AN1833 Freescale Semiconductor / Motorola, AN1833 Datasheet - Page 3

• Manufacturer Part Number: AN1833
• Description: A Low-Power Wireless Remote Control Transmitter and Receiver
• Manufacturer: Freescale Semiconductor / Motorola

AN1833
MOTOROLA
meters. At band edges, the tighter limit of 3750 microvolts per meter
applies. Field strength of spurious emissions are 1/10 of the fundamental
frequency of the intentional radiator. The bandwidth of the emission shall
not be wider than 0.25 percent of the center frequency. Bandwidth is
determined at the points 20 dB down from the modulated carrier.
Although continuous transmissions such as voice, video, and data are
not permitted, the transmission of recognition codes is allowed. These
codes are used to identify a sensor or switch that is activated or to
identify the particular component as being part of the system. The
intentional radiator is restricted to the transmission of control signals
such as those used with security alarm systems, door openers, keyless
entry, remote switches, and remote sensing/telemetry, etc.
The general system may consist of a number of transmitters used to
provide control signals from remote sites. The receiver demodulates the
signal and recognizes the remote sites; then the system may initiate a
response in several ways such as sounding an alarm, making an
automatic distress call, turning on a light, opening a door, and turning on
sprinklers, etc. Each site may use a coded address that would be
broadcast to indicate the intended receiver. Some applications are more
critical than others, such as a security alarm or distress calling systems.
It is essential that the system is dependable.
The receiver has the job of extracting and reproducing information from
the modulated RF (radio frequency) signal that has been corrupted by
noise in the channel. Consistent recovery and error-free replication of
the modulating signal requires a receiver which has reliable
performance.
The two main classes of radio frequency receivers are:
The TRF receiver may consist of several cascaded high gain RF
amplifier and tunable bandpass filter stages followed by an appropriate
detector (envelope detector, product detector, FM (frequency
modulation) detector, etc.). A reliable TRF receiver at UHF (ultra-high
frequency) frequencies is difficult to achieve because appreciable
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Freescale Semiconductor, Inc.
For More Information On This Product,
Tuned radio frequency (TRF)
Superheterodyne receivers
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Application Overview
Application Note
3