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.
Basic range testing can be performed with the transceiver evaluation
boards. To prepare the board for range testing, turn it on by switching the
power switch to the ON position. Pressing S0 or S2 will activate the buzzer
on the receiver board, while S1 or S3 activates the LED. The CONFIRM
LED provides an indication that the signal has traveled round trip, so only
one person is needed to conduct range testing.
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 multi-path 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 section has been attenuated
to approximate legal limits by resistor R9 so that the range test results
will approximate the results from a well-designed, 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 Output Power vs. LADJ Resistance graph in the LT Series Transceiver
Module Data Guide.
To achieve maximum range, keep objects such as your hand away from
the antenna and ensure that the antenna on the transmitting board has a
clear and unobstructed line-of-sight path to the receiving board. Range
performance is determined by many interdependent factors. If the range
you are able to achieve is significantly less than what is 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.
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