RXD-315-KH RXD-418-KH RXD-433-KH WIRELESS MADE SIMPLE ® KH SERIES RECEIVER / DECODER DATA GUIDE DESCRIPTION The KH Series is ideally suited for volume use in OEM applications such as remote control / command and keyless entry. It combines an RF receiver with an on-board decoder. When paired with a matching KH Series transmitter / encoder module, a highly reliable 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) different addresses for security and uniqueness. Housed in a compact SMD package, the KH module utilizes a highly optimized SAW architecture to achieve an unmatched blend of performance, size, efficiency, and cost. No external RF components, are required (except an antenna), making design integration straightforward. 1.430" 0.630" RF RECEIVER/DECODER RXD-418-KH LOT 1000 0.180" Figure 1: Package Dimensions FEATURES Low cost On-board decoder 8 parallel binary outputs 310 addresses for security and uniqueness No external RF components required Ultra-low power consumption Compact SMD package Stable SAW-based architecture Received data output Transmission validation No production tuning APPLICATIONS INCLUDE Remote Control / Command Keyless Entry Garage / Gate Openers Lighting Control Call Systems Home / Industrial Automation Fire / Security Alarms Remote Status Monitoring Wire Elimination ORDERING INFORMATION PART # DESCRIPTION TXE-315-KH Transmitter / Encoder 315MHz TXE-418-KH Transmitter / Encoder 418MHz TXE-433-KH Transmitter / Encoder 433MHz RXD-315-KH Receiver / Decoder 315MHz RXD-418-KH Receiver / Decoder 418MHz RXD-433-KH Receiver / Decoder 433MHz EVAL-***-KH Basic Evaluation Kit *** = Frequency Receivers are supplied in tubes of 20 pcs. Revised 10/12/06 Parameter POWER SUPPLY Operating Voltage: With Dropping Resistor Supply Current Power-Down Current ABSOLUTE MAXIMUM RATINGS Designation Min. Typical Max. Units Notes VCC 2.7 4.7 5.0 – 3.0 5.0 7.0 700 4.2 5.2 8.0 950 VDC VDC mA µA – 1 – – – FIF N3DB – – – – -75 – – 100 315 418 433.92 – 10.7 280 – – – – +75 – – 5,000 MHz MHz MHz kHz MHz kHz bps – – – – – 2 – VOL VOH – 0.0 VCC - 0.3 -92 – – -102 0.3 VCC -106 VDC VDC dBm 3 3,4 5 ICC IPDN Supply Voltage VCC Supply Voltage VCC, Using Resistor Any Input or Output Pin RF Input Operating Temperature Storage Temperature Soldering Temperature RECEIVER SECTION Receive Frequency: RXD-315-KH RXD-418-KH RXD-433-KH Center Frequency Accuracy IF Frequency Noise Bandwidth Data Rate Data Output: Logic Low Logic High Receiver Sensitivity FC RIN – 50 – Ω – – 5.0 7.0 10.5 mSec 6 These performance parameters are based on module operation at 25°C from a 3.0VDC supply unless otherwise noted. Figure 2 illustrates the connections necessary for testing and operation. It is recommended all ground pins be connected to the ground plane. The pins marked NC have no electrical connection and are designed only to add physical support. – – FENC – – – 26 bits 3x 50% 70 – – – – – kHz – – – – 0.6 1.0 1.2 mA 7 – -30 – +70 °C – DECODER SECTION TX Data Length Average Data Duty Cycle Decoder Oscillator Output Drive Current ENVIRONMENTAL Operating Temperature Range 1 2 3 4 5 3VDC 6 7 8 9 10 11 12 13 14 NC D0 D1 GND VCC PDN D2 D3 D4 DATA VT D5 D6 D7 ANT GND NC NC A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 28 27 26 25 24 23 22 21 20 19 18 17 16 15 TYPICAL PERFORMANCE GRAPHS VSWR 1. *CRITICAL* In order to operate the device over this range, it is necessary for a 200Ω resistor to be placed in series with VCC. 2. Potential rate of data recovered on the DATA line (pin 10). The decoder rate is internally fixed at about 2kbps. 3. When operating from a 5V source, it is important to consider that the output will swing to well less than 5 volts as a result of the required dropping resistor. Please verify that the minimum voltage will meet the high threshold requirement of the device to which data is being sent. 4. VCC referenced to voltage on the VCC pin after dropping resistor. 5. For a BER of 10-5 at 4,800 baud. Sensitivity is affected by the antenna’s SWR. 6. Time to valid data output. 7. Maximum drive capability of data outputs. 5VDC 200Ω External Resistor Figure 2: Test / Basic Application Circuit Table 1: KH Series Receiver Electrical Specifications Notes VDC VDC VDC dBm °C °C PERFORMANCE DATA TIMING Receiver Turn-On Time: Via VCC to +4.2 to +5.2 to +3.6 0 -30 to +70 -45 to +85 +225°C for 10 seconds *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. ANTENNA PORT RF Input Impedance -0.3 -0.3 -0.3 10.0 6.0 5.0 4.0 3.0 2.5 2.0 1.5 1.0 0 0.18 0.5 0.9 1.25 1.94 2.53 3.10 4.80 Sensitivity Decrease (dB) Figure 3: Sensitivity vs. VSWR Supply Current (mA) ELECTRICAL SPECIFICATIONS 16 12 8 4 0 2.7 3 3.5 4 Supply Voltage (V) Figure 4: Consumption vs. Supply Voltage Data Out Data Out Carrier Carrier *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. Page 2 Figure 5: RF In vs. Receiver Response Time Figure 6: Receiver Turn-Off Time Page 3 PIN ASSIGNMENTS MODULE DESCRIPTION 1 2 3 4 5 6 7 8 9 10 11 12 13 14 NC D0 D1 GND VCC PDN D2 D3 D4 DATA VT D5 D6 D7 ANT GND NC NC A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 28 27 26 25 24 23 22 21 20 19 18 17 16 15 The KH Series module combines the popular Linx LC Series receiver with a decoder IC in a convenient SMD package. The module is ideal for generalpurpose remote control and command applications. When paired with a matching Linx KH Series transmitter/encoder, a highly reliable RF link is formed, capable of transferring control and command data over line-of-sight distances in excess of 300 feet. The on-board receiver/decoder combination provides eight switched outputs that correspond to the state of the data lines on the transmitter’s encoder. Ten tri-state address lines are also provided to allow up to 59,049 (310) unique identification codes. 50Ω RF IN (Ant.) RF Stage Gilbert Cell Mixer/Amp Band Select Filter 10.7MHz Bandpass Filter DATA preamplifier Figure 7: KH Series Receiver Pinout (Top View) 10.7MHz AM Detector Limiting Amp Ceramic Filter Data Slicer PIN DESCRIPTIONS Pin # Name Description 1 NC No Connection. For physical support only. SAW Local Oscillator Decoder Stage Oscillator Divider Data Output Lines. Upon a valid transmission, these lines will be set to replicate the state of the transmitter’s address lines. Buffer Data Collector Sync. Detector 2, 3, 7, 8, 9, 12, 13, 14 D0-D7 4 GND Analog Ground 5 VCC Supply Voltage 8-bit Shift Register Latch Circuit AND Circuit D0 D1 D2 D3 D4 D5 D6 D7 Buffer Comparator Comparator Control Logic Transmission Gate Circuit 6 PDN Power Down. Pulling this line low will place the receiver into a low-current state. The module will not be able to receive a signal in this state. 10 DATA Data output of the receiver prior to the encoder. 11 VT Valid Transmission. This line will go high when a valid transmission is received. 15-24 A0-A9 Address Lines. The state of these lines must match the state of the transmitter’s address lines in order for a transmission to be accepted. 25 NC No Connection. For physical support only. 26 NC No Connection. For physical support only. 27 GND Analog Ground 28 RF IN 50-ohm RF Input A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 Figure 8: KH Series Receiver Block Diagram THEORY OF OPERATION Page 4 The KH Series receiver module is designed to receive transmissions from a matching KH Series transmitter module or other compatible Linx transmitter product. When transmitted data is received, the data is presented to the onboard decoder. If the incoming address data matches the local address settings, the decoder’s outputs are set to replicate the states of the transmitter’s data lines. The RF section of the KH module utilizes an advanced single-conversion superhet design that incorporates a Surface Acoustic Wave (SAW) device, high IF frequency, and multi-layer ceramic filters. The SAW device provides a highly accurate Local Oscillator (LO) frequency source with excellent immunity to frequency shift due to age or temperature. The use of SAW devices in both the KH transmitter and receiver modules allows the receiver’s pass band to be quite narrow, thus increasing sensitivity and reducing susceptibility to near-band interference. Page 5 DECODER OPERATION THE DATA OUTPUTS The KH Series receiver utilizes the HT658 decoder from Holtek. The decoder receives data transmitted by the encoder and interprets the first 10 bits of the code period as address and the last 8 bits as data. A signal on the DATA line activates the oscillator, which in turn decodes the incoming address and data. The decoder will check the received address twice continuously. If the received address code matches the decoder’s local address, the 8 bits of data are replicated on the output lines, and the VT line is set high to indicate the reception of a valid transmission. That will last until the address code is incorrect or no signal has been received. The VT line is high only when the transmission is valid, otherwise it is low. The data outputs are momentary, and follow the encoder during a valid transmission, then reset. Power On Standby Mode No Disable VT & Ignore the Rest of This Word Code In? Yes Address Bits Matched? In addition to the decoded data outputs, raw data is also available via a CMOScompatible data output (DATA, Pin 10). The output of this line is the actual received data stream from the receiver and is always active regardless of address line status. It is made available for troubleshooting or monitoring internal data flow. It can also be used in mixed-mode systems where data may come from another source in addition to a KH Series transmitter module. This data can then be channeled to an external processor for decoding. No Yes Store Data Match Previous Stored Data? No Yes No RECEIVING DATA 2 Times of Checking Completed? Although the internal decoder handles all of the decoding and output for transmissions from a KH Series transmitter or an OEM transmitter, the KH Series receiver will output the raw received data on the DATA line. This allows the designer to create a mixed system of KH Series or OEM transmitters for encoded data as well as LC or LR Series transmitters for custom data. Yes Data to Output & Activate VT No Address or Data Error? The oscillator is disabled in the standby Yes state and activated as long as a logic “high” signal is applied to the DATA line, so the Figure 9: Decoder Flowchart DATA line should be kept “low” if there is no signal input. The KH Series receiver module contains the LC Series receiver, which has a CMOS-compatible output capable of directly driving a microprocessor, an RS232 level converter, or a Linx QS Series USB module. The LC Series receiver manual can be consulted for more details on the operation of the receiver itself. < 1 Word Encoder Data Out 3 Words Transmitted Continuously 3 Words 214 Clocks 214 Clocks Decoder VT 2 Words Check Check Decoder Data Out 1/2 Clock Time 1/2 Clock Time Figure 10: Encoder / Decoder Timing Diagram SETTING THE RECEIVER ADDRESS The module provides ten tri-state address lines. This allows for the formation of up to 59,049 (310) unique receiver-transmitter relationships. Tri-state means that the address lines can be set to one of three distinct states: high, low, or floating. These lines 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 When using the KH for custom data transmissions, it is up to the designer to implement a noise-tolerant protocol to ensure the integrity of the data. The Protocol Guidelines section will provide some suggestions, as well as Application Note AN-00160. 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 receiver sensitivity; therefore, providing a clean power supply for the module should be a high priority during design. Vcc TO MODULE 10Ω Vcc IN + Encoder Transmit Enable When data is received and the incoming address data matches with the local address settings, the module’s eight data output lines are set to replicate the state of the transmitter’s data lines. In addition, the valid transmission line (VT, Pin 11) will go high to indicate reception and decoding of the data. The data lines have a low sink and source capability, so external buffering is generally required if loads are to be driven directly. 10μF Figure 11: 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 of supply power is poor. These values may need to be adjusted depending on the noise present on the supply line. Note that operation from 4.7 to 5.2 volts requires the use of an external 200Ω resistor placed in-line with the supply to prevent VCC from exceeding 4.2 volts, so the dropping resistor can take the place of the 10Ω resistor in the supply filter. 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. 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. The figure below shows an example of a basic remote control receiver utilizing the KH Series receiver module. When a key is pressed on the transmitter, a corresponding line on the receiver goes high. A schematic for the transmitter / encoder circuit may be found in the KH Series Transmitter Data Guide. These circuits are implemented in the KH Series Basic Evaluation Kit. They can be easily modified for a custom application and clearly demonstrate the ease of using the Linx KH Series modules for remote control applications. VCC VCC BZ1 BUZZER S4 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. Q1 2N2222 ANT1 1 R4 10k 2 VCC 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 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. 3 VCC GND LED1 RED LED 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. R2 2.2k 4 GND 5 6 7 R6 220 OHM Q2 2N2222 8 R3 2.2k 9 10 11 12 R5 10k 13 14 GND NC ANT D0 GND D1 NC GND NC VCC A9 PDN A8 D2 A7 D3 A6 D4 A5 DATA A4 VT A3 D5 A2 D6 A1 D7 A0 B1 CR2032 3V LITHIUM 28 27 GND 26 25 GND S1 24 23 22 21 20 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 19 SW-DIP-10 18 17 GND 16 15 RXD-XXX-KH Figure 12: Basic Remote Control Receiver 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 line outputs can only source about 1mA of current, so transistor buffers are used to drive the buzzer and LED. 1mA is sufficient to activate most microcontrollers, but the manufacturer’s data guides should be consulted to make sure. The KH Series receiver / decoder module is also suitable for use with Linx OEM handheld transmitters. These transmitters are FCC certified, making product introduction extremely quick. Information on these transmitters can be found on the Linx website at www.linxtechnologies.com. 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. Figure 13: Linx OEM Transmitters Page 8 Figure 14: Linx OEM Keyfobs 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. 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 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. GROUND PLANE ON LOWER LAYER 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 highfrequency 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 FR4 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. Trace Figure 15: 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. 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. Page 10 Figure 16: Microstrip Formulas Dielectric Constant Width/Height (W/d) Effective Dielectric Constant Characteristic Impedance 4.80 4.00 1.8 2.0 3.59 3.07 50.0 51.0 2.55 3.0 2.12 48.0 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 17: 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. Soldering Iron Tip 220oC 210oC 200 180oC 150 Reflow Zone 125oC 20-40 Sec. Soak Zone 100 50 Ramp-up Solder PCB Pads Forced Air Reflow Profile 2 Minutes Max. Preheat Zone 2-2.3 Minutes Cooling 1-1.5 Minutes 0 Castellations Figure 18: Soldering Technique 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. Absolute Maximum Solder Times 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 Ideal Curve Limit Curve 250 Temperature (oC) HAND ASSEMBLY Pads located on the bottom of the module are the primary mounting surface. 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. 300 0 30 60 90 120 150 180 210 240 270 300 330 360 Time (Seconds) Figure 19: Maximum Reflow Profile 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 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. Page 13 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. A professionally designed Figure 20: Linx Antennas antenna, such as those from Linx, will help ensure maximum performance and FCC compliance. 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. 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. You may wish to review Application Note AN-00500 “Antennas: Design, Application, Performance” ANTENNA SHARING In cases where a transmitter and receiver VDD module are combined to form a transceiver, Transmitter 0.1μF it is often advantageous to share a single Module 0.1μF Antenna antenna. To accomplish this, an antenna 0.1μF GND switch must be used to provide isolation 0.1μF between the modules so that the full 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 Figure 21: Typical Antenna Switch are cost-effective and easy to use. Among 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. Page 14 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 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 USEABLE an alternative antenna style such as a helical, loop, or patch may be utilized Figure 22: Ground Plane Orientation 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 1/4-wave VERTICAL λ/4 GROUNDED ANTENNA (MARCONI) whips, the ground plane acts as a counterpoise, DIPOLE forming, in essence, a 1/2-wave dipole. For this ELEMENT 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 GROUND surface area > the overall length of the 1/4-wave PLANE VIRTUAL λ/4 radiating element. This is often not practical due to DIPOLE size and configuration constraints. In these instances, a designer must make the best use of the Figure 23: Dipole Antenna area available to create as much ground 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. E λ/4 I λ/4 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. 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. CASE NUT GROUND PLANE (MAY BE NEEDED) Figure 24: Remote Ground Plane Page 15 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. Whip Style L= A whip-style antenna provides outstanding overall performance 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. 234 F MHz Where: L = length in feet of quarter-wave length F = operating frequency in megahertz The wavelength of the operational frequency determines an antenna’s overall length. Since a full wavelength is often quite 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. Specialty Styles Loop Style 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. 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. 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 ® www.linxtechnologies.com • • • • • Latest News Data Guides Application Notes Knowledgebase Software Updates 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! 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. www.connectorcity.com Through its Connector City division, Linx offers a wide selection of high-quality RF connectors, including FCCcompliant 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. Page 17 LEGAL CONSIDERATIONS 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. 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. 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 precompliance 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. 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 Columbia, MD 21046 Phone: (301) 725-1585 Fax: (301) 344-2050 E-Mail: [email protected] 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. Page 18 ACHIEVING A SUCCESSFUL RF IMPLEMENTATION Adding an RF stage brings an exciting new 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. DECIDE TO UTILIZE RF RESEARCH RF OPTIONS ORDER EVALUATION KIT(S) TEST MODULE(S) WITH BASIC HOOKUP CHOOSE LINX MODULE INTERFACE TO CHOSEN CIRCUIT AND DEBUG CONSULT LINX REGARDING ANTENNA OPTIONS AND DESIGN LAY OUT BOARD In reviewing this sample design path, you may SEND PRODUCTION-READY PROTOTYPE TO LINX FOR EMC PRESCREENING notice that Linx offers a variety of services (such as antenna design and FCC prequalification) that are OPTIMIZE USING RF SUMMARY GENERATED BY LINX unusual for a high-volume component manufacturer. SEND TO PART 15 These services, along with an exceptional level of TEST FACILITY technical support, are offered because we recognize RECEIVE FCC ID # that RF is a complex science requiring the highest caliber of products and support. “Wireless Made COMMENCE SELLING PRODUCT Simple” is more than just a motto, it’s our Typical Steps For commitment. By choosing Linx as your RF partner Implementing RF and taking advantage of the resources we offer, you 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. NOTE APPLICATION 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-00300 Addressing Linx OEM Products AN-00500 Antennas: Design, Application, Performance 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 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.