Going WirelessThe duration of transmissions has limits that vary with the activation method
and purpose:- A transmitter with automatic activation must cease transmitting within 5
seconds of activation. - A transmitter with manual activation must cease transmitting within 5
seconds of being released after use. - Polling to determine system integrity in security or safety applications is
allowed for a total of up to 2 s/hr per transmitter. - Operation of any duration is allowed during an emergency.
Subsection e allows these additional uses with further restrictions: - Voice and video.
- Toy control.
- Variable data without a control code.
- Periodic transmissions at regular, predetermined intervals (other than
polling for system integrity as described in subsection a).
Transmissions under subsection e have these restrictions: - The maximum allowed field strength of the fundamental frequency and
spurious emissions are up to 60% less compared to transmitters under
subsectionsa–d. - The maximum transmission time is 1 second.
- The minimum period between transmissions is at least 10 seconds and
must be at least 30 times longer than the transmission period. For exam-
ple, after transmitting for 0.3 second, a device must wait 10 seconds
before transmitting again. After transmitting for 1 second, a device must
wait 30 seconds before transmitting again.
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A quick way to implement an RF link for asynchronous serial data is to use
transceivers with built-in asynchronous serial interfaces. Sources include Linx
Technologies, Inc. (www.linxtechnologies.com) and MaxStream, Inc.
(www.maxstream.net). Chips, modules, and complete units are available for
incorporating into designs.
The Linx TXM-433-LR transmitter module has an asynchronous serial input
that can connects to a UART’s data output and a 433-MHz output that can