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that is, the complex ratio of the averaged Cross Spectrum
GAs (k)
and
the
averaged
Autospectrum
GAA (k),
which define the gain and phase lag introduced by a linear
system excited with a(n) and responding with b(n). Similarly:
GsA (k)
Gss (k)
( =
Gss(k) )
G~B (k)
( =
G~
8
(k)
)
Gss (k)
In Dual Signal Enhancement mode, H
1
is the complex ratio of the Enhanced Spectra
Ge(k)
and
GA(k),
that is:
- - - = - -
There is no equivalent of H
2
in Signal Enhancement mode.
H
1
(k),
1 /H
1
(k),
H
2
(k),
and 1 /H
2
(k)
can be displayed in terms of:
Real part
Imaginary part
Magnitude
Phase
Nyquist plot
Nichols plot
13.2.12. Coherence
152
The Coherence expresses the amount of linear dependence between the signal a(n)
.
and b(n), that is the amount of the signal b(n) which can be related by a linear frequen-
cy response function to the signal a(n). It is defined as:
IGAs(k)l
2
'Yis(k) = - - - - -
GAA(k)
·
Gss(k)
It
is
a
real-valued
function
and
0
~
')'
2
AB
(k)
~
1.
The
displayed
function
,
is
'Yis(k)
for 0
~ k ~
800.
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