RCT-XXX-AS
Embedding the wireless future..
Low-Cost SAW-stabilized surface mount
OOK RF transmitter
Typical Applications
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Remote Keyless Entry (RKE)
Remote Lighting Controls
On-Site Paging
Asset Tracking
Wireless Alarm and Security Systems
Long Range RFID
Automated Resource Management
Features
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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 SAW-
stabilized 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 low-
cost 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.
-i-
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.
- ii -
RCT-XXX-AS
Low-Cost SAW-stabilized surface mount OOK RF transmitter
© 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
© 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
V
cc
I
cc
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
TOL
fc
F
c
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
© 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 start-
up 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 1/8
th
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
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