Technician License Class

Chapter 4Propagation, Antennas, and

Feed Lines

PropagationRadio waves travel outward from an

antenna in a straight line3 phenomena possible after that:

ReflectionBouncing wave off reflective surface

RefractionGradual bending of wave while traveling

through atmosphereDiffraction

Redirection of wave around edge of solid object

PropagationLine-of-sight (LOS)

Direct from transmitting antenna to receiving antenna

Radio horizon Point at which radio signals are blocked by curvature

of the earth Slightly greater than visual horizon Refraction increases radio horizon distance by

about 15%

PropagationDiffraction: Redirection of wave around edge

of solid object

Knife edge diffraction

PropagationMulti-path

Transmitted radio waves reflected off various objects will arrive at receive antenna at different timesResult: “Picket fencing”

PropagationRadio waves can pass through openings in

solid objectsLongest dimension of opening at least ½

wavelengthBecause of shorter wavelength, UHF signals can pass

through building openings better than VHF signals

PropagationTropospheric Ducting

Radio waves can travel for long distances along vertical boundaries of different temperature air layers

Propagation of 300 miles or more possible on VHF or UHF

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 typeB. Turn on the CTCSS toneC. Ask the other operator to adjust his squelch controlD. Try moving a few feet or changing the direction of your antenna if possible, as 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 distanceB. The shorter wavelength allows them to more

easily penetrate the structure of buildingsC. This is incorrect; VHF works better than UHF

inside buildingsD. UHF antennas are more efficient than VHF

antennas

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 -- Which of the following is a likely cause of irregular fading of signals received by ionospheric reflection?

A. Frequency shift due to Faraday rotationB. Interference from thunderstormsC. Random combining of signals arriving via different paths D. Intermodulation distortion

T3C05 -- Which of the following effects might cause radio signals to be heard despite obstructions between the transmitting and receiving stations?

A. Knife-edge diffractionB. Faraday rotationC. Quantum tunneling D. Doppler shift

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

T3C08 -- What causes tropospheric ducting?

A. Discharges of lightning during electrical stormsB. Sunspots and solar flaresC. Updrafts from hurricanes and tornadoesD. Temperature inversions in the atmosphere

T3C10 -- What is the radio horizon?

A. The distance over which two stations can communicate by direct pathB. The distance from the ground to a horizontally mounted antennaC. The farthest point you can see when standing at the base of your antenna towerD. The shortest distance between two points on the Earth's surface

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 lightB. Radio waves are not blocked by dust particlesC. The Earth seems less curved to radio waves than to lightD. Radio waves are blocked by dust particles

PropagationIonosphere

The upper layers of the atmosphere are ionized by UV radiation from the sun30 to 260 miles above

the Earth’s surface


The ionosphere is divided into layers or regionsEach layer has unique

characteristics


Transmissions in some radio frequency bands (e.g., HF & lower VHF) will be refracted off the ionosphere and returned to earth Called “skip” Skip distances are well beyond the range of line-of-

sight Several hundred to several thousand miles

• Maximum of about 2500 miles for a single hop• Can have multiple hops


The higher the amount of ionization, the better radio waves are refracted by the ionosphere

Amount of ionization varies with time of daySunrise to sunset higher ionization level

Amount of ionization varies with sunspot activityMore sunspots higher ionization levelLarger sunspots higher ionization levelNumber and size of sunspots varies over an 11-year

cycleCurrently in declining portion of Cycle 24http://www.spaceweather.com/



Skip is refraction (bending), not reflection (bouncing)The shorter the wavelength (higher frequency), the less

the signal is refracted (bent).At some given frequency, the wave is no longer bent

enough to return to earthKnown as the “critical frequency”

Skip normally occurs in the F-layer (F1 & F2)Can occur in the E-layer


The highest frequency that can be used to communicate between 2 points is called the Maximum Useable Frequency (MUF)

The lowest frequency that can be used to communicate between 2 points is called the Lowest Useable Frequency (LUF)

MUF & LUF vary over any 24-hour period depending on the amount of ionization in the ionosphere



E-Layer PropagationSporadic-E

Can occur any time during the solar cycleHighest probability: Early summer and mid-winterBands: 10 meters, 6 meters, and 2 meters

Aurora (Northern latitudes)Rapid signal strength changesSounds fluttery or distortedPrimarily on 6 meters

Meteor scatterPrimarily 6 meters


The lowers regions of the ionosphere absorb radio wavesPrimarily D-layer

Some absorption in E-layerThe longer the wavelength (lower frequency), the

more absorptionLittle to no communications possible on lower

frequency bands during the day when D and E layer are present

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

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

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 spaceB. Signals are arriving by sub-surface ductingC. Signals are being reflected by lightning storms in your areaD. Signals are being refracted from a sporadic E layer

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

A. Signals from distances of 10,000 or more miles are commonB. The signals exhibit rapid fluctuations of strength and often sound distortedC. These types of signals occur only during winter nighttime hoursD. These types of signals are generally strongest when your antenna is aimed west

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

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

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

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

A. From dawn to shortly after sunset during periods of high sunspot activityB. From shortly after sunset to dawn during periods of high sunspot activityC. From dawn to shortly after sunset during periods of low sunspot activityD. From shortly after sunset to dawn during periods of low sunspot activity

T3C12 -- Which of the following bands may provide long distance communications during the peak of the sunspot cycle?

A. Six or ten metersB. 23 centimetersC. 70 centimeters or 1.25 metersD. All of these choices are correct

Antenna FundamentalsDefinitions:

Antenna: Converts an RF electrical signal into an electromagnetic wave (radio wave) or vice versaAny electrical conductor can act as an antenna

Some sizes and configurations work better than othersFeed-line: Conducts the RF electrical signal

to/from the antennaa.k.a. Transmission line


Feed Point: Place where the feed-line is connected to the antenna

Feed Point Impedance: Ratio of RF voltage to RF current at the feed pointIf impedance is purely resistive (no reactance) then

antenna is said to be “resonant”


Antenna Elements: Conductive parts of an antennaDriven Element: Element that feed-line is connected

toDriven Array: More than one driven element

Parasitic Element(s): Element(s) not directly connected to feed-lineReflectorDirector

Antenna FundamentalsPolarization

An electromagnetic wave consists of an electric wave and magnetic wave that propagate at right angles to each other

Polarization is the orientation of the electric wave with respect to the earth


If the electric wave is horizontal (parallel to the ground), then wave is said to be horizontally polarized

If electric wave is vertical (perpendicular to the ground), then wave is said to be vertically polarized



The direction of the electric field is the same as the orientation of the antenna element

Loop antennas and circular polarization are exceptionsAt VHF and UHF frequencies, if polarizations of

transmit and receive antenna do not match, reduced received signal strength results

Polarization of refracted sky wave signals is random and continuously changing

Elliptically polarizedAn antenna of any orientation may be used

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 invertedB. 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

T3A09 -- Which of the following results from the fact that skip signals refracted from the ionosphere are elliptically polarized?

A. Digital modes are unusableB. Either vertically or horizontally polarized antennas may be used for transmission or receptionC. FM voice is unusableD. Both the transmitting and receiving antennas must be of the same polarization

T3B02 -- What property of a radio wave is used to describe its polarization?

A. The orientation of the electric fieldB. The orientation of the magnetic fieldC. The ratio of the energy in the magnetic field to the energy in the electric fieldD. The ratio of the velocity to the wavelength

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

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 EarthB. The electric field is perpendicular to the EarthC. The phase is invertedD. The phase is reversed

Antenna Fundamentals

DecibelsThe difference in strength between 2 signals is

often expressed in decibels (dB)Ratio between 2 values… a comparisonBased on logarithmic scale

Antenna FundamentalsDecibels

Commonly used to:Specify gain of an amplifierSpecify gain of an antennaSpecify loss in a feed line

Comparing output vs input level

Antenna FundamentalsDecibels

Ratio between 2 values One value is often a standard reference value, e.g.,

1 watt or 1 milliwatt Logarithmic scale Power ratio: dB = 10 log10(P2/P1) Voltage ratio: dB = 20 log10(E2/E1)

Where P2 is output and P1 is input If dB is positive => gain If dB is negative => loss

Antenna FundamentalsdB Ratio

0 1.000

-1 0.794

-2 0.631

-3 0.501

-4 0.398

-5 0.316

-6 0.250

-7 0.200

-8 0.159

-9 0.126

-10 0.100

dB Ratio

0 1.000

1 1.259

2 1.585

3 1.995

4 2.512

5 3.162

6 4.000

7 5.012

8 6.310

9 7.943

10 10.00

Loss Gain

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

T5B10 -- What is the approximate amount of change, measured in decibels (dB), of a power decrease from 12 watts to 3 watts?

A. -1 dBB. -3 dBC. -6 dBD. -9 dB

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

Antenna FundamentalsAntenna Gain

Omni-directional antennas radiate equally in all directions

Directional antennas focus radiation in one or more specific directions, e.g., beam antennas

Gain is the apparent increase in power in a particular direction because energy is focused in that directionMeasured in decibels (dB)

Antenna FundamentalsRadiation Patterns

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 (gain)

Antenna FundamentalsRadiation Patterns

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

A. The additional power that is added to the transmitter powerB. The additional power that is lost in the antenna when transmitting on a higher frequencyC. The increase in signal strength in a specified direction when compared to a reference antennaD. The increase in impedance on receive or transmit compared to a reference antenna

Feed Lines and SWRFeed Lines

Feed lines are used for:Conducting RF voltage between radio and antennaConnecting RF voltage between pieces of equipment

Feed lines are constructed using special materials and configurations. Objectives:Maintain constant impedanceMinimize losses

SWR: Standing Wave Ratio


Coaxial cableUsually shortened to “coax”Most popular typeEasy to work withLow characteristic impedance

Typically 50Ω or 75ΩModerate to high loss

Loss varies with frequencyHigher frequency higher loss


Coaxial cable 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, RG-213, LMR-400 75Ω = RG-6, RG-11, RG-59


Coaxial cableEnergy lost in feed line is converted to heatLoss is primarily determined by size of cable and by

the cable’s insulating materialLarger diameter Lower lossAir is lowest loss insulatorFoam dielectric coax has lower loss than solid

dielectric coax because it has more airAir-insulated hard line


Parallel-wire transmission lineOpen-wire line, window line, twin leadMore difficult to work withHigh characteristic impedance

Typically 300Ω to 600ΩVery low loss

Feed Lines and SWRCharacteristic Impedance

Every transmission line has a characteristic impedanceDenoted as Z0

Measure of how RF energy flows down the lineDetermined by the physical dimensions of cableNOT the same as the ohmic resistance of the

conductors that make up the line

Feed Lines and SWRCharacteristic Impedance

Parallel-wire transmission lineCharacteristic impedance determined by ratio of

diameter of conductors to distance between them Larger distance higher impedance Smaller diameter conductors higher impedance

T7C07 -- What happens to power lost in a feed line?

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

T7C12 -- Which of the following is a common use of coaxial cable?

A. Carrying dc power from a vehicle battery to a mobile radioB. Carrying RF signals between a radio and antennaC. Securing masts, tubing, and other cylindrical objects on towersD. Connecting data signals from a TNC to a computer

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

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

A. It is easy to use and requires few special installation considerationsB. It has less loss than any other type of feed lineC. It can handle more power than any other type of feed lineD. It is less expensive than any other types of feed line

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

T9B11 -- Which of the following types of feed line has the lowest loss at VHF and UHF?

A. 50-ohm flexible coaxB. Multi-conductor unbalanced cableC. Air-insulated hard lineD. 75-ohm flexible coax

Break

Feed Lines and SWRStanding Wave Ratio (SWR)

If feed line impedance = antenna impedance, then:All energy is delivered to the antennaPerfect matchSWR = 1:1

If feed line impedance ≠ antenna impedance, then:Some energy is reflected back towards the sourceReflected energy is often lost as heatSWR = ZLine / ZAnt or SWR = ZAnt / Zline

Ratios are always greater than 1:1, e.g., 1.3:1, 2:1, 3:1

Feed Lines and SWRStanding Wave Ratio (SWR)

Rule-of-thumb guidelines:1:1 = Perfect2:1 = Acceptable

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

2:1 to 3:1= Useable (with tuner)Many transceivers have an internal antenna tuner which will

match SWRs up to 3:13:1 or more = Really bad

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

A. A measure of how well a load is matched to a transmission lineB. The ratio of high to low impedance in a feed lineC. The transmitter efficiency ratioD. An indication of the quality of your station’s ground connection

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

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

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

A. Loss of -4dBB. Good impedance matchC. Gain of +4dBD. Impedance mismatch

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

A. To reduce television interference B. To allow the efficient transfer of power and reduce lossesC. To prolong antenna lifeD. All of these choices are correct

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

A. The transmitter is being modulatedB. A loose connection in an antenna or a feed lineC. The transmitter is being over-modulatedD. Interference from other stations is distorting your signal

Practical Antenna Systems

Dipoles and Ground PlanesDipole (Horizontal)

Most basic antennaTwo conductors, equal lengthFeed line connected in the middleTotal length is 1/2 wavelength (1/2 λ)Length (feet) = 468 / Frequency (MHz)

Practical Antenna SystemsDipoles and Ground Planes

Dipole antenna construction


Typical dipole antenna installations


Dipole radiation pattern (azimuthal)


Dipole (Vertical)One half of a dipole oriented perpendicular to

the Earth’s surfaceOther half of the dipole is replaced by a ground

plane, e.g., Earth, car roof, trunk lid, or other metal surface

When “Earth mounted”, radial wires requiredOmni-directionalLength (feet) = 234 / Frequency (MHz)


Vertical antennas dimensions


Vertical antenna installation


Mobile antennasMost mobile antennas are a variation of the vertical

(ground plane) antennaIf antenna cannot be a full 1/4λ long, an inductor

(coil) is added to make antenna electrically longerMounting antenna in center of roof gives most

uniform radiation pattern


Mobile antennasA popular mobile antenna for VHF & UHF is the 5/8λ

verticalLow angle of radiation (“low take-off angle”)Provides a gain of 1.5 dB over a 1/4λ vertical antenna


“Rubber Duck” AntennasVariation of the ground-planeCommonly used on hand-held transceiversCoil of wire enclosed in rubber (plastic) coveringShorter than normal ground-planeMuch less efficient than full-sized ground-plane

Side note: Using a rubber duck antenna inside your vehicle is ineffective and not a good idea because….Signals transmitted outside the vehicle are weaker due to the shielding provided by the vehicle’s body

Practical Antenna SystemsLoop Antennas

Loop of wireCircumference is one wavelength (1λ) longCircular, triangular (delta), or square (quad)

configurationsOriented vertically or horizontallyIf oriented 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

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 antennaB. 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 antenna to make it resonant on a higher frequency?

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

radiating wires

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

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

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 from 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 feed line

T9A12 -- What is a reason to use a properly mounted 5/8 wavelength antenna for VHF or UHF mobile service?

A. It offers a lower angle of radiation and more gain than a 1/4 wavelength antenna and usually provides improved coverageB. It features a very high angle of radiation and is better for communicating via a repeaterC. The 5/8 wavelength antenna completely eliminates distortion caused by reflected signalsD. The 5/8 wavelength antenna offers a 10-times power gain over a 1/4 wavelength design

T9A13 -- Why are VHF or UHF mobile antennas often mounted in the center of the vehicle roof?

A. Roof mounts have the lowest possible SWR of any mounting configurationB. Only roof mounting can guarantee a vertically polarized signalC. A roof mounted antenna normally provides the most uniform radiation pattern D. Roof mounted antennas are always the easiest to install

T9A14 -- Which of the following terms describes a type of loading when referring to an antenna?

A. Inserting an inductor in the radiating portion of the antenna to make it electrically longerB. Inserting a resistor in the radiating portion of the antenna to make it resonantC. Installing a spring at the base of the antenna to absorb the effects of collisions with other objectsD. Making the antenna heavier so it will resist wind effects when in motion

Practical Antenna SystemsDirectional antennas

Directional antennas focus or direct RF energy in a given direction

GainApparent increase in power in the desired direction

(both transmit and receive)


The most common type of directional antenna is the beam

The most common type of beam antennas is:Yagi-Uda arrayNormally just called a “Yagi”Invented in 1926 by Dr. Shintaro Uda, in

collaboration with Dr. Hidetsugu Yagi


All beam antennas are made up of elementsMetal rodsLoops of wire

Driven element is connected to the radio by the feed line

Reflector element is on the side opposite the desired radiation direction

Director element is on the side toward the desired directionCan have more then one director


Yagi antennaHorizontally-polarized Yagi antenna is commonly

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


Quad antennaSquare wire loop elements

Practical Antenna SystemsDirectional Antennas

Parabolic DishLarge, round, curved

reflectorVery high gain

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 polarizationB. Try to find a path that reflects signals to the repeaterC. Try the long pathD. Increase the antenna SWR

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

Practical Antenna SystemsPractical feed lines and associated

equipmentFeed line selection and maintenance

Coax vs. Open WireCoax is easier to useVHF & UHF installations almost always use

coaxial cableOpen wire has lower lossNormally used only with HF wire antennas

Practical Antenna SystemsPractical feed lines and associated equipment

Feed line selection and maintenanceNeed to consider:

Frequency Length of cable Power level Budget Loss Larger cable generally has lower loss Foam dielectric cable has lower loss

Practical Antenna SystemsType Impedance Loss @ 30MHz

(dB/100ft)Loss @ 150MHz

(dB/100ft)Cost

(per foot)

RG-174 50Ω 4.6 dB 10.3 dB $0.20

RG-58 50Ω 2.5 dB 5.6 dB $0.28

RG-8X 50Ω 2.0 dB 4.5 dB $0.30

RG-8 50Ω 1.1 dB 2.5 dB $1.00

RG-213 50Ω 1.1 dB 2.5 dB $0.89

LMR-400 50Ω 0.7 dB 1.5 dB $1.11

Type Impedance Loss @ 30MHz(dB/100ft)

Loss @ 150MHz(dB/100ft)

Cost(per foot)

RG-59 75Ω 1.8 dB 4.1 dB $0.16

RG-6 75Ω 1.4 dB 3.3 dB $0.24

RG-11A 75Ω 0.7 dB 1.6 dB $0.97


Feed line selection and maintenanceCoaxial cable must be protected

Worst enemy is moisture getting into the cable Moisture increases loss in cable Avoid nicks or 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


equipmentCoaxial feed line connections

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



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



Type “N” connectors Up to 10 GHz High power (>1.5 kW) Constant impedance Both 50Ω and 75Ω versions Weather resistant Relatively expensive Relatively difficult to install



BNC Connectors Up to 4 GHz Low power Constant impedance Both 50Ω and 75Ω versions Commonly used on:

Older hand held radios Test equipment


equipmentCoaxial feed line connectionsSMA connectors

Up to 18 GHzLow powerConstant impedanceOnly 50Ω availableUsed on most new hand held radios

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 radiationB. Ultraviolet light can increase losses in the cable’s jacketC. Ultraviolet and RF signals can mix together, causing interferenceD. Ultraviolet light can damage the jacket and allow water to enter the cable

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

Practical Antenna SystemsSoldering

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 solderFlux is a material used to prevent the

formation of oxides during the soldering process


Types of solderStandard solder is a mixture of tin and lead

Ratio of tin to lead is adjusted for lowest melting temperature

63/37 or 60/40 Melting point is about 183°C (361°F)

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

standard solder


Types of fluxResin

Used for electrical/electronic connectionsAcid

Used for plumbing

NEVER use acid–core solder or acid flux to solder electronic connections!


It takes a little bit of skill to make a good solder jointGood 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

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


equipmentSWR meters and Wattmeters

SWR meter a.k.a. SWR bridge Connects between transmitter and feed line Displays amount of mismatch (SWR) between transmitter

and antenna system Antenna system = antenna + feed line

Make adjustments to antenna system to minimize mismatch


SWR meters and WattmetersSWR meter location

Practical Antenna SystemsPractical feed lines

and associated equipmentSWR meters and WattmetersSimple SWR meter

Set to “FWD”Adjust “CAL” for full

scale readingSet to “REF” and read

SWR

Practical Antenna SystemsPractical feed lines

and associated equipmentSWR Meters and

WattmetersCross-needle SWR

meterNo adjustments

necessary

Practical Antenna SystemsPractical feed lines and

associated equipmentSWR Meters and

WattmetersDirectional Wattmeter

Measures both forward power (PF) & reflected power (PR)

SWR can then be calculated from PF & PR


equipmentAntenna tuner

Used to make antenna matching adjustmentsTuners are impedance transformersWhen used appropriately they are effectiveWhen used inappropriately all they do is make a

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


Antenna tunera.k.a. TransmatchDoes NOT “tune” the antennaMakes transmitter think all impedances are matched


Antenna analyzerMeasures antenna impedance (Z)

Resistance (R)Reactance (X)

Several other useful functions


Dummy loadA non-radiating load used for testingTypically 50Ω

T4A05 -- Where should an in-line SWR meter be connected to monitor the standing wave ratio of the station antenna system?

A. In series with the feed line, between the transmitter and antennaB. In series with the station's groundC. In parallel with the push-to-talk line and the antennaD. In series with the power supply cable, as close as possible to the radio

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 feed line and antenna are properly matched?

A. VoltmeterB. OhmmeterC. Iambic pentameterD. Directional wattmeter

Questions?

Documents

Technician License Class