{"id":34,"date":"2026-09-19T11:18:17","date_gmt":"2026-09-19T11:18:17","guid":{"rendered":"https:\/\/myradiostuff.co.uk\/?p=34"},"modified":"2026-09-19T11:18:17","modified_gmt":"2026-09-19T11:18:17","slug":"signal-filtering-for-sdr-part-one","status":"publish","type":"post","link":"https:\/\/myradiostuff.co.uk\/?p=34","title":{"rendered":"Signal filtering for SDR &#8211; Part One"},"content":{"rendered":"\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"383\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1228-1024x383.jpg\" alt=\"\" class=\"wp-image-36\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1228-1024x383.jpg 1024w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1228-300x112.jpg 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1228-766x287.jpg 766w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1228-1536x575.jpg 1536w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1228-2048x767.jpg 2048w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Where I live, just North of London, there are some VERY strong AM signals which broadcast on frequencies just under the 160m band. As a result, these can overpower Rx stages or &#8216;deafen&#8217; a receiver to the rest of the HF spectrum. As I use a full-spectrum SDR receiver for the receiver side of my station, the goal is to filter these out with minimal effect on the HF bands.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"678\" height=\"522\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1233.jpg\" alt=\"\" class=\"wp-image-37\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1233.jpg 678w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/08\/Capture260821-1233-300x231.jpg 300w\" sizes=\"auto, (max-width: 678px) 100vw, 678px\" \/><figcaption class=\"wp-element-caption\">You can see here just how strong these signals are&#8230;<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Living in a typical UK property, i don&#8217;t have the space for an antenna to do the 160m band justice, i have accepted that to filter these signals out i may have to take the 160m band with them to reduce them and the harmonics they produce, but i would like to keep 80m clean so i can later enter some of the UK contests held on that band, I in intially considered a notch filter at approximately 1.2Mhz, but in reality at my station anything under the 80m band is not for me, so i figured a high pass filter sitting just below the 80m band would be the way to go.<br><br>My first attempt was a 5th-order High-Pass Butterworth filter just below the 80m band; while it did a good job attenuating the AM signals, testing showed it attenuated too much in the 80m band.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">So the next attempt was to make a 7th-order Butterworth at 1.7 MHz; this worked fairly well, and it only had minimal effect on the 160m band.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1019\" height=\"296\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/schematic-1.png\" alt=\"\" class=\"wp-image-42\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/schematic-1.png 1019w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/schematic-1-300x87.png 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/schematic-1-768x223.png 768w\" sizes=\"auto, (max-width: 1019px) 100vw, 1019px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"222\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/img_4757-e1789815622163-1024x222.jpeg\" alt=\"\" class=\"wp-image-45\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/img_4757-e1789815622163-1024x222.jpeg 1024w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/img_4757-e1789815622163-300x65.jpeg 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/img_4757-e1789815622163-768x167.jpeg 768w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/img_4757-e1789815622163-1536x333.jpeg 1536w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/img_4757-e1789815622163.jpeg 1660w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"559\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/nanovna-h4_2026-09-17_16-56-52-1024x559.png\" alt=\"\" class=\"wp-image-43\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/nanovna-h4_2026-09-17_16-56-52-1024x559.png 1024w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/nanovna-h4_2026-09-17_16-56-52-300x164.png 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/nanovna-h4_2026-09-17_16-56-52-768x419.png 768w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/nanovna-h4_2026-09-17_16-56-52-1536x838.png 1536w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/nanovna-h4_2026-09-17_16-56-52-2048x1118.png 2048w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Approx -20 dB at the frequencies causing the biggest problems &#8211; Good, but not enough&#8230;<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Before adding the filter.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"184\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF2-1024x184.jpg\" alt=\"\" class=\"wp-image-48\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF2-1024x184.jpg 1024w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF2-300x54.jpg 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF2-767x138.jpg 767w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF2-1536x276.jpg 1536w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF2.jpg 1907w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"239\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF-1024x239.jpg\" alt=\"\" class=\"wp-image-47\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF-1024x239.jpg 1024w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF-300x70.jpg 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF-768x179.jpg 768w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF-1536x358.jpg 1536w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/BeforeHPF.jpg 1904w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">After adding the filter.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"220\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF2-1024x220.jpg\" alt=\"\" class=\"wp-image-50\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF2-1024x220.jpg 1024w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF2-300x64.jpg 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF2-765x164.jpg 765w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF2-1536x329.jpg 1536w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF2.jpg 1907w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"211\" src=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF-1024x211.jpg\" alt=\"\" class=\"wp-image-51\" srcset=\"https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF-1024x211.jpg 1024w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF-300x62.jpg 300w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF-768x158.jpg 768w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF-1536x316.jpg 1536w, https:\/\/myradiostuff.co.uk\/wp-content\/uploads\/2026\/09\/AfterHPF.jpg 1905w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><br>You can see just how much the dynamic range has increased by reducing the signals at 909KHz and 1.089 MHz. You can also see, after adding the filter, just how strong some of the other Short and Medium Wave stations are, absolutely overpowering the signals received on the HF bands.<br><br>Coming up in Part 2&#8230; Custom PCB&#8217;s to aid development and testing&#8230;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Where I live, just North of London, there are some VERY strong AM signals which broadcast on frequencies just under the 160m band. As a result, these can overpower Rx stages or &#8216;deafen&#8217; a receiver to the rest of the HF spectrum. As I use a full-spectrum SDR receiver for the receiver side of my [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":36,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","hide_page_title":"","footnotes":""},"categories":[3],"tags":[],"class_list":["post-34","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tech"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Signal filtering for SDR - Part One - MyRadioStuff<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/myradiostuff.co.uk\/?p=34\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Signal filtering for SDR - Part One - MyRadioStuff\" \/>\n<meta property=\"og:description\" content=\"Where I live, just North of London, there are some VERY strong AM signals which broadcast on frequencies just under the 160m band. 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As a result, these can overpower Rx stages or &#8216;deafen&#8217; a receiver to the rest of the HF spectrum. 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