[Elecraft] NVIS HF vs VHF line-of-sight & CB

[Jim Brown]

On Sun,4/30/2017 11:34 AM, kevinr at coho.net wrote:
> Plus the antennas can be ad hoc - tossed into trees or even an old 
> fence line.

There's a bit of fiction in the belief that antennas must be very low 
for NVIS. Fact is that higher is better, up to a quarter wave. The 
optimum height for a horizontal antenna for NVIS is a quarter wave 
length, and performance declines only slightly (1 dB) up to 3/8 
wavelength. High angle radiation for an antenna a quarter wave high is 
4dB stronger than for one at one-tenth wavelength high. Thus, optimum 
heights are 30 ft for 40M, 60 ft for 80M, and high angle radiation is 
only 1dB down for 45 ft on 40M and 90 ft on 80M.

http://k9yc.com/AntennaPlanning.pdf  addresses this with a table and 
graphs. See Fig 36 and Table 1 on page 11.

73, Jim K9YC