Range Testing
Several complex mathematical models exist for determining path loss in
many environments. These models vary as the transmitter and receiver are
moved from indoor operation to outdoor operation. Although these models
can provide an estimation of range performance in the field, the most
reliable method is to simply perform range tests using the transmitter and
receiver in the intended operational environment.
Simple range testing can be performed with the transmitter and receiver
evaluation boards. To prepare the board for range testing, simply turn it
on by switching the power switch to the ON position. Pressing S0 on the
transmitter will activate the buzzer on the receiver board, while S1 activates
the LED. Switches SW0 and SW1 have been provided to jumper the
buttons and continuously transmit. This will allow the designer to turn on
the transmitter and walk with the receiver.
As you near the maximum range of the link in your area, it is not
uncommon for the signal to cut in and out as you move. This is normal
and can result from other interfering sources or fluctuating signal levels due
to multipath effects. This results in cancellation of the transmitted signal
as direct and reflected signals arrive at the receiver at differing times and
phases. The areas in which this occurs are commonly called “nulls” and
simply walking a little farther will usually restore the signal.
Since the evaluation boards are intended for use by design engineers,
they are not FCC certified. The transmitter has been set to approximate
legal limits by resistor R9 so that the range test results will approximate the
results from a welldesigned, certified product. For applications where Part
15 limits are not applicable or output levels can be legally raised due to
protocol duty cycle, R9 can be changed according to the graph on Page 3
of the LC Series Transmitter Data Guide.
To achieve maximum range, keep objects such as your hand away from
the antenna and ensure that the antenna on the transmitter has a clear and
unobstructed line-of-sight path to the receiver board. Range performance
is determined by many interdependent factors. If the range you are able to
achieve is significantly less than specified by Linx for the products you are
testing, then there is likely a problem with either the board or the ambient
RF environment in which the board is operating. First, check the battery,
switch positions, and antenna connection. Next, measure the receiver’s
RSSI voltage with the transmitter turned off to determine if ambient
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