{"id":267,"date":"2018-01-24T15:31:46","date_gmt":"2018-01-24T15:31:46","guid":{"rendered":"https:\/\/geekblog.febo.com\/wp\/?p=267"},"modified":"2018-01-24T15:31:46","modified_gmt":"2018-01-24T15:31:46","slug":"rtl-sdr-com-dongle-measurements-part-2-results","status":"publish","type":"post","link":"https:\/\/blog.febo.com\/?p=267","title":{"rendered":"RTL-SDR.com Dongle Measurements (Part 2 — Results)"},"content":{"rendered":"

In Part 1<\/a> I described some background about SDR dynamic range as an introduction to the measurements I did on a RTL-SDR.com v3 USB “dongle” SDR<\/a>. Now for the results.<\/p>\n

I wrote a Gnu Radio<\/a> program to help measure the dongle. It tunes the dongle, sets its front-end gain, shows a spectrum display, and also shows the power in a 500 Hz bandwidth around the tuned frequency. That power reading is what I used for these measurements. The flowgraph is available at my Github repository<\/a>.<\/p>\n

With the dongle set to receive a 192 kHz bandwidth, and using an HP 8642A signal generator and 10 dB attenuator, I obtained these results at 144.2 MHz:<\/p>\n

\n\n\n\n\n\n\n\n\n
Gain<\/span><\/td>\nNoise<\/span><\/td>\nMDS<\/span><\/td>\nClipping<\/span><\/td>\nDynamic Range<\/span><\/td>\n<\/tr>\n
0.0<\/td>\n-77 dBFS<\/td>\n-95 dBm<\/td>\n-15 dBm<\/td>\n80 dB<\/td>\n<\/tr>\n
12.5<\/td>\n-77 dBFS<\/td>\n-112 dBm<\/td>\n-33 dBm<\/td>\n79 dB<\/td>\n<\/tr>\n
22.9<\/td>\n-77 dBFS<\/td>\n-122 dBm<\/td>\n-44 dBm<\/td>\n78 dB<\/td>\n<\/tr>\n
32.8<\/td>\n-77 dBFS<\/td>\n-131 dBm<\/td>\n-52 dBm<\/td>\n79 dB<\/td>\n<\/tr>\n
42.1<\/td>\n-74 dBFS<\/td>\n-135 dBm<\/td>\n-60 dBm<\/td>\n75 dB<\/td>\n<\/tr>\n
49.6<\/td>\n-71 dBFS<\/td>\n-138 dBm<\/td>\n-67 dBm<\/td>\n71 dB<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n

This shows more dynamic range than theory suggests. I’m not sure why. It does show clearly the impact of increasing the front-end gain: as the gain increases, the minimum discernible signal (“MDS”) gets lower, but so does the clipping level. All the gain does is move the operating range of the radio; it does not change it (much). But at gains >40, we do see the noise floor start to go up, and the dynamic range come down. That indicates that internal noise starts to become a factor, and suggests keeping the gain below that point.<\/p>\n

By the way, I also did some spot tests at other frequencies. While there is a dB or two of difference, the results generally hold, at least through 1 GHz.<\/p>\n","protected":false},"excerpt":{"rendered":"

In Part 1 I described some background about SDR dynamic range as an introduction to the measurements I did on a RTL-SDR.com v3 USB “dongle” SDR. Now for the results.…<\/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":[4,9,7],"tags":[],"class_list":["post-267","post","type-post","status-publish","format-standard","hentry","category-ham-radio","category-sdr","category-test-and-lab-equipment"],"_links":{"self":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/267","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=267"}],"version-history":[{"count":12,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/267\/revisions"}],"predecessor-version":[{"id":281,"href":"https:\/\/blog.febo.com\/index.php?rest_route=\/wp\/v2\/posts\/267\/revisions\/281"}],"wp:attachment":[{"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=267"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=267"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.febo.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=267"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}