Chapter 6 ______________________________________________________ Processing Algorithms
VAISALA______________________________________________________________________ 253
6.9 Signal Generator Testing of the Algorithms
This section describes a variety of IF signal generator tests that can be used
to verify correctness of the RVP900 processing algorithms. These tests are
performed whenever new algorithms and/or major modes are added to the
processor. We have include a few of the test descriptions here so that they
can be used by customers who need to debug their systems, or who want
to better understand how they work. Additional tests for receiver
sensitivity and dynamic range can be found in Appendix C, Installation and
Test Procedures, on page 355.
6.9.1 Linear Ramp of Velocity with Range
Suppose that a continuous-wave IF waveform has an instantaneous
frequency f (t)in Hertz (cycles/sec). Consider a range bin located at time
τ
bin
within a set of pulses that are separated by τ
s
= 1/PRF. The phase
measured at that bin on the n
th
pulse will be the integral of the frequency
within that pulse starting from range zero (since the RVP900 is phase
locked to range zero):
If we assume that the input frequency is a linear Frequency Modulation
(FM) at the rate of M cycles/sec/sec on top of a base frequency T
o
, then:
which, remarkably, is independent of both T
o
and n. Thus, a linear FM
input signal produces a fixed (I,Q) phase difference from pulse-to-pulse at
any given range. The magnitude of the phase difference is proportional to
the range, and the slope is(M τ
s
) cycles for each second of delay in range.
For example, if the test signal generator is sweeping 100KHz every two
seconds, then the velocity observed at a range of 300 km at 250 Hz PRF
will be:
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