Question File Number 27

• In this diagram the item U corresponds to the:
• boom
• reflector
• driven element
• director
• ==========================
• In this diagram the item V corresponds to the:
• boom
• reflector
• driven element
• director
• ==========================
• In this diagram the item X corresponds to the:
• boom
• reflector
• director
• driven element
• ==========================
• The antenna in this diagram has two equal lengths of wire shown as 'X' forming a dipole between insulators. The optimum operating frequency will be when the:
• length X+X equals the signal wavelength
• dimensions are changed with one leg doubled in length
• length X+X is a little shorter than one-half of the signal wavelength
• antenna has one end grounded
• ==========================
• The antenna in this diagram can be made to operate on several bands if the following item is installed at the points shown at 'X' in each wire:
• a capacitor
• an inductor
• a fuse
• a parallel-tuned trap
• ==========================
• The physical length of the antenna shown in this diagram can be shortened and the electrical length maintained, if one of the following items is added at the points shown at 'X' in each wire:
• an inductor
• a capacitor
• an insulator
• a resistor
• ==========================
• The approximate physical length of a half-wave antenna for a frequency of 1000 kHz is:
• 300 metres
• 600 metres
• 150 metres
• 30 metres
• ==========================
• The wavelength for a frequency of 25 MHz is:
• 15 metres
• 32 metres
• 4 metres
• 12 metres
• ==========================
• Magnetic and electric fields about an antenna are:
• parallel to each other
• determined by the type of antenna used
• perpendicular to each other
• variable with the time of day
• ==========================
• Radio wave polarisation is defined by the orientation of the radiated:
• magnetic field
• electric field
• inductive field
• capacitive field
• ==========================
• A half wave dipole antenna is normally fed at the point of:
• maximum voltage
• maximum current
• maximum resistance
• resonance
• ==========================
• An important factor to consider when high angle radiation is desired from a horizontal half-wave antenna is the:
• size of the antenna wire
• time of the year
• height of the antenna
• mode of propagation
• ==========================
• An antenna which transmits equally well in all compass directions is a:
• dipole with a reflector only
• quarterwave grounded vertical
• dipole with director only
• half-wave horizontal dipole
• ==========================
• A groundplane antenna emits a:
• horizontally polarised wave
• elliptically polarised wave
• axially polarised wave
• vertically polarised wave
• ==========================
• The impedance at the feed point of a folded dipole antenna is approximately:
• 300 ohm
• 150 ohm
• 200 ohm
• 100 ohm
• ==========================
• The centre impedance of a 'half-wave' dipole in 'free space' is approximately:
• 52 ohm
• 73 ohm
• 100 ohm
• 150 ohm
• ==========================
• The effect of adding a series inductance to an antenna is to:
• increase the resonant frequency
• have no change on the resonant frequency
• have little effect
• decrease the resonant frequency
• ==========================
• The purpose of a balun in a transmitting antenna system is to:
• reduce unbalanced standing waves
• protect the antenna system from lightning strikes
• match unbalanced and balanced transmission lines
• ==========================
• A dummy antenna:
• attenuates a signal generator to a desirable level
• provides more selectivity when a transmitter is being tuned
• matches an AF generator to the receiver
• duplicates the characteristics of an antenna without radiating signals
• ==========================
• A half-wave antenna resonant at 7100 kHz is approximately this long:
• 20 metres
• 40 metres
• 80 metres
• 160 metres
• ==========================
• An antenna with 20 metres of wire each side of a centre insulator will be resonant at approximately:
• 3600 kHz
• 3900 kHz
• 7050 kHz
• 7200 kHz
• ==========================
• A half wave antenna cut for 7 MHz can be used on this band without change:
• 10 metre
• 15 metre
• 20 metre
• 80 metre
• ==========================
• This property of an antenna broadly defines the range of frequencies to which it will be effective:
• bandwidth
• front-to-back ratio
• impedance
• polarisation
• ==========================
• The resonant frequency of an antenna may be increased by:
• increasing the height of the radiating element
• ==========================
• Insulators are used at the end of suspended antenna wires to:
• increase the effective antenna length
• limit the electrical length of the antenna
• make the antenna look more attractive
• prevent any loss of radio waves by the antenna
• ==========================
• To lower the resonant frequency of an antenna, the operator should:
• lengthen the antenna
• centre feed the antenna with TV ribbon
• shorten the antenna
• ground one end
• ==========================
• A half-wave antenna is often called a:
• bi-polar
• Yagi
• dipole
• beam
• ==========================
• The resonant frequency of a dipole antenna is mainly determined by:
• its height above the ground
• its length
• the output power of the transmitter used
• the length of the transmission line
• ==========================
• A transmitting antenna for 28 MHz for mounting on the roof of a car could be a:
• vertical long wire
• quarter wave vertical
• horizontal dipole
• full wave centre fed horizontal
• ==========================
• A vertical antenna which uses a flat conductive surface at its base is the:
• vertical dipole
• quarter wave ground plane
• rhombic
• long wire
• ==========================
• The main characteristic of a vertical antenna is that it:
• requires few insulators
• is very sensitive to signals coming from horizontal aerials
• receives signals from all points around it equally well
• is easy to feed with TV ribbon feeder
• ==========================
• At the ends of a half-wave dipole the:
• voltage and current are both high
• voltage is high and current is low
• voltage and current are both low
• voltage low and current is high
• ==========================
• An antenna type commonly used on HF is the:
• parabolic dish
• 13-element Yagi
• helical Yagi
• ==========================
• A Yagi antenna is said to have a power gain over a dipole antenna for the same frequency band because:
• it radiates more power than a dipole
• more powerful transmitters can use it
• it concentrates the radiation in one direction
• it can be used for more than one band
• ==========================
• The maximum radiation from a three element Yagi antenna is:
• in the direction of the reflector end of the boom
• in the direction of the director end of the boom
• at right angles to the boom
• parallel to the line of the coaxial feeder
• ==========================
• The reflector and director(s) in a Yagi antenna are called:
• oscillators
• tuning stubs
• parasitic elements
• matching units
• ==========================
• An isotropic antenna is a:
• half wave reference dipole
• infinitely long piece of wire
• hypothetical point source
• ==========================
• The main reason why many VHF base and mobile antennas in amateur use are 5/8 of a wavelength long is that:
• it is easy to match the antenna to the transmitter
• it is a convenient length on VHF
• the angle of radiation is high giving excellent local coverage
• most of the energy is radiated at a low angle
• ==========================
• A more important consideration when selecting an antenna for working stations at great distances is:
• sunspot activity
• impedance
• bandwidth
• ==========================
• On VHF and UHF bands, polarisation of the receiving antenna is important in relation to the transmitting antenna, but on HF it is relatively unimportant because:
• the ionosphere can change the polarisation of the signal from moment to moment
• the ground wave and the sky wave continually shift the polarisation
• anomalies in the earth's magnetic field profoundly affect HF polarisation
• improved selectivity in HF receivers makes changes in polarisation redundant
• ==========================

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Compiled Sun Nov 28 2010 at 8:42:55pm

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