{"id":4644,"date":"2014-12-20T16:31:27","date_gmt":"2014-12-20T22:31:27","guid":{"rendered":"http:\/\/w0ep.us\/OM\/?p=4644"},"modified":"2014-12-20T16:56:23","modified_gmt":"2014-12-20T22:56:23","slug":"nichrome-inductor-part-2","status":"publish","type":"post","link":"http:\/\/w0ep.us\/OM\/?p=4644","title":{"rendered":"Nichrome Inductor – part 2"},"content":{"rendered":"

[today’s run: 5 miles]<\/p>\n

Well, I’m glad I did the measurements yesterday but it turned out to be a bit of a wild goose chase.\u00a0 I was using the circuit layout for a low pass filter and the frequency response I measured was a low pass response.\u00a0 I was expecting to see a dip or a peak but my circuit wasn’t the right one for that kind of measurement.<\/p>\n

Like all good hams, I then decided to read the directions.\u00a0 The EMRFD book, chapter 7, section 7.9 talks about how to measure the Q of a resonant LC circuit.\u00a0 And today I did that.\u00a0 And it worked just like they said it would.\u00a0 Amazing!<\/p>\n

Here is the circuit I used today:<\/p>\n

\"CIR1\"<\/a><\/p>\n

We have a 50 Ohm signal generator on the left, a 50 ohm power meter or spectrum analyzer on the right and our circuit elements in the middle in series. We tune for a null (dip) and record the minimum signal and the frequency at that point. Then I tuned to both sides of the dip to the point +3 dB from the null and record the frequency at those two points.<\/p>\n

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

Since I was not too sure about my circuit elements yesterday I made up a pair today: two coils, one with copper wire and one with the Type A nichrome wire, each having 4 turns on FT37-62 ferrite toroid. Again I used the 470 pF mica capacitor in each case.<\/p>\n

Here is the spectrum analyzer plot for the copper coil. I measured the null frequency at 7.62 MHz. The +3 dB frequencies were 7.64 and 7.61. I calculated the Q as 7.62\/(7.64-7.61) = 254<\/p>\n

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

Here is the plot for the nichrome coil. I measured null at 7.61, +3 dB at 7.50 and 7.75. The resonance is the same as for the copper coil, within the margin of error for coil winding, but this time the Q is 30.4.<\/p>\n

So my conclusion is that you can make resonant circuits with the high resistance wire but it lowers the Q by quite a bit. In this case the resistance of the NiCr coil was 1.8 Ohms and the Q was down by a factor of 8.<\/p>\n

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

Here is the plot for yesterdays coil: 31 turns of nichrome type A wire on an FT50-6 toroid in series with the 470 pF capacitor. I measured the resistance of this coil at 11 Ohms and the Q is 9. Not very high. But it did give a definite null that I could measure.<\/p>\n","protected":false},"excerpt":{"rendered":"

[today’s run: 5 miles] Well, I’m glad I did the measurements yesterday but it turned out to be a bit of a wild goose chase.\u00a0 I was using the circuit layout for a low pass filter and the frequency response I measured was a low pass response.\u00a0 I was expecting to see a dip or […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-4644","post","type-post","status-publish","format-standard","hentry","category-ham-radio"],"_links":{"self":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts\/4644","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4644"}],"version-history":[{"count":2,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts\/4644\/revisions"}],"predecessor-version":[{"id":4650,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts\/4644\/revisions\/4650"}],"wp:attachment":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4644"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4644"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4644"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}