The BT factor on the Gaussian pulse shaping filter is often used for narrowing spectral emissions at the Tx side to fit into a regulatory / applications standard mask requirement. On how to adjust the BT factor on the EZRadioPro familiy you can read here.
Note that adjusting the BT factor will only alter the spectrum emission of the modulated signal, it will not affect discrete spurious emissions that are not part of the modulation, like these.
Adjusting the BT factor, however does have an effect on sensitivity at the Rx side. This is quite often overlooked and may result in a huge loss in the link budget. To that end find below two graphs showing sensitivity versus BT factor parameterized with modulation index. (These measurements were taken on revision revB1B but hold up for revC2A/ A2A.)
Don’t ever go to a lower BT factor than 0.25 if the modulation index <= 2. If narrower emissions are required lower the modulation index instead.
Also be prepared that the frequency offset tolerance of the Rx degrades by dropping BT and / or the modulation index.
Si4x6x radios can operate in High-performance or Low-power modes, which can be set in GLOBAL_CONFIG property. In order to save some current consumption (typically 2-3mA), low-power mode can be enabled, however it has some tradeoff in RX performance (sensitivity, linearity).
If the crystal parameters meet the requirements listed in AN785 section 1, both high-performance mode and low-power mode should result robust crystal operation on a properly designed PCB layout (crystal placed as close to the XTAL pins as possible).
In high-performance mode there is some margin on the required crystal parameters, but still it is recommended to stay within the ranges listed in AN785 section 1 for safe operation. Crystal start-up issues might occur if the parameters are not met.
In low-power mode meeting the required crystal parameters is more critical, i.e crystal start-up issues might happen even if the RF crystal parameters are near the edge. Low-power mode can be used robustly with a crystal that easily meets the recommended parameters. AN785 Table 1 provides a list of recommended crystals that will ensure safe operation both in high-performance and low-power mode.
If crystal start-up problem occurs in low-power mode, there are 2 possible options to avoid the issue:
Silicon Labs provides RF range calculators for customers to help estimating the actual range of their wireless applications. Simple RF Range Calculator is available to download from the following link below.
RF range depends on the following parameters:
Simple RF Range Calculator
Simple RF Range Calculator is for those customers who don’t want to deal with difficult RF questions, just simply would like to get fast and reasonable results for both outdoor and indoor environments.
Simple RF Range Calculator provides fast and accurate result as the customer selected the frequency band and set TX and RX parameters.
Frequency bands and custom frequency channels can also be selected.
TX Output Power and RX Sensitivity need to set up based on the radio device’s actual link parameters based on the data sheet.
If the exact antenna parameters are unknown notes at the right side can help to determine the closest values.
The achievable RF range depends on many other factors as well. See the following KBA article for further details on RF range factors:
How can I make the frequency bandwidth of PCB antennas wider?
In some cases/applications the BW of printed antennas might not be sufficient. This article summarizes some design tricks on how to make a printed antenna wider bandwidth.
- Increase the board size (e.g. GND plane in the case of monopole-type antennas). Avoid using RF modules that have smaller size than quater-wavelength. Small modules generally have poor antenna gain and narrow bandwidth (due to the high Q factor).
- Increase the board thickness. Of course, it's typically limited by design.
- Decrease the dielectric constant of the PCB. Select PCB material with low epsilon value.
- Use wider and/or tapered traces in the PCB antenna structure.
- Do some tricks in the external antenna matching network. I.e. use more components to do the match (to stay within a given constant Q ellipse on the Smith Chart); create resonators in the matching network. Also, see Bode-Fano, Youla matching techniques.