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
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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