{"id":1,"date":"2018-06-14T22:39:34","date_gmt":"2018-06-14T22:39:34","guid":{"rendered":"https:\/\/www.funwithelectronics.com\/wordpress\/?p=1"},"modified":"2018-06-17T18:21:56","modified_gmt":"2018-06-17T18:21:56","slug":"hello-world","status":"publish","type":"post","link":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/2018\/06\/14\/hello-world\/","title":{"rendered":"AIS Packets (Automatic Identification System)"},"content":{"rendered":"

AIS signals are GFSK modulated signals at 161.975 or 162.025 MHz. Packets are sent with a preamble and the HDLC packet protocol is used. Below are pictures showing frequency vs time plots.<\/p>\n

\"\"<\/a><\/p>\n

\"\"<\/a><\/p>\n

Download flow graph here: https:\/\/www.funwithelectronics.com\/wordpress\/other_data\/demod_gfsk_for_blog.grc<\/a><\/p>\n

When connecting the sync_and_strobe<\/em> (gr-capture_tools<\/a>) block to this signal and configuring it correctly, we get this:<\/p>\n

\"\"<\/a><\/p>\n

Zoomed in on the first part:<\/p>\n

 <\/p>\n

\"\"<\/a><\/p>\n

\"\"<\/a><\/p>\n

AIS packets are “encoded” in multiple steps:<\/p>\n

    \n
  1. The fields of various sizes are packed together as a bit sequence.<\/li>\n
  2. Every 8 bit bundle is then reversed<\/li>\n
  3. Bit-stuffing is performed: Every 111111 is converted to 1111101<\/li>\n
  4. The stream is inverted, 1101 becomes 0010<\/li>\n
  5. Differential encoding is performed. So every 1 becomes a transition, every 0 causes no change<\/li>\n
  6. Then the header and end word are added at the start and the end.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

    AIS signals are GFSK modulated signals at 161.975 or 162.025 MHz. Packets are sent with a preamble and the HDLC packet protocol is used. Below are pictures showing frequency vs time plots. Download flow graph here: https:\/\/www.funwithelectronics.com\/wordpress\/other_data\/demod_gfsk_for_blog.grc When connecting the sync_and_strobe (gr-capture_tools) block to this signal and configuring it correctly, we get this: Zoomed in … Continue reading “AIS Packets (Automatic Identification System)”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2],"tags":[],"_links":{"self":[{"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/1"}],"collection":[{"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=1"}],"version-history":[{"count":15,"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/1\/revisions"}],"predecessor-version":[{"id":83,"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/1\/revisions\/83"}],"wp:attachment":[{"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=1"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=1"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.funwithelectronics.com\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=1"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}