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
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
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
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.