radio_basics

This shows you the differences between two versions of the page.

Both sides previous revision Previous revision Next revision | Previous revision Last revision Both sides next revision | ||

radio_basics [2015/11/19 13:28] cwh0009 [Test Quesitons] |
radio_basics [2015/11/19 14:47] cwh0009 [Amplitude] |
||
---|---|---|---|

Line 63: | Line 63: | ||

==== Wavelength ==== | ==== Wavelength ==== | ||

- | The wavelength (λ) is the actual distance traveled by a wave in a single cycle. The wavelength is inversely related to the frequency. This means that as the wavelength increases, the frequency decreases, and as the wavelength decreases, the frequency increases. Frequency and wavelength are related to each other by the speed of light, according to the following equation: | + | The wavelength (λ) is the actual distance traveled by a wave in a single cycle. The wavelength is inversely related to the frequency. This means that as the wavelength increases, the frequency decreases, and as the wavelength decreases, the frequency increases. |

+ | | ||

+ | ^Wavelength | | ||

+ | |{{:wavelength.png}}| | ||

+ | |Wavelength is measured by the distance it takes for a wave to complete a single cycle. A cycle is defined as the amount of space required for a wave to repeat itself. This can be determined from any point in the wave. The diagram above shows the wavelength measured from peak-to-peak, along the central axis, and trough-to-trough. All of these wavelengths are the same. | | ||

+ | |Image credits: Richard Lyon. [[https://commons.wikimedia.org/wiki/File:Sine_wavelength.svg|Wikimedia Commons]]. Image reused under a [[https://creativecommons.org/licenses/by-sa/3.0/deed.en|CC BY-SA 3.0]] license. | | ||

+ | | ||

+ | Frequency and wavelength are related to each other by the speed of light, according to the following equation: | ||

{{:frequency_equation.png}} | {{:frequency_equation.png}} | ||

Line 83: | Line 90: | ||

Using this equation, you can quickly convert between a station's frequency and its wavelength. | Using this equation, you can quickly convert between a station's frequency and its wavelength. | ||

- | |||

==== Amplitude ==== | ==== Amplitude ==== | ||

+ | Amplitude is the magnitude of a wave. One example of the amplitude of a wave is the height of a wave in the sea. The amplitude of an electrical signal is measured in Volts (V). There are numerous methods used to measure the voltage in a signal. The simplest method is to measure from a central axis to a peak, this is called the peak voltage. Another way of reporting the voltage is the peak-to-peak voltage. This is measured from the highest peak of an electrical signal to the lowest trough. The peak-to-peak voltage is double the peak voltage. The root means square voltage (RMS voltage) is calculated by dividing the peak voltage by the square root of 2. | ||

+ | |||

+ | If the voltage of an alternating current (AC) signal is measured with a simple voltmeter, the voltage reported is the RMS voltage. This is typically 120 V in the United States. The actual form of the wave can be examined using a tool called an oscilloscope. | ||

+ | |||

+ | ^Wave Amplitude | | ||

+ | |{{:amplitude.png|}}| | ||

+ | |There are different methods of measuring the amplitude. The numbers indicated (1) the peak amplitude, (2) the peak-to-peak amplitude, (3) the root means square amplitude (RMS), and (4) the wavelength (which is not an amplitude). A standard AC electrical power outlet carries 120 Volts at 60 Hz. AC voltages are reported as root mean square voltages. The actual peak amplitude is about 170 Volts and the peak-to-peak voltage is about 340 Volts. | | ||

+ | |Image credits: Matthias Krüger. [[https://commons.wikimedia.org/wiki/File:Sine_voltage.svg|Wikimedia Commons]]. This image was released into the Public Domain by the author. | | ||

==== Phase ==== | ==== Phase ==== | ||

+ | Phase is a little more abstract than the previous three concepts. Phase is a measure of the starting angle of a trigonometric function. For example, a sine wave has an amplitude of 0 at 0°. A cosine wave has an amplitude of 1 at 0 degrees. A sine wave with a phase shift of 90° also has an amplitude of 1 at 0 degrees and is identical to an cosine wave. This is represented by the expression sin(x + 90°) = cos(x). | ||

+ | |||

+ | ---- | ||

+ | |||

+ | **Note:** If you are unfamiliar with trigonometric functions, you may wish to [[http://www.visionlearning.com/en/library/Math-in-Science/62/Wave-Mathematics/131|review them]]. You will not be tested on them in the Technician exam, but an understanding of trigonometry is critical to many disciplines in engineering, science, and mathematics. In amateur radio, trigonometric functions are commonly used to express electromagnetic waves, model the behavior of circuits, and express methods of signal modulation. | ||

+ | |||

+ | ---- | ||

+ | |||

+ | Phases of electrical signals represent a shift in time and are almost always reported in relation to other signals. Signals that have the same starting point have a phase shift of 0° relative to each other and are said to be //in phase//. Signals with a phase shift between them are said to be //out of phase// relative to each other. | ||

+ | |||

+ | ^Phase Shifts | | ||

+ | |{{:phase.png?500|}}| | ||

+ | |The phase (θ) of the blue signal is being measured relative to the red signal. In this example, the blue signal is a little less than 45° out of phase with the red signal.| | ||

+ | |Image credits: User [[https://commons.wikimedia.org/w/index.php?title=User:Peppergrower|Peppergrower]]. [[https://commons.wikimedia.org/wiki/File:Phase_shift.svg|Wikimedia Commons]]. Image reused under a [[https://creativecommons.org/licenses/by-sa/3.0/deed.en|CC BY-SA 3.0]] license. | | ||

==== Section Summary ==== | ==== Section Summary ==== | ||

radio_basics.txt · Last modified: 2015/11/19 14:47 by cwh0009