W Linx Technology Satellite Radio TXE 315 KH User Manual

TXE-315-KH  
TXE-418-KH  
TXE-433-KH  
WIRELESS MADE SIMPLE ®  
KH SERIES TRANSMITTER / ENCODER DATA GUIDE  
DESCRIPTION  
The KH Series is ideally suited for volume use  
in OEM applications such as remote control and  
1.220"  
command, and keyless entry. Housed in a  
compact SMD package, it combines a highly-  
optimized RF transmitter with an on-board  
encoder. When paired with a matching KH  
Series receiver / decoder module, a reliable  
RF TRANSMITTER/ENCODER  
0.630"  
TXE-418-KH  
LOT 2000  
wireless link is formed, capable of transferring  
the status of 8 parallel inputs over distances in  
excess of 300 feet. Ten tri-state address lines  
provide 59,049 (310) addresses for security and  
uniqueness. No external RF components are  
required (except an antenna), making  
0.180"  
Figure 1: Package Dimensions  
integration straightforward.  
FEATURES  
Low cost  
Ultra-low power consumption  
Compact SMD package  
Stable SAW-based architecture  
Adjustable output power  
Transmit enable line  
On-board encoder  
8 parallel binary inputs  
10  
3 addresses for security and  
uniqueness  
No production tuning  
No external RF components  
required  
APPLICATIONS INCLUDE  
ORDERING INFORMATION  
Remote Control / Command  
Keyless Entry  
PART #  
DESCRIPTION  
TXE-315-KH  
TXE-418-KH  
TXE-433-KH  
RXD-315-KH  
RXD-418-KH  
RXD-433-KH  
EVAL-***-KH  
Transmitter 315MHz  
Transmitter 418MHz  
Transmitter 433MHz  
Receiver 315MHz  
Receiver 418MHz  
Receiver 433MHz  
Basic Evaluation Kit  
Garage / Gate Openers  
Lighting Control  
Call Systems  
Home / Industrial Automation  
Fire / Security Alarms  
Remote Status Monitoring  
Wire Elimination  
*** = 315, 418 (Standard), 433.92MHz.  
Transmitters are supplied in tubes of 20 pcs.  
Revised 10/12/06  
 
PIN ASSIGNMENTS  
MODULE DESCRIPTION  
The KH Series transmitter / encoder module combines a high-performance  
Surface Acoustic Wave (SAW) based transmitter with an on-board encoder.  
When combined with a Linx KH Series receiver / decoder, a highly reliable RF  
link capable of transferring control or command data over line-of-sight distances  
in excess of 300 feet is formed. The module accepts up to 8 parallel inputs, such  
as switches or contact closures, and provides ten tri-state address lines for  
security and creation of 59,049 (310) unique transmitter / receiver relationships.  
The KH’s compact surface-mount package integrates easily into existing designs  
and is friendly to hand production or automated assembly.  
1
2
3
4
5
6
7
8
9
LADJ/GNDANT 24  
D0  
GND 23  
A9 22  
A8 21  
A7 20  
A6 19  
A5 18  
A4 17  
A3 16  
A2 15  
A1 14  
A0 13  
D1  
GND  
VCC  
TE  
D2  
D3  
D4  
10 D5  
11 D6  
12 D7  
Address Inputs  
A0-A9  
TX Enable  
SAW  
Oscillator  
Parallel  
Inputs  
D0-D7  
50Ω RF OUT  
Divider  
Figure 6: KH Series Transmitter Pinout (Top View)  
OSC  
(ANT)  
Counter  
Keyed Output  
PIN DESCRIPTIONS  
Pin # Name  
TRI-Detect  
RF Amplifier  
Output Isolation  
& Filter  
Description  
Level Adjust. This line can be used to adjust the output  
power level of the transmitter. Connecting to GND will give  
the highest output, while placing a resistor to GND will  
lower the output level.  
RF STAGE  
ENCODER STAGE  
1
GND / LADJ  
Figure 7: KH Series Transmitter Block Diagram  
THEORY OF OPERATION  
Data Input Lines. When TE goes high, the module will  
encode the state of these lines for transmission. Upon  
receipt of a valid transmission, the receiver / decoder will  
replicate these lines on its output lines.  
2, 3,  
7-12  
The KH Series transmitter operation is straightforward. When the Transmit  
Enable (TE) line is taken high, the on-board encoder IC is activated. The encoder  
detects the logic states of the data and address lines. These states are formatted  
into a 3-word transmission, which continues until the TE line is taken low. The  
encoder creates a serial data packet that is used to modulate the transmitter.  
D0 - D1  
4
5
GND  
VCC  
Analog Ground  
Supply Voltage  
The transmitter section is based on a simple, but highly-optimized, architecture  
that achieves a high fundamental output power with low harmonic content. This  
ensures that most approval standards can be met without external filter  
components. The KH Series transmitter is exceptionally stable over variations in  
time, temperature, and physical shock as a result of the precision SAW device  
that is incorporated as the frequency reference.  
Transmit Enable Line. When this line goes high, the  
module will encode the states of the address and data lines  
into a packet and transmit the packet three times.  
6
TE  
The transmitted signal may be received by any Linx KH Series receiver / decoder  
module or Linx LC or LR Series receiver combined with the appropriate decoder  
IC. Once data is received, it is decoded using a decoder IC or custom  
microcontroller. The transmitted address bits are checked against the address  
settings of the receiving device. If a match is confirmed, the decoder’s outputs  
are set to replicate the transmitter’s inputs.  
Address Lines. The state of these lines must match the  
state of the receiver’s address lines in order for a  
transmission to be accepted.  
13-22  
A0-A9  
23  
24  
GND  
ANT  
Analog Ground  
50-ohm RF Output  
Page 4  
Page 5  
 
ENCODER OPERATION  
POWER SUPPLY REQUIREMENTS  
The KH Series transmitter internally utilizes  
the HT640 encoder from Holtek. The  
encoder begins a three-word transmission  
cycle when the Transmission Enable line  
(TE) is pulled high. This cycle will repeat  
itself for as long as the TE line is held high.  
Once TE falls low, the encoder output  
completes its final cycle and then stops as  
shown in the Encoder / Decoder Timing  
diagram. When a transmission enable signal  
is applied, the encoder scans and transmits  
the status of the 10 bits of the address code  
and the 8 bits of the data serially in the order  
A0 to A9, D0 to D7.  
The module does not have an internal voltage  
regulator; therefore it requires a clean, well-regulated  
power source. While it is preferable to power the unit  
from a battery, it can also be operated from a power  
supply as long as noise is less than 20mV. Power  
supply noise can affect the transmitter modulation;  
therefore, providing a clean power supply for the  
module should be a high priority during design.  
Vcc TO  
MODULE  
Power On  
10Ω  
Vcc IN  
Standby Mode  
+
10μF  
No  
Transmission  
Enabled?  
Figure 10: Supply Filter  
A 10Ω resistor in series with the supply followed by a  
10µF tantalum capacitor from VCC to ground will help in cases where the quality  
Yes  
3 Data Words  
Transmitted  
of supply power is poor. These values may need to be adjusted depending on  
the noise present on the supply line.  
DATA INPUTS  
No  
Transmission  
Still Enabled?  
The status of each address / data pin can be  
individually preset to logic high, low, or  
floating. The floating state on the data input  
is interpreted as logic low by the decoders  
since the decoder output only has two  
states. The address pins are usually set to  
transmit particular security codes by DIP  
switches or PCB wiring, while the data is  
selected using push buttons or electronic  
When the Transmit Enable (TE) line goes high, the states of the eight data input  
lines are recorded and encoded for transmission. The data lines are tri-state,  
which means that they can be high, low, or floating, though the decoder will  
interpret the floating state as a low. This feature means that the data lines do not  
require pull-up or pull-down resistors. The states of the data lines can be set by  
switches, jumpers, microcontrollers, or hardwired on the PCB.  
Yes  
3 Data Words  
Transmitted  
Continuously  
The encoder will send the states of the address and data lines three times. If the  
TE line is still high, it will begin the cycle again. This means that the states of the  
data lines are refreshed with each cycle, so the data lines can be changed  
without having to pull TE low. There can be up to a 150mS lag in response as  
the transmitter finishes one cycle then refreshes and starts over.  
Figure 8: Encoder Flowchart  
switches. The floating state allows the KH transmitter to be used without pull-up  
or pull-down resistors on the data and address input lines.  
Encoder  
Transmit  
ENABLING TRANSMISSION  
Enable  
< 1 Word  
The module’s Transmit Enable (TE) line controls transmission status. When  
taken high, the module initiates transmission, which continues until the line is  
pulled low or power to the module is removed. In some cases this line will be  
wired permanently to VCC and transmission controlled by switching VCC to the  
Encoder  
Data Out  
Transmitted Continuously  
Clocks  
3 Words  
3 Words  
2 Words  
Check  
14  
14  
2
Clocks  
2
module. This is particularly useful in applications where the module powers up  
and sends a transmission only when a button is pressed on the remote.  
Decoder VT  
Check  
USING LADJ  
Decoder  
Data Out  
The LADJ line allows the transmitter’s output power to be easily adjusted for  
range control, lower power consumption, or to meet legal requirements. This is  
done by placing a resistor between GND and LADJ. When LADJ is connected  
directly to GND, the output power will be at its maximum. Placing a resistor will  
lower the output power by up to 7dB, as shown on Page 3 of this data guide.  
1/2 Clock Time  
1/2 Clock Time  
Figure 9: Encoder / Decoder Timing Diagram  
SETTING THE TRANSMITTER ADDRESS  
This is very useful during FCC testing to compensate for antenna gain or other  
product-specific issues that may cause the output power to exceed legal limits.  
A variable resistor can be used so that the test lab can precicely adjust the output  
power to the maximun level allowed by law. The resistor’s value can be noted  
and a fixed resistor substituted for final testing. Even in designs where  
attenuation is not anticipated, it is a good idea to place a resistor pad connected  
to LADJ and GND so that it can be used if needed.  
The module provides ten tri-state address lines. This allows for the formation of  
up to 59,049 (310) unique transmitter-receiver relationships. Tri-state means that  
the address lines have three distinct states: high, low, or floating. These pins  
may be hardwired or configured via a microprocessor, DIP switch, or jumpers.  
The receiver’s address line states must match the transmitter’s exactly for a  
transmission to be recognized. If the transmitted address does not match the  
receiver’s local address, then the receiver will take no action.  
Page 6  
Page 7  
 
PROTOCOL GUIDELINES  
TYPICAL APPLICATIONS  
While many RF solutions impose data formatting and balancing requirements,  
Linx RF modules do not encode or packetize the signal content in any manner.  
The received signal will be affected by such factors as noise, edge jitter, and  
interference, but it is not purposefully manipulated or altered by the modules.  
This gives the designer tremendous flexibility for protocol design and interface.  
Below is an example of a basic remote control transmitter utilizing the KH Series  
transmitter. When a key is pressed on the transmitter, a corresponding line on  
the receiver goes high. A schematic for the receiver / decoder circuit may be  
found in the KH Series Receiver Data Guide. These circuits are implemented in  
the KH Series Basic Evaluation kit. They can be easily modified for custom  
applications and clearly demonstrate the ease of using the KH Series modules  
for remote control applications.  
Despite this transparency and ease of use, it must be recognized that there are  
distinct differences between a wired and a wireless environment. Issues such as  
interference and contention must be understood and allowed for in the design  
process. To learn more about protocol considerations, we suggest you read Linx  
Application Note AN-00160.  
VCC  
1
2
24  
23  
22  
21  
20  
19  
18  
17  
16  
15  
14  
13  
GND/LADJ  
D0  
ANT  
GND  
A9  
GND  
3
GND  
1
2
20  
Errors from interference or changing signal conditions can cause corruption of  
the data packet, so it is generally wise to structure the data being sent into small  
packets. This allows errors to be managed without affecting large amounts of  
data. A simple checksum or CRC could be used for basic error detection. Once  
an error is detected, the protocol designer may wish to simply discard the corrupt  
data or implement a more sophisticated scheme to correct it.  
D1  
19  
VCC  
4
3
GND  
VCC  
TE  
A8  
4
17  
16  
GND  
5
5
A7  
6
6
7
14  
A6  
8
7
9
12  
11  
D2  
A5  
10  
8
D3  
A4  
SW-DIP-10  
9
D4  
A3  
INTERFERENCE CONSIDERATIONS  
10  
11  
12  
GND  
D5  
A2  
D6  
A1  
The RF spectrum is crowded and the potential for conflict with other unwanted  
sources of RF is very real. While all RF products are at risk from interference, its  
effects can be minimized by better understanding its characteristics.  
D7  
A0  
TXE-xxx-KH  
3
4
3
4
3
4
3
4
2
1
2
1
2
1
2
1
Interference may come from internal or external sources. The first step is to  
eliminate interference from noise sources on the board. This means paying  
careful attention to layout, grounding, filtering, and bypassing in order to  
eliminate all radiated and conducted interference paths. For many products, this  
is straightforward; however, products containing components such as switching  
power supplies, motors, crystals, and other potential sources of noise must be  
approached with care. Comparing your own design with a Linx evaluation board  
can help to determine if and at what level design-specific interference is present.  
VCC  
DPAK-X2  
DPAK-X2  
DPAK-X2  
DPAK-X2  
CR2032 3V LITHIUM  
GND  
External interference can manifest itself in a variety of ways. Low-level  
interference will produce noise and hashing on the output and reduce the link’s  
overall range.  
R2  
100K  
GND  
Figure 11: Basic Remote Control Transmitter  
High-level interference is caused by nearby products sharing the same  
frequency or from near-band high-power devices. It can even come from your  
own products if more than one transmitter is active in the same area. It is  
important to remember that only one transmitter at a time can occupy a  
frequency, regardless of the coding of the transmitted signal. This type of  
interference is less common than those mentioned previously, but in severe  
cases it can prevent all useful function of the affected device.  
The ten-position DIP switch is used to set the address to either ground or  
floating. Since the floating state is a valid state, no pull-up resistors are needed.  
The data lines are pulled high by momentary pushbuttons. Since the floating  
state is interpreted as a low by the decoder, no pull-down resistors are needed.  
Diodes are used to pull the TE line high when any data line goes high, while  
isolating the data lines from each other. This will make the transmitter send data  
when any button is pressed without affecting any of the other data lines.  
Although technically it is not interference, multipath is also a factor to be  
understood. Multipath is a term used to refer to the signal cancellation effects  
that occur when RF waves arrive at the receiver in different phase relationships.  
This effect is a particularly significant factor in interior environments where  
objects provide many different signal reflection paths. Multipath cancellation  
results in lowered signal levels at the receiver and, thus, shorter useful distances  
for the link.  
The KH Series transmitter / encoder module is also suitable for use with the Linx  
OEM function receivers. These receivers are FCC certified, making product  
introduction extremely quick. Information on these products can be found on the  
Page 8  
Page 9  
 
BOARD LAYOUT GUIDELINES  
MICROSTRIP DETAILS  
If you are at all familiar with RF devices, you may be concerned about  
specialized board layout requirements. Fortunately, because of the care taken by  
Linx in designing the modules, integrating them is very straightforward. Despite  
this ease of application, it is still necessary to maintain respect for the RF stage  
and exercise appropriate care in layout and application in order to maximize  
performance and ensure reliable operation. The antenna can also be influenced  
by layout choices. Please review this data guide in its entirety prior to beginning  
your design. By adhering to good layout principles and observing some basic  
design rules, you will be on the path to RF success.  
A transmission line is a medium whereby RF energy is transferred from one  
place to another with minimal loss. This is a critical factor, especially in high-  
frequency products like Linx RF modules, because the trace leading to the  
module’s antenna can effectively contribute to the length of the antenna,  
changing its resonant bandwidth. In order to minimize loss and detuning, some  
form of transmission line between the antenna and the module should be used,  
unless the antenna can be placed very close (<1/8in.) to the module. One  
common form of transmission line is a coax cable, another is the microstrip. This  
term refers to a PCB trace running over a ground plane that is designed to serve  
as a transmission line between the module and the antenna. The width is based  
on the desired characteristic impedance of the line, the thickness of the PCB,  
and the dielectric constant of the board material. For standard 0.062in thick FR-  
4 board material, the trace width would be 111 mils. The correct trace width can  
be calculated for other widths and materials using the information below. Handy  
software for calculating microstrip lines is also available on the Linx website,  
The adjacent figure shows the suggested  
GROUND PLANE  
PCB footprint for the module. The actual pad  
dimensions are shown in the Pad Layout  
section of this manual. A ground plane (as  
large as possible) should be placed on a  
lower layer of your PC board opposite the  
module. This ground plane can also be critical  
to the performance of your antenna, which will  
be discussed later. There should not be any  
ground or traces under the module on the  
same layer as the module, just bare PCB.  
ON LOWERR LAYER  
Trace  
Figure 12: Suggested PCB Layout  
Board  
During prototyping, the module should be soldered to a properly laid-out circuit  
board. The use of prototyping or “perf” boards will result in horrible performance  
and is strongly discouraged.  
Ground plane  
No conductive items should be placed within 0.15in of the module’s top or sides.  
Do not route PCB traces directly under the module. The underside of the module  
has numerous signal-bearing traces and vias that could short or couple to traces  
on the product’s circuit board.  
The module’s ground lines should each have their own via to the ground plane  
and be as short as possible.  
AM / OOK receivers are particularly subject to noise. The module should, as  
much as reasonably possible, be isolated from other components on your PCB,  
especially high-frequency circuitry such as crystal oscillators, switching power  
supplies, and high-speed bus lines. Make sure internal wiring is routed away  
from the module and antenna, and is secured to prevent displacement.  
The power supply filter should be placed close to the module’s VCC line.  
In some instances, a designer may wish to encapsulate or “pot” the product.  
Many Linx customers have done this successfully; however, there are a wide  
variety of potting compounds with varying dielectric properties. Since such  
compounds can considerably impact RF performance, it is the responsibility of  
the designer to carefully evaluate and qualify the impact and suitability of such  
materials.  
Figure 13: Microstrip Formulas  
Effective Dielectric  
Constant  
Characteristic  
Impedance  
Dielectric Constant Width/Height (W/d)  
The trace from the module to the antenna should be kept as short as possible.  
A simple trace is suitable for runs up to 1/8-inch for antennas with wide  
bandwidth characteristics. For longer runs or to avoid detuning narrow bandwidth  
antennas, such as a helical, use a 50-ohm coax or 50-ohm microstrip  
transmission line as described in the following section.  
4.80  
4.00  
2.55  
1.8  
2.0  
3.0  
3.59  
3.07  
2.12  
50.0  
51.0  
48.0  
Page 10  
Page 11  
 
PAD LAYOUT  
AUTOMATED ASSEMBLY  
The following pad layout diagram is designed to facilitate both hand and  
automated assembly.  
For high-volume assembly, most users will want to auto-place the modules. The  
modules have been designed to maintain compatibility with reflow processing  
techniques; however, due to the their hybrid nature, certain aspects of the  
assembly process are far more critical than for other component types.  
0.065"  
Following are brief discussions of the three primary areas where caution must be  
observed.  
Reflow Temperature Profile  
0.610"  
The single most critical stage in the automated assembly process is the reflow  
stage. The reflow profile below should not be exceeded, since excessive  
temperatures or transport times during reflow will irreparably damage the  
modules. Assembly personnel will need to pay careful attention to the oven’s  
profile to ensure that it meets the requirements necessary to successfully reflow  
all components while still remaining within the limits mandated by the modules.  
The figure below shows the recommended reflow oven profile for the modules.  
0.070"  
0.100"  
Figure 14: Recommended PCB Layout  
PRODUCTION GUIDELINES  
The modules are housed in a hybrid SMD package that supports hand or  
automated assembly techniques. Since the modules contain discrete  
components internally, the assembly procedures are critical to ensuring the  
reliable function of the modules. The following procedures should be reviewed  
with and practiced by all assembly personnel.  
300  
250  
200  
150  
100  
50  
Ideal Curve  
Limit Curve  
Forced Air Reflow Profile  
220oC  
210oC  
180oC  
HAND ASSEMBLY  
Pads located on the bottom of the  
Reflow Zone  
125oC  
module are the primary mounting  
surface. Since these pads are  
inaccessible during mounting,  
Soldering Iron  
Tip  
20-40 Sec.  
Soak Zone  
2 Minutes Max.  
Preheat Zone  
2-2.3 Minutes  
castellations that run up the side of  
the module have been provided to  
Cooling  
Ramp-up  
facilitate solder wicking to the  
module’s underside. This allows for  
very quick hand soldering for  
prototyping and small volume  
1-1.5 Minutes  
Solder  
0
0
30  
60  
90  
120 150 180 210 240 270 300 330 360  
Time (Seconds)  
PCB Pads  
Castellations  
Figure 16: Maximum Reflow Profile  
Figure 15: Soldering Technique  
production.  
If the recommended pad guidelines have been followed, the pads will protrude  
slightly past the edge of the module. Use a fine soldering tip to heat the board  
pad and the castellation, then introduce solder to the pad at the module’s edge.  
The solder will wick underneath the module, providing reliable attachment. Tack  
one module corner first and then work around the device, taking care not to  
exceed the times listed below.  
Shock During Reflow Transport  
Since some internal module components may reflow along with the components  
placed on the board being assembled, it is imperative that the modules not be  
subjected to shock or vibration during the time solder is liquid. Should a shock  
be applied, some internal components could be lifted from their pads, causing  
the module to not function properly.  
Washability  
Absolute Maximum Solder Times  
The modules are wash resistant, but are not hermetically sealed. Linx  
recommends wash-free manufacturing; however, the modules can be subjected  
to a wash cycle provided that a drying time is allowed prior to applying electrical  
power to the modules. The drying time should be sufficient to allow any moisture  
that may have migrated into the module to evaporate, thus eliminating the  
potential for shorting damage during power-up or testing. If the wash contains  
contaminants, the performance may be adversely affected, even after drying.  
Hand-Solder Temp. TX +225°C for 10 Seconds  
Hand-Solder Temp. RX +225°C for 10 Seconds  
Recommended Solder Melting Point +180°C  
Reflow Oven: +220°C Max. (See adjoining diagram)  
Page 12  
Page 13  
 
ANTENNA CONSIDERATIONS  
GENERAL ANTENNA RULES  
The choice of antennas is a critical  
The following general rules should help in maximizing antenna performance.  
and  
consideration.  
often  
overlooked  
The  
design  
range,  
1. Proximity to objects such as a user’s hand, body, or metal objects will cause an  
antenna to detune. For this reason, the antenna shaft and tip should be  
positioned as far away from such objects as possible.  
performance, and legality of an RF link  
are critically dependent upon the  
antenna. While adequate antenna  
performance can often be obtained by  
trial and error methods, antenna  
design and matching is a complex  
2. Optimum performance will be obtained  
from a 1/4- or 1/2-wave straight whip  
mounted at a right angle to the ground  
plane. In many cases, this isn’t desirable  
OPTIMUM  
for practical or ergonomic reasons, thus,  
NOT RECOMMENDED  
task.  
A
professionally designed  
Figure 17: Linx Antennas  
USEABLE  
an alternative antenna style such as a  
helical, loop, or patch may be utilized  
antenna, such as those from Linx, will  
help ensure maximum performance and FCC compliance.  
Figure 19: Ground Plane Orientation  
and the corresponding sacrifice in performance accepted.  
Linx transmitter modules typically have an output power that is slightly higher  
than the legal limits. This allows the designer to use an inefficient antenna, such  
as a loop trace or helical, to meet size, cost, or cosmetic requirements and still  
achieve full legal output power for maximum range. If an efficient antenna is  
used, then some attenuation of the output power will likely be needed. This can  
easily be accomplished by using the LADJ line or a T-pad attenuator. For more  
details on T-pad attenuator design, please see Application Note AN-00150.  
3. If an internal antenna is to be used, keep it away from other metal components,  
particularly large items like transformers, batteries, PCB tracks, and ground  
planes. In many cases, the space around the antenna is as important as the  
antenna itself. Objects in close proximity to the antenna can cause direct  
detuning, while those farther away will alter the antenna’s symmetry.  
4. In many antenna designs, particularly 1/4-wave  
VERTICAL λ/4 GROUNDED  
ANTENNA (MARCONI)  
whips, the ground plane acts as a counterpoise,  
forming, in essence, a 1/2-wave dipole. For this  
reason, adequate ground plane area is essential.  
A receiver antenna should be optimized for the frequency or band in which the  
receiver operates and to minimize the reception of off-frequency signals. The  
efficiency of the receiver’s antenna is critical to maximizing range performance.  
Unlike the transmitter antenna, where legal operation may mandate attenuation  
or a reduction in antenna efficiency, the receiver’s antenna should be optimized  
as much as is practical.  
E
DIPOLE  
ELEMENT  
λ/4  
The ground plane can be a metal case or ground-fill  
I
areas on a circuit board. Ideally, it should have a  
surface area > the overall length of the 1/4-wave  
radiating element. This is often not practical due to  
size and configuration constraints. In these  
instances, a designer must make the best use of the  
area available to create as much ground plane as  
GROUND  
PLANE  
VIRTUAL λ/4  
DIPOLE  
λ/4  
It is usually best to utilize a basic quarter-wave whip until your prototype product  
is operating satisfactorily. Other antennas can then be evaluated based on the  
cost, size, and cosmetic requirements of the product. You may wish to review  
Application Note AN-00500 “Antennas: Design, Application, Performance”  
Figure 20: Dipole Antenna  
possible in proximity to the base of the antenna. In cases where the antenna is  
remotely located or the antenna is not in close proximity to a circuit board,  
ground plane, or grounded metal case, a metal plate may be used to maximize  
the antenna’s performance.  
ANTENNA SHARING  
In cases where a transmitter and receiver  
module are combined to form a transceiver,  
0.1μF  
it is often advantageous to share a single  
Module  
V
DD  
Transmitter  
0.1μF  
Antenna  
5. Remove the antenna as far as possible from potential interference sources. Any  
frequency of sufficient amplitude to enter the receiver’s front end will reduce  
system range and can even prevent reception entirely. Switching power  
supplies, oscillators, or even relays can also be significant sources of potential  
interference. The single best weapon against such problems is attention to  
placement and layout. Filter the module’s power supply with a high-frequency  
bypass capacitor. Place adequate ground plane under potential sources of noise  
to shunt noise to ground and prevent it from coupling to the RF stage. Shield  
noisy board areas whenever practical.  
antenna. To accomplish this, an antenna  
switch must be used to provide isolation  
between the modules so that the full  
0.1μF  
GND  
0.1μF  
GND  
Receiver  
Module  
transmitter output power is not put on the  
0.1μF  
sensitive front end of the receiver. There  
Select  
are a wide variety of antenna switches that  
are cost-effective and easy to use. Among  
Figure 18: Typical Antenna Switch  
the most popular are switches from Macom and NEC. Look for an antenna  
switch that has high isolation and low loss at the desired frequency of operation.  
Generally, the Tx or Rx status of a switch will be controlled by a product’s  
microprocessor, but the user may also make the selection manually. In some  
cases, where the characteristics of the Tx and Rx antennas need to be different  
or antenna switch losses are unacceptable, it may be more appropriate to utilize  
two discrete antennas.  
6. In some applications, it is advantageous to  
place the module and antenna away from the  
CASE  
main equipment. This can avoid interference  
problems and allows the antenna to be  
oriented for optimum performance. Always use  
GROUND PLANE  
NUT  
(MAY BE NEEDED)  
50Ω coax, like RG-174, for the remote feed.  
Figure 21: Remote Ground Plane  
Page 15  
Page 14  
 
COMMON ANTENNA STYLES  
ONLINE RESOURCES  
There are literally hundreds of antenna styles and variations that can be  
employed with Linx RF modules. Following is a brief discussion of the styles  
most commonly utilized. Additional antenna information can be found in Linx  
Application Notes AN-00100, AN-00140, and AN-00500. Linx antennas and  
connectors offer outstanding performance at a low price.  
®
• Latest News  
A whip-style antenna provides outstanding overall performance  
Whip Style  
and stability. A low-cost whip is can be easily fabricated from a  
wire or rod, but most designers opt for the consistent  
performance and cosmetic appeal of a professionally-made  
model. To meet this need, Linx offers a wide variety of straight  
and reduced-height whip-style antennas in permanent and  
connectorized mounting styles.  
• Data Guides  
• Application Notes  
• Knowledgebase  
• Software Updates  
The wavelength of the operational frequency determines an  
antenna’s overall length. Since a full wavelength is often quite  
If you have questions regarding any Linx product and have Internet access,  
intuitive format to immediately 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!  
long, a partial 1/2- or 1/4-wave antenna is normally employed.  
Its size and natural radiation resistance make it well matched to  
Linx modules. The proper length for a straight 1/4-wave can be  
easily determined using the adjacent formula. It is also possible  
to reduce the overall height of the antenna by using a helical  
winding. This reduces the antenna’s bandwidth, but is a great  
way to minimize the antenna’s physical size for compact  
applications. This also means that the physical appearance is  
not always an indicator of the antenna’s frequency.  
234  
L =  
F
MHz  
Where:  
L
=
length in feet of  
quarter-wave length  
F = operating frequency  
in megahertz  
Specialty Styles  
Linx offers a wide variety of specialized antenna styles.  
Many of these styles utilize helical elements to reduce the  
overall antenna size while maintaining reasonable  
performance. A helical antenna’s bandwidth is often quite  
narrow and the antenna can detune in proximity to other  
objects, so care must be exercised in layout and placement.  
The Antenna Factor division of Linx offers  
a diverse array of antenna styles, many of  
which are optimized for use with our RF  
modules. From innovative embeddable  
antennas to low-cost whips, domes to  
Yagis, and even GPS, Antenna Factor  
likely has an antenna for you, or can  
design one to meet your requirements.  
A loop- or trace-style antenna is normally printed directly on a  
product’s PCB. This makes it the most cost-effective of antenna  
styles. The element can be made self-resonant or externally  
resonated with discrete components, but its actual layout is  
usually product specific. Despite the cost advantages, loop-style  
antennas are generally inefficient and useful only for short-range  
applications. They are also very sensitive to changes in layout and  
PCB dielectric, which can cause consistency issues during  
production. In addition, printed styles are difficult to engineer,  
requiring the use of expensive equipment, including a network  
analyzer. An improperly designed loop will have a high SWR at the  
desired frequency, which can cause instability in the RF stage.  
Loop Style  
Through its Connector City division, Linx offers a wide  
selection of high-quality RF connectors, including FCC-  
compliant types such as RP-SMAs that are an ideal  
match for our modules and antennas. Connector City  
focuses on high-volume OEM requirements, which  
allows standard and custom RF connectors to be offered  
at a remarkably low cost.  
Linx offers low-cost planar and chip antennas that mount directly  
to a product’s PCB. These tiny antennas do not require testing and  
provide excellent performance in light of their small size. They  
offer a preferable alternative to the often-problematic “printed”  
antenna.  
Page 16  
Page 17  
 
LEGAL CONSIDERATIONS  
ACHIEVING A SUCCESSFUL RF IMPLEMENTATION  
Adding an RF stage brings an exciting new  
DECIDE TO UTILIZE RF  
NOTE: Linx RF modules are designed as component devices that require  
external components to function. The modules are intended to allow for full Part  
15 compliance; however, they are not approved by the FCC or any other agency  
worldwide. The purchaser understands that approvals may be required prior to  
the sale or operation of the device, and agrees to utilize the component in keeping  
with all laws governing its use in the country of operation.  
dimension to any product. It also means that  
additional effort and commitment will be needed to  
bring the product successfully to market. By utilizing  
premade RF modules, such as the LR Series, the  
design and approval process is greatly simplified. It  
is still important, however, to have an objective view  
of the steps necessary to ensure a successful RF  
integration. Since the capabilities of each customer  
vary widely, it is difficult to recommend one  
particular design path, but most projects follow steps  
similar to those shown at the right.  
RESEARCH RF OPTIONS  
ORDER EVALUATION KIT(S)  
TEST MODULE(S) WITH  
BASIC HOOKUP  
CHOOSE LINX MODULE  
When working with RF, a clear distinction must be made between what is technically  
possible and what is legally acceptable in the country where operation is intended. Many  
manufacturers have avoided incorporating RF into their products as a result of  
uncertainty and even fear of the approval and certification process. Here at Linx, our  
desire is not only to expedite the design process, but also to assist you in achieving a  
clear idea of what is involved in obtaining the necessary approvals to legally market your  
completed product.  
INTERFACE TO CHOSEN  
CIRCUIT AND DEBUG  
CONSULT LINX REGARDING  
ANTENNA OPTIONS AND DESIGN  
LAY OUT BOARD  
In reviewing this sample design path, you may  
notice that Linx offers a variety of services (such as  
antenna design and FCC prequalification) that are  
unusual for a high-volume component manufacturer.  
These services, along with an exceptional level of  
technical support, are offered because we recognize  
that RF is a complex science requiring the highest  
caliber of products and support. “Wireless Made  
Simple” is more than just a motto, it’s our  
commitment. By choosing Linx as your RF partner  
and taking advantage of the resources we offer, you  
SEND PRODUCTION-READY  
PROTOTYPE TO LINX  
FOR EMC PRESCREENING  
OPTIMIZE USING RF SUMMARY  
GENERATED BY LINX  
In the United States, the approval process is actually quite straightforward. The  
regulations governing RF devices and the enforcement of them are the responsibility of  
the Federal Communications Commission (FCC). The regulations are contained in Title  
47 of the Code of Federal Regulations (CFR). Title 47 is made up of numerous volumes;  
however, all regulations applicable to this module are contained in Volume 0-19. It is  
strongly recommended that a copy be obtained from the Government Printing Office in  
Washington or from your local government bookstore. Excerpts of applicable sections are  
included with Linx evaluation kits or may be obtained from the Linx Technologies website,  
radiates RF energy be approved, that is, tested for compliance and issued a unique  
identification number. This is a relatively painless process. Linx offers full EMC pre-  
compliance testing in our HP / Emco-equipped test center. Final compliance testing is  
then performed by one of the many independent testing laboratories across the country.  
Many labs can also provide other certifications that the product may require at the same  
time, such as UL, CLASS A / B, etc. Once your completed product has passed, you will  
be issued an ID number that is to be clearly placed on each product manufactured.  
SEND TO PART 15  
TEST FACILITY  
RECEIVE FCC ID #  
COMMENCE SELLING PRODUCT  
Typical Steps For  
Implementing RF  
will not only survive implementing RF, you may even find the process enjoyable.  
HELPFUL APPLICATION NOTES FROM LINX  
It is not the intention of this manual to address in depth many of the issues that  
should be considered to ensure that the modules function correctly and deliver  
the maximum possible performance. As you proceed with your design, you may  
wish to obtain one or more of the following application notes, which address in  
depth key areas of RF design and application of Linx products. These  
contacting the Linx literature department.  
Questions regarding interpretations of the Part 2 and Part 15 rules or measurement  
procedures used to test intentional radiators, such as Linx RF modules, for compliance  
with the technical standards of Part 15, should be addressed to:  
Federal Communications Commission  
Equipment Authorization Division  
Customer Service Branch, MS 1300F2  
7435 Oakland Mills Road  
NOTE  
AN-00100  
APPLICATION NOTE TITLE  
RF 101: Information for the RF Challenged  
Columbia, MD 21046  
Phone: (301) 725-1585 Fax: (301) 344-2050 E-Mail: [email protected]  
AN-00125  
AN-00130  
AN-00140  
AN-00150  
AN-00160  
AN-00300  
AN-00500  
Considerations For Operation Within The 260-470MHz Band  
Modulation Techniques For Low-Cost RF Data Links  
The FCC Road: Part 15 From Concept To Approval  
Use and Design of T-Attenuation Pads  
International approvals are slightly more complex, although Linx modules are designed  
to allow all international standards to be met. If you are considering the export of your  
product abroad, you should contact Linx Technologies to determine the specific suitability  
of the module to your application.  
All Linx modules are designed with the approval process in mind and thus much of the  
frustration that is typically experienced with a discrete design is eliminated. Approval is  
still dependent on many factors, such as the choice of antennas, correct use of the  
frequency selected, and physical packaging. While some extra cost and design effort are  
required to address these issues, the additional usefulness and profitability added to a  
product by RF makes the effort more than worthwhile.  
Considerations For Sending Data Over a Wireless Link  
Addressing Linx OEM Products  
Antennas: Design, Application, Performance  
Page 18  
Page 19  
 
WIRELESS MADE SIMPLE ®  
U.S. CORPORATE HEADQUARTERS  
LINX TECHNOLOGIES, INC.  
159 ORT LANE  
MERLIN, OR 97532  
PHONE: (541) 471-6256  
FAX: (541) 471-6251  
Disclaimer  
Linx Technologies is continually striving to improve the quality and function of its products. For  
this reason, we reserve the right to make changes without notice. The information contained in  
this Data Guide is believed to be accurate as of the time of publication. Specifications are based  
on representative lot samples. Values may vary from lot to lot and are not guaranteed. Linx  
Technologies makes no guarantee, warranty, or representation regarding the suitability or  
legality of any product for use in a specific application. None of these devices is intended for use  
in applications of a critical nature where the safety of life or property is at risk. The user assumes  
full liability for the use of product in such applications. Under no conditions will Linx Technologies  
be responsible for losses arising from the use or failure of the device in any application, other  
than the repair, replacement, or refund limited to the original product purchase price.  
© 2006 by Linx Technologies, Inc. The stylized Linx logo,  
Linx, “Wireless Made Simple”, CipherLinx and the stylized  
CL logo are the trademarks of Linx Technologies, Inc.  
Printed in U.S.A.  
 

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