B-006 — Feedlines and antenna systems

Getting the signal out: antennas, feedlines, SWR, baluns, matching, and why antenna length depends on frequency.

All 140 questions

• B-006-001-001 What connects your transceiver to your antenna?
• B-006-001-002 The characteristic impedance of a transmission line is determined by the:
• B-006-001-003 The characteristic impedance of a 20-metre piece of transmission line is 52 ohms. What would the impedance be if 10 metres were cut off?
• B-006-001-004 Why can coaxial cables of different diameters have the same characteristic impedance?
• B-006-001-005 What commonly available transmission line can be buried directly in the ground for some distance without adverse effects?
• B-006-001-006 A transmitter is delivering radio frequency (RF) energy into a coaxial cable with a characteristic impedance of 50 ohms. The cable is terminated by a purely resistive load. What value of load resistance will absorb all the RF energy it receives?
• B-006-001-007 What is the major factor influencing the velocity factor of a coaxial cable?
• B-006-001-008 The characteristic impedance of an open-wire transmission line depends, in part, on the diameter of its conductors. What other dimension determines its characteristic impedance?
• B-006-001-009 A transmission line is terminated by an impedance that differs significantly from the characteristic impedance of the line. What impedance will be measured at the input of the line?
• B-006-001-010 What factors determine the characteristic impedance of an open-wire transmission line?
• B-006-001-011 What factors determine the characteristic impedance of a coaxial transmission line?
• B-006-002-001 What kind of transmission line has a centre wire inside an insulating material that is covered by a metal shield or sleeve?
• B-006-002-002 What kind of transmission line has two wires side-by-side embedded in insulating material?
• B-006-002-003 What kind of transmission line is made of two conductors held apart by insulated rods?
• B-006-002-004 What is the purpose of a balun?
• B-006-002-005 Where would you install a balun to feed a dipole antenna with 50-ohm coaxial cable?
• B-006-002-006 What causes a transmission line to be unbalanced?
• B-006-002-007 What device can be installed to feed a balanced antenna with an unbalanced transmission line?
• B-006-002-008 What device should you use to connect a coaxial cable to window line?
• B-006-002-009 A balanced transmission line:
• B-006-002-010 Your antenna tuner does not have a balanced output and you wish to use window line to feed an HF antenna. What device should you use between the tuner and the transmission line?
• B-006-002-011 What kind of transmission line has two conductors maintained side by side, a constant distance apart, using insulated spreaders?
• B-006-003-001 A transmission line must be supported for several metres by attaching it to a metal fence. What type of transmission line will NOT be adversely affected by proximity to the fence?
• B-006-003-002 A common-mode current choke can be made by winding coaxial cable on a ferrite toroid. Why is cable with solid dielectric preferred over foam dielectric?
• B-006-003-003 Why do most amateur radio antenna systems use coaxial cable, rather than other types of transmission line?
• B-006-003-004 What type of connector is commonly installed on RG-213 coaxial cable for connection to an HF transceiver?
• B-006-003-005 What type of connector usually joins a modern hand-held transceiver to its antenna?
• B-006-003-006 Which popular RF connector is designed to be moisture resistant?
• B-006-003-007 What type of RF connector is commonly used for low-power transceivers and test instruments?
• B-006-003-008 Why should you regularly clean and tighten all antenna connectors?
• B-006-003-009 What type of coaxial outer conductor offers the best shielding?
• B-006-003-010 If your location is frequently affected by icing conditions, which type of transmission line would be the most suitable?
• B-006-003-011 What is the primary advantage of choosing a coaxial cable with a foam dielectric instead of a solid dielectric?
• B-006-004-001 What is the major adverse consequence of using RG-58 coaxial cable for a transmission line operating on the 70 cm band?
• B-006-004-002 What is the major advantage of open-wire transmission line?
• B-006-004-003 If your transmitter and antenna are 15 metres apart, but are connected by 60 metres of RG-58 coaxial cable, what should be done to reduce transmission line loss?
• B-006-004-004 As the length of a transmission line is changed, what happens to signal loss?
• B-006-004-005 As the frequency of a signal is changed, what happens to signal loss in a transmission line?
• B-006-004-006 Assuming the same transmitter and RF output power are used, what is the effect of changing the transmission line from RG- 213 coaxial cable to RG-58?
• B-006-004-007 The lowest loss transmission line on HF is:
• B-006-004-008 In what values are RF transmission line losses expressed?
• B-006-004-009 If the length of a coaxial transmission line is increased from 20 metres to 40 metres, how would this affect the line loss?
• B-006-004-010 If the operating frequency is increased, how does the transmission line loss change?
• B-006-005-001 What does an SWR reading of 1:1 mean?
• B-006-005-002 What does an SWR reading of less than 1.5:1 mean?
• B-006-005-003 What is the most likely cause of erratic readings on an SWR meter?
• B-006-005-004 Which of the following can cause a high SWR reading?
• B-006-005-005 What is the main adverse effect due to operating with high SWR?
• B-006-005-006 What instrument is useful in adjusting the physical length of an antenna?
• B-006-005-007 If the characteristic impedance of the transmission line does not match the antenna input impedance then:
• B-006-005-008 The result of the presence of standing waves on a transmission line is:
• B-006-005-009 What does an SWR meter measure to determine the SWR?
• B-006-005-010 What information can be obtained with an antenna analyzer?
• B-006-005-011 What is the effect of line loss on the SWR reading at the station?
• B-006-006-001 Which of the following antenna system conditions will cause a modern solid-state HF transceiver to automatically reduce power?
• B-006-006-002 What does an antenna tuner do?
• B-006-006-003 An end-fed half-wave antenna (EFHW) has a very high feed point impedance. What device could be used to provide a good match to 50-ohm coaxial cable?
• B-006-006-004 If both source and load impedances are purely resistive, what value of load impedance will result in maximum power delivery to the load?
• B-006-006-005 What is the advantage of locating an antenna tuner near the antenna feed point, over locating it near the transceiver?
• B-006-006-006 How does an antenna tuner compensate for an impedance mismatch in an antenna system?
• B-006-006-007 What advantage does a transformer present when used for impedance matching at radio frequencies?
• B-006-006-008 Where does impedance matching need to be done to minimize transmission line losses in an antenna system?
• B-006-006-009 If an antenna is correctly matched to a transmission line, the length of the transmission line:
• B-006-006-010 Why is an antenna tuner (external or internal) frequently used with modern solid-state transceivers?
• B-006-006-011 If a transmission line with a characteristic impedance of 50 ohms feeds a folded dipole with a feed point impedance close to 300 ohms, what impedance transformation ratio is needed to match the two?
• B-006-007-001 What does horizontal wave polarization mean?
• B-006-007-002 What does vertical wave polarization mean?
• B-006-007-003 What electromagnetic wave polarization does a Yagi antenna have when its elements are parallel to the Earth's surface?
• B-006-007-004 What electromagnetic wave polarization does a half-wavelength antenna have when it is perpendicular to the Earth's surface?
• B-006-007-005 Polarization of an antenna is determined by:
• B-006-007-006 An isotropic antenna is:
• B-006-007-007 What is the three-dimensional radiation pattern of an isotropic radiator?
• B-006-007-008 VHF signals from a mobile station using a vertical whip antenna will normally be best received using a:
• B-006-007-009 A dipole antenna will emit a vertically polarized wave if it is:
• B-006-007-010 If an electromagnetic wave leaves an antenna vertically polarized and reaches the receiving location by ground wave, what will be its final polarization?
• B-006-007-011 Compared with a horizontal antenna, a vertical antenna will receive a vertically polarized radio wave:
• B-006-008-001 A wire dipole has a resonant frequency of 3900 kHz. How can you change its resonant frequency to 3600 kHz?
• B-006-008-002 A wire dipole has a resonant frequency of 3600 kHz. How can you change its resonant frequency to 3900 kHz?
• B-006-008-003 What is the wavelength in free space of a 25 MHz signal?
• B-006-008-004 The velocity of propagation of radio frequency energy in free space is:
• B-006-008-005 Adding a series inductance to an antenna would:
• B-006-008-006 The resonant frequency of an antenna may be increased by:
• B-006-008-007 The speed of a radio wave:
• B-006-008-008 Why are insulators used at the ends of a suspended wire antenna?
• B-006-008-009 To lower the resonant frequency of an antenna, the operator should:
• B-006-008-010 Some antennas are constructed with traps. What is a trap?
• B-006-008-011 What is the wavelength in free space of a 2 MHz signal?
• B-006-009-001 How is a parasitic antenna element energized?
• B-006-009-002 How can the directivity of a half-wave dipole be increased?
• B-006-009-003 If a half-wave dipole is converted to a Yagi by adding a slightly shorter parasitic element, in what direction(s) does the radiation strength increase?
• B-006-009-004 If a half-wave dipole is converted to a Yagi by adding a slightly longer element, in what direction(s) does the radiation strength increase?
• B-006-009-005 The property of an antenna that defines the range of frequencies to which it will respond, is called its:
• B-006-009-006 What is the approximate gain of a half-wave dipole in free space relative to an isotropic radiator?
• B-006-009-007 What is meant by antenna gain?
• B-006-009-008 What is meant by antenna bandwidth?
• B-006-009-009 In free space, what is the radiation pattern of a half-wave dipole?
• B-006-009-010 The gain of an antenna, especially on VHF and above, is quoted in dBi. The "i" in this expression stands for:
• B-006-009-011 An antenna is said to have a gain of 4.1 dBi. How much gain is this over a half-wave dipole antenna?
• B-006-010-001 How do you calculate the approximate length in metres of a quarter-wavelength antenna for use on frequencies below 30 MHz?
• B-006-010-002 If you made a quarter-wavelength vertical antenna for 21.125 MHz, approximately how long would it be?
• B-006-010-003 If you made a half-wavelength vertical antenna for 223 MHz, approximately how long would it be?
• B-006-010-004 Why is a five-eighths wavelength vertical antenna better than a quarter-wavelength vertical antenna for VHF or UHF mobile operations?
• B-006-010-005 If a quarter-wavelength vertical antenna is placed on the roof of a car, in what direction does it send out radio energy?
• B-006-010-006 What is an advantage of downward sloping radials on a ground plane antenna?
• B-006-010-007 What configuration of radials will match an elevated quarter-wave vertical antenna to a 50-ohm coaxial cable?
• B-006-010-008 Which of the following transmission lines will give the best match to the base of a quarter-wave ground-plane antenna?
• B-006-010-009 How can a vertical antenna, 2 metres in length, be made to resonate in the 80-metre band for mobile use?
• B-006-010-010 Why is a loading coil often used with an HF mobile vertical antenna?
• B-006-010-011 When using a ground mounted vertical HF antenna, what can you do to reduce ground losses?
• B-006-011-001 What design feature allows a single Yagi antenna to function on the 20-metre, 15-metre and 10-metre bands?
• B-006-011-002 What is the approximate length of the driven element of a Yagi antenna for 14.0 MHz?
• B-006-011-003 What is the approximate length of the director element of a Yagi antenna for 21.1 MHz?
• B-006-011-004 What is the approximate length of the reflector element of a Yagi antenna for 28.1 MHz?
• B-006-011-005 What is one effect of increasing the boom length and adding directors to a Yagi antenna?
• B-006-011-006 What is the major advantage of increasing element spacing on a Yagi antenna?
• B-006-011-007 Why are Yagi antennas often used on HF bands from 20 metres to 10 metres?
• B-006-011-008 What does "antenna front-to-back ratio" mean in reference to a Yagi antenna?
• B-006-011-009 How can the bandwidth of a Yagi antenna be increased?
• B-006-011-010 For a three-element Yagi antenna, what approximate element spacing (in wavelengths) provides the best compromise between gain and front-to-back ratio?
• B-006-011-011 If the forward gain of a six-element Yagi is about 10 dBi, what would the gain of two of these antennas be if they were "stacked"?
• B-006-012-001 If you made a half-wavelength dipole antenna for 28.150 MHz, approximately how long would it be?
• B-006-012-002 What is one disadvantage of a random wire antenna?
• B-006-012-003 What is the three-dimensional radiation pattern of a half-wavelength dipole in free space?
• B-006-012-004 What is the impedance at the feed point of a half-wave dipole in free space?
• B-006-012-005 Ignoring ground effects, what is the radiation pattern of a horizontal half-wave dipole installed with the ends pointing North/South?
• B-006-012-006 What is a major advantage of an end-fed half-wave antenna (EFHW)?
• B-006-012-007 What is a disadvantage of using an antenna equipped with traps?
• B-006-012-008 What is an advantage of using a trap antenna?
• B-006-012-009 If you were to cut a half-wave dipole for 3.75 MHz, what would be its approximate length?
• B-006-013-001 What is a quad antenna?
• B-006-013-002 What is a delta loop antenna with parasitic elements?
• B-006-013-003 What is the approximate length of the driven element of a quad antenna designed for 21.4 MHz?
• B-006-013-004 What is the approximate length of the driven element of a quad antenna designed for 14.3 MHz?
• B-006-013-005 What is the approximate length of a delta loop antenna designed for 28.7 MHz?
• B-006-013-006 What is a major disadvantage of a quad antenna, as compared to a Yagi antenna with the same number of elements and boom length?
• B-006-013-007 You are constructing an HF delta loop antenna. It is oriented with the bottom element parallel to the ground. Where should you locate the feed point for horizontal polarization?
• B-006-013-008 Moving the feed point of a quad antenna from a side parallel to the ground to a side perpendicular to the ground will have what effect?
• B-006-013-009 What is the approximate length of the wire for a horizontal loop tuned at 7.15 MHz?
• B-006-013-010 The quad antenna consists of two or more square loops of wire. The driven element has an approximate overall length of:
• B-006-013-011 What is the approximate overall length of a delta loop antenna?