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Small 500 KHz Transmitting Antennas VE3KL

Small 500 KHz Transmitting Antennas VE3KL. Top Hat. Insulated Base. Vertical 500 KHz Antenna….. Courtesy (Gunnar SM6BGP) Height = 30 metres R (antenna) = 22 Ohms ….. measured. Many Possible Antenna Types. Gunnar….SM6BGP. N Monopoles Separately Fed Closely Spaced STAR-H Patent.

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Small 500 KHz Transmitting Antennas VE3KL

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  1. Small 500 KHz Transmitting AntennasVE3KL Top Hat Insulated Base Vertical 500 KHz Antenna….. Courtesy (Gunnar SM6BGP) Height = 30 metres R (antenna) = 22 Ohms ….. measured David Conn VE3KL

  2. Many Possible Antenna Types Gunnar….SM6BGP N Monopoles Separately Fed Closely Spaced STAR-H Patent 6/10/2014 David Conn VE3KL

  3. Presentation Outline Basics..Radiation Resistance, Efficiency, Bandwidth Vertical Antennas Inverted L Antenna…..briefly Loop Antennas Other types including the Horizontal Dipole Bibliography 6/10/2014 David Conn VE3KL 3

  4. 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) 6/10/2014 David Conn VE3KL 4

  5. The Problem Selecting and Designing reasonably sized transmitting antennas for 600 metre wavelength amateur radio applications. 6/10/2014 David Conn VE3KL 5

  6. 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 6/10/2014 David Conn VE3KL 6

  7. Design Issues(Small Antennas) Radiation/Ground Resistance Bandwidth Efficiency 6/10/2014 David Conn VE3KL 7

  8. 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 6/10/2014 David Conn VE3KL 8

  9. Radiation Resistance, RrDefinition Prad = Io2Rr/2 [Watts] Prad = Power radiated from an antenna I = IoCos(2πft) Rr for a half wave dipole = 73 Ohms 6/10/2014 David Conn VE3KL 9

  10. Antenna Efficiency Rr = Radiation Resistance RLoss = copper loss plus ground loss Efficiency = Rr/Rloss (for small Rr) Doubling Rr doubles the antenna efficiency David Conn VE3KL 6/10/2014 10

  11. Antenna Efficiency Rr = radiation resistance…….Rloss = loss resistance Example: Rrad = 0.5 Ohms, Rloss = 22 Ohms Efficiency = 0.5/22.5 = 0.022 = 2.2% (-17dB) 6/10/2014 David Conn VE3KL 11

  12. Antenna Bandwidth SWR B 2.0 1.0 • Several ways to define Bandwidth: 3 dB, SWR, Return Loss • Calculated from Antenna Equivalent Circuit • Can be very small ( 1 KHz ) for small antennas Example B = 4 KHz for SWR = 2:1 Frequency 6/10/2014 David Conn VE3KL 12

  13. 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 6/10/2014 David Conn VE3KL 13

  14. L L Short Vertical Monopoles Base Fed Top Hat Current Current Ground Short Vertical Monopoles with and without a TopHat. Top Hat forces current to be nearly uniform along antenna. Radiation resistance increased with a Top Hat. 6/10/2014 David Conn VE3KL 14

  15. Star-H Vertical Cage Concept Similar to Folded Dipole Monopoles Receive Equal Power Closely Spaced Tightly Coupled D Top View Monopole Side View L Voltage Source Ground Big Increase in Rr, B and Efficiency 6/10/2014 David Conn VE3KL 15

  16. Radiation ResistanceBasic Vertical Elements Small Current Element….basic element Short Vertical Monopole…no top hat Short Vertical Monopole…ideal top hat 6/10/2014 David Conn VE3KL 16

  17. Radiation Resistance (Rr)Basics…..Small Current Element IoCOS(2πfot) L metres long Power Radiated = Io2Rr/2 [Watts] 6/10/2014 David Conn VE3KL 17

  18. Radiation Resistance (Rr)Small Current Element..ExampleL/λ = 0.05 Io = 5.0 Amps IoCOS(2πfot) 30 metres long Rr = 2 [Ohms] PowerRadiated = Io2Rr/2 = 25 [Watts] 6/10/2014 David Conn VE3KL 18

  19. Short Vertical MonopoleA Simple Basic Antenna L/λ = 0.05 L= 30 metres @500 KHz H=L Current varies linearly on antenna Approximately 16 Ground Radials Rr = 1.0 Ohm 6/10/2014 David Conn VE3KL 19

  20. Short Vertical MonopoleEfficiency ON7YD Diagram Short Vertical Monopole L = H 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) 6/10/2014 David Conn VE3KL 20

  21. Short Vertical MonopoleCapacitance L=30 m Rg must be measured 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 6/10/2014 David Conn VE3KL 21

  22. SWR B 2.0 1.0 Antenna Bandwidth Vertical Antennas(Radio Definition…SWR based) Antenna TransMatch Tuning Coil Cv Rr +Rloss SWR Bandwidth: Frequency range between specified SWR level SWR =1.0 @ fo fo 6/10/2014 David Conn VE3KL 22

  23. Antenna BandwidthVertical Antennas(Radio Definition…SWR based) • 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 6/10/2014 David Conn VE3KL 23

  24. Bandwidth.. Vertical No Top Hat Example: Vertical Antenna No Top Hat Height = 0.05 wavelengths SWR = 2.0 Rantenna = 22 Ω Xo = 2015 Ω BW = 3.8 KHz Our Range 6/10/2014 David Conn VE3KL 24

  25. 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 6/10/2014 David Conn VE3KL 25

  26. 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 6/10/2014 David Conn VE3KL 26

  27. Short Vertical Monopole with Top Hat Analysis for one Top Hat Element Approximate analysis..only vertical Ra considered Generally many Hats are used 6/10/2014 David Conn VE3KL 27

  28. Short Vertical Monopole with ideal Top HatRadiation Resistance Four times that of the Vertical With no top hat Rr = 4.00 Ohms for 30 metre high antenna with ideal top hat 6/10/2014 David Conn VE3KL 28

  29. Short Vertical Monopole with ideal Top HatSummary Increased Radiation Resistance Increased Capacitance Same Ground Loss Hence increased efficiency Increased Bandwidth 6/10/2014 David Conn VE3KL 29

  30. Summary..Radiation Resistance of Basic Elements Note the Vertical Scale 4 Ohms 1 Ohm 6/10/2014 David Conn VE3KL 30

  31. Good Time for a Break 6/10/2014 David Conn VE3KL 31

  32. Monopoles Receive Equal Power D Top View Monopole Side View L Voltage Source Ground Star-H Vertical Cage Concept Similar to Folded Dipole Closely Spaced Tightly Coupled Big Increase in Rr, B and efficiency 6/10/2014 David Conn VE3KL 32

  33. Star-H Vertical Cage Based on Closely Coupled Line Analysis (Ramo-Whinnery-VanDuzer) Zin = Z11 +Z12 Z12 ≈ Z11 for close coupling Zin = 2 Z11 1 2 Input impedance doubled 1 Amp 1 Amp 6/10/2014 David Conn VE3KL 33

  34. Radiation Resistance Star-H CageNo Top Hat Increases with N 6/10/2014 David Conn VE3KL 34

  35. Radiation Resistance Star-H CageWith Ideal Top Hat Four times Increases with N 6/10/2014 David Conn VE3KL 35

  36. Radiation Resistance Star-H Cage Note the Scale Example: N = 8 L = 0.05 Rr = 7 Ohms 6/10/2014 David Conn VE3KL 36

  37. Radiation Resistance Star-H Cage Note the Scale Example: N = 8 L = 0.05 Rr > 25 Ohms Very Easy to Match 6/10/2014 David Conn VE3KL 37

  38. 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 6/10/2014 David Conn VE3KL 38

  39. Small Loop Antenna Dual of the Short Dipole L Example: Perimeter = p = 120 m λ = 600 m RA = 0.07 Ohms A2 = L 4 L Wires Source Small Rloss = 4ρL Ohms 6/10/2014 David Conn VE3KL 39

  40. 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 L2 L1 + L2 = λ/4 L1 Ground Source Ra = 6 Ohms for L1 = 0.05λ 6/10/2014 David Conn VE3KL

  41. 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 6/10/2014 David Conn VE3KL 41

  42. Summary • Presented guidelines for selecting and designing 600 metre transmitting antennas • Showed the relationship between Radiation Resistance, Bandwidth and Efficiency 73 Dave VE3KL 6/10/2014 David Conn VE3KL 42

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