How to choose a suitable crystal for narrowband application to our Si4x6x/Si4x55 ISM band radios?
For low DR (narrowband) applications a TCXO is recommended. Calibrating an XO is time consuming at manufacturing and implementing a temperature compensation loop adds complexity into the system. Moreover at very low data rate (< 1.2 kbps; i.e. very narrowband) applications a TCXO is not only recommended but mandatory as its frequency stability is superior to an XO’s. This means that there is much less slow frequency drift on TCXOs than on XOs. At very narrowband applications where the packets tend to be long in time with an XO it may happen that the slow drift on the XO makes the receive detuned from the incoming signal.
For more detail, please refer to AN785. http://www.silabs.com/Support%20Documents/TechnicalDocs/AN785.pdf