{"id":295,"date":"2013-06-20T21:15:21","date_gmt":"2013-06-20T20:15:21","guid":{"rendered":"http:\/\/chris-stubbs.co.uk\/wp\/?p=295"},"modified":"2013-06-20T21:33:54","modified_gmt":"2013-06-20T20:33:54","slug":"rfm22b-temperature-cycling-tests","status":"publish","type":"post","link":"https:\/\/chris-stubbs.co.uk\/wp\/?p=295","title":{"rendered":"RFM22B temperature cycling tests"},"content":{"rendered":"

I recently ran a test to investigate why the rfm22b often fails at low temperatures, with some interesting results.<\/p>\n

\"8982032990_0c6a7376f1_c\"<\/a> \"8980841043_2cab9994ae_h\"<\/a><\/p>\n

The radio module was set up in a test chamber and cycled from +20 to -50 degrees Celsius and repeated 5 times. The board was powered and the output frequency monitored and logged using an SDR.<\/p>\n

\"rfmtest1\"<\/a><\/p>\n

The above results were surprising, as I was expecting the rfm22b to drop out around -40, however it carried on transmitting just fine all the way to -50. However as the temperature rose back out to ambient the module stopped transmitting as the temperature passed about -10. This happened consistently 4 out of the 5 times tested. I believe this is caused by dew forming on the crystal and pulling the frequency way out. You can see the frequency clearly shoot off to the side in this screen capture:<\/p>\n

\"2013-06-07_10-12-35-928\"<\/a><\/p>\n

 <\/p>\n

You can see in the graph below how the temperature affected the frequency, and where the module dropped out. I have also put together a time lapse of the SDR output to illustrate the drifting.<\/p>\n

\"rfmtest2\"<\/a><\/p>\n