Spectral mask

Spectral mask

In telecommunications, a spectral mask, also known as a channel mask or transmission mask, is a mathematically-defined set of lines applied to the levels of radio (or optical) transmissions. The spectral mask is generally intended to reduce adjacent-channel interference by limiting excessive radiation at frequencies beyond the necessary bandwidth. Attenuation of these spurious emissions is usually done with a band-pass filter, tuned to allow through the correct center frequency of the carrier wave, as well as all necessary sidebands.

The spectral mask is usually one of the things defined in a bandplan for each particular band. It is essential in assuring that a transmission stays within its channel. An FM radio station, for example, must attenuate everything beyond ±75kHz from the center frequency by a few decibels, and anything beyond ±100 kHz (the channel boundary) by much more. Emissions on further adjacent channels must be reduced to almost zero.

FM broadcast subcarriers are normally required to stay under 75 kHz (and up to 100 kHz if reduced) to comply with the mask. The introduction of in-band on-channel (IBOC) digital radio in the United States has been slowed down by issues concerning the subcarriers it uses – and the corresponding increase in the amount of energy in the sidebands – overstepping the bounds of the spectral mask set forth for FM by the NRSC and enforced by the FCC.

Other types of modulation have different spectral masks for the same purpose. Many digital modulation methods such as COFDM use the electromagnetic spectrum very efficiently, allowing for a very tight spectral mask. This allows placement of broadcast stations or other transmissions on channels right next to each other without interference, allowing for an increase in a band's total capacity. Conversely, it is allowing the U.S. to eliminate TV channels 52 to 69, freeing up 108 MHz (from approximately 700 to 800 MHz) for emergency services and to be auctioned off to the highest bidder, while still retaining (although moving) all existing TV stations.

Wikimedia Foundation. 2010.

Поможем сделать НИР

Look at other dictionaries:

  • Spectral splatter — In radio electronics or acoustics, spectral splatter (also called switch noise ) refers to spurious emissions that result from an abrupt change in the transmitted signal, usually when transmission is started or stopped.For example, a device… …   Wikipedia

  • Mask (disambiguation) — A mask is an artifact normally worn on the face, typically for protection, concealment, performance, or amusement. The word can also refer to: In computing and technology Affinity mask, a bit mask indicating what processor a thread or process… …   Wikipedia

  • IEEE 802.11 — is a set of standards for wireless local area network (WLAN) computer communication, developed by the IEEE LAN/MAN Standards Committee (IEEE 802) in the 5 GHz and 2.4 GHz public spectrum bands.General descriptionThe 802.11 family includes over… …   Wikipedia

  • HD Radio — HD Radio, which originally stood for Hybrid Digital , is the trademark for iBiquity s in band on channel (IBOC) digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their… …   Wikipedia

  • Digital radio — has several meanings: 1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting (DAB) system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros… …   Wikipedia

  • Masking — can mean: Applying or using a mask Auditory masking, a class of sensory phenomena where the perception of one sound is affected by the presence of another sound Temporal masking Simultaneous masking Backmasking, a recording technique in which a… …   Wikipedia

  • Blanketing — is interference caused by strong radio signals. Although the spectral mask of a radio station s transmitter suppresses spurious emissions on other frequencies in the band, being extremely close to a station may allow them to still be strong… …   Wikipedia

  • Title 47 CFR Part 15 — In the U.S., Part 15 is an often quoted section of Federal Communications Commission (FCC) rules and regulations, mainly regarding unlicensed transmissions. It is a part of Title 47 of the Code of Federal Regulations (CFR), and regulates… …   Wikipedia

  • Bandplan — A bandplan or band plan is a plan for utilizing a particular band of radio frequencies, that are a portion of the electromagnetic spectrum . Each bandplan defines the frequency range to be included, how channels are to be defined, and what will… …   Wikipedia

  • Ganondorf — Personnage de jeu vidéo apparaissant dans The Legend of Zelda Nom original ガノンドロフ (Gano …   Wikipédia en Français

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”