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RECEIVER SENSITIVITY PERFORMANCE
The sensitivity of a receiver is critical to the overall range-performance of a
wireless link. Among wireless manufacturers this measurement is particularly
subject to specmanship due to the variety of methods and conditions under
which sensitivity can be tested.
A hallmark of Linx designs is outstanding sensitivity, but more importantly our
sensitivity specifications are based on harsh testing. The receiver sensitivity for
the HP Series-II is specified for a given bit-error-rate (BER), which is measured
using a pseudo-random bitstream generated by a bit-error-rate-tester (BERT). A
sample of each lot of modules is tested for sensitivity, and therefore the quoted
sensitivity is a characterization of the module, and not a guaranteed
specification. The receiver sensitivity test setup used by Linx is shown in the
figure below.
Figure 7 on page 3 shows the typical BER versus input power for the HP Series-
II receivers. This graph can be used to determine the actual sensitivity you can
attain for a given application. For instance, high-rate data communications would
require a BER of <1
-5
where a low-rate data application with redundant data
transmission may only require a BER of <1
-2
.
Based on the sensitivity characterization of the HP-II receiver and the output
power of the transmitter as legally allowed by the FCC, a path loss model can be
used to show that the open field range of an HP-II link can exceed 1,000 feet. The
actual ability of a particular product utilizing the HP Series-II receivers to attain
this range-performance depends on many factors including:
1). Quality of receiving antenna
2). Actual path loss model (open field, inter-building, city, etc.)
3). Quality of power supply
The HP-II development kit you purchased contains two development boards that
can be used to properly evaluate an HP-II data link's range-performance. If you
have any difficulties duplicating the same range with your own product, you
should carefully review all Linx documentation for hints on what the problem
might be. If all else fails, contact Linx and discuss your design with an application
engineer.
Figure 19: Sensitivity Test Setup
RF
IN
RF Out
EXT 1
Data
Out
HP Receiver
Under Test
Phoenix 5500
BER Tester
Hewlett Packard ES-3000
Signal Generator
RxD
IN
TXD OUT
