{"id":111,"date":"2016-01-29T22:30:11","date_gmt":"2016-01-29T22:30:11","guid":{"rendered":"https:\/\/geekblog.febo.com\/wp\/?p=111"},"modified":"2016-01-29T22:38:43","modified_gmt":"2016-01-29T22:38:43","slug":"tass-system-multi-board-rf-performance","status":"publish","type":"post","link":"https:\/\/blog.febo.com\/?p=111","title":{"rendered":"TASS System Multi-board RF Performance"},"content":{"rendered":"<p>The <A HREF=\"http:\/\/tapr.org\/kits_tass.html\">TASS switch system<\/A> made a design compromise that means its RF performance has some variation depending on which combination of ports is selected.  When using a port that&#8217;s not at the far end of the board from the common, there is a transmission line stub of varying length that affects VHF performance.  A single TASS board works well through 150 MHz.  The question has been what happens when you build a multi-board system?  Now that I have the <A HREF=\"https:\/\/blog.febo.com\/?p=99\">TASS multiplexer system<\/A> assembled, I can do that test.<\/p>\n<p>First, here is the best possible configuration: port 8 of board B, which feeds all the way through boards A and B, and then through coax to board D, feeding port 8 at the far end of that board, meaning that there are no stub sections:<\/p>\n<p><a href=\"http:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a8-d8.gif\" data-rel=\"penci-gallery-image-content\" ><img decoding=\"async\" src=\"http:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a8-d8-300x225.gif\" alt=\"tass_system_a8-d8\" width=\"300\" height=\"225\" class=\"alignnone size-medium wp-image-112\" srcset=\"https:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a8-d8-300x225.gif 300w, https:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a8-d8-800x600.gif 800w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<p>This shows very nice performance to at least 100 MHz.<\/p>\n<p>Now, here&#8217;s the other extreme &#8212; port A1 to port D5:<\/p>\n<p><a href=\"http:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a1-d5.gif\" data-rel=\"penci-gallery-image-content\" ><img decoding=\"async\" src=\"http:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a1-d5-300x225.gif\" alt=\"tass_system_a1-d5\" width=\"300\" height=\"225\" class=\"alignnone size-medium wp-image-113\" srcset=\"https:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a1-d5-300x225.gif 300w, https:\/\/blog.febo.com\/wp-content\/uploads\/2016\/01\/tass_system_a1-d5-800x600.gif 800w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<p>In this case the signal path has two stubs: one about 10 inches long (3 inches of PCB microstrip on each board, plus a coax jumper about four inches long), forming a 10 inch stub, and another made of the 3 inch microstrip on board &#8220;D&#8221;.  You can see the effect.<\/p>\n<p>This worst-case configuration is usable through about 40 MHz (where the SWR is 2:1 and insertion loss a bit over 0.5dB), and completely falls apart a bit below 60 MHz.  What&#8217;s more important is that depending on the port selected, you may get either the great, not-so-great, or somewhere-in-between response.  In my application measuring pulse-per-second signals, the variation won&#8217;t have a material effect,<sup>*<\/sup> but the multi-board TASS system won&#8217;t be at its best if the goal is precision RF measurements, particularly above 30 MHz.<\/p>\n<p>* The frequency response limitation will soften the rising edge of the PPS pulses, but not to the extent that noticeable accuracy is lost.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The TASS switch system made a design compromise that means its RF performance has some variation depending on which combination of ports is selected. When using a port that&#8217;s not&hellip;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","ngg_post_thumbnail":0,"footnotes":""},"categories":[5,7,2],"tags":[],"class_list":["post-111","post","type-post","status-publish","format-standard","hentry","category-tapr-projects","category-test-and-lab-equipment","category-time-and-frequency"],"_links":{"self":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/111","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=111"}],"version-history":[{"count":8,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/111\/revisions"}],"predecessor-version":[{"id":121,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/111\/revisions\/121"}],"wp:attachment":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=111"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=111"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=111"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}