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11. I/Q DIGITAL OUTPUT IN DETAILS FOR DEVELOPERS
1
GENERAL
The I/Q digital output of the AR-ALPHA represents the actual signal used after digital processing in
the receiver. The digital I/Q output interface streams I/Q data to the PC through USB2.0 isochronous
mode, with nearly 100Mbps.wide bandwidth.
A Windows XP device driver is provided free of charge for software developers, to allow them to
develop their own I/Q software, or to integrate the AR-ALPHA I/Q acquisition feature to their existing
software..
2
SIGNAL FLOW
In the AR-ALPHA circuitry, 10.7MHz of intermediate frequency (IF) is being sampled directly at
42.8MHz. No AGC is applied at the preceding stage in order to obtain a digital signal with wider
dynamic range.
The output of the ADC is digitally heterodyned to ZERO frequency to obtain an I/Q signal.
Thereafter, the I/Q signal is being filtered to limit the bandwidth and further down sampling for DSP
processing.
The USB2.0 is running at a top speed of approx. 100Mbps in isochroous mode in order to obtain a
wide bandwidth.
The I/Q output utilizes a CIC filter to simplify the circuit. The high frequency of the I/Q output signal
may contain aliasing noise, therefore a 500KHz low-pass filter is needed on the PC side.
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