Transcript NVIS Propagation - Colorado ARES of Douglas and Elbert

NVIS Propagation
Ron Hranac, N0IVN
NVIS Propagation
• VHF and UHF simplex and repeater
operation can provide generally reliable
local and regional communications
• But these modes are limited to line-ofsight!
Line-of-Sight Propagation
Source: http://www.ycars.org
NVIS Propagation
• What happens if there is no repeater
coverage available, and VHF/UHF
simplex doesn’t work because of
terrain obstructions or distance?
• Is there an option for regional or
statewide radio communications?
NVIS Propagation
• The solution? NVIS
•Near vertical incidence skywave
•RF propagation suited for close-in radio
communications, typically in the 50-300
miles range
• Ideal for regional or statewide
communications in the MF and HF
spectrum
• Works well in rugged terrain where
line-of-sight communications is difficult
or impossible
Ionospheric Propagation
Source: http://www.radio-electronics.com
Ionospheric Propagation
300 mile radius coverage
Source: http://www.mapquest.com
Dipole Radiation Pattern vs. Height
Source: http://www.moonraker.com.au
NVIS Frequencies
• Amateur bands in the lower part of the HF
spectrum
75 meters/80meters
60 meters
40 meters
• In Colorado, 80 meters and 60 meters are
likely to provide the most reliable NVIS
communications
North America Ionospheric Map
Source: Australian Government IPS Radio and Space Services
http://www.ips.gov.au/HF_Systems
Hourly Area Predictions (HAP) Chart
Source: Australian Government IPS Radio and Space Services
http://www.ips.gov.au/HF_Systems
NVIS Antennas
• Full-size half-wave dipole
• Reduced-length half-wave dipole (that is,
trapped or inductively loaded)
• Multi-band dipole
•
End-fed random wire
• Full- or half-wave square
• Dual Hamstick dipole or Buddipole
NVIS Antenna Height
“The Near Vertical Incident Skywave (NVIS)
antenna is a half-wave dipole antenna mounted not
over 1/8th wave above ground (at the highest
operating frequency). While 1/8th wave works
reasonably well, better coverage is obtained if the
antenna is mounted at about 1/20th wavelength
above ground. A second advantage of lowering the
antenna to near 1/20th wavelength is a lowering of
the background noise level.”
Pat Lambert, W0IPL
NVIS References
“Near Vertical Incident Skywave (NVIS) Antenna” by Pat Lambert, W0IPL
http://www.w0ipl.com/ECom/NVIS/nvis.htm
“NVIS - What it is and how to use it” by Patricia Gibbons, WA6UBE
http://www.tactical-link.com/field_deployed_nvis.htm
“Some Notes on NVIS Cloud Burners” by L.B. Cebik, W4RNL
http://www.cebik.com/wire/cb.html
“Make A Quick, Easy, Cheap, NVIS Antenna for Roadside Operating” by D.
W. Thorne, K6SOJ
http://www.emcomm.org/projects/nvis.htm
Australian Government IPS Radio and Space Services
http://www.ips.gov.au/HF_Systems