The term "beam antenna" is just another name for a directional antenna; it's an antenna that concentrates signals in one direction. You can think of it as "beaming" the signals in a certain direction.

This term may be in common usage, but using it to identify an antenna is not a good practice. More accurate alternatives are "high gain", "directional", or "electrically large" antenna.

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Tags: antenna directional antenna

Remember that with an electromagnetic (RF) signal, it is the electrical field that emanates outwards parallel to the originating antenna, which means with a vertical antenna it is the electric (not the magnetic!) field that is perpendicular to the Earth.

Using the Right Hand Rule of electromagnetic fields would tell you that if the fingers wrap in the direction of the magnetic (B) field, the thumb will point in the direction of the electric (E) field.

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Tags: antenna propagation antenna polorization

The orientation of the conductor of an antenna relative to the earth's surface determines its "polarization". If the polarization of the sending station's antenna does not match the polarization of the receiving station's antenna significant loss in signal can be the result.

If the antenna is vertical (perpendicular to the ground), as most antennas are thought to be, then it is "vertically polarized" and if it is horizontal (parallel to the ground), then it is "horizontally polarized".

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Tags: antenna polorization antenna

Smaller antennas use electrical components to maintain resonance on the target frequencies, but having less surface area they don't absorb (or emit) as much power. Therefore they do not transmit or receive as effectively as a regular full-sized antenna.

As a general rule of thumb, the shorter the antenna on a given band the worse the performance will be and the longer the better. Of course, other factors such as the resonance of the antenna on the frequencies used can also affect this!

The only reasons to use rubber duck type antennas are that they take up less space and are usually more durable than longer antennas, along with generally being cheaper. This makes it easier to keep an HT on your belt compared to a possibly much longer antenna. These sorts of tradeoffs are more typically worthwhile for commercial users such as security guards who will be near a repeater or other HT users almost all the time, so they aren't nearly as concerned as much about gain as most amateur operators.

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Tags: troubleshooting antenna

Antenna length is inversely related to frequency. The higher the frequency, the SHORTER the wavelength. Cannot be longer!

Another way to remember it: Antenna length is directly related to the wavelength. Recalling that wavelength and frequency are inversely related, we must shorten the antenna length.

Also note that coils are inductors, and adding inductors to an antenna is a way to electrically lengthen the antenna, therefore adding a coil and lengthening the antenna both achieve the same result. Since there is no 'All of the above' answer, you can immediately eliminate those two answers.

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Tags: antenna radio waves

These are all examples of "beam antennas", also called Directional Antennas. Yagi are the most common type in ham radio and you've probably seen TV antennas that are yagi antennas; they have long elements in the back and short ones in the front and make a sort of V shape with their outline. Dish antennas, such as those commonly used by satellite TV systems, are another type, and are much more obviously directional.

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Tags: directional antenna antenna

A rubber duck antenna is a sub-performant antenna to start out with, but when you're inside your car you are surrounded by a metal shield that impedes the RF energy to and from your radio, which means that the signal will often be significantly weaker than if you were outside of your vehicle. In addition some rubber duck antennas are too long to be held vertically which changes the polarization of the signal and causes additional loss.

One easy solution to this is to get a cheap magnetic mount antenna that can be placed on top of your car and then connected to your handheld radio. These can be found for under $20 on ebay.

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Tags: antenna troubleshooting

146 MHz is in the 2 meter band. \(\frac{300}{146}\approx2\text{ m}\)

2 meters is almost 80 inches.

\(\frac{1}{4}\times80\text{ in} = 20\text { in}\).

19 inches is the closest answer.

OR

\begin{align} \frac{300}{146\text{ MHz}} = 2.0547 \text{ m}\\ 2.0547 \text{ m} \times 39.37 \text{ in/m} = 80.89\text{ in} \end{align}

Then to determine size of antenna from the question, \(80.89 \times \frac{1}{4}[\lambda] = 20.22 \text{ in}\) rounded to nearest whole number is \(20\text{ in}\).

OR

The speed of light may be expressed as \(11.8 \text{ GHz}\times\text{inches}\). To get the length of the wave divide by the frequency in GHz.

\begin{align} \frac{11.8 \text{ GHz}\times\text{in}}{0.146\text{ GHz}} \approx 80\text{ in} \end{align} \[80 \times \frac{1}{4}[\lambda] = 20 \text{ in}\]

Since the question asked for quarter wave we must divide by four. For more information Google: "speed of light in gigahertz inches".

Mnemonic: (146 MHz) 14+6=20 19 is the closest.

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Tags: antenna 2 meter math

There are many factors that will affect the amount of length needed for the 1/2 wave dipole antenna, such as the physical characteristics of the wire or nearby conductive sources. But the easiest way to solve this problem is to remember that a meter is a little longer than a yard, or approximately 39 inches. To calculate this, half of the 6 meter wavelength would be 3 meters. To convert that to inches, multiply by 39 inches per meter:

\begin{align} 3\text{ m} \times 39\text{ in/m} = 117\text{ in} \end{align}

112 inches is the closest to this.

For those interested in the formula to get the closest answer:

To get half-wavelength dipole antenna lengths in feet, divide 468 by the frequency in megahertz:

1. First convert the wavelength to the frequency in megahertz. Approximate speed of light divided by length in meters: \[\frac{300}{6} = 50\text{ MHz}\]
2. Then divide 468 by that number: \[\frac{468}{50} = 9.36 \text{ feet}\]
3. With 12 inches in a foot, you get \[9.36\text{ ft}\times12\text{ in} = 112.32\text{ in}\]

Quarter wavelength dipole is the same, but divide 234 by the frequency in megahertz. This is easier to remember (since 234's digits are sequential), so just remember that one and convert up when needed!

ALTERNATE METHOD

1. We are looking for a half wavelength antenna length, so we can begin by dividing the 6 meter wavelength by 2, which gives us a 3 meter wavelength

2. Convert 3 meter wavelength to frequency in MHz \[\frac{300}{3} = 100\text{ MHz}\]

3. Then divide that by 1000 to convert it to GHz \[\frac{100}{1000} = .1\text{ GHz}\]

4. Now that you have converted to GHz, you can divide the speed of light expressed as 11.8 GHz×inches (gigahertz inches) by the frequency in GHz to arrive at a length in Inches \[\frac{11.8}{.1} = 118\text{in}\]

112 inches is the closest to this.

Mnemonic: 6 and 12 are related, so answer is 112.

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Tags: antenna 6 meter math

The radio waves emit out along the length of the dipole outward, and is strongest at the middle. There is little to no RF energy coming out the ends of the antenna. So Broadside is the correct answer. A good way to think about dipoles is to picture a fluorescent tube or a glow stick. They appear brightest when looking at the side, but you don't see anything when looking at the ends.

An isotropic antenna radiates equally in all directions. This kind of antenna is only theoretical, there is no actually isotropic antenna in reality.

The feed line has no effect in the emission of a dipole antenna if properly chocked off by a baluns

see http://en.wikipedia.org/wiki/Dipole_antenna

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Tags: antenna polorization antenna propagation

Think of gain as a focusing quality of an antenna, like the reflector on a flash light.

By the geometry of the antenna we can change how the antenna emits radio waves, or RF energy. We can focus it like a spot light by using a yagi antenna, or we can let it flood out more evenly like a room shop light, by using a dipole antenna.

The higher the gain, the more focused the beam of RF energy, which results in an increased signal strength in a particular direction.

Remember that, since energy can't come from nowhere, there cannot be a power increase from nothing. If there was something in the middle adding power (amplifying) the signal, it would be an amplifier.

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Tags: antenna transmit power