Hello team.
We plan to develop a low data rate modem for applications in Railways. At the moment we are working with Evaluation boards developed by CML (UK based company specializing in data modems). The boards are initialized using a script file which configures all the devices on the Evaluation board. The PLL+VCO device is from TI and the device part number is LMX2571. The script offers 12 RF channels within 400 to 464MHz band. The register vales are provided in the script file corresponding to these 12 channels. We however are interested in a shorter sub-band spanning over 424-430MHz and hence trying to configure the device by using a new set of register values obtained from TICS pro. One of the requirements is to be able to set any channel at a step size of 5/12.5/25KHz spacing. We tried programming new set of register values in the CML evaluation board but transmission stops. When the register vales are reverted to old values the transmission starts again.
We are using fractional N PLL for the first time and hence have limited knowledge in calculating the Numerator and denominator values and its use in achieving the desired step size.
If we could have some sample calculations for values of N, Numerator and Denominator that would be very helpful. Our frequency reference is 38.4MHz.
The PLL registers being programmed are R1, R2, R3, R4 and R6.
Appreciate if you could please guide us through. Thanks
