release 1.0 – september 2006 1 antennas once you get your license and that first radio, you’re...

1Release 1.0 – September 2006

Antennas

Once you get your license and that first radio, you’re going to need a good antenna to get your signal on the air. Antennas need not be expensive, but you do need to take some care in selecting the right antenna for the job.


Beam Antennas

A “beam antenna” is an antenna that concentrates signals in one direction. It is designed to focus all of the energy produced by your transmitter in the direction you want to work. Focusing your signal power in one direction makes for a stronger signal in that direction. Beams are effective, but depending on the bands covered and type, they can be expensive.


Beam Antennas - Quad

The quad, Yagi, and dish are all examples of beam antennas. A quad antenna looks something like a metal frame for a box kite. If you look closely, you can see the antenna wires supported by the “X” framework.


Beam Antennas - Yagi

The yagi is a one dimensional beam antenna consisting of several elements. It may be mounted horizontally, as shown here, or vertically.


Beam Antennas - Dish

Another beam antenna is the dish or parabolic reflector. It is often used to receive UHF signals or TV signals beamed from satellites, such as Dish Network ® antennas.


Vertical AntennasA “vertical antenna” is an antenna that

consists of a single element mounted perpendicular to the Earth's surface. Most mobile antennas are verticals.

Verticals usually require some sort of counterpoise to work their best. In a fixed station, a vertical may either be mounted on the ground or on a mast, and it may also have several radials for counterpoise. These radials may be laid out on the ground, as in the next slide, or mounted just underneath the vertical element, as in an elevated ground plane.

In a mobile installation, the metal body of the car usually serves as the counterpoise.


Typical Ground-Mounted Vertical

This is a rough diagram of a ground-mounted vertical. The orange radials you see may be laid along the top of the ground or buried just beneath the surface. Multi-band verticals are sometimes a good compromise between price and performance for a new ham.


Ground Plane Antenna

Here is a ground plane antenna – another type of vertical. It is designed to be mounted on a mast, and it usually has three or four radials coming from the base of the antenna.


Vertical Antenna Design

Many vertical antennas are designed to be equal in length to one-quarter wavelength of the desired operating frequency.

For a 1/4 wave vertical:

234Length (feet) = -----------------

Frequency (MHz)

You’ll need to remember this formula!


Sample Problem from the Question Pool

For example, suppose you want to know the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz.

Using the formula in the previous slide:

234Length = ------ = 1.6 feet

146

To get inches, multiply 1.6 times 12 (since there are 12 inches in a foot) to get 19.2 or about 19 inches.


5/8 Wave Verticals

Some vertical designs call for a 5/8 wave rather than a 1/4 wave. The advantage of 5/8 wavelength over 1/4 wavelength vertical antennas is that their radiation pattern concentrates energy at lower angles. (Radiation pattern describes the shape of the radiated signal, and a lower radiation angle usually means traveling a greater distance – better DX!)


Magnet Mount Verticals (Mag Mounts)

As already noted, verticals are very common in mobile installations. One type of antenna that offers good efficiency when operating mobile and can be easily installed or removed is the magnet mount vertical antenna. They are also fairly inexpensive and don’t require you to drill a hole in that new vehicle!


Horizontal Antennas

A “horizontal antenna” is an antenna that is a simple dipole mounted so the elements are parallel to the Earth's surface. So what’s a dipole?


Dipole Antennas

A dipole antenna is a simple antenna designed to work best on a single band. It consists of two sections that are each approximately one-quarter of the wavelength of that band, so that the total length is equal to about one-half wavelength. The transmission line from the radio is connected to this antenna in the middle of the two sections. It looks something like what you’ll see on the next slide.


Dipole Antenna

This is an example of a dipole antenna. Many hams getting on HF for the first time often start with a dipole. If you have the room for one, the dipole is cheap and easy to build.


More on Dipoles

Dipoles may be mounted either horizontally or vertically, depending on the intended use. Also, they may be made from wire or metal tubing, and are very easy for a new ham to construct. Wire dipoles are also fairly inexpensive and simple to design. With an antenna tuner, they can also be made to work on several bands. For these reasons, they are very popular with new hams on the HF bands.


Dipole DesignSince dipoles are fairly easy to build, it

is important to know how to determine their total length. The formula for the length of a 1/2 wave dipole is:

468Length (feet) = -----------------

Frequency (MHz)

When designing a dipole, you should choose the lowest frequency for the band you want to work!

You will need to remember this formula!


Sample Problem from the Question Pool

What is the approximate length, in inches, of a 6-meter 1/2 wavelength wire dipole antenna?

Now this one can be done two ways. First, you are given the band wavelength already – 6 meters. This is approximate for the band, but it will do. Half of that wavelength is 3 meters. Since there are about 39 inches in a meter, that gives you an answer of 117 inches. The only answer close to that in the question pool question is 112 inches, so that’s the one you go with. But there is another way...


Using the FormulaTo use the formula, you have to pick a

frequency. In the U.S., the six meter band is 50 to 54 MHz. The lowest frequency is 50 MHz, so that’s the one you use. When you apply the formula,

468Length (feet) = ----- = 9.36 feet

50

When you multiply 9.36 times 12 (to get inches), you get 112.32, which is a lot closer to 112. But remember, you use the lowest frequency in the band as your design frequency, or at least the lowest frequency you want to work.


Dipoles – Frequency Goes Up, Length Goes Down

The physical size of half-wave dipole antenna changes with operating frequency. It becomes shorter as the frequency increases.

As you might imagine, the opposite is also true. It becomes longer as the frequency decreases.


Rubber Ducky – Not for the Bathtub

For years, the little antenna that comes with most handheld radios has been called a “rubber duck” or “rubber ducky.” The main advantage of a rubber duck is its size. However, when range is important, the main disadvantage of the "rubber duck" antenna supplied with most hand held radio transceivers is that it simply does not transmit or receive as effectively as a full sized antenna.

If you need to increase the range of your handheld, you’ll have to connect it to a better antenna than the ducky!


Rubber Ducky – Not for the Car, either!

You really don’t want to try to use your "rubber duck" antenna inside your car because signals can be 10 to 20 times weaker than when you are outside of the vehicle. Much of the RF energy leaving your antenna will be absorbed by the metal in your car.


Dummy Load – Dummies Don’t Use Them!

You may remember that a dummy load is used when you are testing a transmitter. It absorbs the RF energy generated by your antenna so that the signals don’t interfere with stations operating on the frequency. The primary purpose of a dummy load is to avoid radiating interfering signals when making tests.


Check-Up Time!

Now let’s try the questions from this group.

You should make a note of any that you miss for later review.


T9A01

What is a beam antenna?

A. An antenna built from metal I-beams

B. An antenna that transmits and receives equally well in all

directionsC. An antenna that concentrates signals in one direction

D. An antenna that reverses the phase of received signals


T9A01 Answer - C

A beam antenna radiates best in only one direction, concentrating the signal power in that direction. HINT: Think flashlight beam or laser beam.


T9A02

What is an antenna that consists of a single element mounted perpendicular to the Earth's surface?

A. A conical monopoleB. A horizontal antennaC. A vertical antennaD. A traveling wave antenna


T9A02 Answer - C

Math whizzes will immediately recognize that perpendicular to the earth is vertical. The rest of us have to learn it now!


T9A03

What type of antenna is a simple dipole mounted so the elements are parallel to the Earth's surface?

A. A ground wave antennaB. A horizontal antennaC. A rhombic antennaD. A vertical antenna


T9A03 Answer - B

The math whizzes get another break. If the elements are parallel to the earth's surface, they must be horizontal.


T9A04

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


T9A04 Answer - A

The rubber duck antenna used on most handhelds is a compromise antenna. It is OK for casual operating, but there are times when it just isn't good enough. If you need the range, you are better off disconnecting the rubber duck and connecting a full size antenna.


T9A05

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


T9A05 Answer - C

The length of the dipole is inversely related to frequency. As the frequency increases, the dipole length decreases.


T9A06

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 noiseD. Their radiation pattern concentrates energy at higher angles


T9A06 Answer - B

The 5/8 wavelength antenna (or simply, "5/8 wave") has the advantage of a lower angle radiation pattern. Radiation at a lower angle is better, because it sends the signal closer to the ground, rather than up into the sky where it is not as likely to be heard.


T9A07

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


T9A07 Answer - A

A dummy load is hooked up in the place of an antenna to allow an operator to test or tune a transmitter without radiating a signal that could interfere with other stations.


T9A08

What type of antennas are the quad, Yagi, and dish?

A. Antennas invented after 1985B. Loop antennasC. Directional or beam antennasD. Antennas that are not permitted for amateur radio stations


T9A08 Answer - C

Each of these antennas - the quad, the yagi and the dish - are directional antennas. They are designed to radiate or receive signals best in one direction only.


T9A09

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


T9A09 Answer - D

A magnet mount vertical antenna (also known as a "mag mount") uses a magnet at its base to hold it to the metal roof or trunk of a car. It can easily be removed for storage or use on another vehicle.


T9A10

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


T9A10 Answer - A

Remember that a rubber duck antenna is a compromise antenna. It is small so that it can be portable, but it is not as efficient as a full size antenna. Also, when you are inside a car using the rubber duck, much of the signal is absorbed by the metal that surrounds you. It is much better to get a full size mobile antenna outside the vehicle where it will do the most good.


T9A11

What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?

A. 112 inchesB. 50 inchesC. 19 inchesD. 12 inches


T9A11 Answer - C

The formula for figuring the length of a quarter wave vertical is:

234

Length (feet) = ----------------

Frequency in MHz

So...


T9A11 Answer - C

234 Length = --- = 1.625 feet 144

To convert that to inches, multiply 1.625 times 12 (there are 12 inches in a foot) to give you 19.5 inches. That is very close to the best answer of 19 inches.


T9A12

What is the approximate length, in inches, of a 6-meter 1/2 wavelength wire dipole antenna?

A. 6 inchesB. 50 inchesC. 112 inchesD. 236 inches


T9A12 Answer - C

Here, the wavelength is 6 meters. A half wavelength is 3 meters. Since there are approximately 39 inches in a meter, 3 times 39 will give you 117, which is close to the best answer.

There is another way that will get you a little closer...


T9A12 Answer - CThe formula for determining the length of a half wave dipole in

feet is:

468Length (feet) = ----------------

Frequency in MHz

To use this formula, you have to know that the lowest frequency of the six meter band is 50 Mhz.

468Then... Length = --- = 9.36 feet

50

To convert to inches, multiply 9.2 times 12 to get 112.32 inches.


Group T9B

Group T9B covers propagation, fading, multipath distortion, reflections, radio horizon, terrain blocking, wavelength

vs. penetration, and antenna orientation.


Propagation of Radio Waves

Radio waves at different frequencies travel through space very differently. How they travel determines how far away you can communicate. The study of “propagation,” or how radio waves move through space, can be a very complicated subject, but every amateur needs to know some of the basics. Fortunately, the basics are not hard.


The IonosphereThere are

several layers of charged particles surrounding the earth. Together, these layers form the “ionosphere.” The layers of the ionosphere are constantly changing. They change as the seasons change, as well as during the course of a day.


The Ionosphere

The ionosphere is very important for radio communications because it has the ability to reflect some radio waves back to earth. This allows radio to be used to communicate for long distances. Whether or how much a radio wave is reflected depends on the frequency of the radio wave as well as the condition of the ionosphere at any given time.


Radio Horizon

To a certain extent, all radio waves travel away from an antenna along the ground. But because the earth is curved and radio waves travel in straight lines, sooner or later the radio waves will be too high above the surface to be picked up by a radio receiver. The radio horizon is the point where radio signals between two points are blocked by the curvature of the Earth.


Radio Horizon and Visual Horizon

We usually think of the horizon as the farthest point of land or ocean where it appears to meet the sky. Standing on a beach and looking out on the ocean, this may be about thirteen miles. We usually call this “line of sight.” If we climb up a tower (where antennas live) that line of sight distance can be much greater. But radio waves traveling along the ground from that same tower can actually travel beyond the visual line of sight. The distance they can travel is to the radio horizon, rather than the visual horizon. How far that distance is depends on the frequency of the radio wave.


Radio Horizon of VHF and UHF Waves

VHF and UHF Radio signals usually travel about a third farther than the visual line of sight distance between 2 stations because the Earth seems less curved to radio waves than to light. Another way of saying this is that radio waves are bent slightly as they move along the surface.


VHF and UHF Signals – Line of Sight to the Radio Horizon

Only!

VHF and UHF signals are not normally heard over long distances because they are usually not reflected by the ionosphere.


VHF DX

While long distance VHF contacts are fairly rare, they can occur due to a phenomenon known as “sporadic E.” On rare occasions, VHF waves may be reflected off the “E” layer of the ionosphere. So when you hear a VHF signal from long distances, one possible cause is sporadic E reflection from a layer in the ionosphere. (Note the “E” layer in the diagram a few slides back.)


Receiver Overload

Sometimes you might be listening to VHF or UHF and hear sudden bursts of tones or fragments of different conversations that interfere with these signals. If so, one likely cause is that strong signals are overloading the receiver and causing undesired signals to be heard.


Signal Fluctuations

Sometimes you may be talking on a mobile or portable radio and the other station may report a change in your signal quality. Suppose a station reports that your signals were strong just a moment ago, but now they are weak or distorted. You might want to try moving a few feet, since random reflections may be causing multi-path distortion. This can easily happen near large buildings, under bridges, or close to large metal structures.


UHF and VHF Signals Inside Buildings

UHF signals often work better inside of buildings than VHF signals because the shorter wavelength of UHF signals allows them to more easily penetrate urban areas and buildings. Cell phones and many cordless phones operate in the UHF region, in part because of this difference.


Vertical Polarization

Most repeater antennas are verticals, so their signals are vertically polarized. As a result, if you are using your hand-held VHF or UHF radio to reach a distant repeater, one good thing to remember is to keep your antenna as close to vertical as you can. This will keep the polarization of your signal vertical as well, increasing your ability to make it into the repeater.


More on Polarization

Polarization of your antenna can make a significant difference. Signals are received much more efficiently if both radios are either vertical or horizontal If the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization (one vertical and the other horizontal) signals could be as much as 100 times weaker!


Obstructions on UHF and VHF

Since VHF and UHF communications are mostly line of sight to the radio horizon, buildings or other large objects can sometimes block this line of sight. If this happens, you want to relocate if possible. If you can’t move, another possible way to reach a distant repeater if buildings or obstructions are blocking the direct line of sight path might be to try using a directional antenna to find a path that reflects signals to the repeater. This way, you might be able to use large obstructions to your advantage.


Picket Fencing

“Picket fencing” is a term commonly used to describe the rapid fluttering sound sometimes heard from mobile stations that are moving while transmitting. It sounds a little like a kid dragging a stick across a picket fence as he walks along. This is caused by radio waves being received with reflections from multiple pathways (multi-path) from the other transmitter to you.


Check-Up Time!




T9B01

Why are VHF/UHF signals not normally heard over long distances?

A. They are too weak to go very far B. FCC regulations prohibit them from going more than 50 miles

C. VHF and UHF signals are usually not reflected by the ionosphere

D. They collide with trees and shrubbery and fade out


T9B01 Answer - C

The ionosphere routinely reflects high frequency (HF) waves so that they can travel long distances. With the exception of six meters, VHF and UHF almost always travel line of sight and are not usually reflected by the ionosphere.


T9B02

What might be happening when we hear a VHF signal from long distances?

A. Signals are being reflected from outer space

B. Someone is playing a recording to usC. Signals are being reflected by lightning storms in our area

D. A possible cause is sporadic E reflection from a layer in the ionosphere


T9B02 Answer - D

The E layer of the ionosphere may sometimes reflect VHF waves and long distance reception is possible. This is not common, but as the name suggests, is sporadic.


T9B03What is the most likely cause of sudden bursts of tones or fragments of different conversations that interfere with VHF or UHF signals?

A. The batteries in your transceiver are failing B. Strong signals are overloading the receiver and

causing undesired signals to be heardC. The receiver is picking up low orbit satellitesD. A nearby broadcast station is having transmitter

problems


T9B03 Answer - B

Strong nearby signals can overload a receiver.


T9B04

What is the radio horizon?

A. The point where radio signals between two points are blocked by the curvature of the Earth

B. The distance from the ground to a horizontally mounted antenna

C. The farthest point you can see when standing at the base of your antenna tower

D. The shortest distance between two points on the Earth's surface


T9B04 Answer - A

The radio horizon is usually farther away than the visible horizon because radio waves can bend slightly to follow the curvature of the earth.


T9B05

What should you do if a station reports that your signals were strong just a moment ago, but now they are weak or distorted?

A. Change the batteries in your radio to a different type

B. Speak more slowly so he can understand your better

C. Ask the other operator to adjust his squelch control

D. Try moving a few feet, random reflections may be causing multi-path distortion.


T9B05 Answer - D

Many surfaces can reflect radio waves, particularly VHF and UHF waves. Sometimes these reflections can mix and interfere with the main signal, causing your signal to be weak or distorted. If you are near large objects such as buildings or bridges, the cure might be to move away from them.


T9B06

Why do UHF signals often work better inside of buildings than VHF signals?

A. VHF signals lose power faster over distance

B. The shorter wavelength of UHF signals allows them to more easily penetrate urban areas and buildings

C. This is incorrect; VHF works better than UHF inside buildings

D. UHF antennas are more efficient than VHF antennas


T9B06 Answer - B

Because of their shorter wavelength, UHF signals can more easily penetrate buildings. This is also true of cell phones which usually operate in the 800-900 MHz range. Even though they are relatively low powered transceivers, they still work inside many buildings.


T9B07

What is a good thing to remember when using your hand-held VHF or UHF radio to reach a distant repeater?

A. Speak as loudly as possible to help your signal go farther

B. Keep your transmissions short to conserve battery power

C. Keep the antenna as close to vertical as you can

D. Turn off the CTCSS tone


T9B07 Answer - C

When trying to reach a distant repeater, you should try to keep your antenna vertical. Why? Because the antenna on the repeater is vertical, and it can better receive signals coming from an antenna that is also vertical. The fancy name for this is vertical polarization.


T9B08

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?

A. The modulation sidebands might become inverted

B. Signals could be as much as 100 times weaker

C. Signals have an echo effect on voicesD. Nothing significant will happen


T9B08 Answer - B

Polarization makes a big difference in ability to receive. Ideally, both the transmitting and receiving antenna should be polarized the same way - either both vertical or both horizontal.


T9B09

What might be a way to reach a distant repeater if buildings or obstructions are blocking the direct line of sight path?

A. Change from vertical to horizontal polarization

B. Try using a directional antenna to find a path that reflects signals to the repeater

C. Ask the repeater owners to repair their receiver

D. Transmit on the repeater output frequency


T9B09 Answer - B

If you can use a directional antenna, you might be able to "bounce" the signal off of some object such as a building that has a clear line of sight to the repeater.


T9B10

What term is commonly used to describe the rapid fluttering sound sometimes heard from mobile stations that are moving while transmitting?

A. Flip-flopping

B. Picket fencing

C. Frequency shifting

D. Pulsing


T9B10 Answer - B

Think of the kid running a stick along a picket fence and you'll see why this is called "picket fencing."


T9B11

Why do VHF and UHF Radio signals usually travel about a third farther than the visual line of sight distance between 2 stations?

A. Radio signals move somewhat faster than the speed of light and travel farther in the same amount of time

B. Radio waves are not blocked by dust particles

C. The Earth seems less curved to radio waves than to light

D. Radio waves are blocked by dust particles


T9B11 Answer - C

Another way of saying this is that radio waves will bend slightly to follow the curvature of the earth. Either way you look at it, VHF and UHF waves can travel a little farther near to the ground than the visible horizon.


Group T9C

Group T9C covers feedlines types, losses vs. frequency, SWR concepts, measuring

SWR, matching and power transfer, weather protection, and feedline failure

modes.


Standing Wave Ratio (SWR)

In general terms, standing wave ratio (SWR) is a measure of how well a load is matched to a transmitter. This load is a combination of the antenna and feedline.


Impedance and Best SWR

Impedance is a quantity we measure to determine SWR. Like resistance, it is measured in ohms. A typical amateur radio transmitter has an impedance of 50 ohms at the feed point (where it connects to the antenna). In a perfect world, the feedline and antenna should have an impedance of 50 ohms as well. If it does, this is as good as it gets. We say that the SWR is 1:1 (or “1 to 1”). A reading on a SWR meter of 1 to 1 indicates a perfect impedance match between the antenna and the feed line.


Erratic SWR Readings

Your SWR may be very good, or not so good, but it should not change very much when you key the transmitter. If you see erratic changes in SWR readings, you should suspect a loose connection in your antenna or feedline. When installing and connecting any antenna, you should always make certain that your electrical connections are good and tight.


SWR Protection

Most solid state radios work at their best with an SWR of near 1 to 1. They will continue to work if the SWR is a little higher than that, but if the SWR gets too high, the radio will begin to reduce power to avoid damage. 2 to 1 is the SWR value where the protection circuits in most solid-state transmitters begin to reduce transmitter power. If you begin to see a drop in output power, you might want to check your SWR.


Power Lost due to High SWR

As SWR increases, the efficiency of your transmitted signal decreases. This is because some of your transmit power is lost in the feed line. This power lost in the feed line is converted into heat by losses in the line. This is not good news to a ham.


Forward Power and Reflected Power

Forward Power is the power going from the radio to the feed line. Reflected power is the power that is being reflected back to the radio because of a poor impedance match. The presence of reflected power indicates higher than 1 to 1 SWR. Because of this, you can also use a directional wattmeter to determine whether your feedline and antenna are properly matched to your transmitter. Significant reflected power indicates a poor match.


Coaxial Cable Failure

Coaxial cable is widely used as a feedline in amateur radio. Sometimes, it fails. The most common reason for failure of coaxial cables is moisture contamination. If moisture gets inside of the cable, it can corrode the wire or shielding, change the impedance of the cable or even cause a short.


Coaxial Cable and SWRCoaxial cable

(or “coax”) works best when the antenna system has a low SWR. It is important to have a low SWR in an antenna system that uses coaxial cable feedline to allow the efficient transfer of power and reduce losses. It is more critical to have this match with coax than with some other types of feedline such as open wire or ladder line such as shown here.


Old Coax

Nothing lasts forever, including coax. Older coaxial cables that are exposed to weather and sunlight for several years can show a dramatic increase in losses. Coax exposed to the weather should be replaced every few years.


Coax Covering

The outer sheath of most coaxial cables black because black provides the best protection against ultraviolet damage.


Impedance of Coax

The impedance of the most commonly used coaxial cable in typical amateur radio installations is 50 ohms. This represents a good match to the typical transmitter impedance of 50 ohms.


Advantages of Coax

Coaxial cable is used more often than any other feed line for amateur radio antenna systems because it is easy to use and requires few special installation considerations. There are other feed lines that have less loss, can handle more power, or are less expensive than coax, but overall, coax is a good compromise because it is easy to install and use.


Check-Up Time!




T9C01

What, in general terms, is standing wave ratio (SWR)?

A. A measure of how well a load is matched to a transmitter

B. The ratio of high to low impedance in a feed line

C. The transmitter efficiency ratioD. An indication of the quality of your station ground connection


T9C01 Answer - A

The "load" is usually the combination of antenna and feed line. The radio and load perform best when they are closely matched. When they are perfectly matched, the SWR is 1 to 1, or 1:1.


T9C02

What reading on a SWR meter indicates a perfect impedance match between the antenna and the feed line?

A. 2 to 1B. 1 to 3C. 1 to 1D. 10 to 1


T9C02 Answer - C

An SWR of 1 to 1 is as good as it gets. The radio performs at its best with a low SWR.


T9C03

What might be indicated by erratic changes in SWR readings?

A. The transmitter is being modulated B. A loose connection in your antenna or feed line

C. The transmitter is being over modulated

D. Interference from other stations is distorting your signal


T9C03 Answer - B

If the SWR is not fairly steady, you need to see whether the antenna is getting a steady signal from the radio. If it isn't, the most likely cause is a loose connection.


T9C04

What is the SWR value where the protection circuits in most solid-state transmitters begin to reduce transmitter power?

A. 2 to 1B. 1 to 2C. 6 to 1D. 10 to 1


T9C04 Answer - A

High SWR can damage modern transceivers. However, most transceivers are designed to automatically reduce power output when the SWR goes up to 2 to 1 or higher to avoid being damaged. The higher the SWR, the more the power will be reduced. If you notice a decrease in power, check your SWR.


T9C05

What happens to the power lost in a feed line?

A. It increases the SWRB. It comes back into your transmitter and could cause damage

C. It is converted into heat by losses in the line

D. It can cause distortion of your signal


T9C05 Answer - C

High SWR can result in wasted transmit power. You want all those watts to be radiated from your antenna as a signal, but a high SWR will cause some of that power to be converted to heat. From a ham's point of view, that's wasted energy.


T9C06

What instrument other than a SWR meter could you use to determine if your feedline and antenna are properly matched?

A. VoltmeterB. OhmmeterC. Iambic pentameterD. Directional wattmeter


T9C06 Answer - D

A directional wattmeter measures the power leaving your radio, and the power returning back to your radio. Ideally, there should not be any power returning to the radio. If there is, your SWR needs to be checked.


T9C07

What is the most common reason for failure of coaxial cables?

A. Moisture contamination

B. Gamma rays

C. End of service life

D. Overloading


T9C07 Answer - A

Coaxial cable (or "coax") can be harmed by moisture getting inside. When you put up an antenna, you should always use a good sealant around connectors to keep water out.


T9C08

Why is it important to have a low SWR in an antenna system that uses coaxial cable feedline?

A. To reduce television interference B. To allow the efficient transfer of power and reduce losses

C. To prolong antenna life D. To keep your signal from changing polarization


T9C08 Answer - B

You can use a tuner to match the antenna to a transmitter, but if the SWR of an antenna is high, coax is not as efficient for transferring power as other types of feed line and the losses can be fairly high when the antenna system is not resonant.


T9C09

What can happen to older coaxial cables that are exposed to weather and sunlight for several years?

A. Nothing, weather and sunlight do not affect coaxial cable

B. The cable can shrink and break

C. Losses can increase dramatically

D. It will short-circuit


T9C09 Answer - C

Although coax is not likely to shrink or break, its efficiency will decrease after several years of exposure to the weather.


T9C10

Why is the outer sheath of most coaxial cables black in color?

A. It is the cheapest color to use

B. To see nicks and cracks in the cable

C. Black cables have less loss

D. Black provides protection against ultraviolet damage


T9C10 Answer - D

Ultraviolet light in sunlight can degrade certain types of plastic over time. Using black plastic as a cover for coax helps to protect it from harmful ultraviolet (UV) rays, just like your shades protect your eyes from these same UV rays.


T9C11

What is the impedance of the most commonly used coaxial cable in typical amateur radio installations?

A. 8 OhmsB. 50 OhmsC. 600 OhmsD. 12 Ohms


T9C11 Answer - B

50 ohms is a good number to remember. Most amateur transceivers are designed to use 50 ohm coax cable for feedline.


T9C12

Why is coaxial cable used more often than any other feed line for amateur radio antenna systems?

A. It is easy to use and requires few special installation considerations

B. It has less loss than any other type of feed line

C. It can handle more power than any other type of feed line

D. It is less expensive than any other types of line


T9C12 Answer - A

There are better types of feed line than coax for certain purposes, but the main advantage of coax is that it is easy to use.


Nine Down, One to Go!You’re Almost There!

This concludes Study Guide # 3.

Once you are satisfied that you can answer 80% of the questions in this Sub-element, you

are ready to move on to Study Guide # 4.

release 1.0 – september 2006 1 antennas once you get your license and that first radio, you’re...

Documents

vertical antennas

quad antenna

ground plane antenna

good antenna

dimensional beam antenna

right antenna

antenna wires

beam antennas dish