B-006
Subelement B-006
Section B-006-011
Section B-006-011
What design feature allows a single Yagi antenna to function on the 20-metre, 15-metre and 10-metre bands?
-
Large diameter elements
-
T-match feed circuit
-
Multiple reflector elements
-
Correct AnswerElement traps
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.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the approximate length of the driven element of a Yagi antenna for 14.0 MHz?
-
Correct Answer10.21 metres
-
10.71 metres
-
21.43 metres
-
5.09 metres
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.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the approximate length of the director element of a Yagi antenna for 21.1 MHz?
-
3.55 metres
-
7.11 metres
-
Correct Answer6.44 metres
-
3.38 metres
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.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the approximate length of the reflector element of a Yagi antenna for 28.1 MHz?
-
2.67 metres
-
Correct Answer5.34 metres
-
10.68 metres
-
2.54 metres
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.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is one effect of increasing the boom length and adding directors to a Yagi antenna?
-
Correct AnswerGain increases
-
Front-to-back ratio increases
-
Power handling capability increases
-
Beamwidth increases
What is the major advantage of increasing element spacing on a Yagi antenna?
-
Correct AnswerHigher gain
-
Lower feed point impedance
-
Wider bandwidth
-
Better front-to-back ratio
Why are Yagi antennas often used on HF bands from 20 metres to 10 metres?
-
Excellent omnidirectional coverage in the horizontal plane
-
Correct AnswerRotatable high-gain antennas become feasible due to shorter element lengths
-
Their high angle of radiation facilitates long-range communications
-
Their wide bandwidth provides a good match over an entire band
Yagi antennas at such frequencies become feasible. Their gain is useful and their front-to-back ratio reduces noise coming from the opposite direction.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What does "antenna front-to-back ratio" mean in reference to a Yagi antenna?
-
The ratio of the power radiated by the director element, to the power radiated by the reflector element
-
The ratio of the driven element-to-director spacing, to the driven element-to-reflector spacing
-
The ratio of the length of the director element, to the length of the reflector element
-
Correct AnswerThe ratio of the power radiated in the forward direction to the power radiated in the opposite direction
'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.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
How can the bandwidth of a Yagi antenna be increased?
-
Correct AnswerIncrease the diameter of the elements
-
Decrease the element spacing
-
Install loading coils in the elements
-
Use tapered elements
For a three-element Yagi antenna, what approximate element spacing (in wavelengths) provides the best compromise between gain and front-to-back ratio?
-
Correct Answer0.20
-
0.50
-
0.75
-
0.10
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"?
-
7 dBi
-
Correct Answer13 dBi
-
10 dBi
-
20 dBi
This is a trick question. Two identical antennas side by side double 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.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
HamStudy.org™ is copyright 2025 Signal Stuff™, All rights
reserved.
View Privacy Policy | Get help with HamStudy.org™
View Privacy Policy | Get help with HamStudy.org™