The 'boom' supports the elements of the Yagi. Element dimensions on a Yagi; the 'Driven' = a half-wave dipole, 95% of a half-wavelength in free space = (300 / MHz / 2) * 95%. The 'Reflector', in back of the 'driven' = 5% longer than the 'driven'. The 'Director', in front of the 'driven, = 5% shorter than the 'driven'.
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The 'boom' supports the elements of the Yagi. Element dimensions on a Yagi; the 'Driven' = a half-wave dipole, 95% of a half-wavelength in free space = (300 / MHz / 2) * 95%. The 'Reflector', in back of the 'driven' = 5% longer than the 'driven'. The 'Director', in front of the 'driven, = 5% shorter than the 'driven'.
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The 'boom' supports the elements of the Yagi. Element dimensions on a Yagi; the 'Driven' = a half-wave dipole, 95% of a half-wavelength in free space = (300 / MHz / 2) * 95%. The 'Reflector' (in back of the 'driven') = 5% longer than the 'driven'. The 'Director' (in front of the 'driven) = 5% shorter than the 'driven'.
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An electromagnetic wave comprises an electrical field and a magnetic field. Wave Polarization describes the position of the ELECTRIC field with respect to the Earth's surface. On a dipole antenna or on the 'driven' element of a Yagi, the electric field is developed between the tips of the radiating element.
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An electromagnetic wave comprises an electrical field and a magnetic field. Wave Polarization describes the position of the ELECTRIC field with respect to the Earth's surface. On a dipole antenna or on the 'driven' element of a Yagi, the electric field is developed between the tips of the radiating element.
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An electromagnetic wave comprises an electrical field and a magnetic field. Wave Polarization describes the position of the ELECTRIC field with respect to the Earth's surface. On a dipole antenna or on the 'driven' element of a Yagi, the electric field is developed between the tips of the radiating element.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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An electromagnetic wave comprises an electrical field and a magnetic field. Wave Polarization describes the position of the ELECTRIC field with respect to the Earth's surface. On a dipole antenna or on the 'driven' element of a Yagi, the electric field is developed between the tips of the radiating element.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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An electromagnetic wave comprises an electrical field and a magnetic field. Wave Polarization describes the position of the ELECTRIC field with respect to the Earth's surface. On a dipole antenna or on the 'driven' element of a Yagi, the electric field is developed between the tips of the radiating element.
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'Isotropic' means "equal radiation in all directions". An 'isotropic antenna', also called 'isotropic radiator' is an HYPOTHETICAL point source. Plotting the pattern in all planes around the source would yield a 'sphere' as a pattern. The 'isotropic antenna' is used as a reference to compare the gain of real antennas.
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'Isotropic' means "equal radiation in all directions". An 'isotropic antenna', also called 'isotropic radiator' is an HYPOTHETICAL point source. Plotting the pattern in all planes around the source would yield a 'sphere' as a pattern. The 'isotropic antenna' is used as a reference to compare the gain of real antennas.
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key words: VHF, VERTICAL. On 'line of sight' propagation (common at Very High Frequencies) and with Ground Wave propagation (common at the low end of High Frequencies), a significant loss is incurred if the antennas on both extremities do NOT have the same polarization.
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An electromagnetic wave comprises an electrical field and a magnetic field. Wave Polarization describes the position of the ELECTRIC field with respect to the Earth's surface. On a dipole antenna or on the 'driven' element of a Yagi, the electric field is developed between the tips of the radiating element.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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key words: GROUND WAVE. On 'line of sight' propagation (common at Very High Frequencies) and with Ground Wave propagation (common at the low end of High Frequencies), a significant loss is incurred if the antennas on both extremities do NOT have the same polarization.
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On 'line of sight' propagation (common at Very High Frequencies) and with Ground Wave propagation (common at the low end of High Frequencies), a significant loss is incurred if the antennas on both extremities do NOT have the same polarization.
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Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. Wavelength and frequency have an inverse relationship. Antennas on the 80 metre HF (3.5 to 4.0 MHz) band are much longer than antennas on the 2 metre VHF band (144 to 148 MHz).
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Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. Wavelength and frequency have an inverse relationship. Antennas on the 2 metre VHF band (144 to 148 MHz) are much shorter than antennas on the 80 metre HF band (3.5 to 4.0 MHz).
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A series inductance in an antenna is termed a "loading coil". It makes the antenna appear LONGER electrically than its physical size. Making the antenna longer brings down the resonant frequency.
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Wavelength and frequency have an inverse relationship. Increasing the resonant frequency (shorter wavelength) can be achieved by shortening the radiating element.
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Wavelength and frequency have an inverse relationship. Decreasing the resonant frequency (longer wavelength) can be achieved by lengthening the radiating element.
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"Antenna traps" are parallel resonant circuits which exhibit high impedance at resonance. Electrically speaking, they cut-off the antenna at the trap position when operated at the resonant frequency of the trap.
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The term 'parasite' means "feeding off something else". For instance, in a Yagi, there is only one 'driven' element where the transmission line attaches. The 'reflector' and 'director' capture energy off the 'driven' and re-radiate it.
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'Antenna bandwidth' is the range of frequencies over which an antenna is usable. Larger-diameter elements means "thicker" elements. With "fatter" elements, resonance isn't as sharp. Antenna 'bandwidth' is increased.
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key words: PARASITIC, SHORTER. A 'slightly shorter parasitic' element is the description of a 'Director'. A dipole and a 'director' in front of it make up a two-element Yagi. Radiation will be enhanced toward the 'director' at the expense of the back.
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key words: PARASITIC, LONGER. A 'slightly longer parasitic' element is the description of a 'reflector'. A dipole and a 'reflector' behind it make up a two-element Yagi. Radiation will be enhanced away from the 'reflector', towards the radiating element (the dipole, the 'driven').
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An 'isotropic radiator' radiates equally well in ALL directions ( radiation pattern is a 'sphere'). A dipole in free space has a radiation pattern similar to a donut ( maximum radiation broadside from the antenna, none towards the ends ). This concentration of radiation produce a gain of 2.1 dB over an isotropic antenna.
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Antenna Gain is a ratio, expressed in decibel, of the radiation of a given antenna against some reference antenna. For example, the expression 'dBi' means decibel over an isotropic radiator.
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A dipole in free space has a radiation pattern similar to a donut ( maximum radiation broadside from the antenna, none towards the ends ). This concentration of radiation produce a gain of 2.1 dB over an isotropic antenna.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Antenna Gain is a ratio, expressed in decibel, of the radiation of a given antenna against some reference antenna. For example, the expression 'dBi' means decibel over an isotropic radiator.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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'Beam antenna' is another name for a Yagi. 'Front to back' is a ratio in decibels of the power radiated in the most favoured direction (front) to the power radiated towards the back of the antenna.
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key words: QUARTER-wavelength. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. Answer: 95 % of one quarter wavelength in free space = '300 / 4 * 0.95' divided by frequency in megahertz = 71.3 divided by frequency in megahertz.
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key words: QUARTER-wavelength. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. Answer: 95 % of one quarter wavelength in free space = '300 / 4 * 0.95' divided by frequency in megahertz = 71.3 divided by frequency in megahertz. In this example, '300 / 21.125 MHz / 4 * 0.95' = 3.37 metres.
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key words: HALF-wavelength. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. Answer: 95 % of one half wavelength in free space = '300 / 2 * 0.95' divided by frequency in megahertz = 143 divided by frequency in megahertz. In this example, '300 / 223 MHz / 2 * 0.95' = 0.64 metres.
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The 'five eights' wavelength antenna focuses energy somewhat better towards the horizon (lower radiation angle) than a regular quarter-wave antenna.
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Radials are the three or four rods simulating ground at the base of an elevated vertical antenna (ground plane antenna). Sloping radials (lower than 90 degrees) BRING up the impedance from about 30 ohms to 50 ohms for a better direct match to coaxial cable.
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Radials are the three or four rods simulating ground at the base of an elevated vertical antenna (ground plane antenna). Sloping radials (lower than 90 degrees) BRING up the impedance from about 30 ohms to 50 ohms for a better direct match to coaxial cable.
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Short answer: a coil (inductor) has a behaviour totally opposite to capacitors; 'cancelling reactive capacitance' makes sense. A short antenna (e.g., 2.5 m) operated on HF frequencies (wavelengths of 10 to 80 metres) looks like an antenna operated well below its natural resonant frequency. If you think of an ideal antenna as a resonant circuit where capacitive and inductive reactances cancel each other, you'll note that CAPACITIVE reactance ( XC = 1 over '2 * PI * f * C' ) grows below the resonant frequency. A "loading coil" cancels out that capacitive reactance.
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The 'five eights' wavelength antenna focuses energy somewhat better towards the horizon (lower radiation angle) than a regular quarter-wave antenna.
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key word: DRIVEN. Same approximate length as a HALF-WAVE dipole. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. Answer: 95 % of one half wavelength in free space = '(300 / 2) * 0.95' divided by frequency in megahertz = 143 divided by frequency in megahertz. In this example, '(300 / 14 MHz / 2) * 0.95' = 10.18 metres.
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key word: DIRECTOR. About 5% SHORTER than the 'driven' which is itself the approximate length of a HALF-WAVE dipole. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. The 'driven' would be 95 % of one half wavelength in free space = '(300 / 2) * 0.95' divided by frequency in megahertz. The DIRECTOR is another 95% of the length of the 'driven'. In this example, the director becomes (300 / 21.1 MHz / 2) * 0.95 * 0.95 = 6.42 metres.
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key word: REFLECTOR. About 5% LONGER than the 'driven' which is itself the approximate length of a HALF-WAVE dipole. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. The 'driven' would be 95 % of one half wavelength in free space = '(300 / 2) * 0.95' divided by frequency in megahertz. The REFLECTOR is 1.05 times the length of the 'driven'. In this example, the reflector becomes (300 / 28.1 MHz / 2) * 0.95 * 1.05 = 5.32 metres.
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20 metres is an amateur band with global reach. It is open during day time even during solar cycle lows. The directive antenna pattern of a Yagi permits reducing interference by focusing energy in one direction only.
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'Front to back' is a ratio in decibels of the power radiated in the most favoured direction (front) to the power radiated towards the back of the antenna.
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All dimensions in Yagis must be optimized: the lengths and positions of each elements influence final performance. [ Center frequency, feedpoint impedance, forward gain, antenna bandwidth and front-to-back ratio all change with changing physical dimensions. ]
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This is a trick question. Two identical antennas side by side doubles the radiated power. An increase of 2 in power is a gain of +3 dB. The gain of the array becomes 10 dBi + 3 dB = 13 dBi.
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key words: half-wavelength DIPOLE. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. A 'dipole' is approximately 95 % of one half wavelength in free space = '(300 / 2) * 0.95' divided by frequency in megahertz. In this example, the dipole must be (300 / 28.15 MHz / 2) * 0.95 = 5.06 metres. The frequency is in the 10 metre band of 28.0 to 29.7 MHz, a dipole there must be necessarily 5 metres long.
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Because the 'random wire' and 'long wire' antennas frequently originate right at the back of the antenna tuner in your station, stray RF (radio frequency) can be a problem.
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Picture an horizontal dipole viewed from above. If you plotted radiation all around it, the plot would look like a "number eight": peak radiation at 90 degrees (broadside) from the antenna, negligible radiation from the ends.
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Picture an horizontal dipole viewed from above, if you plotted radiation all around it, the plot would look like a "number eight": peak radiation at 90 degrees (broadside) from the antenna, negligible radiation from the ends.
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'Antenna Bandwidth' is the range of frequencies over which Standing Wave Ratio (SWR) is acceptable. The Folded Dipole can be operated over a wider range of frequencies than a regular dipole.
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An antenna with traps is a multi-band antenna (i.e., resonant at more than one frequency). If the transmitter leaks harmonic energy (multiples of the operating frequency), this harmonic energy may be more readily radiated by a multi-band antenna. For example, traps are inserted in an antenna for 80 metres to permit operation on 40 metres; if your transmitter puts out 'harmonics' while you operate on 80 m ( say, 3.5 MHz ), the second harmonic falls in the 40 m band. The antenna is also resonant at that frequency and would freely radiate the harmonics.
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The only reason why antenna traps (parallel resonant circuits) are useful is to permit operation on more than one band from the same physical antenna. Through their high impedance at resonance, traps shorten the antenna by making the antenna sections beyond them inaccessible.
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Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. The dipole is approximately 95 % of one half wavelength in free space = '(300 / 2) * 0.95' divided by frequency in megahertz. In this example, the dipole must be cut to (300 / 3.75 MHz / 2) * 0.95 = 38 metres. [ 3.75 MHz is in the 80 metre band of 3.5 to 4.0 MHz, a DIPOLE there must be below 40 metres long ].
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key word: CUBICAL QUAD. A four-sided loop. Loop antennas are roughly 1 wavelength long. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. The 'driven' element in a LOOP is 2% longer than a full wavelength in free space = '300 * 1.02' divided by frequency in megahertz. In this example, ONE side of the quad becomes (300 * 1.02) / 21.4 MHz / 4 = 3.57 metres.
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key word: CUBICAL QUAD. A four-sided loop. Loop antennas are roughly 1 wavelength long. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. The 'driven' element in a LOOP is 2% longer than a full wavelength in free space = '300 * 1.02' divided by frequency in megahertz. In this example, ONE side of the quad becomes (300 * 1.02) / 14.3 MHz / 4 = 5.35 metres.
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key word: DELTA LOOP. A three-sided loop. Loop antennas are roughly 1 wavelength long. Wavelength (lambda) in metres IN FREE SPACE is 300 divided by frequency in megahertz. The 'driven' element in a LOOP is 2% longer than a full wavelength in free space = '300 * 1.02' divided by frequency in megahertz. In this example, ONE side of the DELTA becomes (300 * 1.02) / 28.7 MHz / 3 = 3.55 metres.
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Because quads and deltas focus energy in both planes, horizontal and vertical, the two-element quad performs similarly to a three-element Yagi.
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In your head, squish the quad from the top down, it now looks like a Folded Dipole. If the Folded dipole is horizontal, it is polarized horizontally. Flip it 90 degrees and it now has a vertical polarization.
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Same as a Yagi. 'Front to back' is a ratio in decibels of the power radiated in the most favoured direction (front) to the power radiated towards the back of the antenna.
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