Can a Vertical antenna be used for NVIS?

A wire half-wave dipole trimmed for the frequency of use is very effective and also the most common type of antenna used for NVIS. To direct the greatest portion of the transmitted signal vertically, the antenna must be positioned relatively low to the ground.

What is NVIS in ham radio?

Near vertical incidence skywave, or NVIS, is a skywave radio-wave propagation path that provides usable signals in the distances range — usually 0–650 km (0–400 miles).

How do you impedance an antenna match?

Impedance matching is the process of designing the antenna’s input impedance (ZL) or matching it to the corresponding RF circuitry’s output impedance (ZO), which would be 50 Ω in most cases. A perfect match is obtained when ZL = ZO in Equation 2, which gives Γ a value of zero, and the SWR becomes unity in Equation 1.

What is a half-wave dipole?

A half-wave antenna (referred to as a dipole, Hertz, or doublet) consists of two lengths of wire rod, or tubing, each 1/4 wavelength long at a certain frequency. It is the basic unit from which many complex antennas are constructed. For a dipole, the current is maximum at the center and minimum at the ends.

At what frequencies does Nvis occur?

NVIS communication uses frequencies between approximately 3 and 10 MHz. A comprehensive overview of NVIS research is given, covering propagation, antennas, diversity, modulation and coding.

What is Nvis night vision?

Night Vision Imaging System (NVIS): A system that integrates all elements necessary to successfully and safely operate a with NVGs. The system includes NVGs, NVIS compatible lighting and other components.

When does the impedance of a NVIS dipole drop?

However the impedance drops by a factor of four (to 12 ohms) when it is lowered to 7 feet ( https://www.w9xt.com/page_radio_gadgets_nvis_antenna.html ). (Note: the author’s numbers seem not to correlate with his factor, but at any rate the impedance drops very low).

Which is the best NVIS antenna to use?

The best NVIS antenna is one which is simple and effective. One favorite is the dual-band dipole. This antenna uses two dipoles, one for 75 meters (about 122 feet), and one for 40 meters (about 65 feet), both connected directly to 50-ohm coax and supported at 5 points by trees at 10-12 feet.

How long is the NVIS dipole feed cable?

The center post holds a plastic box with a current choke made of 13 turns bifilar on an FT140-61 torroid. The feed cable is 66 feet long. I tested it for SWR in the 40-meter band at 10 watts and was able to get SWR of 4:1 at 7.280 MHz, 2:1 at 7.150, and 1.3 at 7.000 MHz.

Which is the best near vertical incident antenna?

Near Vertical Incident Skywave antennas (better known as NVIS antennas) are one of the most viable antenna possibilities that survivalists might use. They are quick to deploy, easily maintained, and are high performance antennas as well.

Can a vertical antenna be used for NVIS?

A wire half-wave dipole trimmed for the frequency of use is very effective and also the most common type of antenna used for NVIS. To direct the greatest portion of the transmitted signal vertically, the antenna must be positioned relatively low to the ground.

What’s the deal about NVIS?

The HF band (3-30 MHz) with Near Vertical Incidence Skywave (NVIS) allows a large coverage area (up to 250 Km) without the need of line of sight. The HF radio links usually need higher power transmissions with larger antennas supported by a mast.

What is meant by critical frequency?

Critical frequency is the highest magnitude of frequency above which the waves penetrate the ionosphere and below which the waves are reflected back from the ionosphere. Its value is not fixed and it depends upon the electron density of the ionosphere.

What is NVIS radio?

Near vertical incidence skywave, or NVIS, is a skywave radio-wave propagation path that provides usable signals in the distances range — usually 0–650 km (0–400 miles).

What is Near Vertical Incidence Skywave NVIS propagation?

What is Nvis amateur radio?

Is Nvis real?

What is an NVIS?

The New Vehicle Information Statement (NVIS) is a record of a new vehicle and provides basic information on the vehicle, the manufacturer/importer, the authorized dealer who sells it, and on the initial purchaser.

How tall does an antenna need to be for NVIS?

Fortunately, installing an antenna with maximum radiation straight up isn’t difficult: a dipole or other horizontally polarized antenna at heights below about 3/8 wavelength will have this type of pattern. Many simple NVIS antennas will have a broad upwards beamwidth, so there is significant radiation even at 60 degrees.

Which is the highest frequency needed for NVIS?

NVIS isn’t just about antennas: it is a communications system that permits coverage up to 500 km (300 miles) or so using relatively low power equipment. To do so, the operating channels must be below the Critical Frequency, the highest frequency where signals radiated straight up will be returned to Earth by the ionosphere.

How are radio waves reflected from the NVIS antenna?

• Due to design the NVIS antenna transmits radio waves vertically (75‐90 degrees from earth’s surface)to the ionosphere where they are reflected back to earth in a circular pattern centered around the antenna.   This propagation is for those frequencies that are most likely to be reflected by the ionosphere.

How is a near vertical incident skywave antenna designed?

A properly designed Near Vertical Incident Skywave (NVIS) antenna will have a directivity pattern that will maximize transmission and reception at high angles while rejecting low angle, long range noise. Further, this antenna must be tunable over at least an octave of frequency to track the local Critical Frequency (CF).