KQ6XA Rule-of-Thumb: Optimum NVIS Transmit Antenna Height [复制链接]

kq6xa rule-of-thumb:
"optimum nvis transmit antenna height"
chart:
band | height above soil surface
80m = 60ft high
60m = 40ft high
40m = 30ft high
30m = 20ft high
20m = 15ft high

kq6xa rule-of-thumb
"optimum nvis transmit antenna height"
formula:
meter band x 0.75 = height in feet

kq6xa rule-of-thumb
"antenna height and transmit signal"
basic:
low antenna = weak transmit signal
high antenna = strong transmit signal

antenna height is measured at the feedpoint or
center of radiation of the driven element.
the type of earth ground affects the optimum height.
for more information about ground effects and using
a wire ground reflector for nvis, see my article:

"length of nvis dipole reflector wires in the field"
at
http://hflink.com/ground/

rule-of-thumb defined: an easily remembered
technique for estimation, used in the field,
to achieve a good result most of the time.

73--- bonnie kq6xa

the higher the better, yeah.

amen, hal…a “high dipole” is mounted half-wavelength or more above ground. for nvis work, mount the antenna wavelength or less above ground.

iow, an 80 meter dipole mounted 60-70 feet up is a good nvis antenna. most hams have their 80 meter antennas far below 100 feet up. a 40 meter dipole mounted below 35 feet is an nvis antenna. a lot of hams have nvis antennas and do not realize it!

nvis dipoles shoot strait up and it matters not what the orientation is. the signal is reflected back down to earth in an omni-directional fashion. a frequency for nvis operation must be chosen that is just below the current f0f2 layer at the time of operation. otherwise the signal will be attenuated below the optimum frequency, or will pass through to outer space when operating above the optimum frequency. the optimum frequency changes on an hourly basis. it takes two to three different bands to maintain nvis operation over a 24 hour period. the f0f2 chart must be consulted regularly to assure that the proper frequency is in use at any given time.



(((73)))

phil, k5pc