LESSON 30

Antenna types – vertical, horizontal, concept of gain,
common portable and mobile antennas, losses with short antennas,
relationships between antenna length and frequency, dummy loads

A great transmitter and an outstanding receiver combined with a poor antenna system will result in a poor communications station. The antenna is the direct link between the transmitting and the receiving stations.

Antenna are sometimes designed with a single element mounted perpendicular to the Earth’s surface so they are known as vertical antennas while a simple dipole antenna is mounted so the elements are parallel to the Earth’s surface so it is a horizontal antenna. By using other antenna elements to concentrate the signal in one direction these antennas become known as beam antennas or directional antennas. Three types of directional antennas are the quad, the Yagi, and the dish antennas.

When the elements are vertical to the Earth’s surface the radiation is vertically polarized and when the elements are horizontal to the Earth’s surface the radiation is horizontally polarized.

The simple vertical antenna and simple dipole, like the wave length of the RF signal, become shorter as the frequency is increased and become longer as the frequency decreases. The formula for determining the length of a half wave antenna is length = 5616/Frequency (Frequency in MHz and length in inches). Thus a half wave 6 meter antenna would be approximately 112 inches. A half wave antenna can be made into a quarter wave antenna by dividing the length by 2 thus a quarter wave 2 meter antenna would be approximately 19 inches.

Frequently hand held radios use a short wide and usually black antenna called affectionately referred to as a “Rubber Duck” antenna. These antennas are convenient from a physical stand point but are not as efficient as a full size antenna for transmitting or receiving.

A magnetic mount vertical antenna provides an effective mobile antenna that is to install and remove. Using a magnetic mount antenna while operating a hand held antenna inside a vehicle will greatly improve its performance. Using just a “Rubber Duck” antenna on a hand held radio inside a vehicle can reduce its efficiency 10 to 20 times (10 to 13 DB loss).

A quarter wave antenna is commonly used for mobile purposes but by using a five eights wave antenna the angle of radiation can be lowered and an additional 3 DB of gain can be realized.

Sometimes it is desired to test a transmitter while not radiating a signal. A transmitter should never be operated with out a load so if it is not desirable to radiate a signal a dummy load should be used in place of the antenna.


1. T9A01 (C)
What is a beam antenna?
A. An antenna built from metal I-beams
B. An antenna that transmits and receives equally well in all directions
C. An antenna that concentrates signals in one direction
D. An antenna that reverses the phase of received signals
~~
2. T9A02 (C)
What is an antenna that consists of a single element mounted perpendicular to the Earth's surface?
A. A conical monopole
B. A horizontal antenna
C. A vertical antenna
D. A traveling wave antenna
~~
3. T9A03 (B)
What type of antenna is a simple dipole mounted so the elements are parallel to the Earth's surface?
A. A ground wave antenna
B. A horizontal antenna
C. A rhombic antenna
D. A vertical antenna
~~
4. T9A04 (A)
What is a disadvantage of the "rubber duck" antenna supplied with most hand held radio transceivers?
A. It does not transmit or receive as effectively as a full sized antenna
B. It is much more expensive than a standard antenna
C. If the rubber end cap is lost it will unravel very quickly
D. It transmits a circular polarized signal
~~
5. T9A05 (C)
How does the physical size of half-wave dipole antenna change with operating frequency?
A. It becomes longer as the frequency increases
B. It must be made larger because it has to handle more power
C. It becomes shorter as the frequency increases
D. It becomes shorter as the frequency decreases
~~
6. T9A06 (B)
What is the advantage of 5/8 wavelength over 1/4 wavelength vertical antennas?
A. They are easier to match to the feed line than other types
B. Their radiation pattern concentrates energy at lower angles
C. They pick up less noise
D. Their radiation pattern concentrates energy at higher angles
~~
7. T9A07 (A)
What is the primary purpose of a dummy load?
A. It does not radiate interfering signals when making tests
B. It will prevent over-modulation of your transmitter
C. It keeps you from making mistakes while on the air
D. It is used for close in work to prevent overloads
~~
8. T9A08 (C)
What type of antennas are the quad, Yagi, and dish?
A. Antennas invented after 1985
B. Loop antennas
C. Directional or beam antennas
D. Antennas that are not permitted for amateur radio stations
~~
9. T9A09 (D)
What is one type of antenna that offers good efficiency when operating mobile and can be easily installed or removed?
A. A microwave antenna
B. A quad antenna
C. A traveling wave antenna
D. A magnet mount vertical antenna
~~
10. T9A10 (A)
What is a good reason not to use a "rubber duck" antenna inside your car?
A. Signals can be 10 to 20 times weaker than when you are outside of the vehicle
B. RF energy trapped inside the vehicle can distort your signal
C. You might cause a fire in the vehicle upholstery
D. The SWR might increase
~~
11. T9A11 (C)
What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?
A. 112 inches
B. 50 inches
C. 19 inches
D. 12 inches
~~
12. T9A12 (C)
What is the approximate length, in inches, of a 6-meter 1/2
wavelength wire dipole antenna?
A. 6 inches
B. 50 inches
C. 112 inches
D. 236 inches

Answers: C C B A C B A C D A C C