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Ewave's RF modems were designed to function and survive in the harshest electrical environments. To achieve this we developed a proprietary hybrid data engine combining the best features of analog and digital modulation schemes.

A TRUE ANALOG AND DIGITAL HYBRID DESIGN

At the front end, we start with digital data. One DSP processes the data, and generates an analog wave form with a high speed Digital to Analog Converter (DAC). The wave form is further enhanced with a Low Noise Analog Filter (LNAF) and shaping network. The signal is then fed directly into the Voltage Controlled Oscillator (VCO) of the radio's transceiver for direct modulation at 900 MHz. Our DAC and LNAF provide a signal to the VCO that is free of high frequency components, and custom tailored for the characteristics of the 900 MHz transceiver.

Custom tailoring of a modulated signal is commonly referred to as pre-distortion compensation. This is a feature usually only found in RF modems costing two or three times as much as ours. Using pre-distortion compensation has many benefits. It allows greater spectrum efficiency, providing higher data rates for a given bandwidth, or spectrum usage. It also makes the job of the receiver and demodulation engine easier. And finally it provides better interference immunity.

Interference immunity is crucial in most real world environments where anything from poorly shielded computers to EMI spikes from AC compressors or lighting strikes may interfere with an RF Modem's data link.

On the demodulating side, the 900 MHz radio signal is detected with a highly sensitive dual conversion super heterodyne receiver. The recovered analog signal from the receiver is first enhanced and processed with a second LNAF. Following this an active analog circuit bit slices the signal. It is then fed to the second DSP for demodulation. The second DSP performs the clock recovery and converts the signal back into digital data.

DUAL-DSPs: TWO HEADS ARE BETTER THAN ONE

Multitasking is a way to share a single processor (or DSP) for multiple tasks, thus reducing costs. Unfortunately, in real-time DSP applications the unpredictable nature of preemptive task switching produces timing variations which translate to "jitter" in analog signals. "Jitter", in turn, makes a signal more difficult to decode and more susceptible to interference.

Ewave has carefully partitioned its modem core such that modem tasks can be mapped onto dual DSP chips executing in parallel. This DualDSP architecture minimizes timing jitter and maximizes performance by devoting two DSPs to critical timing functions.

Furthermore, the pre-distortion compensation and the analog processing from the LNAF makes the job of the demodulation-DSP even easier. In addition to demodulating the data, the second DSP performs all of the functions traditionally done by a supervisory microcontroller: It communicates directly with the outside world via a hardware USART serial port, manages the data FIFO's, generates and checks the data packet's CRCs, and processes all the user's modem commands.

ALL THE ''D-S-P'' IN THE WORLD CAN'T MAKE UP FOR A LOUSY TRANSCEIVER

From the start we knew that the use of a quality transceiver would be the key to performance. With our modular design, the transceiver is a separate circuit board housed in its own shielded case. It uses a dual programmable Phase Locked Loop (PLL), which allows selection of up to 40 unique RF channels. The transceiver is a true full duplex design with RF transmit and receive occurring simultaneously. Like all high quality transceivers, there are many separate tuning adjustments.

PERFORMANCE IS ASSURED BY THOROUGH CALIBRATION AND BURN-IN

All Ewave Radio Modems go through our extensive calibration, test and alignment procedure. The transceivers are adjusted and then put through an extended test and burn in cycle. After the burn in period all parameters are tested again to be in conformance. If any measurement is not within our tight factory specification, the unit is readjusted and then cycled through the Burn-In and Test procedure again.

 

 

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