[TMRA] NVIS operation this Saturday

[Stephen Bellner]

Saturday April 22nd at the Maumee No. 2 fire station after the 9 am 
general ARES meeting. NVIS activity will go into the afternoon. All are 
welcome to attend. we will be monitoring the 147.270 PL 103.5 repeater

73,

Steve/W8TER


NVIS Research Paper Available

A thorough and fully annotated discussion of Near Vertical Incidence 
Skywave (NVIS) is available in the research paper 
<https://link.springer.com/article/10.1007/s11235-017-0287-2>, "Radio 
Communication via Near Vertical Incidence Skywave Propagation: An 
Overview," by Ben A. Witvliet, PE5B/5R8DS, and Rosa Ma Alsina-Pagès.

First investigated in the 1920s, NVIS propagation was rediscovered 
during World War II as "an essential means to establish communications 
in large war zones such as the D-Day invasion in Normandy," the paper 
notes, adding that the US Army subsequently sponsored a lot of NVIS 
field research, especially between 1966 and 1973. More recently, NVIS 
has become a popular means to enable close-in communication on Amateur 
Radio HF bands between 3 and 10 MHZ. NVIS can be used for radio 
communication in a large area (200-kilometer radius) without any 
intermediate manmade infrastructure, and it has been found to be 
especially suited for disaster relief communication, among other 
applications, according to the paper.

"A comprehensive overview of NVIS research is given, covering 
propagation, antennas, diversity, modulation, and coding," the 
/Abstract/ explains. "Both the bigger picture and the important details 
are given, as well as the relation between them." As the paper describes 
it, in NVIS propagation, electromagnetic waves are sent nearly 
vertically toward the ionosphere, and, with appropriate frequency 
selection, these waves are reflected back to Earth.

"The great reflection height of 80 to 350 kilometers results in a large 
footprint and homogeneous field strength across that footprint," the 
paper says. "Due to the steep radiation angles large objects such as 
mountain slopes or high buildings cannot block the radio path."

As for NVIS antennas, the paper stipulates that important parameters are 
antenna diagram, polarization, and bandwidth. "As only high elevation 
angles contribute to NVIS propagation, optimizing the antenna diagram 
for these elevation angles will increase the effectively transmitted 
power and improve the signal-to-interference ratio at reception."