{"id":5534,"date":"2016-01-21T23:30:00","date_gmt":"2016-01-21T12:30:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2016\/01\/21\/high-pass-filter-knocks-down-am-broadcast-interference\/"},"modified":"2025-07-21T19:11:55","modified_gmt":"2025-07-21T09:11:55","slug":"high-pass-filter-knocks-down-am-broadcast-interference","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2016\/01\/21\/high-pass-filter-knocks-down-am-broadcast-interference\/","title":{"rendered":"High-Pass Filter Knocks Down AM Broadcast Interference"},"content":{"rendered":"
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WFAX 1220 AM was starting to bother me. Each morning, I’d be drinking my coffee, listening to nice roundtables on 160 meters, when, right at 6 AM, WFAX would fire up its 5 kW AM transmitter, 1.5 miles from my location. And they would crush the “front end” of my R2 phasing receiver. It doesn’t take much to do that, since the only thing between the SBL-1 mixers in the R2 and the antenna is a signal splitter. Obviously I needed some filtering. <\/b><\/div>\n

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I turned to the free program called Elsie (L-C, get it?) and quickly whipped up a design for a seven element, capacitive input high-pass filter that promised to take about 45 db out of WFAX’s sails, without attenuating even the lowest end of Top Band. <\/b><\/div>\n

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Last night I scrounged through the junk boxes and found suitable capacitors. A visit to an on-line toroid calculator showed that around 35 turns on a T-50-2 (red) iron powder core would yield the needed 6 uH coils. I built the filter this morning — picture below. <\/b><\/div>\n

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It works very well. You can see the results in the picture above. The yellow trace on the ‘scope shows the signal at the antenna terminal. Yikes, it shows around 4 volts rms at 1.220 MHz (the scale is 5 volts\/div). The blue trace below is on the same scale — this is the signal coming out of the filter. Not enough to really measure on the 5 volts\/division scale. <\/b><\/div>\n

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This was a very satisfying “quick and easy” build. I really like the sound of the R2, so much so that I’m not firing up the DX-100 as much as I had been. Instead I find myself just listening to the R2.<\/b><\/div>\n
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WFAX 1220 AM was starting to bother me. Each morning, I’d be drinking my coffee, listening to nice roundtables on 160 meters, when, right at 6 AM, WFAX would fire up its 5 kW AM transmitter, 1.5 miles from my location. And they would crush the “front end” of my R2 phasing receiver. It doesn’t … Continue reading “High-Pass Filter Knocks Down AM Broadcast Interference”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":5535,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[259,16,45,54],"tags":[],"class_list":["post-5534","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-160-meters","category-filters","category-interference","category-phasing-rigs"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/5534","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=5534"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/5534\/revisions"}],"predecessor-version":[{"id":5537,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/5534\/revisions\/5537"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/5535"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=5534"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=5534"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=5534"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}