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RCT-XXX-AS
Embedding the wireless future..
Low-Cost SAW-stabilized surface mount OOK RF transmitter
Typical Applications
* * * * * * * Remote Keyless Entry (RKE) Remote Lighting Controls On-Site Paging Asset Tracking Wireless Alarm and Security Systems Long Range RFID Automated Resource Management
Features
* * * * * * * 315/418/433.92 MHz versions Low Cost .5-12V operation 5mA current consumption at 3V Small size: .30" x .4" 0dBm output power at 3V 4800 baud operation
Description
The RCT-433-AS is ideal for remote control applications where low cost and longer range are required. The transmitter operates from a 1.5-12V supply, making it ideal for battery-powered applications. The transmitter employs a SAWstabilized oscillator, ensuring accurate frequency control for best range performance. Output power and harmonic emissions are easy to control, making FCC and ETSI compliance easy. The manufacturing-friendly SMT style package and lowcost make the RCT-433-AS suitable for high volume applications.
(shown actual size)
Ordering Information
Frequency 315 MHz 418 MHz 433.92 MHz Part Number RCT-315-AS RCT-418-AS RCT-433-AS
Mouser Electronics 1-800-346-6873 (http://www.mouser.com) Haltronics Ltd. 1-800-387-7969 (http://www.haltronicsltd.com/)
Domestic and international orders: Canadian orders:
For a Radiotronix Representative in your area please visit www.radiotronix.com and visit our corporate information page.
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Document Control
Created By Engineering Review Marketing Review Approved - Engineering Approved - Marketing Steve Montgomery Tom Marks Bryan Montgomery Tom Marks Bryan Montgomery 05/21/02 8/21/03 8/21/03 8/21/03 8/21/03
Revision History
Revision Author 1.1.0 1.2.0 1.3.0 SJM BFA SJM Date 05/21/02 07/30/03 8/21/03 Description Document Created Revision Revision. Added troubleshooting and design tips.
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RCT-XXX-AS
Low-Cost SAW-stabilized surface mount OOK RF transmitter
(c) 2001,2002,2003 All Rights Reserved
Pin Out Diagram
Pin Description
Pin No. Pin Name Description
1 2 3
ANT GND DATA
4
VCC
50 ohm antenna output. The antenna port impedance affects output power and harmonic emissions. An L-C low-pass filter may be needed to sufficiently filter harmonic emissions. Transmitter ground. Connect to ground plane. Digital data input. This input is CMOS compatible and should be driven with CMOS level inputs. Pin 4 provides operating voltage for the transmitter. VCC should be bypassed with a .01uF ceramic capacitor and filtered with a 4.7uF tantalum capacitor. Noise on the power supply will degrade transmitter noise performance.
Mechanical Drawing
0.30"
Figure 1: Mechanical Drawing of RCT-XXX-AS Figure 2: Suggested Pad Layout
Absolute Maximum Ratings
Parameter Power Supply and All Input Pins Storage Temperature Soldering Temperature (10sec)1 Min -0.3 -50 NA Max +15 100 350 Units VDC C C
NOTES 1) Hand Solder Only. The Transmitter is not suitable for IR reflow or hot air soldering.
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8/21/2003
RCT-XXX-AS
Low-Cost SAW-stabilized surface mount OOK RF transmitter
(c) 2001,2002,2003 All Rights Reserved
Detailed Electrical Specifications
Parameter (General) Operating Voltage Operating Current DATA=VCC Operating Current DATA=GND Frequency Accuracy Center Frequency Symbol Vcc Icc
Icc
Min 1.5 -----75 ---
Typ. 3.0 4.5 100 0 315.0 418.0 433.92
Max 12 ----+75 ---
Units Volts DC mA uA Khz MHz
Notes
@3V @3V @3V RCT-315-AS RCT-418-AS RCT-433-AS
TOLfc Fc
Output Power Baud Rate - NRZ
--DC
0 --4800
dBm BPS
@3V
Theory of Operation
OOK Modulation
OOK modulation is a binary form of amplitude modulation. When a logical 0 (data line low) is being sent, the transmitter is off, fully suppressing the carrier. In this state, the transmitter current is very low, less than 1mA. When a logical 1 is being sent, the carrier is fully on. In this state, the module current consumption is at its highest, about 4.5mA with a 3V power supply. OOK is the modulation method of choice for remote control applications where power consumption and cost are the primary factors. Because OOK transmitters draw no power when they transmit a 0, they exhibit significantly better power consumption than FSK transmitters. OOK data rate is limited by the start-up time of the oscillator. High-Q oscillators which have very stable center frequencies take longer to start-up than low-Q oscillators. The start-up time of the oscillator determines the maximum data rate that the transmitter can send. DESIGN HINT "Using the RCT-XXX-AS with a microcontroller UART": Data should be inverted when using the transmitter with a UART. The normal marking state of a UART is a logic 1, which will cause constant transmission. By inverting the data, the transmitter will be off in a marking state and on in a spacing state (logical 0), ensuring that the transmitter is on only when data is being sent. The output of the receiver would also need to be inverted to properly recover data.
SAW stabilized oscillator
The transmitter is basically a negative resistance LC oscillator whose center frequency is tightly controlled by a SAW resonator. SAW (Surface Acoustic Wave) resonators are fundamental frequency devices that resonate at frequencies much higher than crystals.
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8/21/2003
RCT-XXX-AS
Low-Cost SAW-stabilized surface mount OOK RF transmitter
(c) 2001,2002,2003 All Rights Reserved
The output of the oscillator is derived directly from the collector of the oscillator transistor. It is, therefore, very sensitive to VSWR. The module is designed to work with a 50 ohm load, which exhibits a VSWR of 1. The designer must ensure that the antenna exhibits no more than a VSWR of 2 to guarantee operation. This is particularly true for PCB trace antennas. If the module does not appear to have any output at the antenna port, it is likely that the antenna does not meet this requirement. TROUBLESHOOTING HINT: If the module appears to have no output at the antenna port, try the following: disconnect the antenna and put a 1000pF cap in series with a 51 ohm resistor to ground. This will ensure that the transmitter is properly loaded. Then look at the output with a scope and you should see the oscillator working. If it is working, the antenna is not properly tuned and that is the reason that the module is not working properly. If not, then check the power supply and data input for proper voltage levels.
Data Rate
The oscillator start-up time is on the order of 40uSec, which limits the maximum data rate to 4.8 kbit/sec. TROUBLESHOOTING HINT: If the module appears to have a good output, but your data rate is corrupted, that could be a sign that the start-up time of the oscillator is too long. The load on the antenna affects oscillator startup time. To determine the start-up time of the oscillator, use a 2 channel digital storage oscilloscope. Attach channel 1 to the data input and channel 2 to the antenna output (don't worry, it won't affect the antenna VSWR). Trigger the scope on a rising edge on channel 1. Now, toggle the data pin from low to high and capture the resulting waveform. You should see a square edge on channel 1 and the oscillator ring-up on channel 2. Measure the time between the rising edge on channel 1 and when the oscillator waveform is at its full voltage swing, and you have the start-up time. To determine if the antenna is the problem, remove it and place a 1000pF cap in series with a 51-ohm resistor to ground and repeat the test. If the start-up time is correct with the test load, the problem is the antenna.
Power Supply
The RCT-433-AS is designed to operate from a 1.5 -12V power supply. It is crucial that this power supply be very quiet. The power supply should be bypassed using a 0.01uF low-ESR ceramic capacitor and a 4.7uF ceramic capacitor. These capacitors should be placed as close to the power pins as possible.
Antenna Output
Pin 1 is a 50 ohm antenna output. It will support most antenna types, including printed antennas integrated directly onto the PCB. The performance of the different antennas varies. There are many good application notes available that describe external and PCB trace antennas. We maintain a list in the technical support section of our website. DESIGN HINT "Antenna traces": Any time a trace is longer than 1/8th the wavelength of the frequency it is carrying, it should be a 50 ohm micro strip. This ensures that a proper match is maintained between the transmitter output and the antenna.
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8/21/2003
RCT-XXX-AS
Low-Cost SAW-stabilized surface mount OOK RF transmitter
(c) 2001,2002,2003 All Rights Reserved
DESIGN HINT "Harmonic Filter": The impedance at the antenna power affects the VSWR, power output, and harmonic output of the transmitter. In most cases, the output of the transmitter may need a low-pass LC filter to reduce harmonic emissions. A good calculator is available on line at http://wwwusers.cs.york.ac.uk/~fisher/lcfilter/. Calculate the filter for a 3dB cut-off of the module's center frequency plus 10%. For example, the cut-off for a 433.92 MHz module would be about 470 MHz.
Contact Information
Address: Phone: Fax: www: support: sales: 207 Industrial Blvd Moore, Oklahoma 73160 405-794-7730 405-794-7477 www.radiotronix.com support@radiotronix.com sales@radiotronix.com
Technical Support Policy
Radiotronix is committed to providing our customers with world-class technical support. We offer several tools to support you during development. Our RApid Development (or RAD) kits are designed to make evaluation of our products simple and fast. They also serve as a known-good reference when debugging your designs. The knowledge base on our website answers the most commonly asked questions regarding our products. If you need to communicate with one of our technical support people, the best way is to post a message in the support forum. Our technical support staff monitor the forum continuously. By using the forum, you will get the fastest response to your technical support questions, and other customers will benefit from the information. Also, you may find that another customer has an answer for your question. You can also e-mail your question to support@radiotronix.com. The forum is given a higher priority than e-mail, but we realize that sometimes you just need direct contact with a support engineer. We also offer telephone technical support at no charge. Generally, the forum is checked more often and you are likely to get a faster response, but we do realize that sometimes nothing replaces a person-to-person conversation. When you call for phone support, your contact information will be recorded and the next available support engineer will call you back. This can take 24-48 hours, depending on the volume of support requests.
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8/21/2003

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