When is the best time to use a NVIS amplifier?
It is common for amplifiers to be employed by NVIS operators in the high daylight part of the day when the D-layer absorption attenuates signals more severely. NVIS propagation minimizes transit through the D-layer with steep angles.
What are the factors that affect the NVIS technique?
The NVIS technique relies upon a combination of station factors, most importantly the frequency used, the power of transmissions, and the antenna configuration. Let’s consider each of these three factors in the context of the NVIS technique. Frequency: The refractive effects of the ionosphere vary with frequency.
How tall do you have to be to use NVIS?
Height above ground is usually less than ¼ wavelength for the NVIS technique, and much lower heights are preferred by many operators due to reported performance improvement. A height of 1/8 to 1/10 wavelength is often used for effective NVIS.
What kind of antenna do you need for NVIS?
Half-wave dipole antennas are great for NVIS, positioned a fraction of a wavelength above the ground. To direct the greatest portion of the transmitted signal vertically, the antenna must be positioned relatively low to the ground.
Can a good NVIS antenna work at DX distances?
– 2 – A good NVIS antenna will not work well at DX distances. Antenna gain is a zero sum game. There is a fixed amount of energy radiating. If we push it all out in one direction (the near-vertical angles), we have to take it away from another direction (the low DX angles).
Which is the best NVIS mode for HF?
Using no skip zone or ground wave, the NVIS mode is used for making reliable HF communications below 10 MHz effective for a range to 600 miles. The NVIS propagation mode works best on HF below 10 MHz since these high angle radio waves are reflected back to Earth.
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How does NVIS work in the ionosphere?
NVIS only works at frequencies from 2 MHz to 10 MHz. The signal must penetrate the D layer of the ionosphere, and bounce off the F layer. Lower-frequency signals will not penetrate the D layer; higher frequencies will not bounce off the F layer at these sharp angles and just goes out into space.