TR-916-SC-S Linx Technologies Inc, TR-916-SC-S Datasheet - Page 7

• Manufacturer Part Number: TR-916-SC-S
• Description: TRANSCEIVER RF 916MHZ 20PIN SMD
• Manufacturer: Linx Technologies Inc
• Series: SCr

Specifications of TR-916-SC-S

• Frequency: 916MHz
• Data Rate - Maximum: 33.6kbps
• Modulation Or Protocol: FM, FSK
• Applications: ISM, Garage Door Opener, Remote Controls, 2-way RKE
• Power - Output: -10dBm
• Sensitivity: -94dBm
• Voltage - Supply: 2.7 V ~ 13 V
• Current - Receiving: 15mA
• Current - Transmitting: 19mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Operating Temperature: 0°C ~ 70°C
• Package / Case: Module
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: TR916SCS

RECEIVER OPERATION (Cont.)
INTERFERENCE CONSIDERATIONS
The receiver features a RSSI output (Received Signal Strength Indicator). The
RSSI pin gives a linear voltage output corresponding to incoming signal level.
The RSSI output has many valuable uses including interference assessment,
signal strength indication, external data squelching and qualification, and
transmitter presence indication. Since RSSI values vary from part to part and
correspond to signal strength and not necessarily distance, the pin is not
recommended for range-finding applications.
When RF transmissions are not present, or when the received signal strength is too
low to ensure proper demodulation, the data output is squelched to a continuous
high state. This ensures compatibility with common serial UART’s. It is important to
note that the squelch level is set just over the transceiver’s internal noise threshold
and any external RF activity above that threshold will produce hashing on the
transceiver output. While the data output is qualified high in low-noise environments,
the designer should always plan for the potential of hashing. This is a key area of
consideration when planning the overall protocol structure.
The two most obvious ways a wireless link differs from a wire are timing and
susceptibility to interference. Brief reviews of each of these critical areas follows:
It must be recognized that many bands are widely used, and the potential for
conflict with other unwanted sources of RF is very real. Despite careful design,
all RF products are at risk from interference.
Interference can manifest itself in many ways. Low-level interference will produce
noise and hashing on the output and reduce the link’s overall range. Thanks to
the capture properties of an FM system, the transceiver will still function when an
intended signal is present at a higher level than the interference.
Another type of interference can be caused by higher-powered devices such as
hopping spread-spectrum devices. Since these devices move rapidly from
frequency to frequency they will usually cause short, intense losses of
information. Such errors are referred to as bursting errors and will generally be
dealt with through protocol.
High-level interference is caused by products sharing the same frequency or
from near-band high-power devices. Fortunately, this type of interference is less
common than those mentioned previously, but in severe cases can prevent all
useful function of the affected device.
Although technically it is not interference, multipath is also a factor to be
understood. Multipath is a term used to refer to the signal cancelation effects that
occur when RF waves arrive at the receiver in different phase relationships. This
is particularly a factor in interior environments where objects provide many
different reflection paths. Multipath results in lowered signal levels at the receiver
and thus shorter useful distances for the link.
A spectrum analyzer is the primary tool of the RF engineer for assessing
interference sources and levels, but is often not available due to its cost.
Fortunately, the RSSI voltage output can also be used to determine the presence
and strength of interference during the development process.
Page 7