{"id":414,"date":"2025-01-20T15:15:37","date_gmt":"2025-01-20T14:15:37","guid":{"rendered":"http:\/\/sp5tof.pl\/?page_id=414"},"modified":"2025-11-21T18:37:29","modified_gmt":"2025-11-21T17:37:29","slug":"sdr-preselector","status":"publish","type":"post","link":"https:\/\/sp5tof.pl\/?p=414","title":{"rendered":"SDR Preselector for 80\/40m"},"content":{"rendered":"<p>Preselector  is a quite narrow input filter intended for receivers, especially needed with present cheap SDR devices where the input filters should be improved in general.<br \/>\nMy goal was to build up such one mainly for two bands : 80m &#038; 40m. My version is based in 100% on DL2NBU &#038; DL6RAI project. It can be currently found on <a href=\"https:\/\/www.bavarian-contest-club.de\/1996\/04\/bcc-preselektor\/\" target=_blank>Bavarian Contest Club<\/a> site.<\/p>\n<p>Please find a schema:<br \/>\n<br \/>\n<img decoding=\"async\" class=\"size-large wp-image-111\" src=\"https:\/\/sp5tof.pl\/wp-content\/uploads\/2025\/01\/preselector_1-1.png\"><\/p>\n<p>Here you can find also a list of necessary toroids and welding methods:<br \/>\n<img decoding=\"async\" class=\"size-large wp-image-111\" src=\"https:\/\/sp5tof.pl\/wp-content\/uploads\/2025\/01\/preselector_2-1.png\"><\/p>\n<p><img decoding=\"async\" class=\"size-large wp-image-111\" src=\"https:\/\/sp5tof.pl\/wp-content\/uploads\/2025\/01\/20240816_224211.jpg\"><\/p>\n<p>I screened the case with copper tape before I installed all listed components. PCB was prepared using just hand drill due to quite not complicated connections(in case of just 2 bands to be covered). If you decide to build up the complex version, PCB is available within the PDF linked in the bottom of this page.<br \/>\n<\/p>\n<p><img decoding=\"async\" class=\"size-large wp-image-111\" src=\"https:\/\/sp5tof.pl\/wp-content\/uploads\/2025\/01\/20240818_133253.jpg\"><\/p>\n<p>I added the single bistable switch for changing band from 80m to 40m (it&#8217;s only about shorting one coil).<\/p>\n<p><img decoding=\"async\" class=\"size-large wp-image-111\" src=\"https:\/\/sp5tof.pl\/wp-content\/uploads\/2025\/01\/20240818_141124.jpg\"><\/p>\n<p>nanoVNA shows a quite good characteristics:<br \/>\n<img decoding=\"async\" class=\"size-large wp-image-111\" src=\"https:\/\/sp5tof.pl\/wp-content\/uploads\/2025\/01\/presel.jpg\"><br \/>\n I noted that it&#8217;s important to use exactly the same toroids like author did. It decreases the attenuation of a filter.<\/p>\n<p>Ready-to-go documentation can be downloaded as PDF from <a href=\"https:\/\/www.bavarian-contest-club.de\/wp-content\/uploads\/2023\/11\/BCC-Preselektor.pdf\">here<\/a><\/p>\n<p align=\"right\">Jakub\/SP5TOF<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Preselector is a quite narrow input filter intended for receivers, especially needed with present cheap SDR devices where the input filters should be improved in general. My goal was to&hellip; <\/p>\n","protected":false},"author":1,"featured_media":445,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"footnotes":""},"categories":[5],"tags":[],"class_list":["post-414","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-radio"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/sp5tof.pl\/index.php?rest_route=\/wp\/v2\/posts\/414","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sp5tof.pl\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sp5tof.pl\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sp5tof.pl\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sp5tof.pl\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=414"}],"version-history":[{"count":17,"href":"https:\/\/sp5tof.pl\/index.php?rest_route=\/wp\/v2\/posts\/414\/revisions"}],"predecessor-version":[{"id":466,"href":"https:\/\/sp5tof.pl\/index.php?rest_route=\/wp\/v2\/posts\/414\/revisions\/466"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/sp5tof.pl\/index.php?rest_route=\/wp\/v2\/media\/445"}],"wp:attachment":[{"href":"https:\/\/sp5tof.pl\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=414"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sp5tof.pl\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=414"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sp5tof.pl\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=414"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}