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Space Challenged NVIS Antenna

75M. 40M. Space Challenged NVIS Antenna. Tom Sanders, W6QJI Ed Bruette, N7NVP. Near Vertical Incident Skywave. Cloud Warmer. What is NVIS?. Propagation Theory. Propagation Theory. NVIS Effect. 300 Mile Coverage. Propagation Considerations. “D” layer losses

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Space Challenged NVIS Antenna

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  1. 75M 40M Space Challenged NVIS Antenna Tom Sanders, W6QJI Ed Bruette, N7NVP

  2. Near Vertical Incident Skywave Cloud Warmer What is NVIS?

  3. Propagation Theory

  4. Propagation Theory

  5. NVIS Effect

  6. 300 Mile Coverage

  7. Propagation Considerations • “D” layer losses • Ionospheric scattering for vertical propagation • Importance of critical frequency

  8. These maps refresh every 5 mins

  9. Does this look like your neighborhood?

  10. Can you spot the antenna?

  11. 75Meters 40 Meters Left side of dual band

  12. Computer Simulation EZNEC Ver. 4.0 High Accuracy Mode

  13. Wire layout Fence line Feed point Fence line Fence line

  14. Top down view Fence line Feed point

  15. 75 Meter SWR 4.0

  16. Bandwidth 75 Meters • 4050 – 2:1 • 3960 – dip • 3860 – 2:1

  17. 75 Meter Vertical Pattern

  18. 75 Meter Current Flow

  19. 40 Meter SWR

  20. 40 Meter Current Flow

  21. Bandwidth 40 Meters • 7190 – 2:1 • 7250 – dip • 7370 – 2:1

  22. 40 Meter Vertical Pattern

  23. Omni Pattern

  24. Depth of Current Penetration

  25. Feed Point Impedance vs. Height

  26. How It Went Together • Materials • Construction • Modifications

  27. Parts List • 1 Center insulator • 1 1.5” PVC Slip coupler • 2 or 3 Hose clamps • 14 ga. Insulated wire • 1 10’ TV mast • 1 5’ TV mast • Tie wraps as desired • 1 Fence stake • Coax to the shack W6QJI

  28. Feed point is at 15’

  29. End of 75M wires are 6’ above ground End of 40M wires are 4’ above ground

  30. Element Lengths • 75 Mtr legs = 57 ft • 40 Mtr legs = 39 ft • Prune these lengths to meet your ground conditions

  31. Beamwidth • 75 Mtrs 41 deg. To 139 deg. • 40 Mtrs 39 deg. To 141 deg.

  32. Night Time Ionosphere (300 mi.)

  33. Hints & tips • Solder wires at the feed point • Solder feed point pigtail to all other wires • Coax should be perpendicular to the antenna

  34. Hints & tips (cont.) • Ground conditions will drive element lengths • Wet vs.. dry • Use an antenna analyzer!!! • Tune 75M first, then 40M • Minimize the catenaries in the wires but not too tight – the wire will stretch • Maintain the spacing between the 75 & 40M elements

  35. Can 60M be Incorporated in This Antenna? • Of course!

  36. 60 Meter elements 48’ 48’ 15’ 6’ 6’ It’s as Easy as Adding 2 Elements!

  37. 60 Meter SWR

  38. SWR for all 3 Bands

  39. Not Enough Real Estate for a Dual Band? Try this!

  40. 32.25’ 32.25’ 4.5’ 15’ 4.5’ 40M wire Tunable on 75M

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