Vaisala RVP900 User Manual

Chapter 3 _______________________________________________________ Hardware Installation
VAISALA_______________________________________________________________________ 73
Trigger jitter can be improved in the case of coherent systems, by phase
locking the IFDR to the same reference clock used to generate the external
triggers (typically the COHO). The improved IF samples may provide as
much as 10 dB of additional sub-clutter visibility.
3.2.10 IF Bandwidth and Dynamic Range
The RVP900 performs best with a wide bandwidth IF input signal. A
wideband signal can be made free of phase distortions within the
(relatively narrow) matched passband of the received signal. The RVP900
uses an external analog anti-aliasing filter at each of its IF and Burst inputs.
These filters block frequencies that would otherwise alias into the matched
filter passband. The anti-alias filters have a nominal passband width of
14 MHz. There are options of providing anti-alias filters centered at
30 MHz, 57.5 MHz, and 60 MHz. Therefore, the nominal pass band width
for the filter centered at 60 MHz is from 53 MHz through 57 MHz. This is
the recommended operating bandwidth for the IF signal, although the
RVP900 still works successfully with lesser IF bandwidth.
At 72 MHz sampling rate, the quantization noise introduced by LSB
uncertainties is spread over an 36 MHz bandwidth. For an ideal 16-bit A/D
converter that saturates at +8 dBm, the effective quantization noise level
is:
If samples, from this ideal converter, are processed with a digital filter
having a bandwidth of 1 MHz, then an input signal at –103 dBm has a
signal-to-noise ratio of 0 dB. A narrower FIR passband (corresponding to
a longer transmitted pulse) decreases the quantization noise even further,
so that 0 dB SNR achieves at an even lower input power.
In practice, achieving the quantization noise level of an ideal convertor
becomes more difficult when increasing the number of bits. The 16-bit
Analog Devices AD9446 chip has been measured to have a wideband SNR
of 79 dB, which is 24 dB less than the 103 dB range expected for an ideal
converter. The above calculation for noise density thus becomes:
The RVP900 receiver power monitor, described in Section 5.5 Pr — Plot
Receiver Waveforms on page 163, shows a filtered power level of
approximately -87 dBm, when the FIR bandwidth is 1 MHz and the IFDR
inputs are terminated in 50.
+8dB m 20log
10
2
16
– 10log
10
36MHz
1MHz
------------------


– 103dB m a t 1MHz BW–=
+8dBm 79dB– 10log
10
36MHz
1MHz
------------------


– 87dBm at 1MHz BW–=

Vaisala RVP900 Specifications

General

Brand	Vaisala
Model	RVP900
Category	Receiver
Language	English