The device will transmit a carrier wave on the ISM (~900 ...



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

[pic]

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

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