LR Series Transmitter Data Guide Datasheet by Linx Technologies Inc.

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Lir'i)'(' TECHNOLOGIES Wireless made simple®
LR Series
Transmitter Module
Data Guide
!Table of Contents
1 Description
1 Features
1 Applications
2 Ordering Information
2 Absolute Maximum Ratings
3 Electrical Specifications
4 Typical Performance Graphs
6 Pin Assignments
6 Pin Descriptions
7 Module Description
8 Theory of Operation
9 The Data Input
9 Using the PDN Line
10 Using the LADJ Line
10 Power Supply Requirements
11 Transferring Data
12 Typical Applications
13 ESD Concerns
14 Antenna Considerations
15 Helpful Application Notes from Linx
15 Protocol Guidelines
16 Interference Considerations
17 Pad Layout
17 Board Layout Guidelines
19 Microstrip Details
20 Production Guidelines
20 Hand Assembly
20 Automated Assembly
22 General Antenna Rules
Warning: Some customers may want Linx radio frequency (“RF”)
products to control machinery or devices remotely, including machinery
or devices that can cause death, bodily injuries, and/or property
damage if improperly or inadvertently triggered, particularly in industrial
settings or other applications implicating life-safety concerns (“Life and
Property Safety Situations”).
SITUATIONS. No OEM Linx Remote Control or Function Module
should be modified for Life and Property Safety Situations. Such
modification cannot provide sufficient safety and will void the product’s
regulatory certification and warranty.
Customers may use our (non-Function) Modules, Antenna and
Connectors as part of other systems in Life Safety Situations, but
only with necessary and industry appropriate redundancies and
in compliance with applicable safety standards, including without
limitation, ANSI and NFPA standards. It is solely the responsibility
of any Linx customer who uses one or more of these products to
incorporate appropriate redundancies and safety standards for the Life
and Property Safety Situation application.
Do not use this or any Linx product to trigger an action directly
from the data line or RSSI lines without a protocol or encoder/
decoder to validate the data. Without validation, any signal from
another unrelated transmitter in the environment received by the module
could inadvertently trigger the action.
All RF products are susceptible to RF interference that can prevent
communication. RF products without frequency agility or hopping
implemented are more subject to interference. This module does not
have a frequency hopping protocol built in.
Do not use any Linx product over the limits in this data guide.
Excessive voltage or extended operation at the maximum voltage could
cause product failure. Exceeding the reflow temperature profile could
cause product failure which is not immediately evident.
Do not make any physical or electrical modifications to any Linx
product. This will void the warranty and regulatory and UL certifications
and may cause product failure which is not immediately evident.
– –
The LR Series transmitter is ideal for the cost-effective
wireless transfer of serial data, control, or command
information in the favorable 260 to 470MHz band.
When paired with a compatible Linx receiver, a reliable
wireless link is formed, capable of transferring serial
data at rates of up to 10,000bps at distances of up
to 3,000 feet (1,000m). Applications operating over
shorter distances or at lower data rates also benefit
from increased link reliability and superior noise immunity. The transmitter’s
synthesized architecture delivers outstanding stability and frequency
accuracy and minimizes the affects of antenna pulling. Housed in a tiny
reflow-compatible SMD package, the transmitter requires no external RF
components except an antenna, which greatly simplifies integration and
lowers assembly costs.
• Long range
• Low cost
• PLL-synthesized architecture
• Direct serial interface
• Data rates up to 10,000bps
• No external RF components
• Low power consumption
• Low supply voltage (2.1 to
• Compact surface-mount package
• Wide temperature range
• Power-down function
• No production tuning
• Remote control
• Keyless entry
• Garage/gate openers
• Lighting control
• Medical monitoring/call systems
• Remote industrial monitoring
• Periodic data transfer
• Home/industrial automation
• Fire/security alarms
• Remote status/position sensing
• Long-range RFID
• Wire elimination
LR Series Transmitter Module
Data Guide
Revised 3/18/2015
0.360 in
(9.14 mm)
0.500 in
(12.7 mm)
0.130 in
(3.3 mm)
LOT RTxxxx
24 Common Antenna Styles
26 Regulatory Considerations
Figure 1: Package Dimensions
– – – –
2 3
LR Series Transmitter Specifications
Parameter Symbol Min. Typ. Max. Units Notes
Power Supply
Operating Voltage VCC 2.1 3.0 3.6 VDC
Supply Current lCC 3.4 mA 1,2
Logic High 5.1 mA 2
Logic Low 1.8 mA
Power Down Current lPDN 5.0 nA
Transmitter Section
Transmit Frequency Range FC
TXM-315-LR 315 MHz
TXM-418-LR 418 MHz
TXM-433-LR 433.92 MHz
Center Frequency Accuracy –50 +50 kHz
Output Power PO–4 0.0 +4 dBm 2
Output Power Control Range –80 +10 dB 3
Harmonic Emissions PH–36 dBc
Data Rate DC 10,000 bps
Data Input:
Logic Low VIL 0.25 VDC
Logic High VIH VCC–0.25 VDC
Power Down Input:
Logic Low VIL 0.25 VDC
Logic High VIH VCC–0.25 VDC
Antenna Port
RF Output Impedance ROUT 50 Ω4
Transmitter Turn-On Time
Via VCC or PDN 1.0 ms 4
Modulation Delay 30.0 ns 4
Operating Temperature –40 +85 ºC 4
Electrical Specifications
1. With a 50% duty cycle
2. With a 750Ω resistor on LADJ
3. See Figure 6 on page 4
4. Characterized, but not tested
Ordering Information
Ordering Information
Part Number Description
TXM-315-LR 315MHz Transmitter
TXM-418-LR 418MHz Transmitter
TXM-433-LR 433MHz Transmitter
RXM-315-LR 315MHz Receiver
RXM-418-LR 418MHz Receiver
RXM-433-LR 433MHz Receiver
EVAL-***-LR LR Series Basic Evaluation Kit
*** = 315, 418 (Standard), 433MHz
Transmitters are supplied in tubes of 50 pcs.
Figure 2: Ordering Information
Absolute Maximum Ratings
Absolute Maximum Ratings
Supply Voltage Vcc −0.3 to +3.6 VDC
Any Input or Output Pin −0.3 to VCC + 0.3 VDC
Operating Temperature −40 to +85 ºC
Storage Temperature −40 to +90 ºC
Soldering Temperature +260ºC for 10 seconds
Exceeding any of the limits of this section may lead to permanent damage to the device.
Furthermore, extended operation at these maximum ratings may reduce the life of this
Figure 3: Absolute Maximum Ratings
Warning: This product incorporates numerous static-sensitive
components. Always wear an ESD wrist strap and observe proper ESD
handling procedures when working with this device. Failure to observe
this precaution may result in module damage or failure.
Figure 4: Electrical Specifications
– – – –
4 5
1. 500mV/div 2. 2.00V/div
9.00 6.00 3.00 0.00 -3.00 -6.00 -9.00 -12.00 -15.00 -18.00 -21.00
Output Power (dBm)
LADJ Resistance (k)
6.00 3.00 0.00 -3.00 -6.00 -9.00 -12.00 -15.00 -18.00 -21.00
Output Power (dBm)
Current Consumption (mA)
Typical Performance Graphs
Figure 5: Modulation Delay
Figure 6: Output Power vs. LADJ Resistor
Figure 7: Current Consumption vs. Output Power (50% of Duty Cycle)
– – – –
6 7
Module Description
The LR Series transmitter is a low-cost, high-performance synthesized
ASK / OOK transmitter, capable of sending serial data at up to 10,000bps.
Because the transmitter is completely self-contained, requiring an
antenna as the only additional RF component, application is extremely
straightforward and assembly and testing costs are reduced. The LR
is housed in a compact surface-mount package that integrates easily
into existing designs and is equally friendly to prototyping and volume
production. LR Series modules are capable of meeting the regulatory
requirements of domestic and international applications.
The module’s low power consumption makes it ideal for battery-powered
products. The transmitter is compatible with many other Linx receiver
products, including the LR, KH3, LT and OEM product families. For
applications where range is critical, the LR receiver is the best choice due
to its outstanding sensitivity.
The transmitter is capable of outputting +10dBm into a 50-ohm load. When
combined with an LR Series receiver, a reliable serial link is formed capable
of transferring data over line-of-site distances of up to 1.5 miles (2,500m)
when used with good antennas. Legal regulations in the various countries
will require the transmitter output power to be reduced which will reduce
range. Following the legal output limit for transmitters in the United States,
systems based on the LR Series can achieve ranges of up to 3,000 feet
Pin Assignments
Pin Descriptions
Pin Descriptions
Pin Number Name I/O Description
1 GND Analog Ground
2DATA I Digital Data Input
3 GND Analog Ground
Level Adjust. This line can be used to adjust
the output power level of the transmitter.
Connecting to VCC gives the highest output,
while placing a resistor to VCC lowers the
output level (see Figure 6 on page 4)
5 ANT — 50Ω RF Output
6 GND Analog Ground
7 VCC Supply Voltage
Power Down. Pulling this line low places
the transmitter into a low-current state. The
module is not be able to transmit a signal in
this state.
Figure 8: LR Series Transmitter Pinout (Top View)
Figure 9: Pin Descriptions
– – – –
8 9
Theory of Operation
The LR Series transmitter generates 1mW of output power into a 50-ohm
single-ended antenna while suppressing harmonics and spurious emissions
to within legal limits. The transmitter is comprised of a VCO locked by a
frequency synthesizer that is referenced to a high precision crystal. The
output of the VCO is amplified and buffered by an internal power amplifier.
The amplifier is switched by the incoming data to produce a modulated
carrier. The carrier is filtered to attenuate harmonics and then output on the
50Ω antenna port.
The synthesized topology makes the module highly immune to the
effects of antenna port loading and mismatch. This reduces or eliminates
frequency pulling, bit contraction, and other negative effects common to
low-cost transmitter architectures. It also allows for reliable performance
over a wide operating temperature range. Like its companion LR Series
receiver, the LR Series transmitter delivers a significantly higher level of
performance and reliability than the LC Series or other SAW-based devices,
yet remains very small and cost-effective.
The Data Input
The CMOS-compatible data input on Pin 2 is normally supplied with a serial
bit stream from a microprocessor or encoder, but it can also be used with
standard UARTs.
When a logic ‘1’ is present on the DATA line and the PDN line is high, then
the Power Amplifier (PA) is activated and the carrier frequency is output on
the antenna port. When a logic ‘0’ is present on the DATA line or the PDN
line is low, the PA is deactivated and the carrier is fully suppressed.
The DATA line should always be driven with a voltage that is common
to the supply voltage present on Pin 7 (VCC). The DATA line should never
be allowed to exceed the supply voltage, as permanent damage to the
module could occur.
Using the PDN Line
The transmitter’s Power Down (PDN) line can be used to power down the
transmitter without the need for an external switch. It allows easy control of
the transmitter’s state from external components, such as a microcontroller.
By periodically activating the transmitter, sending data, then powering
down, the transmitter’s average current consumption can be greatly
reduced, saving power in battery operated applications.
The PDN line does not have an internal pull-up, so it needs to be pulled
high or tied directly to VCC to turn on the transmitter. The pull-up should be
a minimum of 30μA (10kΩ or less). When the PDN line is pulled to ground,
the transmitter enters a low-current (<5nA) power-down mode. In this
mode, the transmitter is completely off and cannot perform any function.
Figure 10: LR Series Transmitter Block Diagram
Note: The voltage on the PDN line should not exceed VCC. When used
with a higher voltage source, such as a 5V microcontroller, an open
collector line should be used or a diode placed in series with the control
line (anode toward the module). Either method avoids damage to the
module by preventing 5V from being placed on the PDN line while
allowing the line to be pulled low.
– – – –
10 11
Using the LADJ Line
The Level Adjust (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 VCC and
LADJ. The value of the resistor determines the output power level. When
LADJ is connected to VCC, the output power and current consumption
are at the maximum. Figure 6 on page 4 shows a graph of the output
power vs. LADJ resistance.
This line 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 temporarily used so that
the test lab can precisely adjust the output power to the maximum level
allowed by law. The variable 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 VCC so that it can be used if needed. For more sophisticated designs,
LADJ can be also controlled by a digital potentiometer to allow precise and
digitally variable output power control.
Power Supply Requirements
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.
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 of the
supply is poor. Note that the values may need to be adjusted depending on
the noise present on the supply line.
Transferring Data
Once a reliable RF link has been established, the challenge becomes how
to effectively transfer data across it. While a properly designed RF link
provides reliable data transfer under most conditions, there are still distinct
differences from a wired link that must be addressed. Since the LR Series
modules do not incorporate internal encoding or decoding, a user has
tremendous flexibility in how data is handled.
If the product transfers simple control or status signals such as button
presses or switch closures and it does not have a microprocessor on board
(or it is desired to avoid protocol development), consider using a remote
control encoder and decoder or a transcoder IC. These chips are available
from a wide range of manufacturers including Linx. They take care of all
encoding and decoding functions, and generally provide a number of data
pins to which switches can be directly connected. In addition, address bits
are usually provided for security and to allow the addressing of multiple
units independently. These ICs are an excellent way to bring basic remote
control / status products to market quickly and inexpensively. Additionally,
it is a simple task to interface with inexpensive microprocessors, IR, remote
control or modem ICs.
It is always important to separate the types of transmissions that are
technically possible from those that are legally allowable in the country
of intended operation. Linx Application Notes AN-00125, AN-00128
and AN-00140 should be reviewed, along with Part 15, Section 231 of
the Code of Federal Regulations for further details regarding acceptable
transmission content in the US All of these documents can be downloaded
from the Linx website at
Another area of consideration is that the data structure can affect the
output power level. The FCC allows output power in the 260 to 470MHz
band to be averaged over a 100ms time frame. Because OOK modulation
activates the carrier for a ‘1’ and deactivates the carrier for a ‘0’, a data
stream that sends more ‘0’s has a lower average output power over
100ms. This allows the instantaneous output power to be increased, thus
extending range.
Figure 11: Supply Filter
Vcc IN
Vcc TO
– – – –
12 13
Typical Applications
Figure 12 shows a circuit using a Linx MS Series encoder. This chip works
with the LICAL-DEC-MS001 decoder to provide simple remote control
capabilities. The decoder detects the transmission from the encoder,
checks for errors, and if everything is correct, replicates the encoder’s
inputs on its outputs. This makes registering key presses very simple.
The transmitter can also be connected to a GPIO of a microcontroller in
applications that use a custom protocol. No buffering is generally required
between the transmitter and microcontroller output. Exceptions to this
include systems where the microcontroller is operating at a different voltage
from the transmitter. In these cases the designer should take care to use
voltage translator circuits as appropriate.
10 11
ESD Concerns
The module has basic ESD protection built in, but in cases where the
antenna connection is exposed to the user it is a good idea to add
additional protection. A Transient Voltage Suppressor (TVS) diode, varistor
or similar component can be added to the antenna line. These should have
low capacitance and be designed for use on antennas. Protection on the
supply line is a good idea in designs that have a user-accessible power
Figure 12: LR Transmitter and MS Encoder
Tum ‘Qiéun
– – – –
14 15
Antenna Considerations
The choice of antennas is a
critical and often overlooked
design consideration. The range,
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
task. Professionally designed antennas such as those from Linx (Figure
13) help ensure maximum performance and FCC and other regulatory
Linx transmitter modules typically have an output power that is 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.
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.
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.
Additional details are in Application Note AN-00500.
Figure 13: Linx Antennas
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. We recommend reading
the application notes listed in Figure 14 which address in depth key areas
of RF design and application of Linx products. These applications notes are
available online at or by contacting Linx.
Protocol Guidelines
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.
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, read Linx
Application Note AN-00160.
Interference or changing signal conditions can corrupt 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.
Helpful Application Note Titles
Note Number Note Title
AN-00100 RF 101: Information for the RF Challenged
AN-00125 Considerations for Operation Within the 260–470MHz Band
AN-00130 Modulation Techniques for Low-Cost RF Data Links
AN-00140 The FCC Road: Part 15 from Concept to Approval
AN-00150 Use and Design of T-Attenuation Pads
AN-00160 Considerations for Sending Data over a Wireless Link
AN-00232 General Considerations for Sending Data with the LC Series
AN-00500 Antennas: Design, Application, Performance
AN-00501 Understanding Antenna Specifications and Operation
Figure 14: Helpful Application Note Titles
– – – –
16 17
Interference Considerations
The RF spectrum is crowded and the potential for conflict with 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
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.
External interference can manifest itself in a variety of ways. Low-level
interference produces noise and hashing on the output and reduces the
link’s overall range.
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.
Although technically 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
shorter useful distances for the link.
Pad Layout
The pad layout diagram in Figure 15 is designed to facilitate both hand and
automated assembly.
Board Layout Guidelines
The module’s design makes integration straightforward; however, it
is still critical to exercise care in PCB layout. Failure to observe good
layout techniques can result in a significant degradation of the module’s
performance. A primary layout goal is to maintain a characteristic
50-ohm impedance throughout the path from the antenna to the module.
Grounding, filtering, decoupling, routing and PCB stack-up are also
important considerations for any RF design. The following section provides
some basic design guidelines.
During prototyping, the module should be soldered to a properly laid-out
circuit board. The use of prototyping or “perf” boards results in poor
performance and is strongly discouraged. Likewise, the use of sockets
can have a negative impact on the performance of the module and is
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.
When possible, separate RF and digital circuits into different PCB regions.
Figure 15: Recommended PCB Layout
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– – – –
18 19
Microstrip Details
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 and 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 in
Figure 16 and examples are provided in Figure 17. Software for calculating
microstrip lines is also available on the Linx website.
Ground plane
Figure 16: Microstrip Formulas
Example Microstrip Calculations
Dielectric Constant Width / Height
Ratio (W / d)
Effective Dielectric
Impedance (Ω)
4.80 1.8 3.59 50.0
4.00 2.0 3.07 51.0
2.55 3.0 2.12 48.8
Figure 17: Example Microstrip Calculations
Make sure internal wiring is routed away from the module and antenna and
is secured to prevent displacement.
Do not route PCB traces directly under the module. There should not be
any copper or traces under the module on the same layer as the module,
just bare PCB. The underside of the module has traces and vias that could
short or couple to traces on the product’s circuit board.
The Pad Layout section shows a typical PCB footprint for the module. A
ground plane (as large and uninterrupted as possible) should be placed on
a lower layer of your PC board opposite the module. This plane is essential
for creating a low impedance return for ground and consistent stripline
Use care in routing the RF trace between the module and the antenna
or connector. Keep the trace as short as possible. Do not pass it under
the module or any other component. Do not route the antenna trace on
multiple PCB layers as vias add inductance. Vias are acceptable for tying
together ground layers and component grounds and should be used in
Each of the module’s ground pins should have short traces tying
immediately to the ground plane through a via.
Bypass caps should be low ESR ceramic types and located directly
adjacent to the pin they are serving.
A 50-ohm coax should be used for connection to an external antenna.
A 50-ohm transmission line, such as a microstrip, stripline or coplanar
waveguide should be used for routing RF on the PCB. The Microstrip
Details section provides additional information.
In some instances, a designer may wish to encapsulate or “pot” the
product. There are a wide variety of potting compounds with varying
dielectric properties. Since such compounds can considerably impact
RF performance and the ability to rework or service the product, it is
the responsibility of the designer to evaluate and qualify the impact and
suitability of such materials.
– – – –
20 21
Production Guidelines
The module is housed in a hybrid SMD package that supports hand and
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.
Hand Assembly
Pads located on the bottom
of the module are the primary
mounting surface (Figure 18).
Since these pads are inaccessible
during mounting, castellations
that run up the side of the module
have been provided to facilitate
solder wicking to the module’s
underside. This allows for very
quick hand soldering for prototyping and small volume 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 in Figure 19.
Automated Assembly
For high-volume assembly, the modules are generally auto-placed.
The modules have been designed to maintain compatibility with reflow
processing techniques; however, due to their hybrid nature, certain aspects
of the assembly process are far more critical than for other component
types. Following are brief discussions of the three primary areas where
caution must be observed.
PCB Pads
Soldering Iron
Figure 18: Soldering Technique
Warning: Pay attention to the absolute maximum solder times.
Figure 19: Absolute Maximum Solder Times
Absolute Maximum Solder Times
Hand Solder Temperature: +427ºC for 10 seconds for lead-free alloys
Reflow Oven: +255ºC max (see Figure 20)
Reflow Temperature Profile
The single most critical stage in the automated assembly process is the
reflow stage. The reflow profile in Figure 20 should not be exceeded
because excessive temperatures or transport times during reflow will
irreparably damage the modules. Assembly personnel 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.
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.
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.
60 12030 150180 210240 270300 330360090
Recommended RoHS Profile
Max RoHS Profile
Recommended Non-RoHS Profile
Temperature (oC)
Time (Seconds)
Figure 20: Maximum Reflow Temperature Profile
– – – –
22 23
General Antenna Rules
The following general rules should help in maximizing antenna performance.
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.
2. Optimum performance is obtained from a ¼- or ½-wave straight whip
mounted at a right angle to the ground plane (Figure 21). In many
cases, this isn’t desirable for practical or ergonomic reasons, thus,
an alternative antenna style such as a helical, loop or patch may be
utilized and the corresponding sacrifice in performance accepted.
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 ¼-wave whips, the ground plane
acts as a counterpoise, forming, in essence,
a ½-wave dipole (Figure 22). For this reason,
adequate ground plane area is essential.
The ground plane can be a metal case or
ground-fill areas on a circuit board. Ideally, it
should have a surface area less than or equal
to the overall length of the ¼-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
Figure 21: Ground Plane Orientation
plane as 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.
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.
6. In some applications, it is advantageous to place the module and
antenna away from the main equipment (Figure 23). This can avoid
interference problems and allows the antenna to be oriented for
optimum performance. Always use 50Ω coax, like RG-174, for the
remote feed.
Figure 23: Remote Ground Plane
Figure 22: Dipole Antenna
– – – –
24 25
Common Antenna Styles
There are 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, AN-00500 and AN-00501. Linx
antennas and connectors offer outstanding performance at a low price.
Whip Style
A whip style antenna (Figure 24) provides
outstanding overall performance and stability.
A low-cost whip 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.
The wavelength of the operational frequency
determines an antenna’s overall length. Since a full
wavelength is often quite long, a partial ½- or ¼-wave
antenna is normally employed. Its size and natural
radiation resistance make it well matched to Linx
modules. The proper length for a straight ¼-wave can
be easily determined using the formula in Figure 25.
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.
Specialty Styles
Linx offers a wide variety of specialized antenna
styles (Figure 26). 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.
L =
Figure 24: Whip Style Antennas
Figure 25:
L = length in feet of
quarter-wave length
F = operating frequency
in megahertz
Figure 26: Specialty Style
Loop Style
A loop or trace style antenna is normally printed
directly on a product’s PCB (Figure 27). 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 VSWR at the desired frequency which can cause
instability in the RF stage.
Linx offers low-cost planar (Figure 28) and chip
antennas that mount directly to a product’s PCB.
These tiny antennas do not require testing and
provide excellent performance despite their small
size. They offer a preferable alternative to the often
problematic “printed” antenna.
Figure 27: Loop or Trace Antenna
Figure 28: SP Series
“Splatch” and uSP
“MicroSplatch” Antennas
– – – –
26 27
Regulatory Considerations
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 a completed
For information about regulatory approval, read AN-00142 on the Linx
website or call Linx. Linx designs products with worldwide regulatory
approval in mind.
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 United States 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 FCC’s
website, 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, In brief, these rules require that any
device that intentionally radiates RF energy be approved, that is, tested for
compliance and issued a unique identification number. This is a relatively
painless process. Final compliance testing is 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 the completed product has passed,
an ID number is issued that is to be clearly placed on each product
Note: Linx RF modules are designed as component devices that require
external components to function. The purchaser understands that
additional 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.
Questions regarding interpretations of the Part 2 and Part 15 rules or the
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
Columbia, MD, US 21046
Phone: + 1 301 725 585 | Fax: + 1 301 344 2050
ETSI Secretaria
650, Route des Lucioles
06921 Sophia-Antipolis Cedex
Phone: +33 (0)4 92 94 42 00
Fax: +33 (0)4 93 65 47 16
International approvals are slightly more complex, although Linx modules
are designed to allow all international standards to be met. If the end
product is to be exported to other countries, contact Linx to determine the
specific suitability of the module to the 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.
Linx Technologies is continually striving to improve the quality and function of its products. For this reason, we
reserve the right to make changes to our products 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. “Typical” parameters can and do vary over lots and
application. Linx Technologies makes no guarantee, warranty, or representation regarding the suitability of any
product for use in any specific application. It is the customer’s responsibility to verify the suitability of the part for
liability are applicable to any and all claims or theories of recovery asserted by Customer, including, without
limitation, breach of contract, breach of warranty, strict liability, or negligence. Customer assumes all liability
(including, without limitation, liability for injury to person or property, economic loss, or business interruption) for
all claims, including claims from third parties, arising from the use of the Products. The Customer will indemnify,
defend, protect, and hold harmless Linx Technologies and its officers, employees, subsidiaries, affiliates,
distributors, and representatives from and against all claims, damages, actions, suits, proceedings, demands,
assessments, adjustments, costs, and expenses incurred by Linx Technologies as a result of or arising from any
Products sold by Linx Technologies to Customer. 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. Devices described in this publication may contain proprietary,
patented, or copyrighted techniques, components, or materials. Under no circumstances shall any user be
conveyed any license or right to the use or ownership of such items.
©2015 Linx Technologies. All rights reserved.
The stylized Linx logo, Wireless Made Simple, WiSE, CipherLinx and the stylized CL logo are trademarks of Linx Technologies.
Linx Technologies
159 Ort Lane
Merlin, OR, US 97532
Phone: +1 541 471 6256
Fax: +1 541 471 6251

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