1. Williamson County ARES 2018 NVIS Exercise
December 14, 2017
Jim Russell NQ5L

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

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

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

5. 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

6. NVIS Challenges
If it were just reflections back to the ground, why not just use 75/80M, or 40M, or 20M?
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)

7. Austin Ionosonde

8. Austin Ionosonde

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

10. 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

11. Exercise Objectives Data (WINLINK):
Exchange s with all stations utilizing N5TW disconnected from the Internet
Establish a connection with an Internet connected server outside the local area

12. 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

13. 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.

14. The End
Questions and Comments?