{"id":3264,"date":"2011-08-08T08:33:12","date_gmt":"2011-08-08T12:33:12","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=3928"},"modified":"2023-04-30T11:11:58","modified_gmt":"2023-04-30T15:11:58","slug":"fm-stereo-vs-station-coverage","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2011\/08\/fm-stereo-vs-station-coverage\/","title":{"rendered":"FM Stereo vs station coverage"},"content":{"rendered":"\n<p>There are a few FM stations around here that intentionally broadcast in mono. \u00a0One is an FM talker, which from a technical standpoint makes a certain amount of sense since any particular human voice is a single-point sound generator.<\/p>\n\n\n\n<p>The other <a rel=\"noopener\" href=\"http:\/\/en.wikipedia.org\/wiki\/WKZE-FM\" target=\"_blank\">FM station<\/a> broadcasting in mono, <a rel=\"noopener\" href=\"http:\/\/www.wkze.com\/\" target=\"_blank\">WKZE<\/a>, \u00a0has a music format with a very eclectic playlist. \u00a0It is a full Class A located in northwestern Connecticut. \u00a0The idea with this station is to garner a larger and more reliable coverage area.<\/p>\n\n\n\n<p>It comes down to a simple physics discussion about free space loss. &nbsp;The basic equation for free space power loss is:<\/p>\n\n\n\n<figure class=\"wp-block-image\"><a href=\"https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/free-space-loss.png\"><img loading=\"lazy\" decoding=\"async\" width=\"459\" height=\"198\" src=\"https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/free-space-loss.png\" alt=\"\" class=\"wp-image-3280\" title=\"free space loss\" srcset=\"https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/free-space-loss.png 459w, https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/free-space-loss-150x64.png 150w, https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/free-space-loss-300x129.png 300w, https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/free-space-loss-400x172.png 400w\" sizes=\"auto, (max-width: 459px) 100vw, 459px\" \/><\/a><\/figure>\n\n\n\n<p>where:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/3\/4\/7\/34712be3047d3330d96255b65d24a76f.png\" alt=\"\\ \\lambda\">\u00a0is the signal wavelength (in meters),<\/li>\n\n\n\n<li><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/6\/1\/6\/616fb717ed0ab1dbf5ded834a72ae83e.png\" alt=\"\\ f\">&nbsp;is the signal frequency (in&nbsp;<a title=\"Hertz\" href=\"http:\/\/en.wikipedia.org\/wiki\/Hertz\">hertz<\/a>),<\/li>\n\n\n\n<li><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/f\/3\/f\/f3f8b30f93a9f9084306c986183f3b8f.png\" alt=\"\\ d\">\u00a0is the distance from the transmitter (in meters),<\/li>\n\n\n\n<li><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/8\/a\/9\/8a95f146c65fedbdfe65ab9a9da9377d.png\" alt=\"\\ c\">&nbsp;is the&nbsp;<a title=\"Speed of light\" href=\"http:\/\/en.wikipedia.org\/wiki\/Speed_of_light\">speed of light in a vacuum<\/a>, 2.99792458 \u00d7 10<sup>8<\/sup>&nbsp;<a title=\"Metres per second\" href=\"http:\/\/en.wikipedia.org\/wiki\/Metres_per_second\">metres per second<\/a>.<\/li>\n<\/ul>\n\n\n\n<p>That formula works for a single frequency, say the carrier frequency, for example. As the signal gets spread out by modulation, the power density on any given frequency is reduced as the energy is divided between many other frequencies.<\/p>\n\n\n\n<p>First, free space loss takes into account the spreading out of electromagnetic energy in free space is determined by the&nbsp;<a title=\"Inverse square law\" href=\"http:\/\/en.wikipedia.org\/wiki\/Inverse_square_law\">inverse square law<\/a>, i.e.<\/p>\n\n\n\n<dl>\n<dd><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/9\/5\/3\/9531f1e9f16631c5f9d0e72be37595c8.png\" alt=\"\\ S = P_t \\frac{1}{4 \\pi d^2} \"><\/dd>\n<\/dl>\n\n\n\n<p>where:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/3\/9\/2\/3926466be16a3c6a43061cf69c80a7ec.png\" alt=\"\\ S\">\u00a0is the power per unit area or power spatial density (in\u00a0<a title=\"Watt\" href=\"http:\/\/en.wikipedia.org\/wiki\/Watt\">watts<\/a>\u00a0per meter-squared) at distance\u00a0<img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/f\/3\/f\/f3f8b30f93a9f9084306c986183f3b8f.png\" alt=\"\\ d\">,<\/li>\n\n\n\n<li><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/b\/0\/2\/b029780d7d6a597fdb45134529350f73.png\" alt=\"\\ P_t\">&nbsp;is the total power transmitted (in watts).<\/li>\n<\/ul>\n\n\n\n<p>Second, with <a href=\"http:\/\/en.wikipedia.org\/wiki\/Frequency_modulation\" target=\"_blank\" rel=\"noopener\">Frequency Modulation<\/a> (FM), the power spectral density is a function of the differences in the highest and lowest frequency:<\/p>\n\n\n\n<dl>\n<dd><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/math\/c\/6\/5\/c65525cb8f70b79651a25d3f921c83d8.png\" alt=\" P=\\int_{F_1}^{F_2}\\,S(f)\\,d f + \\int_{-F_2}^{-F_1}\\,S(f)\\,df. \"><\/dd>\n<\/dl>\n\n\n\n<p>Therefore, the narrower the bandwidth of a signal, the higher the density of the received signal will be in relation to the transmitted power. \u00a0An unmodulated FM signal will have a better, more reliable coverage area than a modulated one. \u00a0Of course, we need to modulate the signal, otherwise, there is no point in having the transmitter on.<\/p>\n\n\n\n<p>A baseband or composite FM signal has several components:<\/p>\n\n\n\n<figure class=\"wp-block-image alignnone\"><a href=\"https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/FM-baseband.png\"><img loading=\"lazy\" decoding=\"async\" width=\"650\" height=\"309\" src=\"https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/FM-baseband-650x309.png\" alt=\"FM baseband signal\" class=\"wp-image-3283\" srcset=\"https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/FM-baseband-650x309.png 650w, https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/FM-baseband-150x71.png 150w, https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/FM-baseband-300x142.png 300w, https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/FM-baseband-400x190.png 400w, https:\/\/www.engineeringradio.us\/blog\/wp-content\/uploads\/2011\/08\/FM-baseband.png 1000w\" sizes=\"auto, (max-width: 650px) 100vw, 650px\" \/><\/a><figcaption class=\"wp-element-caption\">FM baseband signal<\/figcaption><\/figure>\n\n\n\n<p>An FM station transmitting a mono signal will have a much lower bandwidth. With wideband FM, the <a href=\"http:\/\/en.wikipedia.org\/wiki\/Frequency_modulation#Modulation_index\" target=\"_blank\" rel=\"noopener\">modulation index<\/a> is generally <strong>2<em>f\u0394<\/em><\/strong> or two times the maximum audio input frequency. Thus, a mono FM broadcast station will have an approximate deviation of approximately 30 kHz (plus any ancillary services like RDS) vs a stereo FM station, which has a 75-80 kHz deviation using the same carrier power.<\/p>\n\n\n\n<p>For higher power FM stations, FCC Class C and B, this is not much of an issue. &nbsp;Those stations tend to have a great deal headroom when it comes to power density, building penetration, multipath (picket fencing and capture effect). &nbsp;For Class A and LPFM stations, it is a different situation. &nbsp;For those stations, &nbsp;unless FM stereo broadcasting is truly needed, it should be turned off. &nbsp;On low power stations, stereo can be a great detriment to reliable coverage.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>There are a few FM stations around here that intentionally broadcast in mono. \u00a0One is an FM talker, which from a technical standpoint makes a certain amount of sense since any particular human voice is a single-point sound generator. The other FM station broadcasting in mono, WKZE, \u00a0has a music format with a very eclectic &hellip; <a href=\"https:\/\/www.engineeringradio.us\/blog\/2011\/08\/fm-stereo-vs-station-coverage\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">FM Stereo vs station coverage<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[82,70],"class_list":["post-3264","post","type-post","status-publish","format-standard","hentry","category-tech-stuff","tag-fm","tag-fm-processor"],"_links":{"self":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/3264","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/comments?post=3264"}],"version-history":[{"count":19,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/3264\/revisions"}],"predecessor-version":[{"id":11767,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/posts\/3264\/revisions\/11767"}],"wp:attachment":[{"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/media?parent=3264"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/categories?post=3264"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.engineeringradio.us\/blog\/wp-json\/wp\/v2\/tags?post=3264"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}