Medusa Features
Analog Acquisition Channels
The RA16PA and RA4PA standard Medusa Preampli
fi
ers acquire signals using 16-bit PCM
ADCs, which provide quality acquisition with minimal delay. The RA16SD and RA4SD use
Sigma-Delta ADCs, which have several characteristics that improve signal quality.
Oversampling of the signal before conversion removes aliasing of high frequency RF signals.
RA16SD testing indicates that signals greater than 150% of the Nyquist frequency are removed
from the signal. This allows users to acquire at lower sampling rates (6 kHz) without worry of
signi
fi
cant aliasing. In addition, each converter also has a two pole anti-aliasing
fi
lter (12 dB
per Octave) at 7.5 kHz. However, the sigma-delta ADC's have a
fi
xed group delay of 20 samples
(compared to four samples for the RA16PA). When using the RA16SD this group delay must be
taken into account when the data is displayed or acquired (for example, adding a SampDelay to
the RPvdsEx circuit).
Clip Warning Lights
When the input to a channel is greater than -3 db from the preampli
fi
er's maximum voltage
input, a light on the top of the ampli
fi
er is illuminated. The
fi
rst column of lights corresponds to
channels 1-8 and the second column corresponds to channels 9-16. The clip warning light
indicator can be turned off by
fl
ipping a switch on the end of the ampli
fi
er.
Power Light
The power light is in the top corner of the ampli
fi
er. It is illuminated when the device is on. It
fl
ashes quickly if the battery is low. It
fl
ashes slowly while the battery is charging. Note: The
fl
ashing LED indicator is only available when the ampli
fi
er is powered on and connected to a
powered base station.
RA16PA/RA4PA Medusa PreAmps | 5
