Transcript Amateur Radio Technician Class Element 2 Course Presentation

Technician Licensing Class
Antennas
Page 151 to 157
Amateur Radio Technician Class
Element 2 Course Presentation
 ELEMENT 2 SUB-ELEMENTS (Groupings)
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About Ham Radio
Call Signs
Control
Mind the Rules
Tech Frequencies
Your First Radio
Going On The Air!
Repeaters
Emergency!
Weak Signal Propagation
2
Amateur Radio Technician Class
Element 2 Course Presentation
 ELEMENT 2 SUB-ELEMENTS (Groupings)
• Talk to Outer Space!
• Your Computer Goes Ham Digital!
• Multi-Mode Radio Excitement
• Run Some Interference Protection
• Electrons – Go With the Flow!
• It’s the Law, per Mr. Ohm!
• Go Picture These!
 Antennas
• Feed Me with Some Good Coax!
• Safety First!
3
Antennas
Main ideas
• Horizontal or vertical
• Antennas have ideal length based on the radio
wavelength to be used.
• Ideal length: “resonant” at half wavelength:
468
Half wavelength 

feet
f (in MHz)
• Electric field is aligned with the antenna
(horizontal or vertical).
• Directional antennas: send/receive in one direction
4
Antennas: The Dipole
Size of every antenna is based
on the frequency, or the wavelength, l.
l
A “half-wave dipole” has length equal to
Length = Half wavelength 
where
468

f (in MHz)
f = freq in MHz
½ the wavelength.
feet
112 in.
Example: for f = 50 MHz (6 m band)
Length =
468/50
= 9.36 ft, or 112"
5
Antennas: Vertical “Whips”
Vertical whips are often attached to a magnet.
So, they are often called “a “mag-mount.”
Typically, they are
¼ wavelength.
234
Length = ¼ wavelength   feet
f (in MHz)
19”
where f = freq in MHz
Example: for f = 146 MHz
Length = 234/146 = 1.6 ft, or 19.2”
6
Antennas: “Beams”
• Aligned antenna elements
“beam” the radio signal
in one main direction.
• They also receive signals more effectively
from that direction, and “reject” signals from
the opposite direction.
• They perform most efficiently near the design
wavelength.
• Different directional designs: Yagi, quad,
dish.
Antennas
7
Element 2 Technician Class
Question Pool
Antennas
Valid July 1, 2010
Through
June 30, 2014
Which of the following describes a simple
dipole mounted so the conductor is parallel to
the Earth's surface?
T9A03
A.
B.
C.
D.
A
A
A
A
ground wave antenna
horizontally polarized antenna
rhombic antenna
vertically polarized antenna
In which direction is the radiation strongest
from a half-wave dipole antenna in free space?
T9A10
A.
B.
C.
D.
Equally in all directions
Off the ends of the antenna
Broadside to the antenna
In the direction of the feedline
What is the approximate length, in inches,
of a 6 meter ½-wavelength wire dipole antenna?
T9A09
A.
B.
C.
D.
6
50
112
236
112”
How would you change a dipole antenna to
make it resonant on a higher frequency?
T9A05
A.
B.
C.
D.
Lengthen it
Insert coils in series with radiating wires
Shorten it
Add capacity hats to the ends of the
radiating wires
Higher
frequencies
are shorter
Lower
frequencies
are longer
Which of the following is true regarding
vertical antennas?
T9A02
A. The magnetic field is perpendicular
to the Earth
B. The electric field is perpendicular
to the Earth
C. The phase is inverted
D. The phase is reversed
90º
E
What is the approximate length, in inches,
of a quarter-wavelength vertical antenna for
146 MHz?
T9A08
A.
B.
C.
D.
112
50
19
12
19”
What type of antennas are the quad,
Yagi, and dish?
T9A06
A.
B.
C.
D.
Non-resonant antennas
Loop antennas
Directional antennas
Isotropic antennas
T9A01
What is a beam antenna?
A. An antenna built from aluminum I-beams
B. An omnidirectional antenna invented by
Clarence Beam
C. An antenna that concentrates signals in one
direction
D. An antenna that reverses
the phase of received signals
Which of the following methods is used
to locate sources of noise interference or
jamming?
T8C01
A.
B.
C.
D.
Echolocation
Doppler radar
Radio direction finding
Phase locking
RDF
Which of these items would be useful for
a hidden transmitter hunt?
T8C02
A.
B.
C.
D.
Calibrated SWR meter
A directional antenna
A calibrated noise bridge
All of these choices are correct
When using a directional antenna, how might your
station be able to access a distant repeater if buildings or
obstructions are blocking the direct line of sight path?
T3A05
A. Change from vertical to horizontal
polarization
B. Try to find a path that
reflects signals to the
repeater
C. Try the long path
D. Increase the antenna
SWR
You can use a directional antenna
to bounce your signal to reach a
repeater blocked by a building.
T9A11
What is meant by the gain of an antenna?
A. The additional power that is added to the
transmitter power
B. The additional power that is lost in the
antenna when transmitting on a higher
frequency
C. The increase in signal strength in a Remember
3db?
specified direction when compared
6db?
That’s gain!
to a reference antenna
D. The increase in impedance on receive or
transmit compared to a reference antenna
What antenna polarization is normally used
for long-distance weak-signal CW and SSB
contacts using the VHF and UHF bands?
T3A03
A.
B.
C.
D.
Right-hand circular
Left-hand circular
Horizontal
Vertical
What can happen if the antennas at
opposite ends of a VHF or UHF line of sight
radio link are not using the same polarization?
T3A04
A. The modulation sidebands might become
inverted
B. Signals could be
significantly weaker
C. Signals have an echo
effect on voices
D. Nothing significant
will happen