Radio_spectrum - Wikiparency

# Radio spectrum The **radio spectrum** is the portion of the electromagnetic spectrum, running from about 3 hertz up to 3,000 gigahertz, within which a wave can usefully be generated by a transmitter, radiated from an antenna and picked up by a receiver: everything this site describes as [[Radio|radio]], from a submarine's extremely-low-frequency receiver to a satellite dish's microwave feed, is a [[Radio_wave|radio wave]] somewhere on this one ladder. Because two transmitters sharing a frequency in the same place interfere with each other, the whole range is carved up by international agreement into bands, each handed to a particular kind of service, so that a broadcaster, an air-traffic controller and a mobile network can all use radio waves in the same city without one erasing another. A three.js companion sketch renders the whole spectrum as a single log-frequency shelf, with the named bands lit up to show at a glance what typically lives where, and why. The sections below set the spectrum's own limits, lay out the several overlapping ways engineers actually name its bands, and survey what each part is used for. ## Limits Three hertz is not a sharp physical wall; it is roughly where a signal becomes so slow, with a wavelength of about 100,000 kilometres, that generating and receiving it stops looking like ordinary electronics and starts requiring installations on the scale of a small city. Frequencies near this floor have been used for one demanding purpose: reaching a submerged submarine, whose surrounding seawater absorbs anything higher far too quickly to be useful, with an extremely low frequency signal too slow to carry more than a few characters a minute.[^elf] The upper limit, 3,000 gigahertz, is set the opposite way: it is roughly where a wave's wavelength, about a tenth of a millimetre, shrinks into territory better handled by optical rather than circuit techniques, and where the radio spectrum shades into the far infrared. Both limits have moved outward over the medium's history as electronics improved; the underlying physics has no gap at either edge, and the boundary itself is a regulatory convention fixed by the International Telecommunication Union rather than a change in the wave.[^itureg] ## Bands A given frequency does not carry one name; it carries as many as there are engineering communities with a reason to talk about it. Broadcasters, radar engineers, military planners and waveguide manufacturers each built a naming system to solve their own problem, and the four do not line up with one another at their edges. ### Band plan Within one country, a band plan is the detailed schedule that assigns specific channels inside a band to specific uses: which few hundred kilohertz of the medium-frequency band carry AM broadcasting, which slice of UHF carries television, which narrow strip is reserved for aviation distress calls. The regulators described in [[Radio]]'s own Regulation section set these plans nationally, inside the wider bands that the international process allocates in the first place. ### ITU The oldest and most widely used naming system is the International Telecommunication Union's own, which divides the spectrum into consecutive decade-wide bands, each ten times as wide as the one below it, from extremely low frequency up through extremely high frequency and, at the very top, a tremendously high frequency band reaching the spectrum's own upper limit: | Band | Frequency | Wavelength | |---|---|---| | ELF (extremely low) | 3-30 Hz | 100,000-10,000 km | | SLF (super low) | 30-300 Hz | 10,000-1,000 km | | ULF (ultra low) | 300 Hz-3 kHz | 1,000-100 km | | VLF (very low) | 3-30 kHz | 100-10 km | | LF (low) | 30-300 kHz | 10-1 km | | MF (medium) | 300 kHz-3 MHz | 1 km-100 m | | HF (high) | 3-30 MHz | 100-10 m | | VHF (very high) | 30-300 MHz | 10-1 m | | UHF (ultra high) | 300 MHz-3 GHz | 1 m-10 cm | | SHF (super high) | 3-30 GHz | 10-1 cm | | EHF (extremely high) | 30-300 GHz | 1 cm-1 mm | | THF (tremendously high) | 300-3,000 GHz | 1-0.1 mm | Each band's letters describe only its place on this ladder. [[Very_high_frequency|VHF]] and [[Ultra_high_frequency|UHF]], the two bands this site treats in their own articles, sit exactly in the middle of it. ### IEEE radar bands Radar and microwave engineers instead use a separate, older lettering scheme, codified today by the [[Institute_of_Electrical_and_Electronics_Engineers|IEEE]], that has nothing to do with the ITU's: L band for roughly 1 to 2 gigahertz, S band for 2 to 4, C band for 4 to 8, X band for 8 to 12, then Ku, K and Ka bands climbing to about 40 gigahertz. These letters began as deliberately uninformative wartime code names, chosen so that a document mentioning "X band" gave nothing away, and they outlived the secrecy that produced them; [[Radar]] hardware and specifications are still described by them today.[^ieee] ### EU, NATO, US ECM frequency designations A third scheme again, older still and built for electronic countermeasures rather than for radar design, assigns single letters to wide bands running from a few hundred megahertz up past 100 gigahertz. Its boundaries do not match the IEEE radar letters that happen to share some of the same letters, a standing source of confusion between the two communities that use them; this article does not reproduce the full table, since a version that is both reliable and current with present-day NATO and joint-service usage could not be pinned down for this pass.[^ecm] ### Waveguide frequency bands Microwave hardware adds a fourth naming layer, keyed not to the wave at all but to the metal that carries it: a rectangular waveguide works well over only a narrow band set by its own internal dimensions, so each standard waveguide size, given a designation such as WR-90, carries an implied frequency range that engineers use as shorthand for the band itself. As with the countermeasures table, this article does not print the full designation-to-frequency table, pending a verified current source.[^waveguide] ### Comparison of radio band designation standards The result is that a single frequency, ten gigahertz for instance, is SHF to the ITU, X band to a radar engineer, something else again to an electronic-warfare officer, and shorthand for a specific waveguide size to whoever built the hardware, with no one system taking precedence over the others. None of this reflects any ambiguity in the physics; it reflects only that four different professions named the same ladder at different times for different reasons and never had cause to reconcile their vocabularies afterward. ## Applications What lives in each band follows fairly directly from its propagation and its bandwidth. The lowest bands, with their enormous wavelengths and correspondingly tiny usable bandwidths, are reserved for a handful of narrowband, high-value uses such as submarine communication and time signals; medium frequency carries [[AM_broadcasting|AM broadcasting]] over ranges of a few hundred kilometres by ground wave, and high frequency carries [[Shortwave_radio|shortwave]] broadcasting and long-distance amateur and aeronautical communication by skywave. VHF and UHF, wide enough to carry audio, video and now digital data streams, and short enough in wavelength to use a practically sized antenna, carry the bulk of everyday broadcasting, mobile telephony and wireless networking; higher still, the [[Microwave|microwave]] bands carry point-to-point links, satellite communication and radar, where a short wavelength buys a narrow, precisely aimed beam from a dish of manageable size. Because every one of these uses competes for the same fixed resource, the spectrum has grown steadily more congested as the number of services has grown; one measurable symptom is that man-made background radio noise in a city can run more than two hundred times higher than in a quiet rural area at the same frequency, crowding out weak signals a receiver could otherwise hear cleanly.[^congestion] Techniques such as frequency reuse, spread spectrum and, more recently, dynamically sharing an underused band between licensed and unlicensed users are all, at bottom, ways of extracting more communication from a resource that cannot itself be made any larger. ## Microsims This article carries no p5.js sketch of its own; its primary visualization is the three.js companion named above, a new framework sketch that lays the whole spectrum out as a single log-frequency shelf, from the extremely low frequencies at one end to the tremendously high frequencies at the other, with the named bands from the table above lit up along it. Because it is a wholly new build rather than a variant of an existing sketch, its own controls and readouts are documented where the sketch itself is placed rather than here. The interactive sketches that go with the specific ranging and timing ideas touched on in Applications belong to neighbouring articles, and this section points to three of them. *Try:* in the [[Radar]] sketch, drag the pulse width wider and watch two close targets merge into one blob on the zoomed inset; the same trade-off between how wide a pulse is and how finely it can separate two signals in range or in frequency recurs throughout this spectrum wherever a service is squeezed for bandwidth. *Try:* in the [[Doppler_effect]] sketch, set the source moving and read off how far the received frequency shifts from what was sent; the same kind of shift can carry a signal outside its allocated band, which is one reason a band plan leaves guard space at its edges rather than packing channels edge to edge. *Try:* in the [[Sonar]] sketch, notice how narrow a band ordinary sound occupies compared with even a single television channel much higher up this ladder; audio's modest bandwidth demand is exactly why the lowest, most tightly rationed radio bands can still carry it usefully.  **Microsim — three.js (Wikitube framework), pending deploy:** *Radio spectrum: bands on a shelf* will play here once `https://wikitube-3d-microsims.netlify.app/radio/Radio_spectrum.html` is live.  *Built from `MICROSIM_GUIDE/specs/sims/Radio_spectrum.json`; part of the [[PORTAL_Radio|Radio]] set.*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Radio_spectrum) : [Wikitube](https://en.wikitube.io/wiki/Radio_spectrum) Skeleton mirrored at revision 1371480000. Prose, emphasis and the microsims are Wikitube's own. ## See also - [[Radio]] - [[Radio_wave]] - [[Very_high_frequency]] - [[Ultra_high_frequency]] - [[Microwave]] - [[Shortwave_radio]] - [[Radar]] ## Notes Band-letter boundaries in the ITU table above follow the Radio Regulations' own decade divisions; the IEEE, military/ECM and waveguide systems described alongside it are separate engineering conventions that were never harmonized with the ITU's or with each other, and this article does not assert exact current boundaries for the two it could not verify against a current source (see References). ## References [^elf]: Citation needed: a verified primary or technical source (for example a naval or academic account) for a specific extremely-low-frequency submarine communication system, its operating frequency and its dates of operation. [^itureg]: Citation needed: the ITU Radio Regulations provision (Article 2) defining the regulatory range of radio waves, with edition and year. [^ieee]: Citation needed: a current standard (for example an IEEE publication) fixing the exact modern boundaries of the L/S/C/X/Ku/K/Ka radar-band letters. [^ecm]: Citation needed: a verified, current table of NATO/EU/US electronic-countermeasures frequency-designation letters and their boundaries. [^waveguide]: Citation needed: a verified table mapping standard rectangular-waveguide designations (for example WR-90) to their operating frequency ranges. [^congestion]: Ellingson, S. *Radio Systems Engineering - Revised First Edition*. 2023, pp. 106-107 (PDF pages). Open Textbook Library: https://open.umn.edu/opentextbooks/textbooks/radio-systems-engineering . CC BY-NC. ## External links - Authoritative band-plan and standards references (ITU Radio Regulations Article 2; IEEE band-letter standards; national frequency allocation charts), to be pinned once specific editions are confirmed.