Vaisala RVP900, User Manual

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The IF output from the linear amplifier is applied to a pair of mixers that produce
I
and
Q
.
The mixer pair must have very symmetric phase and gain characteristics. Each mixer must
be supplied with an accurate 0° and 90° version of the
COHO
. The latter is usually obtained
by sampling a portion of the transmitted pulse, and then phase locking a COHO that
continues to "ring" afterward. Phase locked COHO of this sort can be troublesome. They
often fail to lock properly, drift with age, and fail to maintain coherence over the full
unambiguous range.
The transmit burst that locks the COHO is also used by the AFC loop. The AFC relies on a FM
discriminator and low-pass filter to produce a correction voltage that maintains a constant
difference between the magnetron frequency and the reference STALO frequency. The AFC
circuit is often troublesome to set and maintain. Also, since it operates continuously, small
phase errors are continually being introduced within each coherent processing interval.
RVP Digital Receiver - Magnetron
For the RVP900 digital receiver, the old parts that remain are the microwave STALO
oscillator and the mixer that produces the transmit burst.
The burst pulse and the analog IF waveform are cabled directly into the IFDR on SMA coax
cables. These cables are the complete interface to the radar's internal signals. No other
connections are required in the receiver cabinet.
3.1.5.1 RVP900 Example Configuration for Magnetron
The following example shows a basic magnetron system that can perform DFT processing in
4200 range bins with advanced algorithms such as random phase second trip echo filtering
and recovery.
RVP900 User Guide M211322EN-J
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