|
|
| Line 1: |
Line 1: |
| {{Unreferenced|date=December 2009}}
| | The writer's name is Christy. Credit authorising is where my main earnings comes from. The favorite pastime for him and his children is to play lacross and he'll be beginning some thing else along with it. I've usually loved living in Alaska.<br><br>My site :: psychic readings online ([http://www.herandkingscounty.com/content/information-and-facts-you-must-know-about-hobbies visit the up coming internet site]) |
| The '''half power point''' of an electronic amplifier stage is that frequency at which the output [[Electric power|power]] has dropped to half of its mid-band value. That is a level of -3 [[Decibel|dB]]. Other names include the [[cutoff frequency]]. | |
| | |
| This occurs when the output [[voltage]] has dropped by 1/√2 or 0.707 (exact: <math>20\log_{10}\left(\tfrac{1}{\sqrt{2}}\right) \approx -3.0103\, \mathrm{dB}</math>) and the power has dropped by half (1/2 or 0.5) (exact: <math>10\log_{10}\left(\tfrac{1}{2}\right) \approx -3.0103\, \mathrm{dB}</math>). A [[bandpass]] amplifier will have 2 half power points, whilst a [[Low-pass filter|low pass]] amplifier will have only one. A [[High-pass filter|high pass]] amplifier stage will have only the lower half power point.
| |
| | |
| The [[Bandwidth (signal processing)|bandwidth]] of an amplifier is usually defined as the difference between the lower and upper half power points. This is therefore also known as the −3 dB bandwidth.
| |
| | |
| == 3 dB ==
| |
| The half power point is approximately 3 dB because <math>\log_{10} 2 = .3010... \approx .3,</math> so <math>10 \log_{10} 2 = 3.010... \approx 3;</math> the decibel measure of a ratio ''r'' is defined as <math>10 \log_{10} r.</math>
| |
| | |
| Using 3 dB rather than the correct value of 3.010... yields a power factor of
| |
| <math>G = 10^\frac{3}{10} \times 1\ = 1.99526... \approx 2 \,</math>
| |
| which differs from a factor of 2 by about 0.24%. As logarithmic errors add, using 6 dB to approximate a factor of 4 difference yields an error of about 0.48%, and so forth.
| |
| | |
| This is the same [[Mathematical coincidence#Concerning base 2|mathematical coincidence]] as <math>2^{10} = 1,024 \approx 1,000 = 10^3</math>, which is the source of the ambiguity of the prefixes [[kilo-]], [[mega-]], etc. in a computing context. Taking the logarithm of both sides of the equation <math>2^{10} \approx 10^3</math> yields <math>10 \log_{10} 2 \approx 3</math>.
| |
| | |
| ==Antennas==
| |
| The '''half power point''' or '''3 dB point''' of an antenna beam is the angle off boresight at which the antenna gain has fallen 3 dB below the peak.
| |
| | |
| == See also ==
| |
| *[[Full width at half maximum]]
| |
| | |
| {{DEFAULTSORT:Half Power Point}}
| |
| [[Category:Electronic amplifiers]]
| |
| [[Category:Antennas]]
| |
The writer's name is Christy. Credit authorising is where my main earnings comes from. The favorite pastime for him and his children is to play lacross and he'll be beginning some thing else along with it. I've usually loved living in Alaska.
My site :: psychic readings online (visit the up coming internet site)