{"id":2346,"date":"2016-10-21T10:05:09","date_gmt":"2016-10-21T17:05:09","guid":{"rendered":"http:\/\/blackcap.name\/blog\/new\/?p=2346"},"modified":"2016-10-21T10:05:09","modified_gmt":"2016-10-21T17:05:09","slug":"demodulating-acars","status":"publish","type":"post","link":"https:\/\/blackcap.name\/blog\/new\/?p=2346","title":{"rendered":"Demodulating ACARS"},"content":{"rendered":"<p>ACARS is a digital protocol used by aircraft to transmit messages. It&#8217;s been around since the late 1970&#8217;s and is decodable using nothing but a sound card and the right software. But, after helping a friend (a technologically-sophisticated one; like me, he has a ham license) who has previously had no luck decoding the messages, it&#8217;s clear there&#8217;s some tricks involved.<\/p>\n<ul>\n<li>Don&#8217;t use squelch. Squelch will chop off the first tiny fraction of information in a packet, causing decoding errors (typically, messages simply won&#8217;t decode). There&#8217;s no need to use squelch, anyhow. Squelch exists to prevent humans from being annoyed by listening to the background noise when a frequency is not in use. Computers don&#8217;t care about being forced to analyze static, and can easily distinguish between static and an ACARS packet.<\/li>\n<li>Use a wide bandwidth. A big part of my friend&#8217;s problem was that he was using the default AM bandwidth on his communications receiver, which was apparently too narrow. I have myself tried using both the wide and narrow filters on my receiver; only the wide one works. ACARS is apparently a wide-bandwidth mode, and a narrow filter throws away critical information needed to decode a message.<\/li>\n<li>If using ACARSD, configuration is critical. ACARSD is the most popular freeware package for decoding ACARS. Alas, it&#8217;s not exactly user-friendly. To install it you must first configure the installer and manually tell it to create the directories it needs. To configure it you must use a separate program that (re)writes the necessary .INI file. Moreover, that program doesn&#8217;t always default to reasonable values as advertised. It claims ACARSD will use the default sound card if none is specified. I found it necessary to explicitly specify the sound card for the default one to be used on my friend&#8217;s computer.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>ACARS is a digital protocol used by aircraft to transmit messages. It&#8217;s been around since the late 1970&#8217;s and is decodable using nothing but a sound card and the right software. But, after helping a friend (a technologically-sophisticated one; like me, he has a ham license) who has previously had no luck decoding the messages, [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7,8],"tags":[],"class_list":["post-2346","post","type-post","status-publish","format-standard","hentry","category-computers","category-radio"],"_links":{"self":[{"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=\/wp\/v2\/posts\/2346","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2346"}],"version-history":[{"count":0,"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=\/wp\/v2\/posts\/2346\/revisions"}],"wp:attachment":[{"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2346"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2346"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blackcap.name\/blog\/new\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2346"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}