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   Link budget - Wikipedia
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});});</script><link href=/w/load.php?lang=en&modules=ext.cite.styles%7Cext.math.styles%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediaBadges%7Cskins.vector.styles.legacy%7Cwikibase.client.init&only=styles&skin=vector rel=stylesheet><script async src=/w/load.php?lang=en&modules=startup&only=scripts&raw=1&skin=vector></script><meta name=ResourceLoaderDynamicStyles><link href=/w/load.php?lang=en&modules=site.styles&only=styles&skin=vector rel=stylesheet><meta content="MediaWiki 1.38.0-wmf.6"name=generator><meta content=origin name=referrer><meta content=origin-when-crossorigin name=referrer><meta content=origin-when-cross-origin name=referrer><meta content=telephone=no name=format-detection><meta content="Link budget - Wikipedia"property=og:title><meta content=website property=og:type><link href=//upload.wikimedia.org rel=preconnect><link media="only screen and (max-width: 720px)"href=//en.m.wikipedia.org/wiki/Link_budget rel=alternate><link title="Edit this page"href=/w/index.php?title=Link_budget&action=edit rel=alternate type=application/x-wiki><link href=/static/apple-touch/wikipedia.png rel=apple-touch-icon><link rel="shortcut icon"href=/static/favicon/wikipedia.ico><link title="Wikipedia (en)"href=/w/opensearch_desc.php rel=search type=application/opensearchdescription+xml><link href=//en.wikipedia.org/w/api.php?action=rsd rel=EditURI type=application/rsd+xml><link href=https://creativecommons.org/licenses/by-sa/3.0/ rel=license><link href=https://en.wikipedia.org/wiki/Link_budget rel=canonical><link href=//meta.wikimedia.org rel=dns-prefetch><link href=//login.wikimedia.org rel=dns-prefetch><body class="mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject mw-editable page-Link_budget rootpage-Link_budget skin-vector action-view skin-vector-legacy"><div class=noprint id=mw-page-base></div><div class=noprint id=mw-head-base></div><div class=mw-body id=content role=main><a id=top> </a><div id=siteNotice></div><div class=mw-indicators></div><h1 class=firstHeading id=firstHeading>Link budget</h1><div class=vector-body id=bodyContent><div class=noprint id=siteSub>From Wikipedia, the free encyclopedia</div><div id=contentSub></div><div id=contentSub2></div><div id=jump-to-nav></div><a class=mw-jump-link href=#mw-head> Jump to navigation </a><a class=mw-jump-link href=#searchInput> Jump to search </a><div class="mw-body-content mw-content-ltr"dir=ltr id=mw-content-text lang=en><div class=mw-parser-output><p class=mw-empty-elt><div class="shortdescription nomobile noexcerpt noprint searchaux"style=display:none>Accounting of signal gains and losses in communications</div><table class="box-More_citations_needed plainlinks metadata ambox ambox-content ambox-Refimprove"role=presentation><tbody><tr><td class=mbox-image><div style=width:52px><a class=image href=/wiki/File:Question_book-new.svg> <img srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x"alt data-file-height=399 data-file-width=512 decoding=async height=39 src=//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png width=50> </a></div><td class=mbox-text><div class=mbox-text-span>This article <b> needs additional citations for <a href=/wiki/Wikipedia:Verifiability title=Wikipedia:Verifiability> verification </a> </b> . <span class=hide-when-compact> Please help <a class="external text"href=https://en.wikipedia.org/w/index.php?title=Link_budget&action=edit> improve this article </a> by <a title="Help:Referencing for beginners"href=/wiki/Help:Referencing_for_beginners> adding citations to reliable sources </a> . Unsourced material may be challenged and removed. <br> <small> <span class=plainlinks> <i> Find sources: </i>   <a class="external text"href=//www.google.com/search?as_eq=wikipedia&q=%22Link+budget%22 rel=nofollow> "Link budget" </a>  –  <a class="external text"href=//www.google.com/search?tbm=nws&q=%22Link+budget%22+-wikipedia&tbs=ar:1 rel=nofollow> news </a>   <b> · </b> <a class="external text"href=//www.google.com/search?&q=%22Link+budget%22&tbs=bkt:s&tbm=bks rel=nofollow> newspapers </a>   <b> · </b> <a class="external text"href=//www.google.com/search?tbs=bks:1&q=%22Link+budget%22+-wikipedia rel=nofollow> books </a>   <b> · </b> <a class="external text"href=//scholar.google.com/scholar?q=%22Link+budget%22 rel=nofollow> scholar </a>   <b> · </b> <a class="external text"href=https://www.jstor.org/action/doBasicSearch?Query=%22Link+budget%22&acc=on&wc=on rel=nofollow> JSTOR </a> </span> </small> </span><span class=date-container> <i> ( <span class=date> March 2016 </span> ) </i> </span><span class=hide-when-compact> <i> ( <a title="Help:Maintenance template removal"href=/wiki/Help:Maintenance_template_removal> Learn how and when to remove this template message </a> ) </i> </span></div></table><p>A <b> link budget </b> is an accounting of all of the <a title="Power (physics)"href=/wiki/Power_(physics)> power </a> gains and losses that a communication <a href=/wiki/Signal title=Signal> signal </a> experiences in a <a class=mw-redirect href=/wiki/Telecommunication title=Telecommunication> telecommunication </a> system; from a transmitter, through a <a title="Communication channel"href=/wiki/Communication_channel> communication medium </a> such as <a title="Radio wave"href=/wiki/Radio_wave> radio waves </a> , <a title="Transmission line"href=/wiki/Transmission_line> cable </a> , <a title="Waveguide (radio frequency)"href=/wiki/Waveguide_(radio_frequency)> waveguide </a> , or <a title="Optical fiber"href=/wiki/Optical_fiber> optical fiber </a> , to the receiver. It is an equation giving the received power from the transmitter power, after the attenuation of the transmitted signal due to propagation, as well as the <a title="Antenna gain"href=/wiki/Antenna_gain> antenna gains </a> and <a class=mw-redirect href=/wiki/Feedline title=Feedline> feedline </a> and other losses, and <a href=/wiki/Amplifier title=Amplifier> amplification </a> of the signal in the <a title="Radio receiver"href=/wiki/Radio_receiver> receiver </a> or any <a href=/wiki/Repeater title=Repeater> repeaters </a> it passes through. A link budget is a design aid, calculated during the design of a communication system to determine the received power, to ensure that the information is received intelligibly with an adequate <a title="Signal-to-noise ratio"href=/wiki/Signal-to-noise_ratio> signal-to-noise ratio </a> . Randomly varying channel gains such as <a href=/wiki/Fading title=Fading> fading </a> are taken into account by adding some margin depending on the anticipated severity of its effects. The amount of margin required can be reduced by the use of mitigating techniques such as <a title="Antenna diversity"href=/wiki/Antenna_diversity> antenna diversity </a> or <a title="Frequency hopping"class=mw-redirect href=/wiki/Frequency_hopping> frequency hopping </a> .<p>A simple link budget equation looks like this:<dl><dd>Received power (dBm) = transmitted power (dBm) + gains (dB) − losses (dB)</dl><p>Power levels are expressed in ( <a href=/wiki/DBm title=DBm> dBm </a> ), Power gains and losses are expressed in <a href=/wiki/Decibel title=Decibel> decibels </a> (dB), which is a <a href=/wiki/Logarithm title=Logarithm> logarithmic </a> measurement, so adding decibels is equivalent to multiplying the actual power ratios.<div aria-labelledby=mw-toc-heading class=toc id=toc role=navigation><input class=toctogglecheckbox id=toctogglecheckbox role=button style=display:none type=checkbox><div class=toctitle dir=ltr lang=en><h2 id=mw-toc-heading>Contents</h2><span class=toctogglespan> <label class=toctogglelabel for=toctogglecheckbox></label> </span></div><ul><li class="toclevel-1 tocsection-1"><a href=#In_radio_systems> <span class=tocnumber> 1 </span> <span class=toctext> In radio systems </span> </a> <ul><li class="toclevel-2 tocsection-2"><a href=#Simplifications_needed> <span class=tocnumber> 1.1 </span> <span class=toctext> Simplifications needed </span> </a><li class="toclevel-2 tocsection-3"><a href=#Transmission_line_and_polarization_loss> <span class=tocnumber> 1.2 </span> <span class=toctext> Transmission line and polarization loss </span> </a><li class="toclevel-2 tocsection-4"><a href=#Endgame> <span class=tocnumber> 1.3 </span> <span class=toctext> Endgame </span> </a><li class="toclevel-2 tocsection-5"><a href=#Equation> <span class=tocnumber> 1.4 </span> <span class=toctext> Equation </span> </a></ul><li class="toclevel-1 tocsection-6"><a href=#Non-line-of-sight_radio> <span class=tocnumber> 2 </span> <span class=toctext> Non-line-of-sight radio </span> </a><li class="toclevel-1 tocsection-7"><a href=#In_waveguides_and_cables> <span class=tocnumber> 3 </span> <span class=toctext> In waveguides and cables </span> </a> <ul><li class="toclevel-2 tocsection-8"><a href=#Earth–Moon–Earth_communications> <span class=tocnumber> 3.1 </span> <span class=toctext> Earth–Moon–Earth communications </span> </a><li class="toclevel-2 tocsection-9"><a href=#Voyager_program> <span class=tocnumber> 3.2 </span> <span class=toctext> Voyager program </span> </a></ul><li class="toclevel-1 tocsection-10"><a href=#See_also> <span class=tocnumber> 4 </span> <span class=toctext> See also </span> </a><li class="toclevel-1 tocsection-11"><a href=#References> <span class=tocnumber> 5 </span> <span class=toctext> References </span> </a><li class="toclevel-1 tocsection-12"><a href=#External_links> <span class=tocnumber> 6 </span> <span class=toctext> External links </span> </a></ul></div><h2><span class=mw-headline id=In_radio_systems> In radio systems </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: In radio systems"href=/w/index.php?title=Link_budget&action=edit&section=1> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h2><p>For a <a title="Line-of-sight propagation"href=/wiki/Line-of-sight_propagation> line-of-sight </a> <a href=/wiki/Radio title=Radio> radio </a> system, the primary source of loss is the decrease of the signal power due to uniform propagation, proportional to the inverse square of the distance (geometric spreading).<ul><li>Transmitting antennas are for the most part neither isotropic (an imaginary class of antenna with uniform radiation in 3 dimensions) nor omnidirectional (a real class of antenna with uniform radiation in 2 dimensions).<li>The use of omnidirectional antennas is rare in telecommunication systems, so almost every link budget equation must consider antenna gain.<li>Transmitting antennas typically concentrate the signal power in a favoured direction, normally that in which the receiving antenna is placed.<li>Transmitter power is effectively increased (in the direction of highest antenna gain). This systemic gain is expressed by including the antenna gain in the link budget.<li>The receiving antenna is also typically directional, and when properly oriented collects more power than an isotropic antenna would; as a consequence, the receiving antenna gain (in decibels from isotropic, dBi) adds to the received power.<li>The antenna gains (transmitting or receiving) are scaled by the wavelength of the radiation in question. This step may not be required if adequate systemic link budgets are achieved.</ul><h3><span class=mw-headline id=Simplifications_needed> Simplifications needed </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: Simplifications needed"href=/w/index.php?title=Link_budget&action=edit&section=2> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h3><p>Often link budget equations are messy and complex, so standard practices have evolved to simplify the <a title="Friis transmission equation"href=/wiki/Friis_transmission_equation> Friis transmission equation </a> into the link budget equation. It includes the transmit and receive antenna gain, the <a title="Free-space path loss"href=/wiki/Free-space_path_loss> free space path loss </a> and additional losses and gains, assuming line of sight between the transmitter and receiver.<ul><li>The wavelength (or frequency) term is part of the free space loss part of the link budget.<li>The distance term is also considered in the free space loss.</ul><h3><span class=mw-headline id=Transmission_line_and_polarization_loss> Transmission line and polarization loss </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: Transmission line and polarization loss"href=/w/index.php?title=Link_budget&action=edit&section=3> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h3><p>In practical situations (deep space telecommunications, weak signal DXing etc.) other sources of signal loss must also be accounted for<ul><li>The transmitting and receiving antennas may be partially cross-polarized.<li>The cabling between the radios and antennas may introduce significant additional loss.<li><a title="Fresnel zone"href=/wiki/Fresnel_zone> Fresnel zone </a> losses due to a partially obstructed line of sight path.<li><a title="Doppler shift"class=mw-redirect href=/wiki/Doppler_shift> Doppler shift </a> induced signal power losses in the receiver.</ul><h3><span class=mw-headline id=Endgame> Endgame </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: Endgame"href=/w/index.php?title=Link_budget&action=edit&section=4> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h3><p>If the estimated received power is sufficiently large (typically relative to the <a title="Sensitivity (electronics)"href=/wiki/Sensitivity_(electronics)> receiver sensitivity </a> ), which may be dependent on the communications protocol in use, the link will be useful for sending data. The amount by which the received power exceeds receiver sensitivity is called the <a title="Fade margin"href=/wiki/Fade_margin> link margin </a> .<h3><span class=mw-headline id=Equation> Equation </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: Equation"href=/w/index.php?title=Link_budget&action=edit&section=5> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h3><p>A link budget equation including all these effects, expressed logarithmically, might look like this:<dl><dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle P_{\text{RX}}=P_{\text{TX}}+G_{\text{TX}}-L_{\text{TX}}-L_{\text{FS}}-L_{M}+G_{\text{RX}}-L_{\text{RX}}\,}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> P </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> RX </mtext> </mrow> </msub> <mo> = </mo> <msub> <mi> P </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> TX </mtext> </mrow> </msub> <mo> + </mo> <msub> <mi> G </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> TX </mtext> </mrow> </msub> <mo> −  </mo> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> TX </mtext> </mrow> </msub> <mo> −  </mo> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> FS </mtext> </mrow> </msub> <mo> −  </mo> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mi> M </mi> </mrow> </msub> <mo> + </mo> <msub> <mi> G </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> RX </mtext> </mrow> </msub> <mo> −  </mo> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> RX </mtext> </mrow> </msub> <mspace width=thinmathspace> </mspace> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle P_{\text{RX}}=P_{\text{TX}}+G_{\text{TX}}-L_{\text{TX}}-L_{\text{FS}}-L_{M}+G_{\text{RX}}-L_{\text{RX}}\,} </annotation> </semantics> </math> </span> <img alt="{\displaystyle P_{\text{RX}}=P_{\text{TX}}+G_{\text{TX}}-L_{\text{TX}}-L_{\text{FS}}-L_{M}+G_{\text{RX}}-L_{\text{RX}}\,}"style="vertical-align: -0.671ex; width:53.653ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/8a583bdadf41d6de192b6bf601c57dd880a2a40f> </span></dl><p>where:<dl><dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle P_{\text{RX}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> P </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> RX </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle P_{\text{RX}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle P_{\text{RX}}}"style="vertical-align: -0.671ex; width:4.167ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/71ad1931255dd3340ec15c7b63021b2547520b2d> </span> , received power (dBm)<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle P_{\text{TX}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> P </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> TX </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle P_{\text{TX}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle P_{\text{TX}}}"style="vertical-align: -0.671ex; width:4.144ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/cb2e4bdec928107ea8a28f2c419663b3670b5842> </span> , transmitter output power (dBm)<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle G_{\text{TX}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> G </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> TX </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle G_{\text{TX}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle G_{\text{TX}}}"style="vertical-align: -0.671ex; width:4.478ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/4650da260355f8b35f4a01bf5ce1cab87d530203> </span> , transmitter <a title="Antenna gain"href=/wiki/Antenna_gain> antenna gain </a> (dBi)<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{TX}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> TX </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{TX}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{TX}}}"style="vertical-align: -0.671ex; width:4.234ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/cbd99bfa4f21855c8f38b59abd6bd5d28f91d443> </span> , transmitter losses (coax, connectors...) (dB)<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{FS}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> FS </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{FS}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{FS}}}"style="vertical-align: -0.671ex; width:3.802ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/9981da0517af1799d7e920c452e7bd3f9cd020b7> </span> , <a title="Path loss"href=/wiki/Path_loss> path loss </a> , usually <a title="Free space loss"class=mw-redirect href=/wiki/Free_space_loss> free space loss </a> (dB)<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{M}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> M </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{M}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{M}}}"style="vertical-align: -0.671ex; width:3.322ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/5b19b704a518846212973d3661e5565b6f27fe5e> </span> , miscellaneous losses ( <a href=/wiki/Fading title=Fading> fading </a> margin, body loss, polarization mismatch, other losses, ...) (dB)<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle G_{\text{RX}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> G </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> RX </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle G_{\text{RX}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle G_{\text{RX}}}"style="vertical-align: -0.671ex; width:4.501ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/bff31513f10903da78c05ec4487249b4dc598972> </span> , receiver <a title="Antenna gain"href=/wiki/Antenna_gain> antenna gain </a> (dBi)<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{RX}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> RX </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{RX}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{RX}}}"style="vertical-align: -0.671ex; width:4.257ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/68ed504f6e80097662968967b39b97fcd2ee22af> </span> , receiver losses (coax, connectors, ...) (dB)</dl><p>The loss due to propagation between the transmitting and receiving antennas, often called the path loss, can be written in dimensionless form by normalizing the distance to the wavelength:<dl><dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{FS}}{\text{(dB)}}=20\log _{10}\left(4\pi {{\text{distance}} \over {\text{wavelength}}}\right)}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> FS </mtext> </mrow> </msub> <mrow class=MJX-TeXAtom-ORD> <mtext> (dB) </mtext> </mrow> <mo> = </mo> <mn> 20 </mn> <msub> <mi> log </mi> <mrow class=MJX-TeXAtom-ORD> <mn> 10 </mn> </mrow> </msub> <mo> ⁡  </mo> <mrow> <mo> ( </mo> <mrow> <mn> 4 </mn> <mi> π  </mi> <mrow class=MJX-TeXAtom-ORD> <mfrac> <mrow class=MJX-TeXAtom-ORD> <mtext> distance </mtext> </mrow> <mrow class=MJX-TeXAtom-ORD> <mtext> wavelength </mtext> </mrow> </mfrac> </mrow> </mrow> <mo> ) </mo> </mrow> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{FS}}{\text{(dB)}}=20\log _{10}\left(4\pi {{\text{distance}} \over {\text{wavelength}}}\right)} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{FS}}{\text{(dB)}}=20\log _{10}\left(4\pi {{\text{distance}} \over {\text{wavelength}}}\right)}"style="vertical-align: -2.505ex; width:37.392ex; height:6.176ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/4615069a86336fd91a04dcf826e0927941f78664> </span> (where distance and wavelength are in the same units)</dl><p>When substituted into the link budget equation above, the result is the logarithmic form of the <a title="Friis transmission equation"href=/wiki/Friis_transmission_equation> Friis transmission equation </a> .<p>In some cases, it is convenient to consider the loss due to distance and wavelength separately, but in that case, it is important to keep track of which units are being used, as each choice involves a differing constant offset. Some examples are provided below.<dl><dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{FS}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> FS </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{FS}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{FS}}}"style="vertical-align: -0.671ex; width:3.802ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/9981da0517af1799d7e920c452e7bd3f9cd020b7> </span> (dB) ≈ 32.45 dB + 20 log[frequency (MHz)] + 20 log[distance (km)] <sup class=reference id=cite_ref-1> <a href=#cite_note-1> [1] </a> </sup><dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{FS}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> FS </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{FS}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{FS}}}"style="vertical-align: -0.671ex; width:3.802ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/9981da0517af1799d7e920c452e7bd3f9cd020b7> </span> (dB) ≈ −27.55 dB + 20 log[frequency (MHz)] + 20 log[distance (m)]<dd><span class=mwe-math-element> <span class="mwe-math-mathml-inline mwe-math-mathml-a11y"style="display: none;"> <math alttext="{\displaystyle L_{\text{FS}}}"xmlns=http://www.w3.org/1998/Math/MathML> <semantics> <mrow class=MJX-TeXAtom-ORD> <mstyle displaystyle=true scriptlevel=0> <msub> <mi> L </mi> <mrow class=MJX-TeXAtom-ORD> <mtext> FS </mtext> </mrow> </msub> </mstyle> </mrow> <annotation encoding=application/x-tex> {\displaystyle L_{\text{FS}}} </annotation> </semantics> </math> </span> <img alt="{\displaystyle L_{\text{FS}}}"style="vertical-align: -0.671ex; width:3.802ex; height:2.509ex;"aria-hidden=true class=mwe-math-fallback-image-inline src=https://wikimedia.org/api/rest_v1/media/math/render/svg/9981da0517af1799d7e920c452e7bd3f9cd020b7> </span> (dB) ≈ 36.6 dB + 20 log[frequency (MHz)] + 20 log[distance (miles)]</dl><p>These alternative forms can be derived by substituting wavelength with the ratio of propagation velocity ( <i> c </i> , approximately <span class=nowrap> <span data-sort-value=7008300000000000000♠> </span> 3 <span style=margin-left:0.25em;margin-right:0.15em;> × </span> 10 <sup> 8 </sup>  m/s </span> ) divided by frequency, and by inserting the proper conversion factors between km or miles and meters, and between MHz and (1/s).<h2><span class=mw-headline id=Non-line-of-sight_radio> Non-line-of-sight radio </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: Non-line-of-sight radio"href=/w/index.php?title=Link_budget&action=edit&section=6> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h2><p>Because of building obstructions such as walls and ceilings, propagation losses indoors can be significantly higher. This occurs because of a combination of attenuation by walls and ceilings, and blockage due to equipment, furniture, and even people.<ul><li>For example, a " <a href=/wiki/Lumber#North_American_softwoods title=Lumber> 2 by 4 </a> " wood stud wall with <a href=/wiki/Drywall title=Drywall> drywall </a> on both sides results in about 6 dB loss per wall.<li>Older buildings may have even greater internal losses than new buildings due to materials and line of sight issues.</ul><p>Experience has shown that line-of-sight propagation holds only for about the first 3 meters. Beyond 3 meters propagation losses indoors can increase at up to 30 dB per 30 meters in dense office environments. This is a good rule-of-thumb, in that it is conservative (it overstates path loss in most cases). Actual propagation losses may vary significantly depending on building construction and layout.<p>The attenuation of the signal is highly dependent on the frequency of the signal.<h2><span class=mw-headline id=In_waveguides_and_cables> In waveguides and cables </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: In waveguides and cables"href=/w/index.php?title=Link_budget&action=edit&section=7> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h2><p>Guided media such as coaxial and twisted pair electrical cable, radio frequency waveguide and optical fiber have losses that are exponential with distance.<p>The <a title="Path loss"href=/wiki/Path_loss> path loss </a> will be in terms of dB per unit distance.<p>This means that there is always a crossover distance beyond which the loss in a guided medium will exceed that of a line-of-sight path of the same length.<p>Long distance <a title="Fiber-optic communication"href=/wiki/Fiber-optic_communication> fiber-optic communication </a> became practical only with the development of ultra-transparent glass fibers. A typical path loss for <a title="Single mode fiber"class=mw-redirect href=/wiki/Single_mode_fiber> single mode fiber </a> is 0.2 dB/km, <sup class=reference id=cite_ref-2> <a href=#cite_note-2> [2] </a> </sup> far lower than any other guided medium.<h3><span id=Earth.E2.80.93Moon.E2.80.93Earth_communications> </span> <span class=mw-headline id=Earth–Moon–Earth_communications> Earth–Moon–Earth communications </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: Earth–Moon–Earth communications"href=/w/index.php?title=Link_budget&action=edit&section=8> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h3><p>Link budgets are important in <a title="EME (communications)"class=mw-redirect href=/wiki/EME_(communications)> Earth–Moon–Earth communications </a> . As the <a href=/wiki/Albedo title=Albedo> albedo </a> of the Moon is very low (maximally 12% but usually closer to 7%), and the <a title="Path loss"href=/wiki/Path_loss> path loss </a> over the <a title="1 E8 m"class=mw-redirect href=/wiki/1_E8_m> 770,000 kilometre </a> return distance is extreme (around 250 to 310 <span class=nowrap>   </span> <a href=/wiki/Decibel title=Decibel> dB </a> depending on VHF-UHF band used, <a href=/wiki/Modulation title=Modulation> modulation </a> format and <a title="Doppler shift"class=mw-redirect href=/wiki/Doppler_shift> Doppler shift </a> effects), high power (more than 100 watts) and <a title="High-gain antenna"class=mw-redirect href=/wiki/High-gain_antenna> high-gain antennas </a> (more than 20 dB) must be used.<ul><li>In practice, this limits the use of this technique to the spectrum at <a class=mw-redirect href=/wiki/VHF title=VHF> VHF </a> and above.<li>The Moon must be above the horizon in order for EME communications to be possible.</ul><p>The first amateur to achieve this utilized a 250 <span class=nowrap>   </span> m wide antenna he built at home. <sup class=reference id=cite_ref-3> <a href=#cite_note-3> [3] </a> </sup><h3><span class=mw-headline id=Voyager_program> Voyager program </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: Voyager program"href=/w/index.php?title=Link_budget&action=edit&section=9> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h3><p>The <a title="Voyager program"href=/wiki/Voyager_program> Voyager program </a> spacecraft have the highest known path loss (308 <span class=nowrap>   </span> dB as of 2002 <sup class=reference id=cite_ref-descanso_4-0> <a href=#cite_note-descanso-4> [4] </a> </sup> <sup class="reference nowrap"> <span title="Page / location: 26"> : 26 </span> </sup> ) and lowest link budgets of any telecommunications circuit. The <a title="Deep Space Network"class=mw-redirect href=/wiki/Deep_Space_Network> Deep Space Network </a> has been able to maintain the link at a higher than expected bitrate through a series of improvements, such as increasing the antenna size from 64 <span class=nowrap>   </span> m to 70 <span class=nowrap>   </span> m for a 1.2 <span class=nowrap>   </span> dB gain, and upgrading to low noise electronics for a 0.5 <span class=nowrap>   </span> dB gain in 2000–2001. During the <a href=/wiki/Neptune title=Neptune> Neptune </a> flyby, in addition to the 70-m antenna, two 34-m antennas and twenty-seven 25-m antennas were used to increase the gain by 5.6 <span class=nowrap>   </span> dB, providing additional link margin to be used for a 4× increase in bitrate. <sup class=reference id=cite_ref-descanso_4-1> <a href=#cite_note-descanso-4> [4] </a> </sup> <sup class="reference nowrap"> <span title="Page / location: 35"> : 35 </span> </sup><h2><span class=mw-headline id=See_also> See also </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: See also"href=/w/index.php?title=Link_budget&action=edit&section=10> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h2><ul><li><a title="Friis transmission equation"href=/wiki/Friis_transmission_equation> Friis transmission equation </a><li><a title="Antenna gain-to-noise-temperature"href=/wiki/Antenna_gain-to-noise-temperature> Antenna gain-to-noise-temperature </a><li><a title="Isotropic radiator"href=/wiki/Isotropic_radiator> Isotropic radiator </a><li><a title="Radiation pattern"href=/wiki/Radiation_pattern> Radiation pattern </a><li><a title="Multipath propagation"href=/wiki/Multipath_propagation> Multipath propagation </a><li><a title="RF planning"href=/wiki/RF_planning> RF planning </a></ul><h2><span class=mw-headline id=References> References </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: References"href=/w/index.php?title=Link_budget&action=edit&section=11> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h2><style data-mw-deduplicate=TemplateStyles:r1011085734>.mw-parser-output .reflist{font-size:90%;margin-bottom:0.5em;list-style-type:decimal}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class=reflist><div class=mw-references-wrap><ol class=references><li id=cite_note-1><span class=mw-cite-backlink> <b> <a href=#cite_ref-1> ^ </a> </b> </span> <span class=reference-text> <a class="external free"href=https://web.archive.org/web/20050901001655/http://people.deas.harvard.edu/~jones/es151/prop_models/propagation.html rel=nofollow> https://web.archive.org/web/20050901001655/http://people.deas.harvard.edu/~jones/es151/prop_models/propagation.html </a> </span><li id=cite_note-2><span class=mw-cite-backlink> <b> <a href=#cite_ref-2> ^ </a> </b> </span> <span class=reference-text> <a class="external free"href=https://web.archive.org/web/20070928054321/http://www.corningcablesystems.com/web/library/litindex.nsf/$ALL/EVO-412-EN/$FILE/EVO-412-EN.pdf rel=nofollow> https://web.archive.org/web/20070928054321/http://www.corningcablesystems.com/web/library/litindex.nsf/$ALL/EVO-412-EN/$FILE/EVO-412-EN.pdf </a> </span><li id=cite_note-3><span class=mw-cite-backlink> <b> <a href=#cite_ref-3> ^ </a> </b> </span> <span class=reference-text> <style data-mw-deduplicate=TemplateStyles:r999302996>.mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}</style> <cite class="citation web cs1"id=CITEREFDanielle2020> Danielle, Grindlay (2020-03-04). <a class="external text"href=https://mobile.abc.net.au/news/2020-03-04/australias-first-moon-bounce-schocked-us-experts/11339552 rel=nofollow> "Australia's first ever moon bounce remembered as a feat that shocked industry experts" </a> . © 2020 ABC Wimmera. </cite> <span class=Z3988 title=ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Australia%27s+first+ever+moon+bounce+remembered+as+a+feat+that+shocked+industry+experts&rft.pub=%C2%A9+2020+ABC+Wimmera&rft.date=2020-03-04&rft.aulast=Danielle&rft.aufirst=Grindlay&rft_id=https%3A%2F%2Fmobile.abc.net.au%2Fnews%2F2020-03-04%2Faustralias-first-moon-bounce-schocked-us-experts%2F11339552&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALink+budget> </span> </span><li id=cite_note-descanso-4><span class=mw-cite-backlink> ^ <a href=#cite_ref-descanso_4-0> <sup> <i> <b> a </b> </i> </sup> </a> <a href=#cite_ref-descanso_4-1> <sup> <i> <b> b </b> </i> </sup> </a> </span> <span class=reference-text> <link href=mw-data:TemplateStyles:r999302996 rel=mw-deduplicated-inline-style> <cite class="citation web cs1"id=CITEREFJPL_Deep_Space_Communications_and_Navigation_Systems2002> JPL Deep Space Communications and Navigation Systems (March 2002). <a class="external text"href=https://descanso.jpl.nasa.gov/DPSummary/Descanso4--Voyager_ed.pdf rel=nofollow> "Voyager Telecommunications" </a> <span class=cs1-format> (PDF) </span> . descanso.jpl.nasa.gov <span class=reference-accessdate> . Retrieved <span class=nowrap> 2017-08-04 </span> </span> . </cite> <span class=Z3988 title=ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Voyager+Telecommunications&rft.pub=descanso.jpl.nasa.gov&rft.date=2002-03&rft.au=JPL+Deep+Space+Communications+and+Navigation+Systems&rft_id=https%3A%2F%2Fdescanso.jpl.nasa.gov%2FDPSummary%2FDescanso4--Voyager_ed.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ALink+budget> </span> </span></ol></div></div><h2><span class=mw-headline id=External_links> External links </span> <span class=mw-editsection> <span class=mw-editsection-bracket> [ </span> <a title="Edit section: External links"href=/w/index.php?title=Link_budget&action=edit&section=12> edit </a> <span class=mw-editsection-bracket> ] </span> </span></h2><ul><li><a class="external text"href=http://home.deds.nl/~pa0hoo/helix_wifi/linkbudgetcalc/wlan_budgetcalc.html rel=nofollow> Link budget calculator for wireless LAN </a><li><a class="external text"href=http://www.sss-mag.com/pdf/an9804.pdf rel=nofollow> Link budget tutorial </a><li><a class="external text"href=http://www.ligowave.com/linkcalc rel=nofollow> Point-to-point link budget calculator </a><li><a class="external text"href=http://www.questinygroup.com/muos rel=nofollow> MUOS Link budget calculator/planner </a><li><a class="external text"href=https://sites.google.com/site/lteencyclopedia/lte-radio-link-budgeting-and-rf-planning/lte-link-budget-comparison rel=nofollow> Example LTE, GSM and UMTS Link Budgets </a><li><a class="external text"href=https://github.com/harrison-caudill/pylink rel=nofollow> Python link budget calculator for satellites </a><li><a class="external text"href=https://nbviewer.jupyter.org/github/kirlf/cubesats/blob/master/LinkBudget/LB.ipynb rel=nofollow> Small satellites link budget (with python examples) </a></ul></div><noscript><img style="border: none; 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