Silicon Laboratories SI4421 Manual de usuario descargar pdf (Pagina 2)

RF WIRELESS FOUNDATION COURSE BOOK ONE

2 Rev. 0.1

LESSON 1: OPTIMIZING THE RF PARAMETERS

Exercise 1—How to Calculate RF Link Parameters

One of the earliest tasks to perform when developing a wireless system is to work out the main RF characteristics

that the system will work with. These RF characteristics often define many of the other system characteristics. A

typical example of this is RF frequency which defines the size of the antenna, and that in turn may define the size

of the housing that the system may be mounted in.

Once you have selected the basic RF characteristics, it is a simple mathematical procedure to optimize the

additional RF parameters.

Required RF Characteristics:

 Frequency :_______________________ [MHz] (typically driven by the market)

 Crystal :_______________________ [ppm] (typically driven by the cost)

 Data Rate :_______________________ [kbps] (typically driven by the range & battery life)

This lesson helps to practice optimizing the RF link parameters through a calculation based on a real life example.

What is the recommended deviation and baseband bandwidth if the data rate of the RF communication is 9.6 kbps,

the accuracy of the selected crystal is 20 ppm and the frequency band is 915 MHz?

1. Calculate the frequency error if selected crystal is used:

2. Calculate the recommended deviation:

3. What is the closest available deviation?

(Tip: Use either the data sheet or WDS to look up what deviation values the Si4421 has available)

4. Calculate the baseband bandwidth:

5. What is the closet possible baseband bandwidth?

6. Calculate the center frequency based on your desk number:

 

kHz

bandfreq

ppmaccxtalf

xtale

_______________

1000000

915000

1000000





kHzfratedatadeviation

xtale

_____________10________26.9102_



















kHz_______________





kHzdeviationBBBW _______________102











kHz_______________





MHznumberdeskf ______________63.0_2.910







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Silicon Laboratories SI4421 Manual de usuario Pagina 2

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