Vaisala RVP900, User Manual, Page: 71 / 484

4.2.11 Configuring IF Gain Based on System Performance
When considering IF gain and system performance for a complete radar receiver, we assume
that an LNA/Mixer has already been selected that offers an appropriate balance between
price and noise figure. The total RF/IF gain between the antenna waveguide and the IFDR
must still be determined.
Assume that the thermal noise (
kT ) of the system is -114 dBm/MHz, and that the noise figure
of the LNA/Mixer is 2 dB. We want to bring this -112 dBm/MHz noise level up into the
working range of the RVP901 IFDR so that the received echoes can be optimally processed.
When selecting the required gain, we must make a trade-off between preserving the
receiver sensitivity that has been established by the LNA, and preserving the overall
dynamic range of the IFDR. This is the same trade-off that is made in traditional multi-stage
analog receiver systems that include a WDR (wide dynamic range) LOG receiver.
Figure 19 Trade-off Between Dynamic Range and Sensitivity
The solid red curve in the figure shows that the two variables interact in a symmetric
manner, so that any operating point (
x , y ) is always matched by a dual operating point at ( y ,
x ). To understand the construction of this plot, let:
Chapter 4 – RVP Hardware
69