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Summary:
The device will transmit an input signal on a carrier wave on the ISM (~900 MHz) band
with a power of at least 1 watt. The device consists of a transmitter (Atmel T5750), an RF
power amplifier (LINX BBA-519-A), a 900 MHz splatch antenna and associated
matching networks.
Transmitter: T5750
Frequency range: 868 – 928 MHz
Modulation: FSK, ASK
Transmit power output: 5.5 dBm
Available through digikey ($2.39)
Usage:
 operating frequency is determined by Crystal oscillator frequency x 64
 ASK or FSK modes are enabled
 Receives input from microcontroller or signal generator
 output is matched to 50 ohms
RF amp: BBA-519-A
General purpose broadband amp
max power in: 13 dBm
max power out: 33 dBm at 1 GHz
internally matched to 50 ohm input and output
Available through digikey ($15)
Antenna: ANT-916-SP
Frequency: 916 MHz (ISM)
Bandwidth: 10 MHz
Input impedance: 50 ohms.
Design and Operation
The T5705 and BBA-519 are both simple to implement. Minimal external circuitry is
needed. Frequency of the transmitter is selected with a 14.2969 MHz Crystal for
operation at 916 MHz. The circuit will provide a DC voltage through a jumper to the
FSK/ASK enable to determine the output mode. A test input from a function generator
will be the input for the transmitter. Since output of the transmitter and input of the power
amp are both matched to 50 ohms, no matching network is needed. Since the devices will
be placed close together, transmission line parameters are not critical. The maximum
output power of the power amp is greater than one watt. The antenna is also matched to
50 ohms but must be placed within .25" of the power amp output. The PCB under the
antenna must not contain a ground plane since the antenna is flat and mounted on the
circuit board.
Block Diagram
Alternatives:
Transceiver:
MC13190
complicated external circuitry
Frequency range: 2.4 GHz
Modulation: Amplitude modulation
Transmit power: 4.8 dBm
Available through Digikey ($5.05)
AT86RF211
Requires development kit for microcontroller programming, complicated external
circuitry
Frequency range: 400 – 900 MHz
Modulation: Frequency Shift Keying
Modes of operation: Transmit and receive
Transmit Power output: 10 dBm @ 916 MHz
Available through Digikey ($9.89)
Usage:
 Crystal oscillators provide frequency selection
 Internal microcontroller registers are programmed by a serial interface with
desired frequency range (dependant on supporting circuitry) and function.
Multiple frequency band usage requires switching of external circuits
 Receives serial data from external microcontroller (requires clock and enable
information). Test data can be provided with a signal generator and DC inputs
 internal microcontroller modulates data using FSK and broadcasts the signal with
no additional processing
RF amp: MRFIC0970R2
Package not suitable for prototyping, complicated supporting circuitry
900 MHz ISM, GSM band amplifier
max power in: 10 dBm
max power out: 35 dBm
internally matched to 50 ohm input and output