Williamson County ARES 2018 NVIS Exercise December 14

Williamson County ARES 2018 NVIS Exercise December 14, 2017 Jim Russell NQ 5 L

County Request What are the options for county wide communication if all repeaters are down? Assumes all other communications forms are also down.

Answer Near Vertical Incidence Skywave NVIS utilizes lower bands (75/80, 60, 40 meters) NVIS utilizes low to the ground antennas (1/8 to 1/4 wavelength)

Utilization Germans and Russians in WW II More recently by US forces

Why NVIS? Normal HF antennas are designed for long distances, with low angle of radiation With NVIS antennas we want a high angle of radiation so signals go almost straight up and then are reflected down near the point of origin In general, do the opposite of what you would do for DX operation

NVIS Challenges If it were just reflections back to the ground, why not just use 75/80 M, or 40 M, or 20 M? There is a “Critical Frequency” that generally goes up with sunlight as the sun excites the ionosphere. As sunlight excites the atmosphere, absorption increases at the lower frequencies The “best” frequency is the one just below the Maximum Useable Frequency (MUF)

Austin Ionosonde

Austin Ionosonde

Exercise Objectives Locations: Approximately in the four corners of the county and the ESOC Net control NOT at any of these locations Antennas: 80 -60 -40 M trapped dipole 80 ft. random length with automatic tuner at the antenna Others as available

Exercise Objectives Voice: Establish links across the county and with the ESOC Record signal strength and readability for all stations at all stations Net control station for coordination VHF net for technical assistance

Exercise Objectives Data (WINLINK): Exchange emails with all stations utilizing N 5 TW disconnected from the Internet Establish a connection with an Internet connected server outside the local area

Exercise Details Advise adjacent counties of the exercise in case they want to participate. They are NOT part of the actual exercise. Proposed timing: January 27 or February 3, 2018 Trial run with all stations one week before

Exercise Issues Availability of operators trained in the use of Pactor modems and RMS Express Availability of antennas (antennas lost and parts no longer commercially available) and antenna tuners (limited to one or two specific models of tuners for commonality). Availability of suitable locations Most of all, availability of ARES members wanting to participate. We’d like five or so operators at each location.

The End � Questions and Comments?