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Welcome to B.A.R.K.’s TECHNICIAN CLASS. Antennas # 18. Transmitted signals contain two fields, the electrical field and the magnetic field. The antenna’s polarization is based on the electrical field. If the electrical field is vertical we say the antenna polarization is vertical.

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Presentation Transcript
slide2

Transmitted signals contain two fields, the electrical field and the magnetic field. The antenna’s polarization is based on the electrical field.

  • If the electrical field is vertical we say the antenna polarization is vertical.
slide3

Antenna types – Vertical, Horizontal

A vertical antenna is an antenna that consists of a single element mounted perpendicular to the Earth's surface.

An example of a horizontal antenna is a dipole mounted so the elements are parallel to the Earth's surface.

slide4

Many hams start with a simple half-wave dipole antenna. To calculate the length required used the formula :

468 divided by frequency in Megahertz = Length in feet

The radiation pattern for a dipole antenna is always broadside to the antenna wire.

slide5
Relationships between antenna length and frequency
    • The physical size of half-wave dipole antenna becomes shorter as the operating frequency increases.
    • The approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz is 19 inches. [Remember the relationship between wavelength and frequency.]
    • The approximate length, in inches, of a 6-meter half- wavelength wire dipole antenna is 112 inches. [Remember the relationship between wavelength and frequency.]
slide6

Length of vertical in feet =

234

f (MHz)

The vertical element is ¼ of the wavelength, the radials are

¼ wavelength. Together they make a half wavelength antenna.

Feed Point

2 Meter-

¼ Wave 19”

6 meter-

½ Wave 112”

Feed Point

¼ Wave Radials

½ Wave Radials

slide7
A beam antenna is an antenna that concentrates signals in one direction.
  • The quad, yagi, and dish are all types of directional or beam antennas.

The yagi pictured has 3 elements.

The longest element is the reflector.

The middle element, where the transmission line is connected, is the driven element.

The shortest element is called the

director.

The lengths of the elements and spacing

Between them is critical to performance.

radio directing finding
Radio Directing Finding

The best type of antenna to use for locating interfering signals or a hidden transmitter hunt would be a directional antenna. The narrower the beam width the better!

slide9

The gain of an antenna is the increase in signal strength in a specified direction when compared to a reference antenna.

Two reference antennas:

Isotropic radiator- an antenna in free space (dbi)

Dipole antenna- a theoretically perfect antenna (dbh)

antennas
Antennas

The take-off angle of an antenna is important to performance. The lower the take-off angle the further the signal travels before it’s reflected off the ionosphere.

Vertical antennas usually have lower take-off angles than

dipoles or yagi’s. An antenna that has a high take-off angle

is called a “Near Vertical Incidence” (NVIS) antenna.

slide11

The best type of antenna to use when working with weak signal CW or SSB signals on the VHF and UHF bands is a horizontally polarized antenna.

If the antennas are cross-polarized then the received signal will be significantly weaker.

slide13

T9A03 Which of the following describes a simple dipole mounted so the conductor is parallel to the Earth's surface?A. A ground wave antennaB. A horizontally polarized antennaC. A rhombic antennaD. A vertically polarized antenna

slide14

T9A03 (B)Which of the following describes a simple dipole mounted so the conductor is parallel to the Earth's surface?A. A ground wave antennaB. A horizontally polarized antennaC. A rhombic antennaD. A vertically polarized antenna

slide15

T9A10 In which direction is the radiation strongest from a half-wave dipole antenna in free space?A. Equally in all directionsB. Off the ends of the antennaC. Broadside to the antennaD. In the direction of the feedline

slide16

T9A10 (C)In which direction is the radiation strongest from a half-wave dipole antenna in free space?A. Equally in all directionsB. Off the ends of the antennaC. Broadside to the antennaD. In the direction of the feedline

slide17
T9A09 What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna?A. 6B. 50C. 112D. 236
slide18
T9A09 (C)What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna?A. 6 B. 50C. 112D. 236
slide19

T9A05 How would you change a dipole antenna to make it resonant on a higher frequency?A. Lengthen itB. Insert coils in series with radiating wiresC. Shorten itD. Add capacity hats to the ends of the radiating wires

slide20

T9A05 (C)How would you change a dipole antenna to make it resonant on a higher frequency?A. Lengthen itB. Insert coils in series with radiating wiresC. Shorten itD. Add capacity hats to the ends of the radiating wires

slide21

T9A02 Which of the following is true regarding vertical antennas?A. The magnetic field is perpendicular to the EarthB. The electric field is perpendicular to the EarthC. The phase is invertedD. The phase is reversed

slide22

T9A02 (B)Which of the following is true regarding vertical antennas?A. The magnetic field is perpendicular to the EarthB. The electric field is perpendicular to the EarthC. The phase is invertedD. The phase is reversed

slide23
T9A08 What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?A. 112B. 50C. 19D. 12
slide24
T9A08 (C)What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?A. 112B. 50C. 19D. 12
slide25

T9A06 What type of antennas are the quad, Yagi, and dish?A. Non-resonant antennasB. Loop antennasC. Directional antennasD. Isotropic antennas

slide26

T9A06 (C)What type of antennas are the quad, Yagi, and dish?A. Non-resonant antennasB. Loop antennasC. Directional antennasD. Isotropic antennas

slide27

T9A01 What is a beam antenna?A. An antenna built from aluminum I-beamsB. An omnidirectional antenna invented by Clarence BeamC. An antenna that concentrates signals in one directionD. An antenna that reverses the phase of received signals

slide28

T9A01 (C)What is a beam antenna?A. An antenna built from aluminum I-beamsB. An omnidirectional antenna invented by Clarence BeamC. An antenna that concentrates signals in one directionD. An antenna that reverses the phase of received signals

slide29

T8C01 Which of the following methods is used to locate sources of noise interference or jamming?A. EcholocationB. Doppler radar C. Radio direction findingD. Phase locking

slide30

T8C01 (C)Which of the following methods is used to locate sources of noise interference or jamming?A. Echolocation B. Doppler radarC. Radio direction findingD. Phase locking

slide31

T8C02 Which of these items would be useful for a hidden transmitter hunt?A. Calibrated SWR meterB. A directional antennaC. A calibrated noise bridgeD. All of these choices are correct

slide32

T8C02 (B)Which of these items would be useful for a hidden transmitter hunt?A. Calibrated SWR meterB. A directional antennaC. A calibrated noise bridge D. All of these choices are correct

slide33

T3A05 When using a directional antenna, how might your station be able to access a distant repeater if buildings or obstructions are blocking the direct line of sight path?A. Change from vertical to horizontal polarizationB. Try to find a path that reflects signals to the repeaterC. Try the long pathD. Increase the antenna SWR

slide34

T3A05 (B)When using a directional antenna, how might your station be able to access a distant repeater if buildings or obstructions are blocking the direct line of sight path?A. Change from vertical to horizontal polarizationB. Try to find a path that reflects signals to the repeaterC. Try the long pathD. Increase the antenna SWR

slide35

T9A11 What is meant by the gain of an antenna?A. The additional power that is added to the transmitter powerB. The additional power that is lost in the antenna when transmitting on a higher frequencyC. The increase in signal strength in a specified direction when compared to a reference antennaD. The increase in impedance on receive or transmit compared to a reference antenna

slide36

T9A11 (C)What is meant by the gain of an antenna?A. The additional power that is added to the transmitter powerB. The additional power that is lost in the antenna when transmitting on a higher frequencyC. The increase in signal strength in a specified direction when compared to a reference antennaD. The increase in impedance on receive or transmit compared to a reference antenna

slide37

T3A03 What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands?A. Right-hand circularB. Left-hand circularC. HorizontalD. Vertical

slide38

T3A03 (C)What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands?A. Right-hand circular B. Left-hand circularC. HorizontalD. Vertical

slide39

T3A04 What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?A. The modulation sidebands might become inverted.B. Signals could be significantly weaker.C. Signals have an echo effect on voices. D. Nothing significant will happen.

slide40

T3A04 (B)What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?A. The modulation sidebands might become inverted.B. Signals could be significantly weaker.C. Signals have an echo effect on voices. D. Nothing significant will happen.

thank you

Thank You !

Antennas # 18