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Idaho ARES - Near Vertical Incidence Skywave Propagation Presentation

Idaho ARES - Near Vertical Incidence Skywave Propagation Presentation. Dan Woodall, N7DKW Fred Bergen, KE7FIX. Basic Concepts. Propagation Antenna Types and Performance Antenna height and Take-off angle. Propogation. Line of Sight and Ground Waves Line of Sight and Ground Waves

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Idaho ARES - Near Vertical Incidence Skywave Propagation Presentation

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  1. Idaho ARES - Near Vertical Incidence Skywave Propagation Presentation Dan Woodall, N7DKW Fred Bergen, KE7FIX

  2. Basic Concepts • Propagation • Antenna Types and Performance • Antenna height and Take-off angle

  3. Propogation • Line of Sight and Ground Waves • Line of Sight and Ground Waves • Line of Sight and Ground Waves • Near Vertical Incidence Skywave Communications

  4. Line of Sight and Ground Waves • Radio waves traveling close to the earth. • Lower frequency radio waves bend around earth obstructions by refraction. • Radio shadows result

  5. Sky wave Communications • Reflecting radio waves off the Ionosphere layer of the earths atmosphere to extend radio communications beyond line of sight

  6. Traditional Skip Communications Traditional DX antennas are designed to produce signals at a low angle to the horizon for skip communications at 1000 miles or more. A radio shadow exists in the “Skip Zone” where communications are not possible.

  7. Near Vertical Incidence Skywave Communications • NVIS propagation extends from the transmitter out to several hundred miles • Range depends on power, antenna, and conditions.

  8. Layers and time of day

  9. Useful bands • Variables: • Sunspot Cycle • Solar Storms • Seasons • Time of Day

  10. Most NIVIS work can be done on 40 and 80 Meters • 40 meter • 7.025 – 7.125MHz Data, 300bps • 7.175 – 7.300MHz LSB • Usually Daytime Use • 80 Meter • 3.525 – 3.600MHz Data, 300bps • 3.800 – 4.000MHz LSB • Usually Night Time Use

  11. Maximum Usable Frequency (MUF) • The highest frequency that will reflect off the ionosphere and return to earth. • Frequencies higher than the MUF continue through the atmosphere into space, and are not usable for NVIS or other skywave communications.

  12. http://www.spacew.com/www/realtime.php

  13. Antenna height and Take-off Angle Low Take Off Angle Mounted high above the ground. High Take Off Angle (NVIS) Mounted 1/20th to 1/8 wavelength above the ground.

  14. NVIS Antennas • Most NVIS antennas are variations of the wire dipole. • Wire Dipole • Inverted V Whip arrangements are also used.

  15. Local Amateur talent using NVIS Fran Wilson W7HDI Recommendation: Inverted “V” 30’ at peak End of legs 2’ off of ground Adjust length of wire to resonate at 17m - 40m or use a tuner (such as SGC model SG230 "smart-tuner”).

  16. Example of Set up Example of inverted “V” Peak of “V” is ladder line fed. Mast Kit

  17. On-line sources • http://www.tactical-link.com/field_deployed_nvis.htm • http://www.qsl.net/wb5ude/nvis/#ant • http://www.ve3fyn.ca/nvis/ • http://www.hamuniverse.com/n4jaantennabook.html

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