{"id":148,"date":"2024-05-26T17:45:02","date_gmt":"2024-05-26T22:45:02","guid":{"rendered":"https:\/\/ka9kqh.net\/?p=148"},"modified":"2024-05-26T17:49:23","modified_gmt":"2024-05-26T22:49:23","slug":"coaxial-stubs-or-how-to-reduce-interference-from-other-nearby-transmitters","status":"publish","type":"post","link":"https:\/\/ka9kqh.net\/?p=148","title":{"rendered":"Coaxial Stubs or how to reduce interference from other nearby transmitters."},"content":{"rendered":"\n<p>A quick search of 1\/4 wave stubs for passing or blocking a frequency will return tons of videos and websites. I&#8217;m the station trustee for the <a href=\"http:\/\/www.svrc.org\">Sangamon Valley Radio Club<\/a> and field day is coming, so are multiple harmonically related operations in close proximity (1000&#8242; diameter circle). Over the decades we have ran anywhere from 2 all the way up to one huge setup (for us) of 11 transmitter setups. I miss our older CW operators as that is how we got that many transceivers on the air.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Back to the point&#8230;<\/h2>\n\n\n\n<p>I had been gifted several spools of 75\u03a9 coax. So I figured, I have a couple of thousand feet of what appears to be RG-6 coax. Let&#8217;s experiment. <br>I needed to know a few things first<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Velocity Factor<\/li>\n\n\n\n<li>Electrical Length<\/li>\n\n\n\n<li>Physical Length<\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">&#8230;and I needed to gather some tools<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NanoVNA (ala Sysjoint SV4401a) but any of the NanoVNAs will get the job done.<\/li>\n\n\n\n<li>Wire Stripper or utility knife to strip the coax<\/li>\n\n\n\n<li>Measuring Tape.  <em>I really like the Harbor Freight 100 ft. Open Reel Measuring Tape as it has Metric on one side thus saving me from having to do either conversions or fractions. <\/em><\/li>\n\n\n\n<li>Compression Crimper for F-Connectors<\/li>\n\n\n\n<li>F Connectors compression style<\/li>\n\n\n\n<li>Adapters to PL-259<\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Okay, all gathered&#8230;<\/h2>\n\n\n\n<p>First I need to know the Velocity Factor or Velocity of Propagation ratio of the coax in hand.  Doing a search based on hard to read numbers on the coax said the Vf is 85% for the coax in hand.  Some more internet research (how did I find this information as a child of the 70&#8217;s) tells me to calibrate my VNA and include the through and isolation.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Velocity Factor, Electrical Length, &amp; Physical length, oh my!<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>With your (properly calibrated) VNA of choice<\/li>\n\n\n\n<li>Connect the coax to both S11 and S21 on my VNA this is Port 1 and Port 2<\/li>\n\n\n\n<li>Turn off all the traces but one.  <br>a. Set the Format for this trace to Phase. <br>b. Set the channel to S21<\/li>\n\n\n\n<li>This trace should provide you with a Saw Tooth Wave. Pick two adjacent peaks and subtract the higher frequency from the lower frequency. now divide <strong>300\/Frequency Difference<\/strong> <strong>= Electrical Length for this coax<\/strong>.<\/li>\n\n\n\n<li>Measure the physical length of your cable and then perform the calculation <strong>(Physical Length\/Electrical Length) * 100 = Vf (Velocity Factor) in Percent. <\/strong><\/li>\n\n\n\n<li>Now if you take the <em><strong>Electrical Length you want multiplied by the Velocity Factor <\/strong><\/em>you will be very close to the physical length you will need for your stub. Pad a few inches or centimeters for final tuning.<\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading\">What to do with the information&#8230;<\/h2>\n\n\n\n<p>Now that I can reliably cut stubs to length and also use the S11 LogMag (that I failed to mention in this post) to see the effect of the stub. I can attempt to protect field day stations or other multiple station operations from harmonic interference.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Lastly&#8230;<\/h2>\n\n\n\n<p>I may not make a complete set of these stubs but I will be making some most likely an 80M shorted, 40M open &amp; shorted, Below is my reiteration of others work or experiments on this. I have made enough and measured them to verify the results. An open quarter-wave stub attenuates the frequency it is cut for and odd harmonics.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td>1\/4 \u03bb Stub<br> for Band<\/td><td>Open or <br>Shorted<\/td><td>Passes<\/td><td>Attenuates<\/td><\/tr><tr><td>160<\/td><td>Shorted<\/td><td>160<\/td><td>80\/40\/20\/15\/10<\/td><\/tr><tr><td>80M<\/td><td>Open<\/td><td>40\/20<\/td><td>80<\/td><\/tr><tr><td>80M<\/td><td>Short<\/td><td>80<\/td><td>40\/20\/15\/10<\/td><\/tr><tr><td>40M<\/td><td>Open<\/td><td>20\/10<\/td><td>40\/15<\/td><\/tr><tr><td>40M<\/td><td>Shorted<\/td><td>40\/15<\/td><td>20\/10<\/td><\/tr><tr><td>20M<\/td><td>Open<\/td><td>10<\/td><td>20<\/td><\/tr><tr><td>20M<\/td><td>Shorted<\/td><td>20<\/td><td>10<\/td><\/tr><tr><td><\/td><td><\/td><td><\/td><td><\/td><\/tr><tr><td><\/td><td><\/td><td><\/td><td><\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">A list of 1\/4 \u03bb Stubs and their effect when open or shorted.<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>A quick search of 1\/4 wave stubs for passing or blocking a frequency will return tons of videos and websites. I&#8217;m the station trustee for the Sangamon Valley Radio Club and field day is coming, so are multiple harmonically related operations in close proximity (1000&#8242; diameter circle). Over the decades we have ran anywhere from [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"powered_cache_disable_cache":false,"footnotes":""},"categories":[3,12,11],"tags":[],"class_list":["post-148","post","type-post","status-publish","format-standard","hentry","category-antennas","category-elmering","category-station-operation"],"_links":{"self":[{"href":"https:\/\/ka9kqh.net\/index.php?rest_route=\/wp\/v2\/posts\/148","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ka9kqh.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ka9kqh.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ka9kqh.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ka9kqh.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=148"}],"version-history":[{"count":5,"href":"https:\/\/ka9kqh.net\/index.php?rest_route=\/wp\/v2\/posts\/148\/revisions"}],"predecessor-version":[{"id":153,"href":"https:\/\/ka9kqh.net\/index.php?rest_route=\/wp\/v2\/posts\/148\/revisions\/153"}],"wp:attachment":[{"href":"https:\/\/ka9kqh.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=148"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ka9kqh.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=148"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ka9kqh.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=148"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}