Vaisala RVP900 - Magnetron Receiver Example; Figure 7 Analog Vs Digital Receiver for Magnetron Systems

3.1.5 Magnetron Receiver Example
Figure 7 Analog vs Digital Receiver for Magnetron Systems
Analog Receiver - Magnetron
In a typical magnetron system analog receiver, the received RF signal from the LNA is first
mixed with the STALO (RF-IF). The resulting IF signal is applied to one of several band pass
filters that match the width of the transmitted pulse. The filter selection is usually done with
relays. The narrow band waveform is then split. Half is applied to a logarithmic amplifier
(LOG), having a dynamic range of 80 dB to 100 dB, from which a calibrated measurement of
signal power can be obtained. The log amplifier is required, because it is almost impossible
to build a linear
amplifier with the required dynamic range.
Phase distortion within the log
amplifier renders it unsuitable for making Doppler
measurements. A separate linear channel is required. The linear
amplifier is fed from the
other half of the band pass filter split. It may be preceded by a gain control circuit (IAGC),
which adjusts the instantaneous signal strength to fall within the limited dynamic range of
the linear
amplifier. The amplitude and phase characteristics of the IAGC attenuator must be
calibrated so that the I and Q samples can be corrected during processing.
Chapter 3 – Functional Description
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