Linx Technologies EVAL-xxx-KH3 - Manual (Page 6)

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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 activates 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 allows the designer to turn on the
transmitter and walk with the receiver.
As the maximum range of the link in an area is approached, it is not
uncommon for the signal to cut in and out as the transmitter moves. This
is normal and can result from other interfering sources or fluctuating signal
levels due to multipath. Multipath 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 further usually restores the signal. If this does not
restore the signal, then the maximum effective range of the link has been
reached.
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 R1 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, R1 can be changed according to the
attenuation graph in the KH3 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
Development Using the Prototyping Area
In addition to their evaluation functions, the boards may also be used for
product development. They feature a prototyping area for the addition of
application-specific circuitry. This area has connections to V
CC
at the top
and to ground at the bottom that can be used to power any circuitry that is
added.
The holes are plated and set at 0.1" on center with a 0.04" diameter,
making it easy to add most industry-standard SIP and DIP packages to the
board.
On the transmitter board, the data lines and the TE line from the encoder
have been wired out to a header on the right side of the prototyping area.
On the receiver board, the data, PDN and DATA lines from the receiver
have been wired out. This allows for easy access to connect external
circuitry to the modules, the encoder, and the decoder. Data line D0 is
connected to the buzzer and the rest are connected to LEDs.
Note: The CR2032-style battery on the transmitter board has very low
current capacity with, only about 3mA available for external circuitry. If
added circuitry requires a higher current, the battery must be removed
and the board powered from an external source.