{"id":525,"date":"2015-06-29T21:50:32","date_gmt":"2015-06-29T20:50:32","guid":{"rendered":"http:\/\/www.sevenwatt.com\/main\/?p=525"},"modified":"2016-01-10T14:07:32","modified_gmt":"2016-01-10T13:07:32","slug":"rfm69-ook-compare-antennas","status":"publish","type":"post","link":"https:\/\/www.sevenwatt.com\/main\/rfm69-ook-compare-antennas\/","title":{"rendered":"RFM69 OOK compare antenna’s"},"content":{"rendered":"

The antenna design of a module like the RFM69 is important for the sensitivity to sognal and noise. Also antenna positioning is important. Putting an Nucleo STM32 with RFM69CW very close to a PC will result in a increase of several dBm’s in noise floor.<\/p>\n

Gain 7 dB sensitivity with JeeNodes<\/p><\/blockquote>\n

The basic antenna design commonly used is a quarter wavelength wire antenna with ground plane.
\n\"quarterwavelengthantenna\"<\/a>
\nFrom this informative paper<\/a> from HopeRF, the manufacturer of the RFM69. Such an antenna has a 1\/4 wavelength monopole, and a ground plane that serves to reflect (mirror) the wire so that one gets a half-wavelength dipole effect.<\/p>\n

The 86mm wire (at 868MHz) connected to small JeeNode like devices is actually not having much of a ground plane. So this can probably be improved. There are very nice commercial designs for this at 868MHz and 433MHz. A.o from Conrad. So lets putthree 1\/4 wavelength antenna’s to the test. The wire is compared to a home build and a commercial 1\/4-wavelength with groundplane antenna. (See picture above this article, the blue wire crossing the Nucleo is the wire-antenna). <\/p>\n

The resulting noise and signal levels are printed in RawRSSI, which can be converted to decibells:<\/p>\n

RSSI (in dBm) = (RawRSSI – 256) \/ 2<\/p><\/blockquote>\n

As explained in the previous post<\/a>, the numbers in brackets are the RawRSSI values during OFF and ON, so
\n(RawRSSI_OFF\/RawRSSI_ON)<\/code><\/p>\n

Wire antenna<\/h4>\n

40622 15 1 FS20 88400031214C (55\/79)
\n 40683 61 2 FS20 88400031214C (57\/82)
\n 40745 62 3 FS20 88400031214C (58\/84)<\/p>\n

45816 5 1 FS20 88400031214C (59\/84)
\n 45877 61 2 FS20 88400031214C (61\/90)
\n 45939 62 3 FS20 88400031214C (59\/89)
\nRSSI: 59(v 13-s 4-m126) THD:fix\/peak\/maxp:71\/69\/114
\n<\/code><\/p>\n

Home build<\/h4>\n

13794 5 1 FS20 88400031214C (50\/85)
\n 13855 61 2 FS20 88400031214C (51\/82)
\n 13917 62 3 FS20 88400031214C (50\/76)<\/p>\n

18987 5 1 FS20 88400031214C (49\/81)
\n 19048 61 2 FS20 88400031214C (47\/82)
\n 19110 62 3 FS20 88400031214C (48\/82)
\nRSSI: 50(v 44-s 7-m127) THD:fix\/peak\/maxp:65\/65\/115
\n<\/code><\/p>\n

Conrad<\/h4>\n

21946 5 1 FS20 88400031214C (46\/99)
\n 22007 61 2 FS20 88400031214C (48\/97)
\n 22069 62 3 FS20 88400031214C (48\/97)<\/p>\n

27140 5 1 FS20 88400031214C (46\/96)
\n 27202 62 2 FS20 88400031214C (46\/97)
\n 27264 62 3 FS20 88400031214C (47\/97)
\nRSSI: 48(v 40-s 7-m126) THD:fix\/peak\/maxp:65\/65\/114
\n<\/code><\/p>\n

What can be seen is that the noise floor drops from ~59 to ~49 to ~47 for the three receivers (-98.5dB, -103.5dB, -104.5dB).<\/p>\n

The noise floor drops by 6 dB with the best antenna.<\/p><\/blockquote>\n

This gains is impressive and enables the reception of much weaker signals. The transmit-ON level varies a lot more. As the height of the antenna’s above the working surface differed somewhat, those figures are less trustworthy. In fact further experiments showed that with careful antenna positioning signal-ON levels are comparable over antenna design, while noise levels (signal-OFF) are always in the range of the reported values above.<\/p>\n

Finally it is good to move the antenna away from the microcontroller or microcomputer used. Moving away the Nucleo STM32 80cm while keeping the Conrad antenna at the same position<\/p>\n

Conrad, Nucleo 80cm away<\/h4>\n

30893 5 1 FS20 88400031214C (45\/98)
\n 30954 61 2 FS20 88400031214C (44\/94)
\n 31016 62 3 FS20 88400031214C (44\/91)<\/p>\n

36086 5 1 FS20 88400031214C (46\/92)
\n 36147 61 2 FS20 88400031214C (47\/93)
\n 36209 62 3 FS20 88400031214C (44\/92)
\nRSSI: 46(v 40-s 7-m134) THD:fix\/peak\/maxp:61\/61\/122
\n<\/code>
\nThe noise floor is now around 45 (=100.5dB), an gain of 7dB!<\/p>\n","protected":false},"excerpt":{"rendered":"

The antenna design of a module like the RFM69 is important for the sensitivity to sognal and noise. Also antenna positioning is important. Putting an Nucleo STM32 with RFM69CW very close to a PC will result in a increase of several dBm’s in noise floor. Gain 7 dB sensitivity with JeeNodes The basic antenna design […]<\/p>\n","protected":false},"author":1,"featured_media":514,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[12,7,15],"tags":[50,38,45,28,33,58,51,52,49,46],"class_list":["post-525","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-jeenode","category-ook","category-rfm69","tag-antenna","tag-jeelib","tag-jeelink","tag-jeenode","tag-nucleo","tag-ook","tag-quarte-wavelength","tag-quarter-lambda","tag-rfm69","tag-stm32"],"_links":{"self":[{"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/posts\/525","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/comments?post=525"}],"version-history":[{"count":8,"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/posts\/525\/revisions"}],"predecessor-version":[{"id":578,"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/posts\/525\/revisions\/578"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/media\/514"}],"wp:attachment":[{"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/media?parent=525"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/categories?post=525"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sevenwatt.com\/main\/wp-json\/wp\/v2\/tags?post=525"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}