{"id":50,"date":"2013-07-09T11:37:10","date_gmt":"2013-07-09T09:37:10","guid":{"rendered":"https:\/\/pa3csg.nl\/?page_id=50"},"modified":"2018-02-06T15:50:15","modified_gmt":"2018-02-06T14:50:15","slug":"70-mhz-low-pass-filter","status":"publish","type":"page","link":"https:\/\/pa3csg.nl\/?page_id=50","title":{"rendered":"70 MHz low pass filter"},"content":{"rendered":"<p><span style=\"font-size: x-large;\"><strong>Low pass filter for 70 MHz<\/strong><\/span><\/p>\n<p>&nbsp;<\/p>\n<p>In need of a low pass filter for my 70 MHz transverter, I decided to build the filter as published on the OZ2M website. The filter published there is working without problem and needs no or very little tuning. The original design can be found here:<\/p>\n<p><a href=\"http:\/\/rudius.net\/oz2m\/70mhz\/lpf.htm\" target=\"_blank\">http:\/\/rudius.net\/oz2m\/70mhz\/lpf.htmhttp:\/\/rudius.net\/oz2m\/70mhz\/lpf.htm<\/a><\/p>\n<p>I build this filter several times for low power applications, using normal ceramic capacitors.<\/p>\n<p>Now I needed a high power version, I didn\u2019t have the correct capacitor but obtained 2 ceramic doorknobs each 50 pF. It needed some adjustments of the inductors to get it working.<\/p>\n<p>The whole filter was build in a available metal box.<\/p>\n<p><img loading=\"lazy\" class=\" wp-image-1203 aligncenter\" src=\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/lpf-70mhz-1-300x213.png\" alt=\"lpf-70mhz\" width=\"654\" height=\"464\" srcset=\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/lpf-70mhz-1-300x213.png 300w, https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/lpf-70mhz-1-600x427.png 600w, https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/lpf-70mhz-1.png 1956w\" sizes=\"(max-width: 654px) 100vw, 654px\" \/><\/p>\n<p>So I ended up with the following values:<\/p>\n<p>C1 and C2 50 pF doorknob<\/p>\n<p>L1 and L3 3 turns on 20mm diameter 50 mm long<\/p>\n<p>L2 3 turns on 20mm diameter and 25mm long<\/p>\n<p>&nbsp;<\/p>\n<p>Results:<\/p>\n<p>Feed through loss measured with my signal generator and mW meter 0,2dB<\/p>\n<p>140 MHz -44 dB<\/p>\n<p>210 MHz around -55dB<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" class=\" wp-image-1204 aligncenter\" src=\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/scrn01-300x218.jpg\" alt=\"scrn01\" width=\"644\" height=\"468\" srcset=\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/scrn01-300x218.jpg 300w, https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/scrn01-600x436.jpg 600w, https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/scrn01.jpg 640w\" sizes=\"(max-width: 644px) 100vw, 644px\" \/><\/p>\n<p><strong>Layout of the filter<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" class=\" wp-image-1205 aligncenter\" src=\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/lpf_schematic-300x134.png\" alt=\"lpf_schematic\" width=\"690\" height=\"308\" \/><\/p>\n<p>&nbsp;<\/p>\n<p>Measuring the filter with the tracking generator, centre frequency 125 MHz, span 250 MHz<\/p>\n<p><img loading=\"lazy\" class=\" wp-image-1207 aligncenter\" src=\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/sweep-70mhz-lpf-300x260.png\" alt=\"sweep-70mhz-lpf\" width=\"633\" height=\"549\" srcset=\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/sweep-70mhz-lpf-300x260.png 300w, https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/sweep-70mhz-lpf-600x520.png 600w, https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/sweep-70mhz-lpf-1024x887.png 1024w, https:\/\/pa3csg.nl\/wp-content\/uploads\/2013\/07\/sweep-70mhz-lpf.png 1884w\" sizes=\"(max-width: 633px) 100vw, 633px\" \/><\/p>\n","protected":false},"excerpt":{"rendered":"<div class=\"mh-excerpt\"><p>Low pass filter for 70 MHz &nbsp; In need of a low pass filter for my 70 MHz transverter, I decided to build the filter <a class=\"mh-excerpt-more\" href=\"https:\/\/pa3csg.nl\/?page_id=50\" title=\"70 MHz low pass filter\">[&#8230;]<\/a><\/p>\n<\/div>","protected":false},"author":1,"featured_media":852,"parent":0,"menu_order":56,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"categories":[38,16],"tags":[],"_links":{"self":[{"href":"https:\/\/pa3csg.nl\/index.php?rest_route=\/wp\/v2\/pages\/50"}],"collection":[{"href":"https:\/\/pa3csg.nl\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/pa3csg.nl\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/pa3csg.nl\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/pa3csg.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=50"}],"version-history":[{"count":5,"href":"https:\/\/pa3csg.nl\/index.php?rest_route=\/wp\/v2\/pages\/50\/revisions"}],"predecessor-version":[{"id":1208,"href":"https:\/\/pa3csg.nl\/index.php?rest_route=\/wp\/v2\/pages\/50\/revisions\/1208"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/pa3csg.nl\/index.php?rest_route=\/wp\/v2\/media\/852"}],"wp:attachment":[{"href":"https:\/\/pa3csg.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=50"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/pa3csg.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=50"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/pa3csg.nl\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=50"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}