NVIS
Near Vertical Incidence Skywave
Antennas
- What is NVIS?
- Applications of NVIS
- Antennas for NVIS
- dipole
- Hard to beat for NVIS
- Highest theoretical gain: .25 wavelengths above ground
- About 33 feet for 40m
- About 67 feet for 80m
- About 3 dB down at .1 wavelengths above ground
- About 13 feet for 40m
- About 27 feet for 80m
- L. B. Cebik W4RLN (SK) modelling suggests ideal height of .175 wavelengths.
- About 22 feet for 40m
- About 41 feet for 80m
- Gain drops sharply at lower heights, but is still NVIS
- Not too unusual to work OK with antenna about head high
- OK to let feedpoint sag a few feet
- Better NVIS performance with dipoles > 1/2 wavelength
- About 1.6 dB for full wave
- About 3 dB for extended double zepp
- Reflector .15 wavelengths below dipole may help.
- Suggestion: jumpered multi-band
- Inverted V
- Only one high support required; directly supports feedline
- Keep included angle >= 120 degrees
- Not suitable for antennas > .5 wavelength long
- Perhaps dual inverted Vs for 40 and 80 with common feedpoint
- End-fed half-wave
- Propagationally similar to half-wave dipole or inverted-V
- No elevated feedline/support required
- Feed with balun transformer or outboard ATU
- Problems with efficiency and/or common mode feedline radiation
- Inverted-L
- End-fed
- 1/4 wave (radials important) to 1/2 wave (radials optional)
- Good low and high angle performer
- Full-wave horizontal loop
- horizontal 1/4-wave wire on mobile mount center conductor
- AS-2259
- Mythical miracle NVIS antenna: Do not buy the myth!
- Actually mediocre vertical gain.
- Two dipoles (four wires) from 15' center support, inv-V style
- Optimized for:
- frequency agility
- ease of deployment
- Not exceptional NVIS gain
- Shirley dipole array
- NVIS Frequency Selection
