{"id":1274,"date":"2019-02-01T10:05:02","date_gmt":"2019-02-01T00:35:02","guid":{"rendered":"http:\/\/serg.org.au\/?p=1274"},"modified":"2019-02-02T11:12:37","modified_gmt":"2019-02-02T01:42:37","slug":"standing-waves-and-swr","status":"publish","type":"post","link":"https:\/\/serg.org.au\/index.php\/2019\/02\/01\/standing-waves-and-swr\/","title":{"rendered":"Standing waves and SWR"},"content":{"rendered":"\n<p>At the meeting on 1\/2\/19 I described how we might use the club&#8217;s antenna analyser to best effect.<\/p>\n\n\n\n<p>An important part of using the analyser is to understand the idea of standing waves.<\/p>\n\n\n\n<p>I found this good illustration on youtube:<\/p>\n\n\n\n<figure class=\"wp-block-embed-youtube wp-block-embed is-type-video is-provider-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"#208: Visualizing RF Standing Waves on Transmission Lines\" width=\"840\" height=\"473\" src=\"https:\/\/www.youtube.com\/embed\/M1PgCOTDjvI?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<p>Hang in there, it&#8217;s a little slow moving but the illustration towards the end gives a really good visualisation of standing waves when there is a correct load and an open circuit.<\/p>\n\n\n\n<p> How to tell if your SWR bridge is misleading you.<br>Have on hand an extension length of coax. It should be a \u00bc wavelength long for the band you are experimenting with. After measuring your SWR, insert the extra length in the line &#8211; this moves your testing point 1\/4 wave along the coax to a different point on the standing wave. <\/p>\n\n\n\n<p>Here are some useful lengths:<br><br>6M band use a length of 1 metre, 2M band use 340 mm,70cm band use 13cm.<br><br>It&#8217;s not too critical. Now if your two SWR readings are similar (e.g. 1.2 and 1.3 then you probably don&#8217;t have a big problem but 1.2 and 2 would be unacceptable and require more investigation.<br><br>To actually calculate the length of the 1\/4 wave section the formula is:<br>75*0.67\/freq in MHz and the answer is in metres.<br><br>e.g. for 2M it&#8217;s 75*0.67\/144.0 = 0.348 metres<br><br>I&#8217;ve used 0.67 as the velocity factor, this is true for many coax cables. Heliax is more likely to be 0.8.<\/p>\n\n\n\n<p>John VK5DJ<\/p>\n ","protected":false},"excerpt":{"rendered":"<p>At the meeting on 1\/2\/19 I described how we might use the club&#8217;s antenna analyser to best effect. An important part of using the analyser is to understand the idea of standing waves. I found this good illustration on youtube: Hang in there, it&#8217;s a little slow moving but the illustration towards the end gives &hellip; <a href=\"https:\/\/serg.org.au\/index.php\/2019\/02\/01\/standing-waves-and-swr\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Standing waves and SWR&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-1274","post","type-post","status-publish","format-standard","hentry","category-posts"],"_links":{"self":[{"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/posts\/1274","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/comments?post=1274"}],"version-history":[{"count":0,"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/posts\/1274\/revisions"}],"wp:attachment":[{"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/media?parent=1274"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/categories?post=1274"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/serg.org.au\/index.php\/wp-json\/wp\/v2\/tags?post=1274"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}