The decibel is a unit of measurement used to express the ratio of one value of a power or field quantity to another on a logarithmic scale, the logarithmic quantity being called the power level or field level, respectively. It can be used to express a change in value or an absolute value. In the latter case, it expresses the ratio of a value to a fixed reference value; when used in this way, a suffix that indicates the reference value is often appended to the decibel symbol. For example, if the reference value is 1 volt, then the suffix is "V", and if the reference value is one milliwatt, then the suffix is "m".
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Typically, prior to some process, such as transmission over cable, or recording to phonograph record or tape, the input frequency range most susceptible to noise is boosted. This is referred to as "pre-emphasis" – "pre-" the process the signal will undergo. Later, when the signal is received, or retrieved from recording, the reverse transformation is applied ("de-emphasis") so that the output accurately reproduces the original input. Any noise added by transmission or record/playback, to the frequency range previously boosted, is now attenuated in the de-emphasis stage.
In telecommunications, net gain is the overall gain of a transmission circuit. Net gain is measured by applying a test signal at an appropriate power level at the input port of a circuit and measuring the power delivered at the output port. The net gain in dB is calculated by taking 10 times the common logarithm of the ratio of the output power to the input power.
The signal-to-crosstalk ratio at a specified point in a circuit is the ratio of the power of the wanted signal to the power of the unwanted signal from another channel.
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 indicates more signal than noise.
In telecommunication, a standard test signal is a single-frequency signal with standardized level used for testing the peak power transmission capability and for measuring the total harmonic distortion of circuits or parts of an electric circuit.
Reduced-carrier transmission is an amplitude modulation (AM) transmission in which the carrier signal level is reduced to reduce wasted electrical power. Suppressed-carrier transmission is a special case in which the carrier level is reduced below that required for demodulation by a normal receiver.
In telecommunications, a third-order intercept point (IP3) is a specific figure of merit associated with the more general Third Order Intermodulation (TOI) distortion, which is a measure for weakly nonlinear systems and devices, for example receivers, linear amplifiers and mixers. It is based on the idea that the device nonlinearity can be modeled using a low-order polynomial, derived by means of Taylor series expansion. The third-order intercept point relates nonlinear products caused by the third-order nonlinear term to the linearly amplified signal, in contrast to the second-order intercept point that uses second-order terms. (IP3) is the generally accepted unambiguous term for the third-order intercept point, although one occasionally sees the use of TOI for this figure-of-merit, such use is considered as incorrect by experts in the field.
In telecommunication, a transmission level point (TLP) is a physical test point in an electronic circuit, typically a transmission channel, where a test signal may be inserted or measured. Typically, various parameters, such as the power of the signal, noise, or test tones inserted are specified or measured at the TLP.
8VSB is the modulation method used for broadcast in the ATSC digital television standard. ATSC and 8VSB modulation is used primarily in North America; in contrast, the DVB-T standard uses COFDM.
Multichannel television sound, better known as MTS, is the method of encoding three additional channels of audio into an analog NTSC-format audio carrier.
This is an index of articles relating to electronics and electricity or natural electricity and things that run on electricity and things that use or conduct electricity.
Audio system measurements are made for several purposes. Designers take measurements so that they can specify the performance of a piece of equipment. Maintenance engineers make them to ensure equipment is still working to specification, or to ensure that the cumulative defects of an audio path are within limits considered acceptable. Some aspects of measurement and specification relate only to intended usage. Audio system measurements often accommodate psychoacoustic principles to measure the system in a way that relates to human hearing.
In telecommunications, Continuous Tone-Coded Squelch System or CTCSS is one type of circuit that is used to reduce the annoyance of listening to other users on a shared two-way radio communications channel. It is sometimes referred to as tone squelch. It does this by adding a low frequency audio tone to the voice. Where more than one group of users is on the same radio frequency, CTCSS circuitry mutes those users who are using a different CTCSS tone or no CTCSS. It is sometimes incorrectly referred to as a sub-channel because no additional channels are created. All users with different CTCSS tones on the same channel are still transmitting on the identical radio frequency, and their transmissions interfere with each other, however the interference is masked under most conditions. The CTCSS feature also does not offer any security.
The SMPTE color bars is a trademarked television test pattern used where the NTSC video standard is utilized, including countries in North America. The Society of Motion Picture and Television Engineers (SMPTE) refers to it as Engineering Guideline EG 1-1990. Its components are a known standard. Comparing it as received to the known standard gives video engineers an indication of how an NTSC video signal has been altered by recording or transmission and what adjustments must be made to bring it back to specification. It is also used for setting a television monitor or receiver to reproduce NTSC chrominance and luminance information correctly. It was originally conceived by Norbert D. Larky and David D. Holmes of RCA Laboratories and first published in RCA Licensee Bulletin LB-819 on February 7, 1951. U.S. patent 2,742,525 Color Test Pattern Generator was awarded on April 17, 1956 to Norbert D. Larky and David D. Holmes. Previously categorized by SMPTE as ECR 1-1978, its development was awarded an Engineering Emmy in 2001-2002.
An extended version of SMPTE Color Bars signal, developed by the Japanese Association of Radio Industry and Businesses as ARIB STD-B28 and standardized as SMPTE RP 219:2002 was introduced to test HDTV signal with an aspect ratio of 16:9 that can be down converted to a SDTV color bar signal with an aspect ratio of either 4:3 or 16:9. The Color Bar signal is generated with unconventionally slow rise and fall time value to facilitate video level control and monitor color adjustments of HDTV and SDTV equipment. Digital test images generated following the SMPTE RP 219:2002 specifications and adapted to perfectly fit 114 standard and non-standard resolutions for both 16bpp and 8bpp, are freely available in the COLOR dataset of the TESTIMAGES archive.
Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency components will form additional components at frequencies that are not just at harmonic frequencies of either, like harmonic distortion, but also at the sum and difference frequencies of the original frequencies and at sums and differences of multiples of those frequencies.
In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, inductive, or conductive coupling from one circuit or channel to another.
dBm0 is an abbreviation for the power in dBm measured at a zero transmission level point.
IEC 61334, known as Distribution automation using distribution line carrier systems, is a standard for low-speed reliable power line communications by electricity meters, water meters and SCADA.
It is also known as spread frequency-shift keying (S-FSK) and was formerly known as IEC 1334 before IEC's most recent renumbering. It is actually a series of standards describing the researched physical environment of power lines, a well-adapted physical layer, a workable low-power media access layer, and a management interface. Related standards use the physical layer, but not the higher layers.
