NVIS

Near Vertical Incidence Skywave

Advantages and Disadvantages

1. What is NVIS?
   • NVIS = High "angle of radiation" or "takeoff angle"
   • NVIS = no skip zone!
   • NVIS coverage = 0 - 300 miles
   • The magic is in:
     • Antenna (e.g. horizontal wire antenna .05 - .25 wavelengths above ground)
     • Right frequency at the right time
     • Coordinating with other parties about freq/time
     • High power (or digital modes) when conditions are marginal
   • NVIS propagation details
   • NVIS advantages & disadvantages

     Among the advantages of NVIS are:

     • NVIS covers the area which is in the skip zone on higher frequencies.
     • NVIS requires no infrastructure such as repeaters or satellites.
     • Pure NVIS propagation is relatively free from fading.
     • Antennas optimized for NVIS are usually low. Simple dipoles work well.
     • Low areas and valleys are no problem for NVIS propagation.

     Disadvantages of NVIS operation include:

     • For best results, both stations should be optimized for NVIS operation.
       • This includes having an antenna which performs well for NVIS.
     • NVIS doesn't work on all HF frequencies.
     • Minimum of two different frequencies must be used to cover day & night.
     • Choice and coordination of frequencies takes some attention.
2. Applications of NVIS
3. Antennas for NVIS
4. NVIS Frequency Selection