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ANTENNA CONSIDERATIONS
The choice of antennas is one of the
most critical and often overlooked
design considerations. The range,
performance, and legality of the
transmitter is critically dependent on
the antenna utilized. While adequate
antenna performance can often be
obtained by trial and error methods,
professionally designed antennas,
such as those offered by Linx, can
provide
superior
repeatability and legal compliance.
For complete details on the Linx antenna line, visit the Linx website at
www.linxtechnologies.com, or call (800)736-6677
The following sections look at some of the basic considerations involved in the design and
selection of antennas. For a more comprehensive discussion please refer to Linx
applications note #00500 "Antennas: Design, Application, Performance".
CONNECTOR OPTIONS
ANTENNA SHARING
In cases where a transmitter and receiver
module are combined to form a transceiver
it is often advantageous to share a single
antenna. To accomplish this an antenna
switch must be used to provide isolation
between the modules. There is a wide
variety of antenna switches available
which are cost-effective and straight-
forward to use. Among the most popular
are switches from Alpha and NEC. Look
for an antenna switch that has high
isolation and low loss at the desired
frequency of operation. Generally, the TX or RX status of a switch will be
controlled by a product's microprocessor, but selection may also be made
manually by the user. In some cases where the characteristics of the TX and RX
antennas need to be different or switch losses are unacceptable it may be more
appropriate to utilize two discrete antennas.
Page 18
performance,
The FCC requires that antennas
designed for use on Part 15
products be either permanently
attached, or utilize a unique and
proprietary connector not available
to the general public. In cases
where the antenna needs to be
removable, Linx offers a full line of
connectors designed to comply with
these requirements.
Figure 26: Linx Antennas
Figure 27: Linx Connectors
V DD
0.1µF
GND
Antenna
0.1µF
Select
Figure 28: Typical Antenna Switch
0.1µF
Transmitter
Module
0.1µF
GND
Receiver
Module
0.1µF
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