cc1101

If you type in "image frequency" in Google search you will get 10's of thousands of hits.

CC1101 uses low side LO injection. The receiver LO frequency (f_LO) is below the carrier frequency (fc). The received carrier fc and f_LO are mixed and downconverted to IF (intermediate frequency). If the receiver topology does not have image rejection. a signal which is IF below the receiver LO frequency (i.e at f_image =  f_LO - IF = fc - 2 x IF) will be received just as well as the wanted signal at f_c. 

CC1101 has image rejection included on-chip.

"Image Rejection" in the CC1101 and CC110L is rather poor and image responses can still be issues!

Can someone help me with the IF frequencies employed in the CC1101 and CC110L for operation i the 902-928 MHz ISM nand and HOW THEY change as IF Bandwidh is changed??  I'm not finding any real help in the datasheets, these forums, or SmartRF Studio.

Help!

The IF frequency positions the receiver bandwidth within the ADC frequency response. Optimum IF frequency has been selected for each preferred setting to ensure best possible performance and robustness. Changing the IF frequency can lead to reduced sensitivity, less robustness of frequency offset, or in the worst case loss of RX functionality.

The ADC frequency response has a dc component so the IF frequency cannot be too low. As an example, if the IF frequency is 100 kHz the RX filter BW cannot be 200 kHz (say) as the dc component will be within the RX fiter BW.

For high frequencies there is quantization noise so the IF frequency cannot be too high. Furthermore, the ADC frequency response is not flat between dc component and quantization noise. The noise is lower for low IF than for higher IF. If you look at the preferred settings in Studio you will see that the IF frequency is lower for lower RX filter BW, but high enough to ensure that the dc component does not affect performance.

Your starting point for finding the best settings should always be one of the "typical settings" in SmartRF Studio. If you change the system parameters (e.g deviation, data rate, modulation, ....) manually under "RF parameters" some registers (e.g FREND1, AGCCTRL, FSCTRL1....) will not change. Only those registers that are calculated based on your manual entry (e.g MDMCFG when changing data rate and RX filter BW) will change. FREND1, AGCCTRL, FSCTRL1 and a few other registers settings are not calculated by SmartRF Studio, but they still need to be set according to the RX BW used.

What you need to do is to select the "typical setting", which closest matches the RX filter BW you are going to use as the FREND1, AGCCTRL, FSCTRL1, TEST2, and TEST1 settings to use depend on the RX BW. As an example, assuming the desired RX BW is 162.5 kHz you should start with the the 76.8 kbps preferred setting (232 kHz RX BW) and change the data rate, deviation, RX BW, and modulation format manually you get the right settings.