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Fred Marshall
Guest
Fri Sep 23, 2011 8:00 pm
On 9/22/2011 7:02 PM, Bret Cahill wrote:
Quote:
Phase sensitive rectification.
Oh cripes and here I thought we were talking about adaptive filters.
But, I've noticed you mentioned matched filters along the way .. I
wasn't "getting it".
I wouldn't generally associate the two directly. Maybe a good Master's
thesis topic:
"The Relationship Between Adaptive Filters and Matched Filters"
But, somehow I think the answer is trivial .. according to my notion of
what those two things are:
- A Matched Filter is one that is matched to a KNOWN signal and outputs
the best SNR in the presence of white Gaussian noise.
- An Adaptive Filter is one that attempts to either remove noise (by
some definition) in the form of an ANC or ALE - one with a noise
reference and one without in their simplest forms. AND is capable of
changing in dynamic conditions of signal and noise.
I suppose if the signal is stable and the noise is white Gaussian then
an ALE may tend to the matched filter. But I don't' think I know that
for sure. And, an ANC will simply shut off and not do anything with
that kind of noise.
But "Phase Senssitive Rectification"? Where did that come from in this
context?
Fred
Bret Cahill
Guest
Sat Sep 24, 2011 2:31 am
The noise free reference,
Vm(t) + L1(di/dt)
for filtering the circuit,
Ground -- Vs(t) -- L1 -- L -- Vn(t) -- Ground
is used to determine the unknown inductance L,
Integral [Vm(t) * (Vm(t) + L1(di/dt))] / Integral [(di/dt) * (Vm(t) +
L1(di/dt))] => L
Quote:
Phase sensitive rectification.
Oh cripes and here I thought we were talking about adaptive filters.
Well?
Could any adaptive filter be made to work with the reference above?
Quote:
But, I've noticed you mentioned matched filters along the way .. I
wasn't "getting it".
I wouldn't generally associate the two directly. Maybe a good Master's
thesis topic:
"The Relationship Between Adaptive Filters and Matched Filters"
What about,
"Various Categorizations of Reference Based Filters"
Quote:
But, somehow I think the answer is trivial .. according to my notion of
what those two things are:
- A Matched Filter is one that is matched to a KNOWN signal and outputs
the best SNR in the presence of white Gaussian noise.
Try match filtering a noisy signal using the reference above, Vm(t) +
L1(di/dt) to determine L and compare it with PSR.
Try both filters using the same signal, same noise and the same
reference.
You can do everything on Excel.
To save time construct the reference in the frequency domain.
Quote:
- An Adaptive Filter is one that attempts to either remove noise (by
some definition) in the form of an ANC or ALE - one with a noise
reference and one without in their simplest forms. AND is capable of
changing in dynamic conditions of signal and noise.
I suppose if the signal is stable and the noise is white Gaussian then
an ALE may tend to the matched filter. But I don't' think I know that
for sure. And, an ANC will simply shut off and not do anything with
that kind of noise.
But "Phase Senssitive Rectification"? Where did that come from in this
context?
The question is if an accurate determination of L could be
accomplished using another reference with _any_ filter.
So far the answer seems to be "no."
Bret Cahill
Bret Cahill
Guest
Sat Sep 24, 2011 3:30 am
Quote:
So there are more than two nodes! I need a picture.
See the three "---" lines between Vs(t) and L1 and L and Vn(t)?
Ground -- Vs(t) --- L1 --- L --- Vn(t) -- Ground
? ? ?
Each one is generally at a different voltage.
. . .
If Vn(t) is significant and in the same band as Vs(t) then the noise
from Vn(t) can be filtered by calculating Vs(t) as a noise free
reference:
Vs(t) = Vm(t) + L1(di/dt) = reference
For phase sensitive rectification,
Integral [Vm(t) * (Vm(t) + L1(di/dt))] / Integral [(di/dt) * (Vm(t) +
L1(di/dt))] => L
How do you measure or compute di/dt?
Analog or digital?
Either way works.
Is there any reason to discuss something that has already been
invented?
Do you have any comments or questions on the reference,
Vm(t) + L1(di/dt)
for filtering the circuit,
Ground -- Vs(t) -- L1 -- L -- Vn(t) -- Ground
OK. So Vs(t) and Vn(t) are voltage generators with one end grounded.
Presumably, Vs(t) can have a very high SNR.
Between 3 - 20.
Quote:
Moreover, there are four
nodes, and L and L! form an inductive voltage divider. Why is noise a
problem? Are the inductances very small?
Small compared to what?
In this case L = ~ 4 L1
Quote:
Why not simply short out Vn(t)?
Supposing that isn't possible?
Quote:
to determine the unknown inductance L,
Integral [Vm(t) * (Vm(t) + L1(di/dt))] / Integral [(di/dt) * (Vm(t) +
L1(di/dt))] => L
There is no need to differentiate. The ratio of the voltages across the
inductors is the ratio of the inductances.
Supposing the voltage across L1 is unknown or very expensive and/or
inaccurate?
Bret Cahill
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