Near-Vertical Incidence Skywave (NVIS) is a radio signal propagation technique for achieving reliable coverage in all directions in a range of about 0-300 miles. Rather than trying to get the antenna to direct the signal straight to the receiving station's signal, the sending station will send the signal (nearly) vertical so the signal will hit the ionosphere and bounce (nearly) straight back down. Depending on time of day, time of year, and space weather conditions, the technique will work on frequencies in the range of 1-10 MHz.
NVIS Day is an annual operating event in the Ohio Section of the American Radio Relay League. Developed by Tim Price K8WFL, the event is an opportunity for field-expedient stations to construct, erect, and test antenna systems optimized for NVIS propagation to see what works best and under which conditions.
The Amateur Radio Emergency Service (ARES) program trains and coordinates volunteer amateur radio operators to establish and operate contingency and emergency communication stations when needed. The National Traffic System (NTS) is a standard set of procedures and schedule for the relay of messages from one station to another. Together, these give amateur radio the ability to provide reliable communications in the face over overload or other failure of communication infrastructure.
As the net for Ohio ARES District 7, a ten-county area including Franklin County and those surrounding it, Central Ohio Traffic Net works on NVIS Day to provide the circuits for radio communication among the counties, as well as to participating state agency stations in the served area.