RXM-418-LC [ETC]
LC SERIES TRANSMITTER MODULE; LC系列变送器模块
| 型号： | RXM-418-LC |
| 厂家： | 
ETC |
| 描述： | LC SERIES TRANSMITTER MODULE |
| 文件： | 总11页 (文件大小：368K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
TXM-315-LC
TXM-418-LC
TXM-433-LC
WIRELESS MADE SIMPLE ®
LC SERIES TRANSMITTER MODULE DATA GUIDE
DESCRIPTION
The LC Series is ideally suited for volume use in
OEM applications such as remote control,
security, identification, and periodic data
RF MODULE
0.360"
transfer. Housed in a compact surface-mount
TXM-418-LC
package, the LC Series transmitter utilizes a
highly-optimized SAW architecture to achieve
an unmatched blend of performance, size,
efficiency, and cost. When paired with a
matching LC Series or LR Series receiver, a
highly reliable wireless link is formed, capable
of transferring serial data at distances in excess
of 300 feet (LC) or up to 3,000 feet (LR). No
external RF components are required (except
an antenna), making design and integration
straightforward, even for engineers without
previous RF experience.
LOT 2000
0.500"
0.150"
Max.
Figure 1: Package Dimensions
FEATURES
Low cost
No external RF components
required
Supports data rates to 5,000bps
Wide supply range
(2.7 to 5.2VDC)
Ultra-low power consumption
Direct serial interface
Compact surface-mount package Low harmonics
Stable SAW-based architecture
No production tuning
APPLICATIONS INCLUDE
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 Sensing
Long-Range RFID
ORDERING INFORMATION
PART #
DESCRIPTION
TXM-315-LC
TXM-418-LC
TXM-433-LC
RXM-315-LC
RXM-418-LC
RXM-433-LC
EVAL-***-LC
*** = Frequency
Transmitter 315MHz
Transmitter 418MHz
Transmitter 433MHz
Receiver 315MHz
Receiver 418MHz
Receiver 433MHz
Basic Evaluation Kit
Transmitters are supplied in tubes of 50 pcs.
Wire Elimination
Revised 1/28/08
ELECTRICAL SPECIFICATIONS
PERFORMANCE DATA
These performance parameters
are based on module operation at
25°C from a 3.3VDC supply unless
Parameter
Designation
Min.
Typical
Max.
Units
Notes
POWER SUPPLY
Operating Voltage
Supply Current
VCC
VCC
ICC
2.7
–
–
3.0
–
5.2
6.0
1.5
VDC
mA
µA
–
1,4
2
1
2
3
4
8
7
6
5
GND
DATA
GND
GND
VCC
GND
otherwise
illustrates
necessary
noted.
the
for
Figure
connections
testing and
2
Power-down Current
TRANSMITTER SECTION
Transmit Frequency:
TXM-315-LC
IPDN
–
LADJ/GND ANT
operation. It is recommended all
ground pins be connected to the
ground plane.
FC
–
–
315
–
–
MHz
MHz
MHz
kHz
–
–
–
–
3
3
–
TXM-418-LC
418
TXM-433-LC
–
433.92
–
Figure 2: Test / Basic Application Circuit
Center Frequency Accuracy
Output Power
–
Po
PH
–
-50
-4
–
–
0
–
–
+50
+4
dBm
dBc
TYPICAL PERFORMANCE GRAPHS
Harmonic Emissions
Data Rate
-40
5,000
12
11
10
9
8
7
6
5
4
3
+8
+7
+6
+5
+4
+3
+2
+1
0
100
bps
Data Input:
Logic Low
VIL
VIH
0.0
2.5
–
–
0.4
VDC
VDC
–
–
Logic High
Vcc
ANTENNA PORT
RF Output Impedance
TIMING
ROUT
–
50
–
Ω
5
-1
-2
2
1
0
-3
Transmitter Turn-On Time
Transmitter Turn-Off Time
ENVIRONMENTAL
Operating Temperature Range
–
–
–
–
30
–
80
µSec
nSec
5
5
-4
-5
100
2.5
3.0
3.5
4.0
4.5
5.0
2.5 3.0 3.5 4.0 4.5 5.0
Supply Voltage (V)
Supply Voltage (V)
–
-30
–
+70
°C
5
With LADJ tied to ground
With LADJ tied to ground
With 430Ω resistor on LADJ
With 430Ω resistor on LADJ
Table 1: LC Series Transmitter Specifications
Figure 3: Current vs. Supply Voltage
Figure 4: Output Power vs. Supply Voltage
Notes
1. Current draw with DATA pin held continuously high.
2. Current draw with DATA pin low.
3. RF out connected to a 50Ω load.
4. LADJ through 430Ω resistor.
Data
5. Characterized, but not tested.
Data
Carrier
ABSOLUTE MAXIMUM RATINGS
Carrier
Supply Voltage VCC
-0.3
to
to
to
to
+6.0
VDC
VDC
°C
Any Input or Output Pin
Operating Temperature
Storage Temperature
Soldering Temperature
-0.3
-30
-45
VCC
+70
+85
Figure 5: Typical Oscillator Turn-On Time
Figure 6: Typical Oscillator Turn-Off Time
°C
+225°C for 10 seconds
+8
+7
+6
+5
+4
+3
+2
+1
0
-1
-2
-3
-4
*NOTE* 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 device.
5V
3V
*CAUTION*
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.
51 100 150 200 240 300 360 430 510 560 620 680 750 820 910 1.1K
LADJ Resistor Value (Ω)
Figure 7: Output Power vs. LADJ Resistor
Page 3
Page 2
PIN ASSIGNMENTS
MODULE DESCRIPTION
The LC Series transmitter is a low-cost, high-performance Surface Acoustic
Wave (SAW) based Carrier-Present Carrier-Absent (CPCA) transmitter capable
of sending serial data at up to 5,000bps. The LC’s compact surface-mount
package integrates easily into existing designs and is equally friendly to
prototype and volume production. The LC’s ultra-low power consumption makes
it ideally suited for battery-powered products. When combined with a Linx LC or
LR Series receiver, a reliable RF link is formed, capable of transferring data over
line-of-sight distances in excess of 300 feet (with the LC Series receiver) or up
to 3,000 feet (with the LR Series receiver).
1 GND
GND
VCC
GND
8
7
6
5
2 DATA
3 GND
4 LADJ/GND ANT
SAW
Vcc
Figure 8: LC Series Transmitter Pinout (Top View)
Oscillator
50Ω RF OUT
(ANT)
Data In
300-5,000bps
Keyed Output
PIN DESCRIPTIONS
Pin # Name
Description
Analog Ground
Digital Data Input
Analog Ground
Output Isolation
& Filter
1
2
3
GND
DATA
GND
RF Amplifier
Figure 9: LC Series Transmitter Block Diagram
THEORY OF OPERATION
Level Adjust. This line can be used to adjust the output
power level of the transmitter. Connecting to ground will
give the highest output, while placing a resistor to ground
will lower the output level (see Figure 7 on Page 3).
The LC Series transmitter transmits data using Carrier-Present Carrier-Absent
(CPCA) modulation. This type of AM modulation is often referred to by other
designations, including Continuous Wave (CW) and On-Off Key (OOK). This
type of modulation represents a logic low ‘0’ by the absence of a carrier and a
logic high ‘1’ by the presence of a carrier. This method affords numerous
benefits. Three of the most important are:
4
LADJ/GND
5
6
7
6
ANT
GND
VCC
50-ohm RF Output
Analog Ground
Supply Voltage
Analog Ground
1) Cost-effectiveness due to design simplicity.
2) No minimum data rate or mark / space ratio requirement.
3) Higher output power and thus greater range in countries (such as the U.S.)
where output power measurements are averaged over time. (Please refer to Linx
Application Note AN-00130).
GND
The LC Series transmitter is based on a simple but highly optimized architecture
that achieves a high fundamental output power with low harmonic content. This
ensures that approval requirements can be met without external filter
components. The LC Series transmitter is exceptionally stable over time,
temperature, and physical shock as a result of the precision Surface Acoustic
Wave (SAW) frequency reference. Due to the accuracy of the SAW device, most
of the output power is concentrated in a narrow bandwidth. This allows the
receiver’s bandwidth to be quite narrow, thus increasing sensitivity and reducing
susceptibility to near-band interference. The quality of components and overall
architecture utilized in the LC Series is extraordinary in a low-cost RF device and
is one reason the LC transmitter is able to outperform more expensive products.
Page 4
Page 5
THE DATA INPUT
POWER SUPPLY REQUIREMENTS
A CMOS / TTL level data input is provided on Pin 2. This line is normally supplied
with a serial bitstream input directly from a microprocessor, encoder, or UART.
During standby, or the input of a logic low, the carrier is fully suppressed and the
transmitter consumes less than 2µA of current. During a logic high, the
transmitter generates a carrier to indicate to the receiver the presence of a logic
‘1’. The applied data should not exceed a rate of 5,000bps. The data input line
should always be driven with a voltage common to the supply voltage present on
Pin 7 (VCC) and should never be allowed to exceed the supply voltage.
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, the unit can also be operated from a power supply as long as noise is
less than 20mV. Power supply noise can significantly
affect the transmitter modulation; therefore, providing
Vcc TO
MODULE
a clean power supply for the module should be a high
design priority.
10Ω
Vcc IN
+
A 10Ω resistor in series with the supply followed by a
10µF tantalum capacitor from VCC to ground will help
10μF
ADJUSTING THE OUTPUT POWER
in cases where the quality of supply power is poor.
Depending on the type of antenna being used and the duty cycle of the data, the
output power of the LC Series transmitter module may be higher than FCC
regulations allow. The output power of the module is intentionally set high to
compensate for losses resulting from inefficient antennas that may be used to
realize cost or space savings. Since attenuation is often required, it is generally
wise to provide for its implementation and allow the FCC test lab to easily
attenuate the transmitter to the maximum legal limit for your product.
These values may need to be adjusted depending on
Figure 11: Supply Filter
the noise present on the supply line.
TRANSMITTING 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 LC Series modules do not
incorporate internal encoding or decoding, a user has tremendous flexibility in
how data is handled.
Two methods of attenuation are available using the LC Series transmitter
module. First, a resistor may be placed between Pin 4 (LADJ) and ground to
achieve up to a 7dB reduction in output power. The resistor value is easily
determined from Figure 7 on Page 3. Do not exceed the resistance values shown
as transmitter instability may result. This method can also be used to reduce the
transmission range and power consumption.
If you want to transfer simple control or status signals, such as button presses or
switch closures, and your product does not have a microprocessor on board, or
you wish to avoid protocol development, consider using an encoder and decoder
IC set. These chips are available from a 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,
such as the Microchip PIC, or one of many IR, remote control, or modem ICs.
Another method commonly used to achieve attenuation, particularly at higher
levels, is the use of a T-pad attenuator. A T-pad is a network of three resistors
that allows for variable attenuation while maintaining the correct match to the
antenna. It is usually prudent to allow space for the addition of a T-pad. An
example of a T-pad attenuator layout is shown in the figure below. For further
details on T-pad attenuators, please refer to Application Note AN-00150.
TYPICAL LAYOUT
CIRCUIT
WITH PROVISION FOR ATTENUATION
ANT
It is always important to separate what types of transmissions are technically
possible from those that are legally allowable in the country of intended
operation. While the LR Series is ideally suited to the long range transfer of
control and command information, it can also be used with great success for the
transfer of true variable data such as temperature, pressure, or sensor data.
However, the 260 - 470MHz band in which the module operates is regulated by
Part 15, Section 231 of the FCC regulations. Many types of transmissions,
especially those involving automatic transmissions or variable data, may need to
be periodic. You may wish to review Application Notes AN-00125 and AN-00140
along with Part 15, Section 231 of the FCC regulations for further details on
acceptable transmission content in the Unites States.
PADS FOR SMD
RESISTORS
ANT
GROUUND PLANE
ON LOWER LAYER
R1
R2
R1
GROUUND
GND
ANT OUT
Another area of consideration is that of data structure or protocol. The data
should be formatted in a predictable way and should be able to deal with errors
due to interference. This will ensure that the data is received and interpreted
correctly. If you are not familiar with the considerations for sending serial data in
a wireless environment, you will want to review Application Note AN-00160.
Figure 10: A T-Pad Attenuator Layout Example
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.
The LC Series transmitter is ideal for the transmission of remote control /
command data. One of the easiest way to transmit on / off data or switch
closures is to use an encoder and decoder. These ICs provide a number of data
lines that can be connected to switches or buttons or even a microcontroller.
When a line is taken high on the encoder, a corresponding line will go high on
the decoder as long as the address matches. The figure below shows an
example using the Linx MS Series encoder.
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.
1
2
3
4
8
7
6
5
GND
DATA
GND
GND
VCC
GND
0
0
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.
750
LADJ/GND ANT
TXM-xxx-LC
OPEN
100k
100k
100k
100k
100k
100k
1
2
3
4
5
6
7
8
9
20
19
18
17
16
15
14
13
12
11
INTERFERENCE CONSIDERATIONS
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.
100k
100k
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.
220
100k
220
10
LICAL-ENC-MS001
Figure 12: Typical Remote Control Example
This circuit uses the LC Series transmitter and the MS Series encoder to transmit
button presses. The MS Series has eight data lines, which are connected to
buttons that will pull the line high when pressed. When not used, the lines are
pulled low by 100kΩ resistors. The encoder will begin a transmission only when
the SEND line is taken high. Diodes are used to pull this line high when any data
line is pulled high while isolating the data lines from each other.
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.
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 MS Series Encoder Data Guide explains this circuit and the many features
of the encoder in detail, so please refer to that document for more information.
A 750Ω resistor is used on the LADJ line of the transmitter to reduce the output
power of the transmitter. This is appropriate for some antennas, but may need to
be adjusted depending on the design. Typically, a resistor pad will be placed on
the board and a potentiometer used by the FCC test lab to adjust the output
power to the maximum legal limit. The potentiometer value would then be
measured and the closest standard value resistor placed for final testing.
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.
If the level adjust resistor does not provide enough attenuation, a T-pad
attenuator can be placed between the transmitter and antenna. This is a network
of three resistors that will provide a set amount of attenuation while maintaining
a 50Ω match between the antenna and the transmitter. Application Note
AN-00150 gives the formulas for calculating the resistor values. If not needed,
the series resistors can be zero ohms or shorted and the parallel one not placed.
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,
www.linxtechnologies.com.
The adjacent figure shows the suggested
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
GROOUUNNDD PPLLAANNEE
OONN BOTTOM LAYER
module. This ground plane can also be critical
to the performance of your antenna, which will
be discussed later. There should not be any
Trace
ground or traces under the module on the
same layer as the module, just bare PCB.
Figure 13: 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 12: 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
0.340"
0.070"
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.
0.100"
Figure 15: Recommended PCB Layout
PRODUCTION GUIDELINES
300
Recommended RoHS Profile
Max RoHS Profile
Recommended Non-RoHS Profile
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.
255°C
250
200
150
100
50
235°C
217°C
185°C
180°C
HAND ASSEMBLY
Pads located on the bottom of the
module are the primary mounting
surface. Since these pads are
inaccessible during mounting,
Soldering Iron
Tip
125°C
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
Solder
PCB Pads
0
30
60
90
120
150
180
210
240
270
300
330
360
Castellations
Time (Seconds)
prototyping and small volume
Figure 17: Maximum Reflow Profile
Figure 16: 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 18: 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 20: 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 21: 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 19: 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 22: 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.
®
www.linxtechnologies.com
• 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,
make www.linxtechnologies.com your first stop. Our website is organized in an
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.
www.antennafactor.com
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
www.connectorcity.com
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,
www.linxtechnologies.com. 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. 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
applications notes are available online at www.linxtechnologies.com or by
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: labinfo@fcc.gov
AN-00125
AN-00130
AN-00140
AN-00150
AN-00160
AN-00232
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
General Considerations For Sending Data With The LC Series
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
www.linxtechnologies.com
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 to our products without notice. The information contained in this
Overview 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 the intended application. NO LINX PRODUCT IS INTENDED FOR USE
IN ANY APPLICATION WHERE THE SAFETY OF LIFE OR PROPERTY IS AT RISK.
Linx Technologies DISCLAIMS ALL WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE. IN NO EVENT SHALL LINX TECHNOLOGIES BE LIABLE FOR ANY OF
CUSTOMER'S INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY FROM ANY DEFECTIVE
OR NON-CONFORMING PRODUCTS OR FOR ANY OTHER BREACH OF CONTRACT BY LINX
TECHNOLOGIES. The limitations on Linx Technologies' 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
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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.
© 2008 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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