{"id":20,"date":"2026-10-28T00:05:27","date_gmt":"2026-10-28T00:05:27","guid":{"rendered":"https:\/\/k0axx.net\/?page_id=20"},"modified":"2026-10-28T00:05:27","modified_gmt":"2026-10-28T00:05:27","slug":"common-mode","status":"publish","type":"page","link":"https:\/\/k0axx.net\/?page_id=20","title":{"rendered":"Common-Mode Current &#038; Station Interference"},"content":{"rendered":"<p class=\"k-kicker wp-block-paragraph\">TECHNICAL NOTE \/ RFI \/ FEED SYSTEMS<\/p><p class=\"wp-block-paragraph\">Unintended RF current on the outside of coax shield can alter an antenna pattern, couple RF into the shack and create receive interference. A low SWR reading is not proof that the feed system is free of common-mode problems.<\/p><h2 class=\"wp-block-heading\">Typical symptoms<\/h2><ul class=\"wp-block-list\"><li>Antenna pattern or receive noise changes when the coax is moved.<\/li><li>Computer, audio or control cables show RF sensitivity during transmit.<\/li><li>Equipment cases or nearby metalwork carry measurable RF current.<\/li><li>RFI shifts with band, power level or antenna direction.<\/li><\/ul><h2 class=\"wp-block-heading\">A disciplined test<\/h2><p class=\"wp-block-paragraph\">Use an appropriate RF current probe or clamp to compare common-mode current at consistent positions and operating conditions. Record frequency, power, antenna direction and test configuration. Change one variable at a time; compare results before and after adding a choke or changing cable routing.<\/p><h2 class=\"wp-block-heading\">Chokes and bonding<\/h2><p class=\"wp-block-paragraph\">Choose choke impedance and thermal capability for the actual band and RF power. Keep station bonding, lightning protection and personnel safety distinct from the RF balance problem; a ferrite choke does not replace protective grounding.<\/p>","protected":false},"excerpt":{"rendered":"<p>Diagnose common-mode RF current and interference without confusing low SWR with a balanced antenna.<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-20","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/k0axx.net\/index.php?rest_route=\/wp\/v2\/pages\/20","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/k0axx.net\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/k0axx.net\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/k0axx.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/k0axx.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=20"}],"version-history":[{"count":0,"href":"https:\/\/k0axx.net\/index.php?rest_route=\/wp\/v2\/pages\/20\/revisions"}],"wp:attachment":[{"href":"https:\/\/k0axx.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=20"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}