USER’S MANUAL__________________________________________________________________
74 __________________________________________________________________ M211322EN-D
The inverse correspondence between filter bandwidth and the 0 dB SNR
signal level leads to an interesting and useful property of wideband digital
receivers, they can operate over a dynamic range that is much greater than
the inherent SNR of their A/D converter would imply. If this particular
A/D chip were performing direct conversion at "base band," it would have
a dynamic range of only 79 dB. However, by utilizing the extra bandwidth
of the converter, the RVP900 is able to extend the dynamic range to
approximately 103 dB.
To understand this, begin with the 95 dB interval between the converter's
+8 dBm saturation level and the -87 dBm 0 dB SNR level at 1 MHz
bandwidth. Add to this:
- 4 dB for the statistical linearization that is performed on signals that
exceed the saturation level. The RVP900 can recover signal power
accurately, even when the A/D converter is driven beyond saturation.
Velocity data is also valid, but spectral width may be overestimated.
- 4 dB for usable dynamic range below the 0 dB SNR level. In practice,
a coherent signal at -4 dB SNR can easily be measured when 25 or
more pulses are used.
The overall dynamic range at 1 MHz bandwidth (approximately 1 µsec
transmit pulse) is 95+4+4 = 103 dB. For a 0.5 µsec pulse, the dynamic
range is reduced to 100 dB, but it increases to 106 dB for a 2.0 µsec pulse.
An actual calibration curve demonstrating this performance is shown in
Figure 19 on page 73, for which the RVP900 digital bandwidth was set to
0.53 MHz. An external signal generator, with steps of 1 dB, were used to
measure the compression and detection thresholds.
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