{"id":24218,"date":"2017-02-16T16:30:52","date_gmt":"2017-02-16T20:30:52","guid":{"rendered":"http:\/\/swling.com\/blog\/?p=24218"},"modified":"2017-02-16T16:30:52","modified_gmt":"2017-02-16T20:30:52","slug":"fm-notch-filter-for-sdrplay-rsp1","status":"publish","type":"post","link":"https:\/\/swling.com\/blog\/2017\/02\/fm-notch-filter-for-sdrplay-rsp1\/","title":{"rendered":"FM Notch Filter for SDRPlay RSP1"},"content":{"rendered":"

\"\"<\/a>RF filters are used (as the name implies) to filter\/remove the frequencies you are not interested in and\/or let frequencies you want pass . They come in lots of types. For example a band-pass filter lets the signals in a frequency range to pass through it and rejects\/attenuates other frequencies. The opposite of band-pass filter is a band-reject or band-stop filter (also called a notch filter) which rejects\/attenuates signals in a specific range and lets other frequencies get through the filter. Lots of different filters are used in SDRs and traditional radios. For example AM low-pass filters (only let frequencies lower than 1.7MHZ or so pass) or band-pass filters for various ham radio bands.<\/p>\n

One of the popular\u00a0use cases for a notch filter is in the FM broadcast range (88-108 MHZ in most parts of the world)<\/p>\n

When you live near a powerful transmitter, it can affect the operation of your receiver in other near frequencies (or overload your receiver’s front-end), but I didn’t want the notch filter for this reason. I’ve got a SDRPlay RSP1 (among many other SDRs) which due to its architecture, has some images of FM band in the UHF range (for example in 330-350 MHZ). In fact they’re the images\u00a0of the product of LO harmonics and FM frequencies.<\/p>\n

You can temporarily move\/shift the frequency by changing the LO frequency which does not remove them, but moves them around.<\/p>\n

Another method to remove these images is using a band-stop filter.<\/p>\n

This is the filter I’m using (Thanks to my friend Amirhosein Hasanpur who designed and built it):<\/p>\n

\"\"<\/a><\/p>\n

Here you can see the effect of using a FM notch filter on my SDRPlay RSP1:<\/p>\n

FM, without filter:<\/p>\n

\"\"<\/a><\/p>\n

FM, with filter:<\/p>\n

\"\"<\/a><\/p>\n

UHF (images) without filter:<\/p>\n

\"\"<\/a><\/p>\n

UHF (images) with filter:<\/p>\n

\"\"<\/a><\/p>\n

Here’s a link to a Zip file containing the PCB (in Protel), schematics (pdf) and S Parameters (pdf):<\/p>\n

https:\/\/www.dropbox.com\/s\/l98kylrofohgqxf\/SWLing.zip?dl=0<\/a><\/p>\n

Note: Like any other SDR test\/review, the results\u00a0depend on lots of different parameters (various gain values, LNA, antenna, software, etc). These pictures are captured with\u00a0the same conditions\u00a0just to show the effectiveness of this filter and your milage will definitely vary, but expect a\u00a0similar outcome. If you live close to a powerful transmitter or use LNAs, you will receive some signals, even when using the filter.<\/p>\n

Final note: this issue is solved in the newer\u00a0version of SDRPlay (RSP2) :\u00a0it has software-selectable notch filters for FM and MW broadcast frequencies.<\/p>\n

Mehdi Asgari, the author of this post, is a regular contributor to the SWLing Post<\/a>. <\/em>Mehdi lives in Tehran and is an active member of the EP2C amateur radio club<\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

RF filters are used (as the name implies) to filter\/remove the frequencies you are not interested in and\/or let frequencies you want pass . They come in lots of types. For example a band-pass filter lets the signals in a frequency range to pass through it and rejects\/attenuates other frequencies. The opposite of band-pass filter […]<\/p>\n","protected":false},"author":56,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[4199,3781,26,158,1113],"tags":[4159,5647,157,3711,3710],"class_list":["post-24218","post","type-post","status-publish","format-standard","hentry","category-accessories","category-fm","category-radios","category-software-defined-radio","category-tutorials","tag-notch-filter","tag-rsp1","tag-sdr","tag-sdrplay","tag-sdrplay-rsp"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/pn3uc-6iC","jetpack-related-posts":[{"id":17502,"url":"https:\/\/swling.com\/blog\/2016\/02\/mikes-low-and-high-pass-filter-deals\/","url_meta":{"origin":24218,"position":0},"title":"Mike’s low and high pass filter deals","author":"Thomas","date":"February 27, 2016","format":false,"excerpt":"SWLing Post contributor, Mike Ladd, is an avid SDR enthusiast and an\u00a0administrator of the SDRplay Facebook group.\u00a0Mike\u00a0contacted me about special pricing he has arranged for low and high pass filters through Rescue Electronics. Mike explains: These filters retail for $70.00 each. I spoke to the builder. I told him who\u2026","rel":"","context":"In "Accessories"","block_context":{"text":"Accessories","link":"https:\/\/swling.com\/blog\/category\/accessories\/"},"img":{"alt_text":"HDSDR-SDRPlay-RSP-PARI","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/10\/HDSDR-SDRPlay-RSP-PARI-1024x554.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/10\/HDSDR-SDRPlay-RSP-PARI-1024x554.jpg?resize=350%2C200 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/10\/HDSDR-SDRPlay-RSP-PARI-1024x554.jpg?resize=525%2C300 1.5x"},"classes":[]},{"id":13506,"url":"https:\/\/swling.com\/blog\/2015\/06\/bonitos-new-high-and-low-pass-filters\/","url_meta":{"origin":24218,"position":1},"title":"Bonito’s new high and low pass filters","author":"Thomas","date":"June 10, 2015","format":false,"excerpt":"Dennis Walter at Bonito has just informed me about two new product's they're offering: high and low pass filters. From the Bonito blog: LP060\u00a0Low Pass Filter The elliptically-formed low pass filter LP060 from NTi suppresses all frequencies above 60 MHz. Highly effective antennas combined with near-by strong FM stations often\u2026","rel":"","context":"In "New Products"","block_context":{"text":"New Products","link":"https:\/\/swling.com\/blog\/category\/new-products\/"},"img":{"alt_text":"high-pass","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/06\/high-pass.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/06\/high-pass.jpg?resize=350%2C200 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/06\/high-pass.jpg?resize=525%2C300 1.5x"},"classes":[]},{"id":22319,"url":"https:\/\/swling.com\/blog\/2016\/11\/announcing-the-new-sdrplay-rsp2\/","url_meta":{"origin":24218,"position":2},"title":"Review of the SDRplay RSP2 software defined radio","author":"Thomas","date":"November 22, 2016","format":false,"excerpt":"This morning, SDRplay Limited announced the release\u2013\u2013and availability\u2013\u2013of their second generation software defined radio, the RSP2. Regular SWLing Post readers will note that I\u2019m a pretty big fan of SDRplay\u2019s first SDR, the RSP, or \u201cRSP1,\u201d as I\u2019ll now call it\u00a0(I published a review of the RSP1 in July 2015).\u2026","rel":"","context":"In "Ham Radio"","block_context":{"text":"Ham Radio","link":"https:\/\/swling.com\/blog\/category\/ham-radio\/"},"img":{"alt_text":"The SDRplay RSP2","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/11\/SDRplay-RSP2-top-angle.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/11\/SDRplay-RSP2-top-angle.jpg?resize=350%2C200 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/11\/SDRplay-RSP2-top-angle.jpg?resize=525%2C300 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/11\/SDRplay-RSP2-top-angle.jpg?resize=700%2C400 2x"},"classes":[]},{"id":17368,"url":"https:\/\/swling.com\/blog\/2016\/02\/a-simple-homebrew-high-pass-filter\/","url_meta":{"origin":24218,"position":3},"title":"A simple homebrew high pass filter","author":"Thomas","date":"February 17, 2016","format":false,"excerpt":"Many thanks to Jon Hudson, of SDRplay, who posted the image above along with the following note on Facebook: David, WA7JHZ has designed and assembled this neat 2.6 MHz high-pass filter (HPF) for use with SDRs. He says that this simple input band-pass filter (BPF) might be of interest to\u2026","rel":"","context":"In "Accessories"","block_context":{"text":"Accessories","link":"https:\/\/swling.com\/blog\/category\/accessories\/"},"img":{"alt_text":"12744054_901043640014242_2651293633303686752_n","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/02\/12744054_901043640014242_2651293633303686752_n.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/02\/12744054_901043640014242_2651293633303686752_n.jpg?resize=350%2C200 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/02\/12744054_901043640014242_2651293633303686752_n.jpg?resize=525%2C300 1.5x"},"classes":[]},{"id":19541,"url":"https:\/\/swling.com\/blog\/2016\/06\/sdruno-sdrplay-introduces-a-free-native-app-for-the-rsp\/","url_meta":{"origin":24218,"position":4},"title":"SDRuno: SDRplay introduces a free native app for the RSP","author":"Thomas","date":"June 19, 2016","format":false,"excerpt":"(Source: SDRplay Press Release) SDRplay is pleased to announce the official release of SDRuno for the RSP. SDRuno is the new name for the RSP compatible version of Studio1, the rights to which we obtained and announced on 28th April. SDRuno contains native support for the SDRplay RSP and no\u2026","rel":"","context":"In "Ham Radio"","block_context":{"text":"Ham Radio","link":"https:\/\/swling.com\/blog\/category\/ham-radio\/"},"img":{"alt_text":"SDRplay-Logo","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/04\/SDRplay-Logo.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/04\/SDRplay-Logo.jpg?resize=350%2C200 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2016\/04\/SDRplay-Logo.jpg?resize=525%2C300 1.5x"},"classes":[]},{"id":29162,"url":"https:\/\/swling.com\/blog\/2017\/11\/sdrplay-announces-the-rsp1a-software-defined-radio\/","url_meta":{"origin":24218,"position":5},"title":"SDRplay announces the RSP1A software defined radio","author":"Thomas","date":"November 15, 2017","format":false,"excerpt":"(Source: SDRplay Press Release) 15\/November\/2017, Wakefield UK: SDRplay announces the RSP1A SDRplay Limited has today announced the launch of a new Software Defined Radio product \u2013 the RSP1A. The SDR-play RSP1A is a major upgrade to the popular RSP1 and is a powerful wideband full featured 14-bit SDR which covers\u2026","rel":"","context":"In "Ham Radio"","block_context":{"text":"Ham Radio","link":"https:\/\/swling.com\/blog\/category\/ham-radio\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/11\/RSP1A1-1024x708.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/11\/RSP1A1-1024x708.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2017\/11\/RSP1A1-1024x708.png?resize=525%2C300&ssl=1 1.5x"},"classes":[]}],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts\/24218","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/users\/56"}],"replies":[{"embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/comments?post=24218"}],"version-history":[{"count":0,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts\/24218\/revisions"}],"wp:attachment":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/media?parent=24218"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/categories?post=24218"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/tags?post=24218"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}