From Transmitter to Receiver
From Transmitter to Receiver
Antennas
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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
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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
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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
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The approximate physical length of a half-wave antenna for a frequency of 1000 kHz is
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Magnetic and electric fields about an antenna are
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Radio wave polarisation is defined by the orientation of the radiated
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A half wave dipole antenna is normally fed at the point of
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An important factor to consider when high angle radiation is desired from a horizontal half-wave antenna is the
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An antenna which transmits equally well in all compass directions is a
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A groundplane antenna emits a
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The impedance at the feed point of a folded dipole antenna is approximately
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The centre impedance of a 'half-wave' dipole in 'free space' is approximately
The feedpoint impedance of a half-wave dipole, installed about one wavelength or higher above ground (i.e. in "free space"), is 72 ohm. When the ends are lowered (i.e. into an "inverted V"), the impedance drops to around 50 ohms. The ends of the antenna should be insulated as they are high-voltage low-current points. The connections of the feedline to the antenna should be soldered because the centre of the dipole is a high-current low-voltage point.
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The effect of adding a series inductance to an antenna is to
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The purpose of a balun in a transmitting antenna system is to
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A dummy antenna
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A half-wave antenna resonant at 7100 kHz is approximately this long
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An antenna with 20 metres of wire each side of a centre insulator will be resonant at approximately
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A half wave antenna cut for 7 MHz can be used on this band without change
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This property of an antenna broadly defines the range of frequencies to which it will be effective
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The resonant frequency of an antenna may be increased by
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Insulators are used at the end of suspended antenna wires to
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To lower the resonant frequency of an antenna, the operator should
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The resonant frequency of a dipole antenna is mainly determined by
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A transmitting antenna for 28 MHz for mounting on the roof of a car could be a
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A vertical antenna which uses a flat conductive surface at its base is the
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The main characteristic of a vertical antenna is that it
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At the ends of a half-wave dipole the
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An antenna type commonly used on HF is the
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A Yagi antenna is said to have a power gain over a dipole antenna for the same frequency band because
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The maximum radiation from a three element Yagi antenna is
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The reflector and director(s) in a Yagi antenna are called
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An isotropic antenna is a
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The main reason why many VHF base and mobile antennas in amateur use are 5/8 of a wavelength long is that
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A more important consideration when selecting an antenna for working stations at great distances is
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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
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