{"id":9129,"date":"2017-05-26T09:33:00","date_gmt":"2017-05-25T23:33:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2017\/05\/26\/homebrew-peppermint-bitx-kc1fsz-goes-scratch-built-and-sweeps-a-filter\/"},"modified":"2025-07-22T02:00:25","modified_gmt":"2025-07-21T16:00:25","slug":"homebrew-peppermint-bitx-kc1fsz-goes-scratch-built-and-sweeps-a-filter","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2017\/05\/26\/homebrew-peppermint-bitx-kc1fsz-goes-scratch-built-and-sweeps-a-filter\/","title":{"rendered":"Homebrew Peppermint BITX: KC1FSZ Goes Scratch-built and Sweeps a Filter"},"content":{"rendered":"
<\/div>\n
<\/div>\n
<\/a><\/div>\n

Hi Bill\/Pete:<\/b> <\/p>\n

<\/b>
<\/div>\n
Congratulations to Bill on the award. Very well deserved! <\/b><\/div>\n
<\/b>
<\/div>\n
I just watched the video that Bill made with Farhan and I really enjoyed it. As usual, lots of useful information there.<\/b><\/div>\n
<\/b>
<\/div>\n
Farhan\u2019s demo of the Sweeperino was particularly timely because this past weekend I was doing something very similar. <\/b><\/div>\n
<\/b>
<\/div>\n
As I\u2019ve mentioned to Bill before, I am working on a scratch-built BITX to accompany the Peppermint BITX-40 module rig<\/a> that I\u2019m running right now. I took Pete\u2019s advice and started from the audio end. After building the audio amplifier, product detector, and first\/last pair of IF amplifiers, I was able to connect the VFO where the BFO is supposed to go and enjoy a pretty reasonable direct conversion receiver. It works great!! My first working receiver.<\/span><\/b><\/div>\n
<\/b>
<\/div>\n
So my next step was the crystal filter. I puzzled over all of the different articles, tried to follow the G3UUR method, sorted crystals, etc. and finally put the whole thing together. But all along I\u2019ve had this doubt that I could have possibly followed all of the steps closely enough to achieve the precision needed for a 3.5 KC SSB filter – it just didn\u2019t seem possible.<\/b><\/div>\n
<\/b>
<\/div>\n
Last week I decided to try to \u201csweep\u201d the filter. This was a multi-day undertaking in itself. I pieced together the microprocessor, an AD9850, a TIA amplifier, the RF power detector from the SSDRA book, and some software that generates the necessary frequency sweep and collects power readings. The picture of the test rig is included below. It\u2019s not much to look at.<\/b>

<\/b> <\/p>\n
<\/a><\/div>\n
<\/div>\n

With low expectations (and wires that are too long), I ran a few seeps and then downloaded the data onto my computer for analysis. No fancy software here, I\u2019m just using Excel. When I put the data into a line chart in Excel, what emerged from the jumble of seemingly random numbers was a thing of beauty: a 3.5 KC passband right below 12 MHz. It\u2019s the next stage beyond the Joy of Oscillation: <\/b>The Joy Of Selectivity!<\/b><\/u><\/div>\n

<\/b>
<\/u><\/div>\n
It\u2019s even showing about the right insertion loss. Note the setup is very primitive and noisy so the fact that I can\u2019t measure anything below -8dB isn\u2019t surprising, you can ignore that part.<\/b><\/div>\n
<\/b>
<\/div>\n
But I\u2019m starting to get the feeling that this might actually work. Onto the diode mixer \u2026<\/b><\/div>\n
<\/b>
<\/div>\n
73s,<\/b><\/div>\n
<\/b>
<\/div>\n
Bruce KC1FSZ <\/b>https:\/\/www.qrz.com\/db\/kc1fsz<\/b><\/a><\/div>\n

<\/b><\/i><\/u><\/sub><\/sup><\/strike><\/p>\n","protected":false},"excerpt":{"rendered":"

Hi Bill\/Pete: Congratulations to Bill on the award. Very well deserved! I just watched the video that Bill made with Farhan and I really enjoyed it. As usual, lots of useful information there. Farhan\u2019s demo of the Sweeperino was particularly timely because this past weekend I was doing something very similar. As I\u2019ve mentioned to … Continue reading “Homebrew Peppermint BITX: KC1FSZ Goes Scratch-built and Sweeps a Filter”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":9130,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28,65,66,16,71],"tags":[],"class_list":["post-9129","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-bitx20","category-bitx40module","category-farhan","category-filters","category-test-gear"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/9129","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=9129"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/9129\/revisions"}],"predecessor-version":[{"id":9132,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/9129\/revisions\/9132"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/9130"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=9129"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=9129"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=9129"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}