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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 9AM and 4PM 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.