antennas and feedlinesk9vic.info/files/classes/2013 amateur extra antennas...• rhombic antenna...

Antennas andFeedlines

Bob, KA9BHDEric, K9VIC

Learning ObjectivesLearning Objectives

Teach you enough to get all the antenna Teach you enough to get all the antenna questions right during the VE Sessionquestions right during the VE Session

Learn a few things from Learn a few things from youyou about antennas and about antennas and your experiencesyour experiences

UnUn--teach you a few things you might have teach you a few things you might have picked up from ‘friendly’ sourcespicked up from ‘friendly’ sources

Have fun (it’s a hobby, right?)Have fun (it’s a hobby, right?) Finish on timeFinish on time

VE SessionVE Session

Eight questions, one each from eight groupsEight questions, one each from eight groups Isotropic and gain antennas: definition; used as a Isotropic and gain antennas: definition; used as a

standard for comparison; radiation pattern; basic standard for comparison; radiation pattern; basic antenna parameters: radiation resistance and antenna parameters: radiation resistance and reactance, gain, beamwidth, efficiencyreactance, gain, beamwidth, efficiency

Antenna patterns: E and H plane patterns; gain as a Antenna patterns: E and H plane patterns; gain as a function of pattern; antenna design (computer function of pattern; antenna design (computer modeling of antennas); Yagi antennasmodeling of antennas); Yagi antennas


Eight questions, one each from eight groupsEight questions, one each from eight groups Wire and phased vertical antennas: beverage Wire and phased vertical antennas: beverage

antennas; terminated and resonant rhombic antennas; terminated and resonant rhombic antennas; elevation above real ground; ground antennas; elevation above real ground; ground effects as related to polarization; takeeffects as related to polarization; take--off anglesoff angles

Directional antennas: gain; satellite antennas; Directional antennas: gain; satellite antennas; antenna beamwidth; losses; SWR bandwidth; antenna beamwidth; losses; SWR bandwidth; antenna efficiency; shortened and mobile antennas; antenna efficiency; shortened and mobile antennas; groundinggrounding


Eight questions, one each from eight groupsEight questions, one each from eight groups Matching: matching antennas to feed lines; power Matching: matching antennas to feed lines; power

dividersdividers Transmission lines: characteristics of open and Transmission lines: characteristics of open and

shorted feed lines: 1/8 wavelength; 1/4 wavelength; shorted feed lines: 1/8 wavelength; 1/4 wavelength; 1/2 wavelength; feed lines: coax versus open1/2 wavelength; feed lines: coax versus open--wire; wire; velocity factor; electrical lengthvelocity factor; electrical length


Eight questions, one each from eight groupsEight questions, one each from eight groups The Smith Chart (not covered this week)The Smith Chart (not covered this week) Effective radiated power; system gains and losses; Effective radiated power; system gains and losses;

radio direction finding antennasradio direction finding antennas

Isotropic RadiatorIsotropic Radiator

TheoreticalTheoretical Omnidirectional (nonOmnidirectional (non--directional pattern)directional pattern) SphereSphere--like pattern with antenna in middlelike pattern with antenna in middle Used to compare antennasUsed to compare antennas

Isotropic RadiatorIsotropic Radiator

Dipole about 2.15 dB gain over an isotropic radiator Dipole about 2.15 dB gain over an isotropic radiator (in free space)(in free space) dBd dBd –– Ideal (freeIdeal (free--space, lossless, infinitely thin dipole)space, lossless, infinitely thin dipole) dBd dBd –– Real Model (up to 0.5 dB change based on height)Real Model (up to 0.5 dB change based on height) dBd dBd –– Real Range (Range test w/ comparable dipole at Real Range (Range test w/ comparable dipole at

same height)same height)

General Antenna CharacteristicsGeneral Antenna Characteristics

Gain (dB = 10 log P1/P2)Gain (dB = 10 log P1/P2) Bandwidth (performance, not limited to SWR alone)Bandwidth (performance, not limited to SWR alone) Beamwidth (3 dB)Beamwidth (3 dB) Radiation resistance (equivalent resistance to what’s Radiation resistance (equivalent resistance to what’s

radiated)radiated) Influenced by L/W of elements and surrounding objectsInfluenced by L/W of elements and surrounding objects Efficiency: (Rad. Resistance/Total Res.) X 100Efficiency: (Rad. Resistance/Total Res.) X 100

Ground lossesGround losses Ohmic lossesOhmic losses

ImpedanceImpedance Match for max power transferMatch for max power transfer

Antenna PatternsAntenna Patterns

EE-- and Hand H--fieldfield Polarization determined by the EPolarization determined by the E--fieldfield Beamwidth, F/B, F/Side ratiosBeamwidth, F/B, F/Side ratios Gain evaluation includes:Gain evaluation includes:

Radiation resistanceRadiation resistance E/H patternsE/H patterns Loss resistanceLoss resistance


Gain evaluation should be at multiple Gain evaluation should be at multiple frequencies; frequency has an effect on:frequencies; frequency has an effect on: GainGain ImpedanceImpedance F/B and lobe formationF/B and lobe formation

‘Snake Oil’ approach to antenna sales‘Snake Oil’ approach to antenna sales


Antenna design can provide balance into gain, Antenna design can provide balance into gain, Z, and F/BZ, and F/B Max gain Yagi (long boom) has low impedanceMax gain Yagi (long boom) has low impedance

F/B might be equally important for certain F/B might be equally important for certain situationssituations

Space Antenna Patterns

• Antenna modeling– Method of moments– Each element broken into sections, each

with distinct current


Antenna ModelingAntenna Modeling NEC (Numerical Electromagnetics Code)NEC (Numerical Electromagnetics Code) MININEC (BASIC version of NEC)MININEC (BASIC version of NEC) Min. number of segments is 20/λMin. number of segments is 20/λ

Below this, source impedance values lose accuracyBelow this, source impedance values lose accuracy

Too many segments increase calculation timeToo many segments increase calculation time Program can calculateProgram can calculate

SWR vs. FrequencySWR vs. Frequency Far Field EFar Field E-- and Hand H--pattern plotspattern plots GainGain


Antenna Modeling ProgramsAntenna Modeling Programs EZNEC (NECEZNEC (NEC--2 and 2 and --4 versions) ($90 4 versions) ($90 -- $800)$800) NEC2GO (NECNEC2GO (NEC--2) ($40)2) ($40) 4NEC2 (NEC4NEC2 (NEC--2 and 2 and --4) (NEC4) (NEC--2 free, NEC2 free, NEC--4 $300)4 $300) MMANAMMANA--GAL (raw MININEC with benefits) GAL (raw MININEC with benefits)

(free)(free)

Trial versions of EZNEC (NECTrial versions of EZNEC (NEC--2) and 2) and NEC2GO are available on line. Full versions of NEC2GO are available on line. Full versions of 4NEC2 (NEC4NEC2 (NEC--2) and MMANA are available on 2) and MMANA are available on line.line.


Antenna Modeling ProgramsAntenna Modeling Programs EZNEC Trial Version:EZNEC Trial Version:http://eznec.com/demoinfo.htmhttp://eznec.com/demoinfo.htm NEC2GO Trail Version:NEC2GO Trail Version:http://www.nec2go.com/downloads.asphttp://www.nec2go.com/downloads.asp 4NEC2:4NEC2:http://home.ict.nl/~arivoors/http://home.ict.nl/~arivoors/ MMANAMMANA--GAL:GAL:http://mmhamsoft.amateurhttp://mmhamsoft.amateur--radio.ca/pages/mmanaradio.ca/pages/mmana--

gal.phpgal.php

Real Antennas

• Some examples of patterns:

Real AntennasReal Antennas

BeamwidthBeamwidth Decreases as gain increasesDecreases as gain increases Can be affected by side lobesCan be affected by side lobes Look at pattern and estimateLook at pattern and estimate


•• What’s the beamwidth (in degrees)?What’s the beamwidth (in degrees)?


Folded DipoleFolded Dipole Same length as ‘normal’ dipole, but second element Same length as ‘normal’ dipole, but second element

added a short distance awayadded a short distance away Current now fed between two parallel conductorsCurrent now fed between two parallel conductors Power the samePower the same Impedance goes up X 4 (2Impedance goes up X 4 (222) to ~300 Ohms) to ~300 Ohms Three conductor dipole impedance up X 9 (3Three conductor dipole impedance up X 9 (322))


Yagi AntennasYagi Antennas Any combination of driven & parasitic elementAny combination of driven & parasitic element Commonly Reflector, DE, and director(s)Commonly Reflector, DE, and director(s) Longer boom typically higher gainLonger boom typically higher gain Design for any one parameter compromises othersDesign for any one parameter compromises others Impedance, gain, F/B typical design characteristicsImpedance, gain, F/B typical design characteristics Most designs via computerMost designs via computer

Good news Good news –– nothing fancy required nownothing fancy required now


Currents on Yagi element centers (3Currents on Yagi element centers (3--element Yagi, 1element Yagi, 1--A,A,at 0 Deg. Feed):at 0 Deg. Feed):

Reflector:Reflector:Magnitude (A.) Phase (Deg.)Magnitude (A.) Phase (Deg.)

0.49185 164.450.49185 164.45Driven Element:Driven Element:

Magnitude (A.) Phase (Deg.)Magnitude (A.) Phase (Deg.)1 0.001 0.00

Director:Director:Magnitude (A.) Phase (Deg.)Magnitude (A.) Phase (Deg.)

0.70308 0.70308 --163.4163.4


Phased Vertical AntennasPhased Vertical Antennas Patterns (painful beyond words)Patterns (painful beyond words) Currents in elementsCurrents in elements

In phase In phase –– broadside (elliptical to 90 degrees)broadside (elliptical to 90 degrees) 180 degree, end fire180 degree, end fire 90 degrees cardioids at ¼ wavelength90 degrees cardioids at ¼ wavelength

Impedance must be resistive and matchedImpedance must be resistive and matched Wilkinson divider:Wilkinson divider:

Divides power equally between multiple loads while preventing Divides power equally between multiple loads while preventing changes in one load from disturbing power flow to the others changes in one load from disturbing power flow to the others

Real Antennas

• Patterns (see the book):


Patterns you need to knowPatterns you need to know All antennas in the plots are oriented vertically with All antennas in the plots are oriented vertically with

respect to the plotrespect to the plot The ‘top’ antenna lags in phase (e.g., if the phase The ‘top’ antenna lags in phase (e.g., if the phase

difference is 90 degrees, the top antenna is difference is 90 degrees, the top antenna is --90 90 degrees, bottom is 0 degrees)degrees, bottom is 0 degrees)

Broadside means perpendicular to a line connecting Broadside means perpendicular to a line connecting the antennasthe antennas

EndEnd--fire means along a line connecting the antennasfire means along a line connecting the antennas

Real Antennas

• 180 degree phase shift, ½ wavelength spacing:

Real Antennas

• 90 degree phase shift, ¼ wavelength spacing:

Real Antennas

• Antennas in phase, ½ wavelength spacing:


Ground effect (on vertical antennas)Ground effect (on vertical antennas) Ground losses in the near field increase total loss, Ground losses in the near field increase total loss,

reducing efficiency (Rreducing efficiency (RRR/R/RTT) X100) X100 Minimum of 16 radials on or just under groundMinimum of 16 radials on or just under ground Roughly size of antennaRoughly size of antenna Mesh also good (counterpoise)Mesh also good (counterpoise) Raised radialsRaised radials

Ground reflections occur far (up to 100 Ground reflections occur far (up to 100 wavelengths) out with TO angle going down as wavelengths) out with TO angle going down as conductivity increases or ground slopes awayconductivity increases or ground slopes away

Real Antennas

• Ground effectVertical over Salt Water (primary)

vs. Poor Earth


Ground effectGround effectGround DescriptionsGround Descriptions

PermittivityPermittivityConductivityConductivity ((Relative DielectricRelative Dielectric

Ground QualityGround Quality (S/m)(S/m) Constant)Constant)Very PoorVery Poor 0.0010.001 55

PoorPoor 0.0020.002 1313Good (Average)Good (Average) 0.0050.005 1313

Very GoodVery Good 0.03030.0303 2020Salt WaterSalt Water 5.05.0 8181


Vertical monopoles: Effects of added radialsVertical monopoles: Effects of added radials Radials provide a ground path for current (current Radials provide a ground path for current (current

flows in the radials flows in the radials –– they radiate)they radiate) More radials, lower ground loss (greater efficiency)More radials, lower ground loss (greater efficiency) Radials don't change ground characteristicsRadials don't change ground characteristics Radials don't appreciably change radiation patternsRadials don't appreciably change radiation patterns Pattern is determined out many wavelengthsPattern is determined out many wavelengths Type of ground (conductivity/permittivity) singleType of ground (conductivity/permittivity) single--most most

determining factor in vertical monopole patterndetermining factor in vertical monopole pattern


Monopole pattern with 4, 64 and 120 radialsMonopole pattern with 4, 64 and 120 radials


Ground effects (on horizontal antennas)Ground effects (on horizontal antennas) Ground has small effect on horizontal antennasGround has small effect on horizontal antennas Multiple lobes form in elevation pattern based on Multiple lobes form in elevation pattern based on

heightheight Lobe/Null formula (approximately):Lobe/Null formula (approximately):

AAEE = sin= sin--11 (N/4h)(N/4h)where:where:AAEE = Elevation angle of lobe= Elevation angle of lobeN = lobe (odd are lobes, even are nulls)N = lobe (odd are lobes, even are nulls)h = height in wavelengths (or fractions thereof)h = height in wavelengths (or fractions thereof)


Ground Effect (horizontal dipole):Ground Effect (horizontal dipole): Example:Example:

Dipole antenna ½ wavelength above ground.Dipole antenna ½ wavelength above ground.First lobe is at:First lobe is at:AAEE = sin= sin--11 (1/(4X0.5))(1/(4X0.5))

= sin= sin--11 0.50.5= 30= 30°°

Real Antennas

• Ground effect– Example:

Dipole antenna ½ wavelength above ground.First lobe is at:


Ground effectGround effect Example:Example:

33--element yagi 5 wavelengths above ground.element yagi 5 wavelengths above ground.11stst lobe is at:lobe is at:AAEE = sin= sin--11 (1/(4X5))(1/(4X5))

= sin= sin--11 0.050.05= 2.9= 2.9°°

Real Antennas

• Ground effect– Example:

Yagi antenna 5 wavelengths above ground.

First lobe is at:


Ground Effect (horizontal antenna):Ground Effect (horizontal antenna): As antenna is raised, more lobes develop (2 per As antenna is raised, more lobes develop (2 per

wavelength)wavelength) Lobes get tighter and tighter with heightLobes get tighter and tighter with height Not restricted to dipolesNot restricted to dipoles Eventually the pattern approaches that of the Eventually the pattern approaches that of the

antenna in free space (with deep nulls)antenna in free space (with deep nulls)

Real Antennas

• Ground Effect– Pattern eventually approaches free space:

3-element Yagi Free Space H-field Plot


Height effect on vertical antennasHeight effect on vertical antennas Impedance changes slightly with heightImpedance changes slightly with height Patterns (azimuthal) show multiple lobes as height Patterns (azimuthal) show multiple lobes as height

increasesincreases


Vertical Antenna Impedance vs. heightVertical Antenna Impedance vs. heightHeight (Height (λλ)) Impedance (Impedance (ΩΩ))

0.250.25 52.20 52.20 –– j 7.120j 7.1200.500.50 46.77 + j1.61246.77 + j1.6121.01.0 47.89 + j 0.36547.89 + j 0.3652.02.0 48.23 48.23 –– j 0.007j 0.0073.03.0 48.31 48.31 –– j 0.369j 0.3694.04.0 48.33 + j 0.23548.33 + j 0.2355.05.0 48.34 48.34 –– j 0.001j 0.001

Free SpaceFree Space 48.36 + j 0.00948.36 + j 0.009

Real Antennas

• Height Effect on Vertical Antenna PatternsAntenna at 0.25 λ

Real Antennas



Length effect on horizontal doubletsLength effect on horizontal doublets Antennas longer than ½ wavelength begin to show Antennas longer than ½ wavelength begin to show

azimuthal lobesazimuthal lobes 2 lobes develop for every wavelength2 lobes develop for every wavelength At half wavelengths, old and new lobes both appear At half wavelengths, old and new lobes both appear

(2n) + (2 (n+1)) = (4n +2) lobes total, (2n) + (2 (n+1)) = (4n +2) lobes total, where n = number of wavelengthswhere n = number of wavelengths

(Note: The Following Slides Aren't on the Test...)(Note: The Following Slides Aren't on the Test...)

Real Antennas

• Length effect on horizontal doublets– 134 foot doublet at 35 feet (typical back-yard

installation – antenna oriented 'up/down')

7.1 MHz (~1 Wavelengths)

Real Antennas


installation) Lobes = 2n(wavelengths)

14.1 MHz (~2 Wavelengths)

Real Antennas


installation)18.2 MHz (~2.5 Wavelengths)

Real Antennas


installation)21.1 MHz (~3 Wavelengths)

Real Antennas


installation) Lobes = (4n + 2)28.3 MHz (~4 Wavelengths)


Beverage AntennaBeverage Antenna More than one wavelength long (relatively low to More than one wavelength long (relatively low to

the ground)the ground) Terminating resistor to groundTerminating resistor to ground Only for receive (ground losses)Only for receive (ground losses) Highly directionalHighly directional

Real Antennas

• Beverage Antenna (1,225 ft.) Patterns:


Rhombic antennasRhombic antennas Resonant: Bidirectional; fourResonant: Bidirectional; four--sided, each side sided, each side

minimum one wavelength long; open at the end minimum one wavelength long; open at the end opposite the transmission line connectionopposite the transmission line connection

Terminated: Added resistor (equal to characteristic Terminated: Added resistor (equal to characteristic impedance) makes it unidirectionalimpedance) makes it unidirectional

Good bandwidth, high gain, high F/B Good bandwidth, high gain, high F/B (advantages)(advantages)

Very BigVery Big antennas (disadvantage)antennas (disadvantage)

Real Antennas

• Rhombic antenna patterns, free space:Unterminated Terminated


Space/Satellite antennasSpace/Satellite antennas Dish antenna gain increases as square of the Dish antenna gain increases as square of the

frequency and size.frequency and size. Double the frequency or the diameter, increase gain by 6 Double the frequency or the diameter, increase gain by 6

dBdB

Gain measured in Effective isotropic radiated power Gain measured in Effective isotropic radiated power (EIRP), dB(EIRP), dBW W Takes into accountTakes into account

Transmit PowerTransmit Power Antenna GainAntenna Gain Feed Line LossFeed Line Loss


Space/Satellite antennasSpace/Satellite antennas EIRP ExampleEIRP Example

5050--Watt TransmitterWatt Transmitter 9.5 dB9.5 dBii Antenna GainAntenna Gain 3.0 dB feedline loss3.0 dB feedline loss

Power (dBPower (dBWW) = 10 log (50 W/1 W) = +17.0 dB) = 10 log (50 W/1 W) = +17.0 dBWW

EIRP = +17.0 EIRP = +17.0 dBdBWW + 9.5 dB+ 9.5 dBii + (+ (--3.0 dB)3.0 dB)EIRP = 23.5 EIRP = 23.5 dBdBWW


Circularly polarized antennasCircularly polarized antennas Two Yagi antennas oriented perpendicular to each Two Yagi antennas oriented perpendicular to each

other and fed outother and fed out--ofof--phase (90 degrees)phase (90 degrees)


Space Satellite AntennasSpace Satellite Antennas Maximum gain might result in too narrow of a Maximum gain might result in too narrow of a

beamwidth to be usefulbeamwidth to be useful Some method of pointing the antenna might be Some method of pointing the antenna might be

necessary regardless of gainnecessary regardless of gain High gain antennas might need a sophisticated High gain antennas might need a sophisticated

system (both azimuthal and elevation angles system (both azimuthal and elevation angles controlled)controlled)

Computer aided tracking Computer aided tracking

Antenna MatchingAntenna Matching

Antenna LoadingAntenna Loading Short antennas HaveShort antennas Have

Low ResistanceLow Resistance High Capacitive ReactanceHigh Capacitive Reactance

Cancel Capacitive Reactance with InductanceCancel Capacitive Reactance with Inductance Match loadMatch load

Inductor Q (reactance/resistance)Inductor Q (reactance/resistance) Low Q (high resistance) = more (Ohmic) lossLow Q (high resistance) = more (Ohmic) loss Q typically in the hundreds, not thousandsQ typically in the hundreds, not thousands


Loading AntennasLoading Antennas Increase coil Q by:Increase coil Q by:

Using Fatter Diameter ConductorUsing Fatter Diameter Conductor Winding wide coils (D > ½ L)Winding wide coils (D > ½ L) AirwoundAirwound Wide space between turnsWide space between turns

Bandwidth of Loaded Antenna Narrows (pick two):Bandwidth of Loaded Antenna Narrows (pick two): High EfficiencyHigh Efficiency Wide BandwidthWide Bandwidth Short LengthShort Length


Making it ‘less worse’Making it ‘less worse’ High Q coilsHigh Q coils Move coils up (theoretically works)Move coils up (theoretically works) Use of top hatUse of top hat

Improves radiation efficiencyImproves radiation efficiency Hat section radiates, but farHat section radiates, but far--field patterns cancelfield patterns cancel Generally not practical in motionGenerally not practical in motion


Coil Placement Coil Placement -- Mobile AntennasMobile Antennas

Base vs. Center LoadedBase vs. Center Loaded(8 foot whip on 3.85 MHz)(8 foot whip on 3.85 MHz)


Coil Placement Coil Placement -- Mobile AntennasMobile Antennas

Coil Q = 200Coil Q = 200


Trap AntennasTrap Antennas Tuned RLC circuits show high impedance at their Tuned RLC circuits show high impedance at their

resonant frequenciesresonant frequencies Inserting RLC loads in antennas effectively cuts off Inserting RLC loads in antennas effectively cuts off

the ends of the antenna at the resonant pointthe ends of the antenna at the resonant point Operated on frequencies lower than the trap Operated on frequencies lower than the trap

resonant frequency, traps look mostly like inductorsresonant frequency, traps look mostly like inductors


Delta Match (high impedance feed to low Delta Match (high impedance feed to low impedance antenna)impedance antenna) Dipole antenna center impedance ~73 OhmsDipole antenna center impedance ~73 Ohms At some equidistant points offAt some equidistant points off--center, there’s a 450 center, there’s a 450

Ohm matchOhm match Feedline is fanned (like greek letter Delta) equal Feedline is fanned (like greek letter Delta) equal

distancesdistances


Gamma MatchGamma Match Commonly used to match low impedance Yagi to 50 Commonly used to match low impedance Yagi to 50

Ohm coaxOhm coax Can be used to feed a grounded towerCan be used to feed a grounded tower UnbalancedUnbalanced Short (fraction of a wavelength) bar attaches to a Short (fraction of a wavelength) bar attaches to a

point off center of antennapoint off center of antenna Antenna looks inductiveAntenna looks inductive Inductance must be tuned outInductance must be tuned out

Gamma capacitor <7 pF/meter wavelengthGamma capacitor <7 pF/meter wavelength Shorten antenna appropriate amountShorten antenna appropriate amount


Hairpin MatchHairpin Match Short, conductive loop attached across split driven Short, conductive loop attached across split driven

elementelement Antenna must be capacitive (short for wavelength)Antenna must be capacitive (short for wavelength) Inductor and capacitive antenna form an LInductor and capacitive antenna form an L--match to match to

the antenna’s resistancethe antenna’s resistance Requires elements be isolated from boomRequires elements be isolated from boom


Coax (1/4 wavelength section)Coax (1/4 wavelength section) Required Impedance = (ZRequired Impedance = (ZAntAnt X ZX ZDesiredDesired))1/21/2

ExampleExample 25 Ohm Yagi, 50 Ohm coax25 Ohm Yagi, 50 Ohm coax

Matching Impedance Required = (25 X 50)Matching Impedance Required = (25 X 50)1/21/2

= 35 Ohms= 35 Ohms Use 2 pieces of 75 Ohm coax in parallelUse 2 pieces of 75 Ohm coax in parallel


Stub MatchingStub Matching Open or shorted stub attached to antennaOpen or shorted stub attached to antenna Feedline attached at some point on stub to give 50 Feedline attached at some point on stub to give 50

Ohm impedanceOhm impedance Works well even if the antenna’s very reactiveWorks well even if the antenna’s very reactive Can be used even when impedance of antenna and Can be used even when impedance of antenna and

feedline are unknownfeedline are unknown

Transmission LinesTransmission Lines

Velocity Factor/Electrical LengthVelocity Factor/Electrical Length Light travels at 300 X 10Light travels at 300 X 1088 m/s in vacuumm/s in vacuum Light goes slower in almost any other mediaLight goes slower in almost any other media Dielectric determines speedDielectric determines speed

Typical RGTypical RG-- type coax (solid DE) VF = 66%type coax (solid DE) VF = 66% Open wire type feedlines 90%Open wire type feedlines 90%

Electrical Length (meters) = (300/f (MHz))X VElectrical Length (meters) = (300/f (MHz))X V Electrical Length (feet) = (984/f (MHz))X VElectrical Length (feet) = (984/f (MHz))X V


Velocity Factor/Electrical LengthVelocity Factor/Electrical Length ExampleExample

What is the length of ¼ wavelength (electrical) piece of RGWhat is the length of ¼ wavelength (electrical) piece of RG--8 8 (VF = 66%) on 14.070 MHz?(VF = 66%) on 14.070 MHz?

One wavelength is:One wavelength is:(300/14.07) X 0.66 = 14.07 meters(300/14.07) X 0.66 = 14.07 meters

(984/14.07) X 0.66 = 46.2 feet(984/14.07) X 0.66 = 46.2 feet¼ Wavelength is:¼ Wavelength is:

14.07 X 0.25 = 3.52 meters14.07 X 0.25 = 3.52 meters46.2 X 0.25 = 11.6 feet46.2 X 0.25 = 11.6 feet


Feed Line LossesFeed Line Losses Loss vs. type of lineLoss vs. type of line

Measured in dB/100 feetMeasured in dB/100 feet Coaxial loss increases with frequencyCoaxial loss increases with frequency Coaxial loss typically decreases with sizeCoaxial loss typically decreases with size Open wire lines generally lower lossOpen wire lines generally lower loss

SWRSWR Reflection coefficientReflection coefficient


Feed Line LossesFeed Line Losses SWRSWR

Impedance mismatch at load results in reflectionImpedance mismatch at load results in reflection Magnitude of reflection can be calculated by reflection Magnitude of reflection can be calculated by reflection

coefficient (Γ)coefficient (Γ) Any impedance mismatch results in standing waves, and Any impedance mismatch results in standing waves, and

an SWR greater than 1:1an SWR greater than 1:1 SWR increases losses in coax (and to a lesser degree, open SWR increases losses in coax (and to a lesser degree, open

wire linewire line


SWR and Reflection CoefficientSWR and Reflection Coefficient Γ = Vr/Vi Vr = Reflected VoltageΓ = Vr/Vi Vr = Reflected Voltage

Vi = Incident VoltageVi = Incident Voltage

Γ = (ZΓ = (ZLL--ZZ00)/(Z)/(ZLL+Z0) Z+Z0) ZL L = Load Impedance= Load ImpedanceZZ0 0 = Xmission Line Impedance= Xmission Line Impedance

SWR = (1 + |Γ|)/(1 SWR = (1 + |Γ|)/(1 -- |Γ|)|Γ|)

SWR = (√PSWR = (√PFF + √P+ √PRR)/(√P)/(√PFF -- √P√PRR) P) PFF = Forward Power= Forward Power√P√PRR = Reflected Power= Reflected Power


SWRSWR


Properties of open and shorted linesProperties of open and shorted lines OpenOpen

1/8 wavelength section is capacitive1/8 wavelength section is capacitive Odd ¼ wavelengths low impedance, max. currentOdd ¼ wavelengths low impedance, max. current Even ¼ wavelengths high impedance, high voltageEven ¼ wavelengths high impedance, high voltage

ShortShort 1/8 wavelength section is inductive1/8 wavelength section is inductive Odd ¼ wavelengths high impedance, high voltageOdd ¼ wavelengths high impedance, high voltage Even ¼ wavelength low impedance, max. currentEven ¼ wavelength low impedance, max. current

Study Tip Study Tip -- Learn just one, the other is the oppositeLearn just one, the other is the opposite Study Tip Study Tip –– Use W9HE Smith Chart methodUse W9HE Smith Chart method

Radio Direction FindingRadio Direction Finding

TriangulationTriangulation ExampleExample PitfallsPitfalls

AntennasAntennas Desired CharacteristicsDesired Characteristics Antennas used in practiceAntennas used in practice

LoopLoop YagiYagi

SaturationSaturation


22--meter RDF antenna on 2meter RDF antenna on 2--metersmeters


22--meter RDF Antenna on 70meter RDF Antenna on 70--cmcm

Questions?Questions?

Presentation and other material is located on line at:Presentation and other material is located on line at:www.k9vic.infowww.k9vic.info

If you have any questions while reviewing theIf you have any questions while reviewing thematerial, please ematerial, please e--mail us at:mail us at:

[email protected]@[email protected]@arrl.net

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