHF and UHF radio signals usually travel somewhat farther than the visual line of sight distance between two stations?

A. Radio signals move somewhat faster than the speed of light

B. Radio waves are not blocked by dust particles

C. The Earth seems less curved to radio waves than to light

D. Radio waves are blocked by dust particles

The Decibel (dB)

• Measures a ratio.• Logarithmic scale.• Power Ratio:

• 2.0 x Power = +3 dB • 0.5 x Power = -3 dB• 10.0 x Power = +10 dB • 0.1 x Power = -10 dB

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The Decibel (dB)

• Commonly used to:• Specify gain of an amplifier.• Specify gain of an antenna.• Specify loss in a feed line.

T5B09 -- What is the approximate amount of change, measured in decibels (dB), of a power increase from 5 watts to 10 watts?

A. 2 dBB. 3 dBC. 5 dBD. 10 dB

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T5B11 -- What is the approximate amount of change, measured in decibels (dB), of a power increase from 20 watts to 200 watts?

A. 10 dBB. 12 dBC. 18 dBD. 28 dB

Antennas

• Black Magic Topic #2.

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The Antenna System

• Antenna.• Converts RF electrical energy into an

electromagnetic wave & vice versa.

• Feed line.• Carries RF electrical energy from

transmitter to antenna.• Carries RF electrical energy from antenna

to receiver.

The Antenna System

• Matching equipment.• Provides efficient coupling of RF energy

between feed line & antenna.• Provides efficient coupling of RF energy

between transmitter/receiver & feed line.

• Test equipment.• Monitors antenna system performance.

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The Antenna

• Definitions:• Element.

• Conducting parts of antenna which radiate or receive radio waves.

• Driven Element.• Element receiving power directly from

transmitter.

• Feed point.• Point where feed line connects to antenna.

The Antenna

• Definitions (cont’d):• Polarization.

• The direction of the electric field relative to the surface of the earth.

• The direction of the electric field is the same as the direction of the antenna element.• Circular polarization is an exception.

• If polarizations are not matched, reduced signal strength results.

• Polarization of sky wave signals is random.

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The Antenna

The Antenna

• Definitions (cont’d):• Omni-directional – radiates equally in all

directions.• Directional – focuses radiation in specific

direction(s).• Gain – apparent increase in power in a

particular direction because energy is focused in that direction.• Measured in decibels (dB)

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Antenna Radiation Patterns

• Radiation patterns are a way of visualizing antenna performance.

• The further the line is away from the center of the graph, the stronger the signal in that direction.

Antenna Radiation Patterns

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T3A04 -- What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?

A. The modulation sidebands might become inverted

B. Signals could be significantly weakerC. Signals have an echo effect on voicesD. Nothing significant will happen

T3A07 -- What type of wave carries radio signals between transmitting and receiving stations?

A. ElectromagneticB. ElectrostaticC. Surface acousticD. Magnetostrictive

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T3A09 -- Which of the following is a common effect of “skip” reflections between the Earth and the ionosphere?

A. The sidebands become reversed at each reflection

B. The polarization of the original signal is randomized

C. The apparent frequency of the received signal is shifted by a random amount

D. Signals at frequencies above 30 MHz become stronger with each reflection

T3B03 -- What are the two components of a radio wave?

A. AC and DCB. Voltage and currentC. Electric and magnetic fieldsD. Ionizing and non-ionizing radiation

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T5C07 -- What is a usual name for electromagnetic waves that travel through space?

A. Gravity wavesB. Sound wavesC. Radio wavesD. Pressure waves

T9A02 -- Which of the following is true regarding vertical antennas?

A. The magnetic field is perpendicular to the Earth

B. The electric field is perpendicular to the Earth

C. The phase is invertedD. The phase is reversed

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T9A11 -- What is meant by the gain of an antenna?

A. The additional power that is added to the transmitter power

B. The additional power that is lost in the antenna when transmitting on a higher frequency

C. The increase in signal strength in a specified direction when compared to a reference antenna

D. The increase in impedance on receive or transmit compared to a reference antenna

Mounting Your Antenna

• Trees.• Towers or masts.

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Feed Lines and SWR

• Feed Line.• a.k.a. – Transmission line.• Carries energy from transmitter to antenna

& from antenna to receiver.• 2 basic types:

• Coaxial.• Open-wire.

• a.k.a – Parallel wire, ladder line, balanced line, twin-lead.

Feed Lines and SWR

• Characteristic Impedance.• Each transmission line has a characteristic

impedance.• Characteristic impedance determined by:

• Geometry of conductors.

• Electrical properties of insulating material.

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Feed Lines and SWR

• Characteristic Impedance.• Each antenna has an impedance that is

determined by:• Antenna design.• Height above ground.• Distance from nearby objects.• Frequency.• Other factors too numerous to mention.

Feed Lines and SWR

• Characteristic Impedance.• Each transmitter has an output (source)

impedance.• Each receiver has an input (load)

impedance.• Input & output impedances are determined

by:• Circuit design.• Frequency.

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Feed Lines and SWR

• Characteristic Impedance.• For best energy transfer, transmitter &

receiver impedances, transmission line impedance, & antenna impedance should all be the same.

Feed Lines and SWR

• Coaxial cable.• Most popular type.• Easy to work with.• Low characteristic

impedance.• Typically 50Ω or 75Ω.

• Moderate to high loss.• Loss varies with frequency.

• Higher frequency higher loss.

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Feed Lines and SWR

• Coaxial cable impedance.• Characteristic impedance primarily

determined by ratio of diameter of shield to diameter of center conductor.• Larger ratio higher impedance.

• 50Ω = RG-8, RG-8X, RG-58, RG-174.• 75Ω = RG-6, RG-11, RG-59.

Feed Lines and SWR

• Coaxial cable losses.• Loss primarily determined by size of cable

& by insulating material.• Larger diameter Lower loss.• Air is lowest loss insulator.

• Foam dielectric coax lower loss that solid dielectric coax because more air.

• Air-insulated hard line.

• Energy lost in feed line converted to heat.

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Feed Lines and SWR

• Open-wire line.• More difficult to work with.• High characteristic impedance.

• Typically 300Ω to 600Ω.

• Very low loss.

Feed Lines and SWR

• Open-wire line.• Characteristic impedance determined by

ratio of diameter of conductors to distance between them.• Larger distance higher impedance.• Smaller diameter higher impedance.

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Feed Lines and SWR

• Standing Wave Ratio (SWR).• If feed line impedance = antenna impedance:

• All energy delivered to the antenna.• Prefect match.• SWR = 1:1.

• If feed line impedance ≠ antenna impedance:• Some energy reflected back towards the source.• Reflected energy often lost as heat.• SWR = ZLine / ZAnt or SWR = ZAnt / ZLine

Feed Lines and SWR

• Standing Wave Ratio (SWR).• Rule-of-thumb guidelines:

• 1:1 = Perfect.• 2:1 = Acceptable.

• Modern transmitters will automatically reduce transmitter output power when SWR is above 2:1.

• 3:1 or more = Really bad.

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T6D11 -- Which of the following is a common use of coaxial cable?

A. Carry dc power from a vehicle battery to a mobile radio

B. Carry RF signals between a radio and antenna

C. Secure masts, tubing, and other cylindrical objects on towers

D. Connect data signals from a TNC to a computer

T7C03 -- What, in general terms, is standing wave ratio (SWR)?

A. A measure of how well a load is matched to a transmission line

B. The ratio of high to low impedance in a feedline

C. The transmitter efficiency ratioD. An indication of the quality of your

station’s ground connection

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T7C04 -- What reading on an SWR meter indicates a perfect impedance match between the antenna and the feedline?

A. 2 to 1B. 1 to 3C. 1 to 1D. 10 to 1

T7C05 -- What is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power?

A. 2 to 1B. 1 to 2C. 6 to 1D. 10 to 1

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T7C06 -- What does an SWR reading of 4:1 mean?

A. An antenna loss of 4 dBB. A good impedance matchC. An antenna gain of 4D. An impedance mismatch

T7C07 -- What happens to power lost in a feedline?

A. It increases the SWRB. It comes back into your transmitter and

could cause damageC. It is converted into heatD. It can cause distortion of your signal

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T9B01 -- Why is it important to have a low SWR in an antenna system that uses coaxial cable feedline?

A. To reduce television interferenceB. To allow the efficient transfer of power and

reduce lossesC. To prolong antenna lifeD. All of these choices are correct

T9B02 -- What is the impedance of the most commonly used coaxial cable in typical amateur radio installations?

A. 8 ohmsB. 50 ohmsC. 600 ohmsD. 12 ohms

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T9B03 -- Why is coaxial cable used more often than any other feedline for amateur radio antenna systems?

A. It is easy to use and requires few special installation considerations

B. It has less loss than any other type of feedline

C. It can handle more power than any other type of feedline

D. It is less expensive than any other type of feedline

T9B05 -- What generally happens as the frequency of a signal passing through coaxial cable is increased?

A. The apparent SWR increasesB. The reflected power increasesC. The characteristic impedance increasesD. The loss increases

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T9B09 -- What might cause erratic changes in SWR readings?

A. The transmitter is being modulatedB. A loose connection in an antenna or a

feedlineC. The transmitter is being over-modulatedD. Interference from other stations is

distorting your signal

Break

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Practical Antennas

• Dipole.• Most basic antenna.

• Two conductors, equal length.• Feed line connected in the middle.

• Total length is 1/2 wavelength (1/2 λ).• Length (feet) = 468 / Frequency (MHz).

Practical Antennas

• Dipole.• Can be mounted in a variety of ways:

• Horizontal.• Inverted “V”.• Sloper.

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Practical Antennas

• Dipole.

Practical Antennas

• Ground-Plane.• One half of a dipole that is oriented

perpendicular to the Earth’s surface.• Other half of the dipole is replaced by a

ground-plane.• Earth• Car roof, trunk lid, or other metal surface.• Radial wires.

• Length (feet) = 234 / Frequency (MHz).

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Practical Antennas

• Ground-Plane.

Practical Antennas

• “Rubber Duck” Antennas.• Variation of the ground-plane.• Commonly used on hand-held transceivers.• Coil of wire enclosed in rubber (plastic)

covering.• Shorter than normal ground-plane.• Much less efficient than full-sized ground-plane.

Side note: Using a rubber duck antenna inside your vehicle is not a good idea because….

Signals are weaker due to shielding by car body.

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Practical Antennas

• Loop Antennas.• Loop of wire.

• Circumference is one wavelength (1 λ) long.• Circular, triangular (delta), or square (quad).• Mounted vertically or horizontally.• If mounted vertically, can be either vertically or

horizontally polarized.

T9A03 -- Which of the following describes a simple dipole mounted so the conductor is parallel to the earth’s surface?

A. A ground wave antennaB. A horizontally polarized antennaC. A rhombic antennaD. A vertically polarized antenna

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T9A04 -- What is a disadvantage of the “rubber duck” antenna supplied with most handheld radio transceivers?

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

B. It transmits a circularly polarized signalC. If the rubber end cap is lost it will unravel

very quicklyD. All of these choices are correct

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

A. Lengthen itB. Insert coils in series with radiating wiresC. Shorten itD. Add capacity hats to the ends of the

radiating wires

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

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

B. It might cause your radio to overheatC. The SWR might decrease, decreasing the

signal strengthD. All of these choices are correct

T9A08 -- What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?

A. 112B. 50C. 19D. 12

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T9A09 -- What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna?

A. 6B. 50C. 112D. 236

T9A10 -- In which direction is the radiation strongest for a half-wave dipole antenna in free space?

A. Equally in all directionsB. Off the ends of the antennaC. Broadside to the antennaD. In the direction of the feedline

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Directional (Beam) Antennas

• Beam antennas focus or direct RF energy in a desired direction.• Gain.

• Apparent increase in power in the desired direction (both transmit and receive).

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.• Director element is on the front side toward

the desired direction.

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Directional (Beam) Antennas

• Yagi.• Rod-like elements. • TV antennas.

Directional (Beam) Antennas

• Yagi.• Most common type of directional antenna

used by amateurs.• Horizontally-polarized Yagi antennas are

commonly used for long distance, weak signal CW & SSB communications on VHF & UHF.

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Directional (Beam) Antennas

• Quad. • Square wire loop elements.

Directional (Beam) Antennas

• Parabolic Dish. • Large, round, curved

reflector.• Very high gain.

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T3A03 -- What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands?

A. Right-hand circularB. Left-hand circularC. HorizontalD. Vertical

T3A05 -- 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?

A. Change from vertical to horizontal polarization

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

C. Try the long pathD. Increase the antenna SWR

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T9A01 -- What is a beam antenna?

A. An antenna built from aluminum I-beamsB. An omnidirectional antenna invented by

Clarence BeamC. An antenna that concentrates signals in

one directionD. An antenna that reverses the phase of

received signals

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

A. Non-resonant antennasB. Loop antennasC. Directional antennasD. Isotropic antennas

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Antenna Supports

Feed Line Selection • Coax vs Open Wire.

• Coax easier to use.• VHF & UHF installations almost always use

coaxial cable.

• Open wire has lower loss.• Normally used only with HF wire antennas.

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Feed Line Selection • Which Coax?

• Need to consider:• Frequency.• Length of cable.• Power level.• Budget.

• Loss.• Larger cable generally has lower loss.• Foam dielectric has lower loss.

Feed Line Selection Type Impedance Loss @ 30MHz

(dB/100ft)Loss @ 150MHz

(dB/100ft)Cost

(per foot)

RG-6 75Ω 1.4 dB 3.3 dB $0.24

RG-8 50Ω 1.1 dB 2.5 dB $1.00

RG-8X 50Ω 2.0 dB 4.5 dB $0.30

RG-11A 75Ω 0.7 dB 1.6 dB $0.97

RG-58 50Ω 2.5 dB 5.6 dB $0.28

RG-59 75Ω 1.8 dB 4.1 dB $0.16

RG-174 50Ω 4.6 dB 10.3 dB $0.20

RG-213 50Ω 1.1 dB 2.5 dB $0.89

LMR-400 50Ω 0.7 dB 1.5 dB $1.11

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Connecting Coaxial Cable• Coaxial Connectors.

• 4 main types commonly used in amateur radio.• Type “N”.• UHF.• BNC.• SMA.

Connecting Coaxial Cable• UHF Connectors.

• Most common type.• Up to 150 MHz.• High power (>1.5 kW).• Not constant impedance.• Not weather resistant.• Inexpensive.• Plug = PL-259.• Socket = SO-239.

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Connecting Coaxial Cable• Type “N” Connectors.

• Up to 10 GHz.• High power (>1.5 kW).• Constant impedance.

• Both 50Ω and 75Ω versions available.

• Weather resistant.• Relatively expensive.• Relatively difficult to install.

Connecting Coaxial Cable• BNC Connectors.

• Up to 4 GHz.• Low power.• Constant impedance.

• Both 50Ω and 75Ω versions available.

• Used on older hand held radios.

• Commonly used on test equipment.

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Connecting Coaxial Cable• SMA Connectors.

• Up to 18 GHz.• Low power.• Constant impedance.

• Only 50Ω available.

• Used on most new hand held radios.

Soldering• Soldering is a process in which two or

more metal items are joined together by melting and flowing a filler metal into the joint.

• The filler metal is called solder.• Flux is a material used to prevent the

formation of oxides during the soldering process.

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Soldering• Types of solder.

• Standard solder is a mixture of tin (63%) and lead (37%).• Melting point is about 183°C (361°F).

• Lead-free solder is a mixture of tin & silver or tin, silver, & copper.• Melting point is about 40°C (72°F) hotter than

standard solder.

Soldering• Types of flux.

• Resin.• Used for electrical/electronic connections.

• Acid.• Used for plumbing.• NEVER use acid–core solder or acid flux to

solder electronic connections!

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Soldering• It takes a little bit of skill to make a good

solder joint.• Good solder joint is bright & shiny.• If joint is not heated enough or if it is moved

before it cools, it can result in a “cold solder joint”.• Cold solder joint is dull & grainy-looking.

Maintaining Coaxial Cable• Coaxial cable must be protected.

• Worst enemy is moisture getting into the cable.• Moisture increases loss in cable.• Avoid nicks of cuts in outer jacket.• Prolonged exposure to sunlight can result in tiny

cracks in outer jacket which can admit moisture.• Seal outside connections against moisture.

• Avoid sharp bends or turns.

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

A. Acid-core solderB. Silver solderC. Rosin-core solderD. Aluminum solder

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

A. Dark black spotsB. A bright or shiny surfaceC. A grainy or dull surfaceD. A greenish tint

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T9B06 -- Which of the following connectors is most suitable for frequencies above 400 MHz?

A. A UHF (PL-259/SO-239) connectorB. A Type N connectorC. An RS-213 connectorD. A DB-23 connector

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

A. They are good for UHF frequenciesB. They are water tightC. They are commonly used at HF

frequenciesD. They are a bayonet type connector

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T9B08 -- Why should coax connectors exposed to the weather be sealed against water intrusion?

A. To prevent an increase in feedline lossB. To prevent interference to telephonesC. To keep the jacket from becoming looseD. All of these choices are correct

T9B10 -- What electrical difference exists between the smaller RG-58 and larger RG-8 coaxial cables?

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

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Measuring SWR

• SWR Meter.• a.k.a. – SWR bridge.• Connects between transmitter & feed line.• Displays amount of mismatch (SWR)

between transmitter & antenna system.• Antenna system = antenna + feed line.

• Make adjustments to antenna system to minimize mismatch.

Measuring SWR

• SWR Meter.

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Measuring SWR

• Simple SWR Meter.• Set to “FWD”.• Adjust “CAL” for full scale reading.• Set to “REF” & read SWR.

Measuring SWR

• Cross-needle SWR Meter.• No adjustments necessary.

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Measuring SWR

• Directional Wattmeter.• Measures both forward power (PF)

& reflected power (PR).• SWR can then be calculated from

PF & PR.

Matching Impedances

• Antenna Tuner.• One way to make antenna matching

adjustments is to use an antenna tuner.• Antenna tuners are impedance transformers.

• 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.

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Matching Impedances

• Antenna Tuner.• a.k.a. -- Transmatch.• Does NOT “tune” the antenna.

• Makes transmitter think all impedances are matched.

Auxiliary Equipment

• Antenna Analyzer.• Measures antenna

impedance (Z).• Resistance (R).• Reactance (X).

• Several other useful functions.

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Auxiliary Equipment

• Dummy Load.• A non-radiating load used for testing.

• Typically 50Ω.

T7C01 - What is the primary purpose of a dummy load?

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

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T7C02 - Which of the following instruments can be used to determine if an antenna is resonant at the desired operating frequency?

A. A VTVMB. An antenna analyzerC. A “Q” meterD. A frequency counter

T7C08 - What instrument other than an SWR meter could you use to determine if a feedline and antenna are properly matched?

A. VoltmeterB. OhmmeterC. Iambic pentameterD. Directional wattmeter

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

A. Moisture contaminationB. Gamma raysC. The velocity factor exceeds 1.0D. Overloading

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

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

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T7C11 - What is a disadvantage of “air core” coaxial cable when compared to foam or solid dielectric types?

A. It has more loss per footB. It cannot be used for VHF or UHF

antennasC. It requires special techniques to prevent

water absorptionD. It cannot be used at below freezing

temperatures

T9B04 - What does an antenna tuner do?

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

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Questions?

Next SessionChapter 5

Amateur Radio Equipment