Chapter 6 ______________________________________________________ Processing Algorithms
VAISALA______________________________________________________________________ 255
Where the and are complex (I,Q) vectors from two receiver
channels A and B, and "<>" denotes expected value. This suggests that
some form of amplitude modulation (AM) of the input signal might be
helpful.
Suppose that the and samples are coming from two signal
generators installed on a dual-receiver system, and that only the B-Channel
is AM modulated so that:
Then the above estimator reduces to:
A simple way to create these data is to set the A-Channel siggen for 95%
AM depth, and use a sinusoidal modulation source of, perhaps, 400 Hz.
The reason for not choosing 100% depth is that we would loose the Burst
phase reference when the amplitude became smallest. The 26 dB reduction
in S
B
is a close enough approximation to zero in the above formula.
If we now observe the two receive channels with the RVP900 at a PRF of
800Hz, we will see the various RHOAB terms varying with range;
reaching a high value of 1.00, and a low value of 0.707. The plots will be
nearly stationary on the ascope screen because the PRF is almost precisely
twice the modulation rate (though they are free-running relative to each
other).
Adjusting the amplitude of either signal generator will not affect the p
terms, but it will have an interesting effect on SQI. If (T,Z,V,W) are being
computed from both channels combined, then the SQI is:
If we solve this equation for SQI=0.5 we find that the individual S
A
terms
must have twice the power of the individual S
B
terms. This can be checked
by adjusting either signal generator until the minimum plotted SQI is 0.5,
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