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USING THE BOARDS AS A DESIGN REFERENCE
The basic evaluation boards included in this kit are very simple, yet they illustrate
some important techniques that you may wish to incorporate into your own board
layout. You will observe that the KH2 mounting pads extend slightly past the
edge of the part. This eases hand assembly and allows for better heat
conduction under the part if rework is necessary. Next, observe the use of a full
ground plane fill on the lower side of the board. This ground plane serves three
important purposes:
First, since a 1/4-wave antenna is employed, the ground plane is critical to serve
as a counterpoise (you may wish to read Application Note AN-00500 Antennas:
Design, Application, and Performance for additional details on how a ground
plane affects antenna function).
Second, a ground plane will suppress the transfer of noise between stages of a
product, as well as unintentional radiation of noise into free space.
Third, a ground plane allows for the implementation of a microstrip feed to the
antenna. The term microstrip refers to a PCB trace running over a ground plane
that is designed to serve as a 50-ohm transmission line between the module and
the antenna. A microstrip is implemented on this evaluation board. If you are
unfamiliar with microstrip calculations, you may wish to refer to the KH2 Series
data guides or the calculator available on our website.
IN CLOSING
Here at Linx, “Wireless Made Simple” is more than just our motto, it is our
commitment. A commitment to the highest caliber of product, service, and
support. That is why, should you have questions or encounter any difficulties
using the evaluation kit, you’ll be glad to know many resources are available to
assist you. First, check carefully for the obvious, then visit our website at
www.linxtechnologies.com or call 541-471-6256 between 7AM and 5PM Pacific
Time to speak with an application engineer.
Legal Notice
All Linx kits and modules are designed in keeping with high engineering standards;
however, it is the responsibility of the user to ensure that the products are operated in a
legal and appropriate manner. The purchaser understands that legal operation may require
additional permits, approvals, or certifications prior to use, depending on the country of
operation.
ONLINE RESOURCES
If you have questions regarding any Linx product and have Internet access,
make www.linxtechnologies.com your first stop. Our website is organized in an
intuitive format to give you the answers you need. Day or night, the Linx website
gives you instant access to the latest information regarding the products and
services of Linx. It’s all here: manual and software updates, application notes, a
comprehensive knowledgebase, FCC information, and much more. Be sure to
visit often!
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, ensure that the
address line DIP switches on both boards are identically set. Turn on the boards
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. Sliding
switch SW0 or SW1 to the right will cause the transmitter to continiously 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 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 or output levels can be legally raised due to protocol duty cycle, R1
can be changed according to the graph on Page 3 of the KH2 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, jumper routing, and
antenna connections. Next, measure the receiver’s RSSI voltage with the
transmitter turned off to determine if ambient interference is present. If this fails
to resolve the issue, please contact Linx technical support.
ABOUT ANTENNAS
The choice of antennas is one of the most critical and often overlooked design
considerations. The range, performance, and legality of an RF link are critically
dependent upon the type of antenna employed. Linx offers a variety of antenna
styles that you may wish to consider for your design. Included with your kit is a
Linx CW Series connectorized whip antenna that should be connected prior to
using the kit. Despite the fact that the antenna is not centered on the board’s
ground plane, it exhibits a VSWR of <1.9 and suitably demonstrates the
module’s best practical performance.
