The CC1020/1021 reference frequency, fref, is the crystal oscillator clock frequency divided by REF_DIV + 1, where REF_DIV is a number between 1 and 7. When operating the CC1020/1021 transceiver in the (European) 868 – 870 MHz frequency band in Tx mode with 14.7456 MHz crystal frequency and REF_DIV = 1, the  highest spurious components have been found at frequencies around 650 MHz, 760 MHz and 862 MHz. The spurious components around 862 MHz are close to the –54 dBm level specified by ETSI EN 300 220. This application note presents a solution that reduces the spurious emission close to 862 MHz by increasing REF_DIV from 1 to 7 in Tx mode.

http://www-s.ti.com/sc/techlit/swra057