simple'' wire'hf'antenna
TRANSCRIPT
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SIMPLE''WIRE'HF'ANTENNA'
OZAUKEE'RADIO'CLUB'W9IPR'AND'GROUP'
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ARRL'Essen2al'Publica2ons'
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ARRL'Wire'Antenna'Publica2ons'
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HF'Wire'Antenna'
• Polariza(on*• Impedance*• Long*Wire*• Loop*• Windom*• Ver(cal*• Antenna*Tuners*
• Dipoles*– Simple*– Sloper*– Inverted*�V�*– Fan*– Trap*– Folded*
• G5RV*• Zepp*– End*fed*– Center*fed**
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Simple'HF'Wire'Antenna'We'will'explore'typical'varia2ons'of'the'wire'dipole'high'frequency'(HF)'antenna'
Typical'Amateur'Radio'''TransmiIng''Antenna'
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Electromagne2c'Wave'Polariza2on'
• Electric'and'magne2c'waves'are'at'right'angles'to'each'other'
• Magne2c'wave'dissipates'within'a'few'wavelengths'of'antenna'
• Electric'wave'facilitates'communica2ons'
• Polariza2on'is'the'orienta2on'of'the'electric'field'of'the'electromagne2c'wave'
• A'horizontally'orientated'antenna,'such'as'a'dipole,'emits'a'horizontally'polarized'electric'wave'that'is'parallel'to'surface'of'the'earth'(like'the'antenna)'
• A'ver2cally'orientated'antenna,'such'as'a'mobile'whip,'emits'a'ver2cally'polarized'electric'wave'that'is'perpendicular'to'the'surface'of'the'earth'(like'the'antenna)'
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How*many*meters?*(or*feet?)*
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RF*Signal*Polariza(on*
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Antenna'Impedance'Z*=*e/i*
• Voltage*and*impedance*is*high*when*end*fed*
• Voltage*and*impedance*is*low*at*center*on*odd*harmonics*
• Voltage*and*impedance*is*high*at*center*on*even*harmonics*
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Random'Length'Long'Wire'Antenna'• Random*length*wire*–*usually*
one*wave*length*at*lowest*frequency*
• Requires*a*�tuner�*due*to*wide*range*of**Z*
• Unbalanced*(single*ended)*feed*
• Typically*employs*a*�pi*sec(on�*tuner*
• RF*in*the*shack*• Ground*wire*length*may*
figure*into*antenna*length*
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Long'Wire'or'Half'Square'
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Horizontal'Loop'• Need'not'be'a'square'• Works'well'as'mul2Nband'antenna'• Open'wire'or'coax'feed'line'• Usually'cut'to'one'wavelength'at'lowest'frequency'
• Balanced'load'• May'require'balun'• Will'require'an'antenna'tuner'• Polariza2on'same'as'plane'of'loop'
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Windom'Mul2Nband'Wire'Antenna'
• Requires*a*�tuner�*due*to*wide*range*of**Z*
• Unbalanced*(single*ended)*load*and*feed*
• Typically*employs*a*�pi*sec(on,*T*sec(on*or*L*sec(on�*tuner*
• RF*in*the*shack*similar*to*long*wire*
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HalfNWavelength'Dipole'
• Most'common'HF'antenna'in'amateur'radio'• Resonate'antenna'on'the'frequency'for'which'it'is'designed'• Lfeet'='468/f'in'MHz'
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Ver2cal'Wire'Antenna'• Actually'a'ver2cally'orientated'
resonate'1/2'wave'dipole'with'the'earth'being'the'�return�'half'
• Due'to'poor'ground'conduc2vity'a'set'of'1/4'wavelength'long'radials'may'be'required'
• Emits'a'low'angle'ver2cally'polarized'electric'field'
• Used'where'space'is'limited'and'for'DX'which'requires'a'low'angle'of'radiated'signal'for'longest'signal'hop'
• Perfect'ground'condi2ons'result'in'a'36'ohm'radia2on'resistance'for'a'1/4'wave'ver2cal'but'in'prac2ce'it'will'be'30'to'100'ohms'
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Mul2band'Wire'Ver2cals'up'a'Tree'
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Inverted'�L�'Antenna'
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Unbalanced'(single'ended)''�L�,'�Pi�'and'�T�'Sec2on'Tuners'
• Unbalanced'transmi^er'output'to'unbalanced'feed'line'(coax)'and'antenna'
• Transforms'the'antenna'impedance'at'the'feed'line'output'to'50'ohms'to'match'the'transmi^er'50'ohm'output'impedance'
• The'capacitors'and'inductor'seIng'must'be'varied'as'the'opera2ng'frequency'and'resul2ng''antenna'impedance''vary''
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HalfNWavelength'Dipole''
• Resonate'antenna'on'the'frequency'for'which'it'is'designed'• Lfeet'='468/f'in'MHz'• Radia2on'resistance'of'72'ohms'when'elevated'at'0.25'wavelength'• Balanced'Load'• Horizontally'polarized'• Most'common'antenna'for'HF'• Invented'by'Heinrich'Hertz'about'1886'
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Center'fed'dipole'is'a'simple,'effec2ve'antenna'
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Radia2on'Pa^ern'Varies'With'Frequency'of'Opera2on'&'Height'
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Impedance'Varies'with'Height'
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Many'Other'Types'of'Dipoles'
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Inverted'�V�'Dipole'Rela2ve'to'Horizontal'Dipole''1. Single'support'2. Slightly'less'gain'3. Slightly'less'direc2onality'4. Slightly'longer'for'freq.'5. Slightly'lower'feed'point'Z'6. SWR'varies'with'apex'angle'
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Half'Wavelength'Sloper'Dipoles'
• Favors*signals*off*the*front*of*antenna*
• No*gain*over*dipole*• Metal*support*acts*as*a*parasi(c*element*and*impacts*gain*and*paXern*
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Off'Center'Fed'Dipole'
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Mul2band'Dipoles'Fan'Dipole'for'several'bands'• Each'dipole'is'a'resonate'circuit'tuned'to'the'band'of'interest.'• The'nonNresonate'dipoles'reject''unrelated'power'
Trap'Dipole'for'40/80'meters''The'LC'circuit'presents'a'high'impedance'at'40'meters'and'low'impedance'at'80'meters'
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Using'Current'Chokes'Transmi^er'current'travels'on'center'conductor'and'inside'of'the'shield'of'coNaxial'cable'feed'line'–'shield'current'feeds'antenna'leg'and'outside'of'shield'–'RF'current'on'outside'of'shield'radiates'like'a'ver2cal'antenna'and'also'travels'back'into'the'shack'–'current'choke'balun'at'
feed'point'�chokes�'the'RF'current'on'outside'of'coNaxial'feed'line''
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Using'Z'Matching'and'Current'Baluns'
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30*
Feed'lines'• Conducts'transmi^ed'power'
from'transmi^er'to'antenna'
• Parallel'conductor'and'coaxial'cable'
• Air'insulated'conductors'have'less'loss'per'foot'
• As'signal'frequency'increases'the'signal'loss'per'foot'increases'
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Open'Wire'(Ladder'Line)'Feeders'1. Ladder*line*provides*a*balanced*
feed*to*a*balanced*load*(antenna)*2. Net*zero*feed*line*radia(on*3. Allows*mul(band*opera(on*4. Tolerates*high*SWR*and*voltage*5. Very*low*transmission*line*loss*6. Requires*a*�balanced*to*
unbalanced�*tuner'
Unbalanced'to'Balanced''Antenna'Tuner'
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''''
Short'Resonate'Dipoles''
1. En(re*length*of*dipole*does*not*have*to*be*co`linear*
2. Bent*ends*may*change*resonate*frequency*slightly*
3. Bent*ends*will*change*radia(on*paXern*
4. Use*of*open*wire*feeder*and*tuner*may*allow*mul(`band*opera(on*
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Dipoles'vs.'Folded'Dipoles'
• All*have*same*radia(on*paXern*• Dipole*Z*=*72*ohms*• Folded*Dipole*Z*=*300*ohms*• 3*wire*Dipole*Z*=*450*to*600*
ohms*• Mul(`wire*dipoles*may*require*a*
balun*and*will*require*a*tuner*• Mul(`wire*dipoles*have*wider*
frequency*range*with*lower*SWR*
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�Clothesline'Folded'Dipole�'
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G5RV'Mul2band'Wire'Antenna'
• 3.5*to*28*MHz*• 102*d.*center*fed*dipole*with*34*d*open*wire*feeders*
• Open*wire*feeders*act*as*a*matching*sec(on*
• Requires*use*of*tuner*with*balanced*output*
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Zepp'(Zeppelin)'Wire'Antenna'
• Mul(`band*antenna*• Use*length*for*lowest*desired*frequency*
• More*wire*–*more*gain*• May*require*a*balun*• Will*require*an*antenna*tuner*
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37*
SWR' • Note'that'as'the'transmi^ed'signal'deviates'from'the'antenna'design'frequency'the'antenna'reactance'and'SWR'increases'
• Increasing'SWR'results'in'increasing'losses'in'feed'line'
• Modern'transceivers'will'reduce'power'when'SWR'is'greater'than'3'
• SWR'='Emax'/'Emin'
• The'forward'and'reverse'power/voltage'can'be'measured'using'a'direc2onal'coupler'
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HF'Wire'Antenna'
• Polariza(on*• Impedance*• Long*Wire*• Loop*• Windom*• Ver(cal*• Antenna*Tuners*
• Dipoles*– Simple*– Sloper*– Inverted*�V�*– Fan*– Trap*– Folded*
• G5RV*• Zepp*– End*fed*– Center*fed**
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ARRL'Wire'Antenna'Publica2ons'