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Small 500 KHz Transmitting Antennas VE3KL 5/5/2015David Conn VE3KL1 Vertical 500 KHz Antenna….. Courtesy (Gunnar SM6BGP) Height = 30 metres R (antenna) = 22 Ohms ….. measured Top Hat Insulated Base

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Many Possible Antenna Types 5/5/2015David Conn VE3KL N Monopoles Separately Fed Closely Spaced STAR-H Patent Gunnar….SM6BGP

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Presentation Outline Basics..Radiation Resistance, Efficiency, Bandwidth Vertical Antennas Inverted L Antenna…..briefly Loop Antennas Other types including the Horizontal Dipole Bibliography 5/5/2015David Conn VE3KL3

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Acknowledgements OARC, RAC, Bryan (VE3QN), Oliver Conn Industry Canada..Justine Sider (computer use) Gunnar….SM6BGP….Permission to use material from Web site RIK..ON7YD……permission to use diagrams from Web site STAR-H Corp….a patented novel short AM monopole with high radiation resistance.. the author wishes to thank STAR-H for permission to experiment with this antenna (non-commercial use) 5/5/2015David Conn VE3KL4

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The Problem Selecting and Designing reasonably sized transmitting antennas for 600 metre wavelength amateur radio applications. 5/5/2015David Conn VE3KL5

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Design Methodology Analytic design using basic equations Very broad in concept…not specific Simulation using method of moments (NEC-4) Specific to an exact configuration Must be careful…many limitations and approximations. Used by VE3KL to evaluate all Canadian license applications Build, Measure and Test The ultimate, but few test ranges available for 500 KHz antennas 5/5/2015David Conn VE3KL6

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Design Issues (Small Antennas) 5/5/2015David Conn VE3KL7 Radiation/Ground Resistance Efficiency Bandwidth

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Design Issues (Small Antennas) Low Radiation Resistance Low Efficiency Narrow Bandwidth….small capacitance Space Limitations…….600 metre λ Simulation Problems….NEC4 needed for buried radials 5/5/2015David Conn VE3KL8

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Radiation Resistance, Rr Definition 5/5/2015David Conn VE3KL9 P rad = I o 2 R r /2 [Watts] P rad = Power radiated from an antenna I = IoCos(2πft) Rr for a half wave dipole = 73 Ohms

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Antenna Efficiency 5/5/2015 David Conn VE3KL 10 Efficiency = Rr/Rloss (for small Rr) Doubling Rr doubles the antenna efficiency Rr = Radiation Resistance RLoss = copper loss plus ground loss

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Antenna Efficiency 5/5/2015David Conn VE3KL11 Rr = radiation resistance…….Rloss = loss resistance Example: Rrad = 0.5 Ohms, Rloss = 22 Ohms Efficiency = 0.5/22.5 = 0.022 = 2.2% (-17dB)

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Antenna Bandwidth 5/5/2015David Conn VE3KL12 Several ways to define Bandwidth: 3 dB, SWR, Return Loss Calculated from Antenna Equivalent Circuit Can be very small ( 1 KHz ) for small antennas Frequency Example B = 4 KHz for SWR = 2:1 SWR B 1.0 2.0

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Vertical Antennas Basics…applies to all antennas Vertical Antenna No Top Hat, Top Hat Case study of a vertical monopole with top hat…SM6BGP Vertical STAR-H Type Antenna 5/5/2015David Conn VE3KL13

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5/5/2015David Conn VE3KL14 Current Short Vertical Monopoles with and without a Top Hat. Top Hat forces current to be nearly uniform along antenna. Radiation resistance increased with a Top Hat. Current Ground Top Hat L L Short Vertical Monopoles Base Fed

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5/5/2015David Conn VE3KL15 D Top View Side View Ground Monopole Voltage Source Monopoles Receive Equal Power L Star-H Vertical Cage Concept Similar to Folded Dipole Closely Spaced Tightly Coupled Big Increase in Rr, B and Efficiency

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Radiation Resistance Basic Vertical Elements Small Current Element….basic element Short Vertical Monopole…no top hat Short Vertical Monopole…ideal top hat 5/5/2015David Conn VE3KL16

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Radiation Resistance (Rr) Basics…..Small Current Element 5/5/2015David Conn VE3KL17 I o COS(2πf o t) L metres long Power Radiated = I o 2 R r /2 [Watts]

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Radiation Resistance (Rr) Small Current Element..Example L/λ = 0.05 Io = 5.0 Amps 5/5/2015David Conn VE3KL18 I o COS(2πf o t) 30 metres long PowerRadiated = I o 2 R r /2 = 25 [Watts] Rr = 2 [Ohms]

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Short Vertical Monopole A Simple Basic Antenna L/λ = 0.05 5/5/2015David Conn VE3KL19 Current varies linearly on antenna Approximately 16 Ground Radials Rr = 1.0 Ohm H=L L= 30 metres @500 KHz

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Short Vertical Monopole Efficiency 5/5/2015David Conn VE3KL20 ON7YD Diagram Short Vertical Monopole Current varies linearly on antenna Length = 30 metres Frequency = 500 KHz Rrad = 1.0 Ohm, Rloss = 21 Ohms (Typical Measured) Efficiency = 1.0/22 = 0.045 = 4.5% (-13 dB) L = H

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Short Vertical Monopole Capacitance L=30 m 5/5/2015David Conn VE3KL21 H = L L = length [m] d = wire diameter [m] Cv in pF Example fo = 500 KHz, L = 30 m, d = 0.001m: Cv = 158 pF Xo = 1/(2πfoCv) = 2015 Ohms Rg must be measured

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5/5/2015David Conn VE3KL22 Rr +RlossCvTuning CoilTransMatch SWR Antenna Bandwidth: Frequency range between specified SWR level Antenna Bandwidth Vertical Antennas (Radio Definition…SWR based) SWR B 1.0 2.0 SWR =1.0 @ fo fo

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Antenna Bandwidth Vertical Antennas (Radio Definition…SWR based) 5/5/2015David Conn VE3KL23 B is the Bandwidth [Hz] R is the input resistance of the antenna [Ohms] Xo is the input reactance of the antenna [Ohms] fo is the operating frequency [Hz] SWR is the maximum permissible SWR Example: SWR = 2:1, R = 22, Xo = 2015, fo = 500 KHz B = 3.8 KHz……. Very low….poor for high speed data communications

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5/5/2015David Conn VE3KL24 Example: Vertical Antenna No Top Hat Height = 0.05 wavelengths SWR = 2.0 R antenna = 22 Ω Xo = 2015 Ω BW = 3.8 KHz Bandwidth.. Vertical No Top Hat Our Range

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5/5/2015David Conn VE3KL25 Bandwidth.. Vertical No Top Hat Narrow Bandwidth creates Temperature and Drifting problems Narrow Bandwidth sets limits on the Transmission Data Rate Lowering loss resistance lowers the Bandwidth Bandwidth dominated by loss resistance

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5/5/2015David Conn VE3KL26 Summary Vertical No Top Hat fo = 500 KHz L = 30 metres Max. SWR = 2:1 Rr = 1.0 Ohms, Cv = 158 pF Rloss = 21 Ohms……based on measurements of SM6BGP Efficiency = 1/22 = 0.045 = 4.5% (-13 dB) BW = 3.8 KHz

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Short Vertical Monopole with Top Hat 5/5/2015David Conn VE3KL27 Analysis for one Top Hat Element Approximate analysis..only vertical Ra considered Generally many Hats are used

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Short Vertical Monopole with ideal Top Hat Radiation Resistance 5/5/2015David Conn VE3KL28 Rr = 4.00 Ohms for 30 metre high antenna with ideal top hat Four times that of the Vertical With no top hat

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Short Vertical Monopole with ideal Top Hat Summary 5/5/2015David Conn VE3KL29 Increased Radiation Resistance Increased Capacitance Same Ground Loss Hence increased efficiency Increased Bandwidth

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5/5/2015David Conn VE3KL30 Summary..Radiation Resistance of Basic Elements Note the Vertical Scale 4 Ohms 1 Ohm

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5/5/2015David Conn VE3KL31 Good Time for a Break

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5/5/2015David Conn VE3KL32 D Top View Side View Ground Monopole Voltage Source Monopoles Receive Equal Power L Star-H Vertical Cage Concept Similar to Folded Dipole Closely Spaced Tightly Coupled Big Increase in Rr, B and efficiency

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5/5/2015David Conn VE3KL33 Star-H Vertical Cage Based on Closely Coupled Line Analysis (Ramo-Whinnery-VanDuzer) 12 1 Amp Zin = Z11 +Z12 Z12 ≈ Z11 for close coupling Zin = 2 Z11 Input impedance doubled

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Radiation Resistance Star-H Cage No Top Hat 5/5/2015David Conn VE3KL34 Increases with N

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Radiation Resistance Star-H Cage With Ideal Top Hat 5/5/2015David Conn VE3KL35 Increases with N Four times

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5/5/2015David Conn VE3KL36 Example: N = 8 L = 0.05 Rr = 7 Ohms Radiation Resistance Star-H Cage Note the Scale

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5/5/2015David Conn VE3KL37 Example: N = 8 L = 0.05 Rr > 25 Ohms Very Easy to Match Radiation Resistance Star-H Cage Note the Scale

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5/5/2015David Conn VE3KL38 Other Antennas Horizontal Dipole Radiation Resistance of ideal horizontal dipole over perfect ground gets very small.. the ground shorts out the electric filed Ra ≤ 2.0 Ohms for a λ/2 dipole 15 metres high @ 500 KHz High ground/copper loss produces very low efficiency

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5/5/2015David Conn VE3KL39 Example: Perimeter = p = 120 m λ = 600 m R A = 0.07 Ohms Small Loop Antenna Dual of the Short Dipole Small L L A 2 = L 4 R loss = 4ρL Ohms Source Wires

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5/5/2015David Conn VE3KL Inverted L Antenna An extension of the top hat vertical Both lines radiate Not easily analyzed ? Very commonly used with good results Amenable to simulation with NEC-4 Needs extensive radial system under the top portion Ground L2 L1 Source L1 + L2 = λ/4 Ra = 6 Ohms for L1 = 0.05λ

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5/5/2015David Conn VE3KL41 Bibliography ON4UN, Low-Band Dxing…..ARRL, get latest version Fields and Waves in Communication Systems, Ramo, Whinnery, Van Duzer, Third edition, John Wiley Star-H corporation ON7YD, SM6BGP, LX/PA6Z, SK6RUD web sites Cebik web site Presentation posted on ve3kl.com web site VE3XK, Ground-Mounted Verticals: West Carleton Amateur Radio Club web site

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5/5/2015David Conn VE3KL42 Summary Presented guidelines for selecting and designing 600 metre transmitting antennas Showed the relationship between Radiation Resistance, Bandwidth and Efficiency 73 Dave VE3KL

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