Technician License Class Chapter 4 Propagation, Antennas, and Feed Lines 1

Propagation Radio waves travel outward from an antenna in a straight line 3 phenomena possible after that: Reflection Bouncing wave off reflective surface Refraction Gradual bending of wave while traveling through atmosphere Diffraction Redirection of wave around edge of solid object

Propagation Line-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%

Propagation Diffraction: Redirection of wave around edge of solid object Knife edge diffraction

Propagation Multi-path Transmitted radio waves reflected off various objects will arrive at receive antenna at different times Result: “Picket fencing”

Propagation Radio waves can pass through openings in solid objects Longest dimension of opening at least ½ wavelength Because of shorter wavelength, UHF signals can pass through building openings better than VHF signals

Propagation Tropospheric 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 type B. Turn on the CTCSS tone C. Ask the other operator to adjust his squelch control D. 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? VHF signals lose power faster over distance The shorter wavelength allows them to more easily penetrate the structure of buildings This is incorrect; VHF works better than UHF inside buildings 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-flopping B. Picket fencing C. Frequency shifting D. 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 rotation B. Interference from thunderstorms C. 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 diffraction B. Faraday rotation C. 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 scatter B. D layer refraction C. F2 layer refraction D. Faraday rotation

T3C08 -- What causes tropospheric ducting? A. Discharges of lightning during electrical storms B. Sunspots and solar flares C. Updrafts from hurricanes and tornadoes D. Temperature inversions in the atmosphere

T3C10 -- What is the radio horizon? A. The distance over which two stations can communicate by direct path 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

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

Propagation Ionosphere The upper layers of the atmosphere are ionized by UV radiation from the sun 30 to 260 miles above the Earth’s surface

Propagation Ionosphere The ionosphere is divided into layers or regions Each layer has unique characteristics

Propagation Ionosphere 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

Propagation Ionosphere The higher the amount of ionization, the better radio waves are refracted by the ionosphere Amount of ionization varies with time of day Sunrise to sunset  higher ionization level Amount of ionization varies with sunspot activity More sunspots  higher ionization level Larger sunspots  higher ionization level Number and size of sunspots varies over an 11-year cycle Currently in declining portion of Cycle 24 http://www.spaceweather.com/

Propagation Ionosphere

Propagation Ionosphere 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 earth Known as the “critical frequency” Skip normally occurs in the F-layer (F1 & F2) Can occur in the E-layer

Propagation Ionosphere 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

Propagation Ionosphere

Propagation Ionosphere E-Layer Propagation Sporadic-E Can occur any time during the solar cycle Highest probability: Early summer and mid-winter Bands: 10 meters, 6 meters, and 2 meters Aurora (Northern latitudes) Rapid signal strength changes Sounds fluttery or distorted Primarily on 6 meters Meteor scatter Primarily 6 meters

Propagation Ionosphere The lowers regions of the ionosphere absorb radio waves Primarily D-layer Some absorption in E-layer The longer the wavelength (lower frequency), the more absorption Little 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 stratosphere B. The troposphere C. The ionosphere D. 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 far B. FCC regulations prohibit them from going more than 50 miles C. UHF signals are usually not reflected by the ionosphere D. 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

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 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? Backscatter Sporadic E D layer absorption Gray-line propagation

T3C07 -- What band is best suited for communicating via meteor scatter? A. 10 meters B. 6 meters C. 2 meters D. 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 activity B. From shortly after sunset to dawn during periods of high sunspot activity C. From dawn to shortly after sunset during periods of low sunspot activity D. 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 meters B. 23 centimeters C. 70 centimeters or 1.25 meters D. All of these choices are correct

Antenna Fundamentals Definitions: Antenna: Converts an RF electrical signal into an electromagnetic wave (radio wave) or vice versa Any electrical conductor can act as an antenna Some sizes and configurations work better than others Feed-line: Conducts the RF electrical signal to/from the antenna a.k.a. Transmission line

Antenna Fundamentals Definitions: 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 point If impedance is purely resistive (no reactance) then antenna is said to be “resonant”

Antenna Fundamentals Definitions: Antenna Elements: Conductive parts of an antenna Driven Element: Element that feed-line is connected to Driven Array: More than one driven element Parasitic Element(s): Element(s) not directly connected to feed-line Reflector Director

Antenna Fundamentals Polarization 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

Antenna Fundamentals Polarization 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

Antenna Fundamentals Polarization

Antenna Fundamentals Polarization The direction of the electric field is the same as the orientation of the antenna element Loop antennas and circular polarization are exceptions At 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 polarized An 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 inverted B. Signals could be significantly weaker C. Signals have an echo effect on voices D. Nothing significant will happen

T3A07 -- What type of wave carries radio signals between transmitting and receiving stations? A. Electromagnetic B. Electrostatic C. Surface acoustic D. Magnetostrictive

T3A09 -- Which of the following results from the fact that skip signals refracted from the ionosphere are elliptically polarized? A. Digital modes are unusable B. Either vertically or horizontally polarized antennas may be used for transmission or reception C. FM voice is unusable D. 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 field B. The orientation of the magnetic field C. The ratio of the energy in the magnetic field to the energy in the electric field D. The ratio of the velocity to the wavelength

T3B03 -- What are the two components of a radio wave? A. AC and DC B. Voltage and current C. Electric and magnetic fields D. Ionizing and non-ionizing radiation

T5C07 -- What is a usual name for electromagnetic waves that travel through space? Gravity waves Sound waves Radio waves 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 inverted D. The phase is reversed

Antenna Fundamentals Decibels The difference in strength between 2 signals is often expressed in decibels (dB) Ratio between 2 values… a comparison Based on logarithmic scale

Antenna Fundamentals Decibels Commonly used to: Specify gain of an amplifier Specify gain of an antenna Specify loss in a feed line Comparing output vs input level

Antenna Fundamentals Decibels Ratio between 2 values Logarithmic scale 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 Fundamentals Loss Gain dB Ratio 1.000 -1 0.794 -2 0.631 -3 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 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

T5B09 -- What is the approximate amount of change, measured in decibels (dB), of a power increase from 5 watts to 10 watts? A. 2 dB B. 3 dB C. 5 dB D. 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 dB B. -3 dB C. -6 dB D. -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 dB B. 12 dB C. 18 dB D. 28 dB

Antenna Fundamentals Antenna 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 direction Measured in decibels (dB)

Antenna Fundamentals Radiation 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 Fundamentals Radiation Patterns

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

Feed Lines and SWR Feed Lines Feed lines are used for: Conducting RF voltage between radio and antenna Connecting RF voltage between pieces of equipment Feed lines are constructed using special materials and configurations. Objectives: Maintain constant impedance Minimize losses SWR: Standing Wave Ratio

Feed Lines and SWR Feed Lines Coaxial cable Moderate to high loss Usually shortened to “coax” 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

Feed Lines and SWR Feed Lines 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

Feed Lines and SWR Feed Lines Coaxial cable Energy lost in feed line is converted to heat Loss is primarily determined by size of cable and by the cable’s insulating material Larger diameter  Lower loss Air is lowest loss insulator Foam dielectric coax has lower loss than solid dielectric coax because it has more air Air-insulated hard line

Feed Lines and SWR Feed Lines Parallel-wire transmission line Open-wire line, window line, twin lead More difficult to work with High characteristic impedance Typically 300Ω to 600Ω Very low loss

Feed Lines and SWR Characteristic Impedance Every transmission line has a characteristic impedance Denoted as Z0 Measure of how RF energy flows down the line Determined by the physical dimensions of cable NOT the same as the ohmic resistance of the conductors that make up the line

Feed Lines and SWR Characteristic Impedance Parallel-wire transmission line Characteristic 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 SWR B. It comes back into your transmitter and could cause damage C. It is converted into heat D. 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 radio B. Carrying RF signals between a radio and antenna C. Securing masts, tubing, and other cylindrical objects on towers D. 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 ohms B. 50 ohms C. 600 ohms D. 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 considerations B. It has less loss than any other type of feed line C. It can handle more power than any other type of feed line D. 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 increases B. The reflected power increases C. The characteristic impedance increases D. The loss increases

T9B11 -- Which of the following types of feed line has the lowest loss at VHF and UHF? A. 50-ohm flexible coax B. Multi-conductor unbalanced cable C. Air-insulated hard line D. 75-ohm flexible coax

Break

Feed Lines and SWR Standing Wave Ratio (SWR) If feed line impedance = antenna impedance, then: All energy is delivered to the antenna Perfect match SWR = 1:1 If feed line impedance ≠ antenna impedance, then: Some energy is reflected back towards the source Reflected energy is often lost as heat SWR = 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 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 2:1 to 3:1= Useable (with tuner) Many transceivers have an internal antenna tuner which will match SWRs up to 3:1 3:1 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 line B. The ratio of high to low impedance in a feed line C. The transmitter efficiency ratio D. 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 1 B. 1 to 3 C. 1 to 1 D. 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 1 B. 1 to 2 C. 6 to 1 D. 10 to 1

T7C06 -- What does an SWR reading of 4:1 indicate? A. Loss of -4dB B. Good impedance match C. Gain of +4dB D. 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 losses C. To prolong antenna life D. All of these choices are correct

T9B09 -- What might cause erratic changes in SWR readings? A. The transmitter is being modulated B. A loose connection in an antenna or a feed line C. The transmitter is being over-modulated D. Interference from other stations is distorting your signal

Practical Antenna Systems Dipoles and Ground Planes Dipole (Horizontal) 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 Antenna Systems Dipoles and Ground Planes Dipole antenna construction

Practical Antenna Systems Dipoles and Ground Planes Typical dipole antenna installations

Practical Antenna Systems Dipoles and Ground Planes Dipole radiation pattern (azimuthal)

Practical Antenna Systems Dipoles and Ground Planes Dipole (Vertical) One half of a dipole oriented perpendicular to the Earth’s surface Other 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 required Omni-directional Length (feet) = 234 / Frequency (MHz)

Practical Antenna Systems Dipoles and Ground Planes Vertical antennas dimensions

Practical Antenna Systems Dipoles and Ground Planes Vertical antenna installation

Practical Antenna Systems Dipoles and Ground Planes Mobile antennas Most mobile antennas are a variation of the vertical (ground plane) antenna If antenna cannot be a full 1/4λ long, an inductor (coil) is added to make antenna electrically longer Mounting antenna in center of roof gives most uniform radiation pattern

Practical Antenna Systems Dipoles and Ground Planes Mobile antennas A popular mobile antenna for VHF & UHF is the 5/8λ vertical Low angle of radiation (“low take-off angle”) Provides a gain of 1.5 dB over a 1/4λ vertical antenna

Practical Antenna Systems Dipoles and Ground Planes “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 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 Systems Loop Antennas Loop of wire Circumference is one wavelength (1λ) long Circular, triangular (delta), or square (quad) configurations Oriented vertically or horizontally If 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 antenna B. A horizontally polarized antenna C. A rhombic antenna D. 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 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

T9A05 -- How would you change a dipole antenna to make it resonant on a higher frequency? Lengthen it Insert coils in series with radiating wires Shorten it 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 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

T9A08 -- What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz? A. 112 B. 50 C. 19 D. 12

T9A09 -- What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna? A. 6 B. 50 C. 112 D. 236

T9A10 -- In which direction is the radiation strongest from a half-wave dipole antenna in free space? A. Equally in all directions B. Off the ends of the antenna C. Broadside to the antenna D. 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 coverage B. It features a very high angle of radiation and is better for communicating via a repeater C. The 5/8 wavelength antenna completely eliminates distortion caused by reflected signals D. 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 configuration B. Only roof mounting can guarantee a vertically polarized signal C. 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 longer B. Inserting a resistor in the radiating portion of the antenna to make it resonant C. Installing a spring at the base of the antenna to absorb the effects of collisions with other objects D. Making the antenna heavier so it will resist wind effects when in motion

Practical Antenna Systems Directional antennas Directional antennas focus or direct RF energy in a given direction Gain Apparent increase in power in the desired direction (both transmit and receive)

Practical Antenna Systems Directional antennas The most common type of directional antenna is the beam The most common type of beam antennas is: Yagi-Uda array Normally just called a “Yagi” Invented in 1926 by Dr. Shintaro Uda, in collaboration with Dr. Hidetsugu Yagi

Practical Antenna Systems Directional antennas All beam antennas are made up of elements Metal rods Loops 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 direction Can have more then one director

Practical Antenna Systems Directional antennas Yagi antenna Horizontally-polarized Yagi antenna is commonly used for long distance, weak signal CW & SSB communications on VHF & UHF

Practical Antenna Systems Directional antennas Quad antenna Square wire loop elements

Practical Antenna Systems Directional Antennas Parabolic Dish Large, round, curved reflector Very 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 circular B. Left-hand circular C. Horizontal D. 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 path D. Increase the antenna SWR

T9A01 -- What is a beam antenna? 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

T9A06 -- What type of antennas are the quad, Yagi, and dish? A. Non-resonant antennas B. Loop antennas C. Directional antennas D. Isotropic antennas

Practical Antenna Systems Practical feed lines and associated equipment Feed line selection and maintenance Coax vs. Open Wire Coax is easier to use VHF & UHF installations almost always use coaxial cable Open wire has lower loss Normally used only with HF wire antennas

Practical Antenna Systems Practical feed lines and associated equipment Feed line selection and maintenance Need to consider: Frequency Length of cable Power level Budget Loss Larger cable generally has lower loss Foam dielectric cable has lower loss

Practical Antenna Systems Type Impedance Loss @ 30MHz (dB/100ft) Loss @ 150MHz Cost (per foot) RG-174 50Ω 4.6 dB 10.3 dB $0.20 RG-58 2.5 dB 5.6 dB $0.28 RG-8X 2.0 dB 4.5 dB $0.30 RG-8 1.1 dB $1.00 RG-213 $0.89 LMR-400 0.7 dB 1.5 dB $1.11 Type Impedance Loss @ 30MHz (dB/100ft) Loss @ 150MHz Cost (per foot) RG-59 75Ω 1.8 dB 4.1 dB $0.16 RG-6 1.4 dB 3.3 dB $0.24 RG-11A 0.7 dB 1.6 dB $0.97

Practical Antenna Systems Practical feed lines and associated equipment Feed line selection and maintenance Coaxial 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

Practical Antenna Systems Practical feed lines and associated equipment Coaxial feed line connections 4 main types commonly used in amateur radio: UHF Type “N” BNC SMA

Practical Antenna Systems Practical feed lines and associated equipment Coaxial feed line connections 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)

Practical Antenna Systems Practical feed lines and associated equipment Coaxial feed line connections 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

Practical Antenna Systems Practical feed lines and associated equipment Coaxial feed line connections BNC Connectors Up to 4 GHz Low power Constant impedance Both 50Ω and 75Ω versions Commonly used on: Older hand held radios Test equipment

Practical Antenna Systems Practical feed lines and associated equipment Coaxial feed line connections SMA connectors Up to 18 GHz Low power Constant impedance Only 50Ω available Used on most new hand held radios

T7C09 -- Which of the following is the most common cause for failure of coaxial cables? A. Moisture contamination B. Gamma rays C. The velocity factor exceeds 1.0 D. 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

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

Practical Antenna Systems Soldering 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

Practical Antenna Systems Soldering Types of solder Standard 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 copper Melting point is about 40°C (72°F) hotter than standard solder

Practical Antenna Systems 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!

Practical Antenna Systems 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

T7D08 -- Which of the following types of solder is best for radio and electronic use? A. Acid-core solder B. Silver solder C. Rosin-core solder D. Aluminum solder

T7D09 -- What is the characteristic appearance of a cold solder joint? A. Dark black spots B. A bright or shiny surface C. A grainy or dull surface D. A greenish tint

Practical Antenna Systems Practical feed lines and associated equipment SWR 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

Practical Antenna Systems Practical feed lines and associated equipment SWR meters and Wattmeters SWR meter location

Practical Antenna Systems Practical feed lines and associated equipment SWR meters and Wattmeters Simple SWR meter Set to “FWD” Adjust “CAL” for full scale reading Set to “REF” and read SWR

Practical Antenna Systems Practical feed lines and associated equipment SWR Meters and Wattmeters Cross-needle SWR meter No adjustments necessary

Practical Antenna Systems Practical feed lines and associated equipment SWR Meters and Wattmeters Directional Wattmeter Measures both forward power (PF) & reflected power (PR) SWR can then be calculated from PF & PR

Practical Antenna Systems Practical feed lines and associated equipment Antenna tuner Used to make antenna matching adjustments 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

Practical Antenna Systems Practical feed lines and associated equipment Antenna tuner a.k.a. Transmatch Does NOT “tune” the antenna Makes transmitter think all impedances are matched

Practical Antenna Systems Practical feed lines and associated equipment Antenna analyzer Measures antenna impedance (Z) Resistance (R) Reactance (X) Several other useful functions

Practical Antenna Systems Practical feed lines and associated equipment Dummy load A non-radiating load used for testing Typically 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 antenna B. In series with the station's ground C. In parallel with the push-to-talk line and the antenna D. 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 VTVM B. An antenna analyzer C. A Q meter D. 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. Voltmeter B. Ohmmeter C. Iambic pentameter D. Directional wattmeter

Questions?