{"id":3795,"date":"2014-02-13T22:22:00","date_gmt":"2014-02-13T11:22:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2014\/02\/13\/bitx-2040-build-update-10-fixing-my-filter\/"},"modified":"2025-07-21T16:06:14","modified_gmt":"2025-07-21T06:06:14","slug":"bitx-2040-build-update-10-fixing-my-filter","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2014\/02\/13\/bitx-2040-build-update-10-fixing-my-filter\/","title":{"rendered":"BITX 2040 Build Update #10 : Fixing my Filter"},"content":{"rendered":"
<\/a><\/div>\n

That dip on the high side of the passband was bothering me. The GPLA crystal design program predicted it, and indeed, when I measured the performance of the actual filter, there it was. The rig was working fine — the receiver sounded fine and everyone tells me that it sounds great on transmit. But still, it bothered me. <\/strong>
<\/strong>
So I started working out with the various crystal filter software packages. <\/strong>
<\/strong>
This filter was — sort of — a Cohn Min-loss filter, but I had built it with four crystals and three shunt caps (80 pf each) and no series caps at the input\/output. This morning I decided to see what would happen if I put the series caps in there. Here is what Wes’s GPLA predicted:<\/strong> <\/p>\n

<\/a><\/div>\n

Wow, that looked a lot nicer. And the 150 ohm terminations seemed to be just about perfect for the BITX design — no need for impedance transformation. I heated up the soldering iron and searched the junkbox for suitable caps (I found 2 82 pf caps — close enough). <\/strong>
<\/strong>
Here is what the results looked like (I didn’t measure insertion loss so the top of the curve is just the peak of the response curve). <\/strong><\/p>\n

<\/a><\/div>\n

<\/strong>
Exactly as predicted! Thanks Wes! And thanks to Farhan for encouraging me to characterize my crystals and to use the available software<\/strong>
<\/strong>
Now I have to go back and de-ripple the 5 MHz filter in my BITX 17. <\/strong><\/p>\n

Our book: “SolderSmoke — Global Adventures in Wireless Electronics” http:\/\/soldersmoke.com\/book.htm<\/a> Our coffee mugs, T-Shirts, bumper stickers: http:\/\/www.cafepress.com\/SolderSmoke<\/a> Our Book Store: http:\/\/astore.amazon.com\/contracross-20<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

That dip on the high side of the passband was bothering me. The GPLA crystal design program predicted it, and indeed, when I measured the performance of the actual filter, there it was. The rig was working fine — the receiver sounded fine and everyone tells me that it sounds great on transmit. But still, … Continue reading “BITX 2040 Build Update #10 : Fixing my Filter”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":3796,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28,66,60,23],"tags":[],"class_list":["post-3795","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-bitx20","category-farhan","category-hayward-wes","category-ssb"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/3795","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=3795"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/3795\/revisions"}],"predecessor-version":[{"id":3799,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/3795\/revisions\/3799"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/3796"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=3795"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=3795"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=3795"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}