subelement t9 antennas and feed lines [2 exam questions - 2 groups] 1antennas & feedlines 2014

SUBELEMENT T9

Antennas and feed lines [2 Exam Questions - 2 Groups]

1Antennas & Feedlines 2014

T9A – Antennas: vertical and horizontal polarization; concept of gain; common portable and mobile antennas; relationships between antenna length and frequency

T9B – Feed lines: types of feed lines; attenuation vs. frequency; SWR concepts; matching; weather protection; choosing RF connectors and feed lines

2Antennas & Feedlines

Antenna Classifications

•Orientation–Horizontal – parallel to the Earth–Vertical – perpendicular to the Earth

•Directivity (Beam)–Yagi, Log Periodic, Quad, Dish

•Size–Wavelength – λ–½ λ, ¼ λ, ⅝ λ, …

3 Antennas & Feedlines

Horizontal AntennasHalf Wavelength Dipole Antenna)


Wavelength (meters) = Wavelength (meters) = 300 300 F (MHz)F (MHz)

Half wavelengthfrom formula

Open wirefeeder

Solder

Spacer

½½λλ Dipole length (inches) = Wavelength / 2 x 39 Dipole length (inches) = Wavelength / 2 x 39

Half wavelength

Meters to inches

½ λ Dipole Radiation


Radiation pattern for a dipole placed ½ λabove ground looking down from above the antenna.

Looks like a doughnut around the wire in 3D space.

Pattern distorts to omnidirectional when placed low to the ground.

Vertical AntennasQuarter Wavelength Vertical


Ground Plane

Ground Plane

Ground

Marconi

Radials

Wavelength (meters) = Wavelength (meters) = 300 300 F (MHz)F (MHz)

¼¼λλ vertical length (inches) = Wavelength / 4 x 39 vertical length (inches) = Wavelength / 4 x 39

Quarter wavelengthMeters to

inches

Quarter Wave Vertical Radiation


A side view of the radiation pattern of a 1/4 wave vertical. From above the pattern is round like a doughnut. A perfect ground would be the center of a metal car roof at VHF/UHF

Maximum Radiation AngleElevation0 dB= 5.10 dBi 7.150 MHz

Perfect Ground

Average Ground

Vertical Antenna


Standard ¼ wave vertical has a feedpoint impedance of ~35 ohms

Sloping ground radials downward raises feedpoint impedance

Beam AntennasYagi Antenna


GainGain

BoomBoom

Feed

line

Feed

line

Reflect

or

Reflect

or

Dir

ect

oD

irect

orr

Dri

ven

D

riven

Ele

men

tEle

men

t

The reflectorThe reflectoracts like a acts like a

mirrormirror

The directorThe directoracts like aacts like a

lenslens

Yagi Radiation Pattern


The yagi antenna focuses RF energy in one direction, giving the appearance ofgetting “free power.”

This free power or Effective Radiated Power (ERP) can be expressed as antenna Gain in Decibels (dB) over a dipole (dBd) or isotropic resonator (dBi).

G9 - Antennas1212Antennas & Feedlines

Quad antenna

G9 - Antennas1313Antennas & Feedlines

Delta Loop

Antenna Traps

•Dipole, vertical and yagi antennas can contain tuned traps in their driven elements. The traps block (or trap) energy of a given frequency making a physically longer appear shorter electrically.


In the dipole shown, any energy on the 15m band will stop at the 15m trap and the antenna will only appear to be the width of a 15m antenna. Similarly, 20m signals will stop at the 20m traps and only see the antenna between the traps. Only 40m signals will pass along the entire length.

Loaded Antennas

“Rubber duck” antennas are loaded antennas where the antenna is wound into a coil to shorten it physically. This is not an efficient radiator and narrows the bandwidth but does allow portable operation. This is particularly important on the HF bands.


The antennas on the left are called “screwdrivers” and use a motor and wiper inside the coil to adjust the amount of loading based on frequency. The center antenna has the whip attached with a “capacitance hat” to provide capacitance to counteract inductance in the load coil and improve performance.

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


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


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


T9A03 - Which of the following describes a simple dipole mounted so the conductor is

parallel to the Earth's surface?

A. A ground wave antenna

B. A horizontally polarized antennaC. A rhombic antennaD. A vertically polarized antenna


T9A04 - What is a disadvantage of the “rubber duck” antenna supplied with most handheld

radio transceivers?

A. It does not transmit or receive as effectively as a full-sized antennaB. It transmits a circularly polarized signalC. If the rubber end cap is lost it will unravel very quicklyD. All of these choices are correct


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 capacitive loading to the ends of the radiating wires


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 wires

C. Shorten itD. Add capacitive loading to the ends of the radiating wires


T9A06 - What type of antennas are

the quad, Yagi, and dish?

A. Non-resonant antennasB. Loop antennasC. Directional antennasD. Isotropic antennas


T9A06 - What type of antennas are

the quad, Yagi, and dish?

A. Non-resonant antennasB. Loop antennas

C. Directional antennasD. Isotropic antennas


T9A07 - What is a good reason not

to use a “rubber duck” antenna inside your car?

A. Signals can be significantly weaker than when it is outside of the vehicleB. It might cause your radio to overheatC. The SWR might decrease, decreasing the signal strengthD. All of these choices are correct


T9A08 - What is the approximate length,

in inches, of a quarter-wavelength vertical antenna for 146 MHz?

A. 112B. 50C. 19D. 12


Calculating Vertical Antenna Length

31Radio Waves, Propagation and

Antennas 2014

Precisely:

300 300 F (MHz)F (MHz)

= 300300146146

=

Approximately: 146 MHz is the 2m band

¼ of 2m is 0.5m1m is 39 inches, so 0.5m is 19.5 inches

Note this is based on free space wavelength. A wave traveling through wire will be slower and have a shorter wavelength. A physical antenna will be smaller.

2.05 meter wavelength

2.05 meters / 4 x 39 inches = 20 inches

T9A08 - What is the approximate length,

in inches, of a quarter-wavelength vertical antenna for 146 MHz?

A. 112B. 50

C. 19D. 12


T9A09 - What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire

dipole antenna?

A. 6B. 50C. 112D. 236


Calculating Dipole Antenna Length

34Radio Waves, Propagation and

Antennas 2014

Precisely:

Approximately: 6m band

½ of 6 m is 3 m1 meter is 39 inches, so 3 m is 117 inches

Note this is based on free space wavelength. A wave traveling through wire will be slower and have a shorter wavelength. A physical antenna will be smaller.

300 300 F (MHz)F (MHz)

= 3003005050

= 6 meter wavelength

(6 meters / 2) x 39 inches = 117 inches

T9A09 - What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire

dipole antenna?

A. 6B. 50

C. 112D. 236


Half Wavelength Dipole Antenna


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 feed line


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


T9A12 - What is a reason to use a properly

mounted 5/8 wavelength antenna for VHF or UHF mobile service?

A. It offers a lower angle of radiation and more gain than a 1/4 wavelength antenna and usually provides improved coverageB. It features a very high angle of radiation and is better for communicating via a repeaterC. The 5/8 wavelength antenna completely eliminates distortion caused by reflected signalsD. The 5/8 wavelength antenna offers a 10-times power gain over a 1/4 wavelength design


T9A13 - Why are VHF or UHF mobile

antennas often mounted in the center of the vehicle roof?

A. Roof mounts have the lowest possible SWR of any mounting configurationB. Only roof mounting can guarantee a vertically polarized signalC. A roof mounted antenna normally provides the most uniform radiation pattern D. Roof mounted antennas are always the easiest to install


T9A14 - Which of the following terms

describes a type of loading when referring to an antenna?

A. Inserting an inductor in the radiating portion of the antenna to make it electrically longerB. Inserting a resistor in the radiating portion of the antenna to make it resonantC. Installing a spring at the base of the antenna to absorb the effects of collisions with other objectsD. Making the antenna heavier so it will resist wind effects when in motion


G9C10 Which of the following is a Yagi antenna design variable that could be

adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth?

A. The physical length of the boomB. The number of elements on the boomC. The spacing of each element along the boomD. All of these choices are correct

47

G9C10 Which of the following is a Yagi antenna design variable that could be

adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth?

A. The physical length of the boomB. The number of elements on the boomC. The spacing of each element along the boom

D. All of these choices are correct

48

G9D01 What does the term "NVIS" mean as related to antennas?

A. Nearly Vertical Inductance SystemB. Non-Visible Installation SpecificationC. Non-Varying Impedance SmoothingD. Near Vertical Incidence Sky wave

49

G9D01 What does the term "NVIS" mean as related to antennas?

A. Nearly Vertical Inductance SystemB. Non-Visible Installation SpecificationC. Non-Varying Impedance Smoothing

D. Near Vertical Incidence Sky wave

50

G9D04 What is the primary purpose of antenna traps?

A. To permit multiband operationB. To notch spurious frequenciesC. To provide balanced feed-point impedanceD. To prevent out of band operation

51

G9D04 What is the primary purpose of antenna traps?

A. To permit multiband operationB. To notch spurious frequenciesC. To provide balanced feed-point impedanceD. To prevent out of band operation

52

G9D05 What is the advantage of vertical stacking of horizontally polarized Yagi

antennas?

A. Allows quick selection of vertical or horizontal polarizationB. Allows simultaneous vertical and horizontal polarizationC. Narrows the main lobe in azimuthD. Narrows the main lobe in elevation

53

G9D05 What is the advantage of vertical stacking of horizontally polarized Yagi

antennas?

A. Allows quick selection of vertical or horizontal polarizationB. Allows simultaneous vertical and horizontal polarizationC. Narrows the main lobe in azimuth

D. Narrows the main lobe in elevation

54

G9D06 Which of the following is an advantage of a log periodic antenna?

A. Wide bandwidthB. Higher gain per element than a Yagi antennaC. Harmonic suppressionD. Polarization diversity

55

G9D06 Which of the following is an advantage of a log periodic antenna?

A. Wide bandwidthB. Higher gain per element than a Yagi antennaC. Harmonic suppressionD. Polarization diversity

56

G9D10 Which of the following describes a Beverage antenna?

A. A vertical antenna constructed from beverage cansB. A broad-band mobile antennaC. A helical antenna for space receptionD. A very long and low directional receiving antenna

57

G9D10 Which of the following describes a Beverage antenna?

A. A vertical antenna constructed from beverage cansB. A broad-band mobile antennaC. A helical antenna for space receptionD. A very long and low directional receiving antenna

58

T9B – Feed lines

types of feed lines; attenuation vs. frequency; SWR concepts;

matching; weather protection; choosing RF connectors and feed

lines


Load Matching

Amateur transceivers have a 50 ohm output impedance

Coax and antennas should be as close to 50 ohms as possible to insure maximum power transfer

Any mismatch creates “standing waves” that can be measured with an SWR or directional watt meter

An SWR of 1:1 indicates perfect power transfer As SWR increases above 2:1, modern transmitters will

automatically reduce output to protect from damage All feed lines have “loss” that increases with frequency

and length caused by resistance in the line Standing waves will eventually be either radiated or

lost as heat in the feed line60

61

Hardline, Heliex, and Coax

Hard line

Coax

Air Core Hard line

Standing Waves

62

T9B01 - Why is it important to have a low

SWR in an antenna system that uses coaxial cable feed line?

A. To reduce television interference B. To allow the efficient transfer of power and reduce lossesC. To prolong antenna lifeD. All of these choices are correct


T9B01 - Why is it important to have a low

SWR in an antenna system that uses coaxial cable feed line?

A. To reduce television interference

B. To allow the efficient transfer of power and reduce lossesC. To prolong antenna lifeD. All of these choices are correct


T9B02 - What is the impedance of the most commonly used coaxial cable in typical amateur radio installations?

A. 8 ohmsB. 50 ohmsC. 600 ohmsD. 12 ohms


T9B02 - What is the impedance of the most commonly used coaxial cable in typical amateur radio installations?

A. 8 ohms

B. 50 ohmsC. 600 ohmsD. 12 ohms


T9B03 - Why is coaxial cable used more

often than any other feed line for amateur radio antenna systems?

A. It is easy to use and requires few special installation considerationsB. It has less loss than any other type of feed lineC. It can handle more power than any other type of feed lineD. It is less expensive than any other types of feed line


T9B04 - What does an antenna tuner

do?

A. It matches the antenna system impedance to the transceiver's output impedanceB. It helps a receiver automatically tune in weak stationsC. It allows an antenna to be used on both transmit and receiveD. It automatically selects the proper antenna for the frequency band being used


T9B05 - What generally happens as the

frequency of a signal passing through coaxial cable is increased?

A. The apparent SWR increasesB. The reflected power increasesC. The characteristic impedance increasesD. The loss increases


T9B05 - What generally happens as the

frequency of a signal passing through coaxial cable is increased?

A. The apparent SWR increasesB. The reflected power increasesC. The characteristic impedance increases

D. The loss increases


Connector Types


T9B06 - Which of the following connectors is most suitable for frequencies above 400 MHz?

A. A UHF (PL-259/SO-239) connectorB. A Type N connectorC. An RS-213 connectorD. A DB-25 connector


T9B06 - Which of the following connectors is most suitable for frequencies above 400 MHz?

A. A UHF (PL-259/SO-239) connector

B. A Type N connectorC. An RS-213 connectorD. A DB-25 connector


T9B07 - Which of the following is true of

PL-259 type coax connectors?

A. They are preferred for microwave operationB. They are water tightC. They are commonly used at HF frequenciesD. They are a bayonet type connector


T9B08 - Why should coax connectors

exposed to the weather be sealed against water intrusion?

A. To prevent an increase in feed line lossB. To prevent interference to telephonesC. To keep the jacket from becoming looseD. All of these choices are correct


T9B09 - What might cause erratic

changes in SWR readings?

A. The transmitter is being modulatedB. A loose connection in an antenna or a feed lineC. The transmitter is being over-modulatedD. Interference from other stations is distorting your signal


82

Coax Cable Signal Loss (Attenuation) in dB per 100ft

Loss RG-174 RG-58 RG-8X RG-213 RG-6 9913 LMR-400

O.D. 0.100in 0.195in 0.242in 0.405in 0.270in 0.405in 0.405in

1MHz 1.9dB 0.4dB 0.5dB 0.2dB 0.2dB 0.2dB 0.3dB








1GHz 32.0dB 21.5dB 13.5dB 8.3dB 6.1dB 4.5dB 4.1dB

Imped 50ohm 50ohm 50ohm 50ohm 75ohm 50ohm 50ohm

T9B10 - What electrical difference exists between the smaller RG-58 and larger

RG-8 coaxial cables?

A. There is no significant difference between the two typesB. RG-58 cable has less loss at a given frequencyC. RG-8 cable has less loss at a given frequencyD. RG-58 cable can handle higher power levels


T9B10 - What electrical difference exists between the smaller RG-58 and larger

RG-8 coaxial cables?

A. There is no significant difference between the two typesB. RG-58 cable has less loss at a given frequency

C. RG-8 cable has less loss at a given frequencyD. RG-58 cable can handle higher power levels


T9B11 - Which of the following types of feed line has the lowest loss at VHF and

UHF?

A. 50-ohm flexible coaxB. Multi-conductor unbalanced cableC. Air-insulated hard lineD. 75-ohm flexible coax


T9B11 - Which of the following types of feed line has the lowest loss at VHF and

UHF?

A. 50-ohm flexible coaxB. Multi-conductor unbalanced cable

C. Air-insulated hard lineD. 75-ohm flexible coax


End ofSUBELEMENT T9

Antennas and feed lines

87Antennas & Feedlines 2014

subelement t9 antennas and feed lines [2 exam questions - 2 groups] 1antennas & feedlines 2014

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