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1、Balun/Unun Construction,Mike,N1IW,Outline,1:1&4:1 Balun descriptionDesign ConsiderationsConstruction MaterialsConstruction StepsParts SourcesQuestions?,Balun Description,Baluns for Antennas,PurposeIsolate transmission line from antenna(suppresses“inverted-L mode”)Provide balanced output currents int
2、o unequal dipole leg impedancesMisconceptionsWill affect antenna bandwidthInefficient&prone to core saturationProvides lightening protection,Why a Balun?,The Basic Current Balun,The 4:1 Gaunella Current Balun,Design Considerations,High choking reactance,250 minimum(limits low frequency response)Low
3、stray capacitance(limits high frequency response)Short transmission line,wave(The shorter,the better)High power handlingMinimize resistive lossesCorrect core selectionRobust mechanical design,Design Considerations,Line Impedance,Z0For 1:1 make equal to load and line impedanceFor 4:1,make geometric m
4、ean of line and load impedance(e.g.,50 to 200 requires 100 line)Transmission line examplesParallel line(wrap with Scotch No.27 glass tape)50:bifilar wound#14,wrap one wire with 1 layer of Scotch No.92 tape to control wire spacing100:bifilar wound#14+Teflon tubing50 CoaxRG303,RG142,RG400EnclosureLigh
5、tweightMechanical integrityWeatherproof,Material Choices,Choose magnetics size for power 0.5”OD cores for QRP and receive applications1.4”-1.5”OD cores for matched loads up to 1 kW2.4”OD cores for reliable legal limit+Cores can also be stackedChoose magnetics material for frequency=250 for 160M(K mi
6、x)=125 for 80M and up(Q1,61)=40 for 20M and up(Q2,67),Rods and Donuts,Ferrite Core Examples(Amidon),Ferrite Core Examples(Amidon),Material Choices,Choose wire for power and Z0Thermaleze or Formvar enamel insulated wire#12,#14 for high power;#16,#18 for medium powerUse tape,spaghetti or insulation to
7、 adjust wire spacingSmaller cores will require smaller wire diameter to get the number of turns neededUse Scotch No.27 glass tape to secure parallel lines50 Coax(RG303,RG142,RG400),1:1 Designs(50 design objective),HP1:10 bifilar turns#12 on 2.4”OD core;wrap one wire with 2 layers of Scotch No.92 tap
8、e of 250 for 160M/80M of 125 for 80M 10M of 40 for 20M-6MHP2:10 bifilar turns#14 on 2.4”OD core;wrap one wire with 1 layers of Scotch 92 tapeMP:8 bifilar turns of#14 on 1.5”OD core(45)LP:10 bifilar turns of#16 on 1.25”OD core,Coax or Parallel Line,1:1,1:1 and 4:1 Examples,200:50 Designs(100 design o
9、bjective),Inputs(50 side)in parallel;outputs(200 side)in series2 X 8 bifilar turns#14 on single 2.4”OD core(cover each wire with teflon tubing)14-16 bifilar turns#14 on 2.4”OD core x 2 cores(cover each wire with teflon tubing)Can substitute#14 solid house wire but take hit in breakdown voltageLP:14
10、bifilar turns#20 insulated hook-up wire on each 1.25”OD core;2 X 7 bifilar turns on single core,Efficiency(Sevick),250 for 160M/80M99%at 1.8 MHz,97%at 30 MHz125 for 80M thru 10M99%at 3.5 MHz,98%at 30 MHz40 for 20M thru 10M99%at 14 MHz and 30 MHz,Construction Steps,Taping the Magnetics,Winding the Torroid,Dressing the Leads,Lining Things Up,Balanced End Connection,Unbalanced End Connections,Getting Close,A Handy Enclosure,Finished Prototype,Additional Reading,Lewallens Article 4:1 QRP BalunPutting a Balun and a Tuner Together,W9CFHybrid Tuner Balun,ZS1AN,
