RCT-315-ASBR Radiotronix, RCT-315-ASBR Datasheet - Page 7

• Manufacturer Part Number: RCT-315-ASBR
• Description: RF Modules & Development Tools 314.3-315.7MHZ Transmitter Mod
• Manufacturer: Radiotronix

Specifications of RCT-315-ASBR

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

RCT-433-ASBR DATASHEET
2. Theory of Operation
2.1. 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-433-ASBR 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.
2.1.1. 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. 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.
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Chapter
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