Revision 1.0
9
Copyright FlexRadio Systems, 2010-2011
20 dB pad to offset the gain of the preamp. The output of the preamp is fed to the QSD
down-mixer, with an output of I and Q baseband signals in the range of 0 to 24 kHz.
The QSD down-mixer is also supplied with a quadrature local oscillator signal which is
derived from the DDS. The DDS operates at twice the desired local oscillator signal,
passes though a 120 MHz low pass filter, into a Johnson Counter that both divides the
DDS frequency by two, as well as generates the two quadrature local oscillator signals.
In transmit, in a reverse manner, I-Q baseband signals from the CODEC in the baseband
range of 0 to 24 kHz are supplied to the QSE, along with the quadrature local oscillator
signals at the operating frequency, resulting in a direct QSE output on the final transmit
frequency, which is routed via the bandpass filters to either the transverter output
connector, or the input to the RFPA.
Baseband Processing
In the receive direction, output I and Q signals from the QSD are passed through a set of
OpAmps that have 18 dB of signal gain and 28 kHz low pass filters, then sent to the
CODEC for digitization and transmission to the host computer.
In transmit, analog I and Q signals output from the CODEC are filtered in a 26 kHz low
pass filter to remove wideband digital noise, then sent to the QSE for up-mixing.
Communications
In the receive configuration, digitized I and Q signals from the CODEC, representing the
received pass band, are transferred using the I2S protocol to the Streaming USB
controller. This controller then transfers this information via the USB protocol to the
host computer. Processed and demodulated audio is returned via the USB protocol to the
controller, then transferred to the CODEC via I2S protocol for conversion into analog
audio signals.
In transmit configuration, digitized microphone audio signals from the CODEC are
transferred using the I2S protocol to the Streaming USB controller. This controller then
transfers this information via the USB protocol to the host computer. Processed transmit
audio in a digital I and Q format is returned via the USB protocol to the controller, then
transferred to the CODEC via I2S protocol for conversion into analog baseband signals to
drive the QSE up-mixer.
In the BITE (Built In Test Equipment) configuration, digitized I and Q signals from the
CODEC, representing the received pass band, are transferred using the I2S protocol to
the Streaming USB controller. This controller then transfers this information via the
USB protocol to the host computer. Transmit test signals in a digital I and Q format are
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