Importance of RF design in networking

by barkkathulla 2012-09-20 16:35:59

<font color=#00004D>RF Transmitter </font>

The RF transmitter used in our project has the following features

i. Complete RF Transmitter Module no external components and no tuning required.
ii. High Performance SAW Based Architecture with a Maximum Range of 100 feet at 4800 bps data rate.
iii. Interface directly to Encoders and Microcontrollers with ease.
iv. Low Power Consumption suitable for battery operated devices
v. 4 Pin Compact size module
vi. Can be directly used in your PCB
vii. Straight Pin out is the standard in these modules.
viii. Right angle Pin out is optional
ix. Can be used with Fixed Code and Rolling Code Encoders or direct with microcontrollers

6.2.1 RF Receiver
The radio frequency receiver module, facilitates the OEM designers to design their remote control applications in the quickest way. The circuit is designed with SMD components and the module size is small enough to be able to be fitted in almost any application.

Fig 6.2 Table Parameter Specification of RF Receiver Noise Immunization
This RF receiver is sensitive to RF noise in the pass band because the desired transmitter signals are at very low power levels. Some common noise sources are microprocessors, brush-type motors and high-speed logic circuits. If the rise time and fall time of the clock in a microprocessor are fast enough to produce harmonics in the frequency range of the receiver input and the harmonics fall within the pass band of the receiver, then special care must be taken to reduce the level of the harmonic at the antenna port of the receiver.
Based on above analysis, the following actions have to be taken:

i. Microprocessor choice: Choose those microprocessors which has lowest rise time and lowest fall time, if available.

ii. Brush-type motor choice: Choose those brush-type motors, which has spark suppression built in or better not to use such type of motors.

iii. Logic circuits choice: High-speed logic circuits generate noise similar to microprocessors. Thus better to choose those circuits with the lowest rise time and the lowest fall time, if available.

iv. Place the receiver and its antenna as far from the noise source as possible.

v. During PCB layout, keep line lengths at a minimum that carry high-speed logic signals or supply brush type motors. Such lines work like antennas that radiate the unwanted noise.

vi. If possible, enclose the noise source in a grounded metal box and use RF-decoupling on the input/output lines.

vii. It is advisable to use separate voltage regulator for the RF receiver. If the same voltage regulator has to be used for cost purpose, then a decoupler circuit is recommended so that high frequency noise can be screened.

viii. The ground path from the receiver module should go directly to the power ground, in between, no other ground paths can join in, otherwise, noise will be introduced in and receiver function will be greatly influenced.

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