RCT-433-ASB-R Radiotronix, RCT-433-ASB-R Datasheet - Page 8

• Manufacturer Part Number: RCT-433-ASB-R
• Description: RF Modules & Development Tools 433 MHz Transmitter High Temp
• Manufacturer: Radiotronix

Specifications of RCT-433-ASB-R

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: RCT-433-ASBR

RCT-433-ASBR DATASHEET
2.1.2. 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.
2.1.3. Power Supply
The RCT-433-ASBR 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.
2.1.4. 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.
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Design Hint (Antenna traces): Any time a trace is longer than 1/8
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.
Design Hint (Harmonic Filters): 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://www-
users.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.
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