{"id":370,"date":"2015-08-08T15:20:00","date_gmt":"2015-08-08T15:20:00","guid":{"rendered":"http:\/\/machineryequipmentonline.com\/video-equipment\/uncategorized\/video-on-magnetic-tapefm-modulation\/"},"modified":"2015-08-08T15:20:00","modified_gmt":"2015-08-08T15:20:00","slug":"video-on-magnetic-tapefm-modulation","status":"publish","type":"post","link":"http:\/\/machineryequipmentonline.com\/video-equipment\/video-on-magnetic-tapefm-modulation\/","title":{"rendered":"VIDEO ON MAGNETIC TAPE:FM MODULATION."},"content":{"rendered":"<div class=\"ullyo6a0dc91bb84eb\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '61e5902552e2353963d8d2f1bd1f4a8f',\n\t\t'format' : 'iframe',\n\t\t'height' : 250,\n\t\t'width' : 300,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/61e5902552e2353963d8d2f1bd1f4a8f\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.ullyo6a0dc91bb84eb {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.ullyo6a0dc91bb84eb {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.ullyo6a0dc91bb84eb {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.ullyo6a0dc91bb84eb {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.ullyo6a0dc91bb84eb {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<h3 align=\"justify\"><em><u>VIDEO ON MAGNETIC TAPE<\/u><\/em><\/h3>\n<p align=\"justify\">The use of magnetic tape to record and replay video signals is now commonplace, but the techniques involved are not so straightforward as for audio recording. The main problem is the relatively large bandwidth of the video signal, which for a broadcast-standard signal extends from d.c. (about 25 Hz in practice) to 5.5 MHz. For domestic videorecorders a more limited response is adequate \u2013 the h.f. roll-off occurs at about 2.5 MHz, permitting a more sparing use of the tape. A magnetic tape system\u2019s output level is proportional to the <i>r<\/i><i>ate of<\/i><i> <\/i><i>c<\/i><i>han<\/i><i>g<\/i><i>e <\/i>of the magnetic \ufb02ux, so that output is directly geared to frequency. Thus each halving of frequency (octave) halves the output signal, giving the tape\/head interface a characteristic 6 dB\/octave curve. Because the difference in levels between magnetic saturation of the tape\u2019s coating and the inherent noise of the system is about 1000:1, corresponding to 60 dB, it is plain that the 6 dB\/octave will permit a maximum of ten octaves to be \ufb01tted between the noise floor and the overload point, so long as massive compensation is provided <\/p>\n<p align=\"justify\">to equalise replay levels across the frequency spectrum. <\/p>\n<h3 align=\"justify\">FM MODULATION<\/h3>\n<p align=\"justify\">A television signal, even the bandwidth-restricted one described above, occupies \ufb01fteen or sixteen octaves, and so cannot be directly recorded on tape by any means. <i>Indirect <\/i>methods of recording are possible, however, and they involve modulation of the video signal onto a carrier. Invariably an f.m. carrier is chosen for this purpose: the use of f.m. increases noise immunity, masks shortfall in signal strength stemming from slight tracking errors and imperfect head\/ tape contact, and permits either (a) its use as recording bias for a second signal carrying the chroma information or (b) the facility to drive the tape coating into magnetic saturation on each f.m. carrier cycle to further improve S\/N ratio. <\/p>\n<p align=\"justify\">The way in which the f.m. carrier technique reduces the octave range is shown in Fig. 13.1. Carrier frequencies are assigned for both extremes of the luminance signal waveform, typically 3.8 MHz for sync tip and 4.8 MHz for peak white. This actually permits the recording of d.c. (zero frequency) video signals since a constant level of white or grey will give a constant f.m. carrier frequency. During each <\/p><div class=\"yxbts6a0dc91bb86a3\" ><script async src=\"https:\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js?client=ca-pub-0778475562755157\"\n     crossorigin=\"anonymous\"><\/script>\n<!-- 300x600 television-and-video -->\n<ins class=\"adsbygoogle\"\n     style=\"display:inline-block;width:300px;height:600px\"\n     data-ad-client=\"ca-pub-0778475562755157\"\n     data-ad-slot=\"6549443290\"><\/ins>\n<script>\n     (adsbygoogle = window.adsbygoogle || []).push({});\n<\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.yxbts6a0dc91bb86a3 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.yxbts6a0dc91bb86a3 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.yxbts6a0dc91bb86a3 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.yxbts6a0dc91bb86a3 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.yxbts6a0dc91bb86a3 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n<div class=\"mkdxy6a0dc91bb85d2\" ><script type=\"text\/javascript\">\n\tatOptions = {\n\t\t'key' : '0c1eb4c533eaedb7b996f49a5a4983a9',\n\t\t'format' : 'iframe',\n\t\t'height' : 300,\n\t\t'width' : 160,\n\t\t'params' : {}\n\t};\n<\/script>\n<script type=\"text\/javascript\" src=\"\/\/www.highperformanceformat.com\/0c1eb4c533eaedb7b996f49a5a4983a9\/invoke.js\"><\/script><\/div><style type=\"text\/css\">\r\n@media screen and (min-width: 1201px) {\r\n.mkdxy6a0dc91bb85d2 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 993px) and (max-width: 1200px) {\r\n.mkdxy6a0dc91bb85d2 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 769px) and (max-width: 992px) {\r\n.mkdxy6a0dc91bb85d2 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (min-width: 768px) and (max-width: 768px) {\r\n.mkdxy6a0dc91bb85d2 {\r\ndisplay: block;\r\n}\r\n}\r\n@media screen and (max-width: 767px) {\r\n.mkdxy6a0dc91bb85d2 {\r\ndisplay: block;\r\n}\r\n}\r\n<\/style>\r\n\n<p align=\"justify\"><a href=\"http:\/\/lh3.googleusercontent.com\/-GE-yDuOf1CE\/VcYeUez89bI\/AAAAAAAB1Fw\/0WWS3CcTXWM\/s1600-h\/VIDEO%252520ON%252520MAGNETIC%252520TAPE-0165%25255B2%25255D.jpg\"><img decoding=\"async\" loading=\"lazy\" style=\"background-image: none; border-bottom: 0px; border-left: 0px; margin: 0px auto; padding-left: 0px; padding-right: 0px; display: block; float: none; border-top: 0px; border-right: 0px; padding-top: 0px\" title=\"VIDEO ON MAGNETIC TAPE-0165\" border=\"0\" alt=\"VIDEO ON MAGNETIC TAPE-0165\" src=\"http:\/\/lh3.googleusercontent.com\/-6w07jVVj-ec\/VcYeWGhRUpI\/AAAAAAAB1F4\/M1K3sJvEphs\/VIDEO%252520ON%252520MAGNETIC%252520TAPE-0165_thumb.jpg?imgmax=800\" width=\"244\" height=\"154\" \/><\/a> <\/p>\n<p align=\"justify\">line sync pulse the carrier falls to 3.8 MHz for its 4.7 \u03bcs duration, and during the 52 \u03bcs active line period the carrier frequency rapidly deviates between 4.1 and 4.8 MHz to describe the levels of light and shade in the TV picture. <\/p>\n<p align=\"justify\">In deviating in this way the f.m. modulator produces sidebands, and the <i>modulation index <\/i>(the relationship between video and f.m. frequencies) is chosen so that virtually all the sideband energy is con\ufb01ned to the \ufb01rst pair of sidebands above and below the carrier frequency itself. In the VHS system, for instance, enough sideband energy is recovered to properly demodulate the f.m. signal when the record and replay frequency response extends from about 1 MHz to about 7 MHz, which embraces the entire lower sideband and a portion of the upper one \u2013 balance is restored by careful shaping of the frequency response of the playback ampli\ufb01er. An operating range of frequencies between 1 and 7 MHz represents an octave range of less than four \u2013 well within the capability of the magnetic tape system.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>VIDEO ON MAGNETIC TAPE The use of magnetic tape to record and replay video signals is now commonplace, but the techniques involved are not so straightforward as for audio recording. The main problem is the relatively large bandwidth of the video signal, which for a broadcast-standard signal extends from d.c. (about 25 Hz in practice) [&hellip;]<br \/><a href=\"http:\/\/machineryequipmentonline.com\/video-equipment\/video-on-magnetic-tapefm-modulation\/\" class=\"more-link\" >Continue reading&#8230;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"aioseo_notices":[],"views":974,"_links":{"self":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts\/370"}],"collection":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/comments?post=370"}],"version-history":[{"count":0,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/posts\/370\/revisions"}],"wp:attachment":[{"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/media?parent=370"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/categories?post=370"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/machineryequipmentonline.com\/video-equipment\/wp-json\/wp\/v2\/tags?post=370"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}