Antennas and Feedlinesk9vic.info/files/Classes/2013 Amateur Extra Antennas...• Rhombic antenna...
Transcript of 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
VE SessionVE Session
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
VE SessionVE Session
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
VE SessionVE Session
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
Antenna PatternsAntenna Patterns
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 PatternsAntenna Patterns
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 PatternsAntenna Patterns
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 PatternsAntenna Patterns
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 PatternsAntenna Patterns
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 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
Real AntennasReal Antennas
•• What’s the beamwidth (in degrees)?What’s the beamwidth (in degrees)?
Real AntennasReal Antennas
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))
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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):
Real AntennasReal Antennas
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:
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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
Real AntennasReal Antennas
Monopole pattern with 4, 64 and 120 radialsMonopole pattern with 4, 64 and 120 radials
Real AntennasReal Antennas
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)
Real AntennasReal Antennas
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:
Real AntennasReal Antennas
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:
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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
• Height Effect on Vertical Antenna PatternsAntenna at 0.50 λ
Real Antennas
• Height Effect on Vertical Antenna PatternsAntenna at 1.0 λ
Real Antennas
• Height Effect on Vertical Antenna PatternsAntenna at 2.0 λ
Real Antennas
• Height Effect on Vertical Antenna PatternsAntenna at 5.0 λ
Real AntennasReal 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
• Length effect on horizontal doublets– 134 foot doublet at 35 feet (typical back-yard
installation) Lobes = 2n(wavelengths)
14.1 MHz (~2 Wavelengths)
Real Antennas
• Length effect on horizontal doublets– 134 foot doublet at 35 feet (typical back-yard
installation)18.2 MHz (~2.5 Wavelengths)
Real Antennas
• Length effect on horizontal doublets– 134 foot doublet at 35 feet (typical back-yard
installation)21.1 MHz (~3 Wavelengths)
Real Antennas
• Length effect on horizontal doublets– 134 foot doublet at 35 feet (typical back-yard
installation) Lobes = (4n + 2)28.3 MHz (~4 Wavelengths)
Real AntennasReal Antennas
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:
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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
Real AntennasReal Antennas
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)
Real AntennasReal Antennas
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
Antenna MatchingAntenna Matching
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
Antenna MatchingAntenna Matching
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
Antenna MatchingAntenna Matching
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)
Antenna MatchingAntenna Matching
Coil Placement Coil Placement -- Mobile AntennasMobile Antennas
Coil Q = 200Coil Q = 200
Antenna MatchingAntenna Matching
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
Antenna MatchingAntenna Matching
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
Antenna MatchingAntenna Matching
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
Antenna MatchingAntenna Matching
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
Antenna MatchingAntenna Matching
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
Antenna MatchingAntenna Matching
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
Transmission LinesTransmission Lines
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
Transmission LinesTransmission Lines
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
Transmission LinesTransmission Lines
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
Transmission LinesTransmission Lines
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
Transmission LinesTransmission Lines
SWRSWR
Transmission LinesTransmission Lines
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
Radio Direction FindingRadio Direction Finding
22--meter RDF antenna on 2meter RDF antenna on 2--metersmeters
Radio Direction FindingRadio Direction Finding
22--meter RDF Antenna on 70meter RDF Antenna on 70--cmcm
Questions?Questions?
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