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# Design Question

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#### bida19

##### New Member
Assume that I have a system with a nominal bandwidth of fc. The input to the system is a signal Vin
given by
Vin = Asin(Kfct)volts: (1)
The output of the system is connected to an envelope detector to detect the signal. The envelope detector
measures the amplitude of the signal, and if it is greater than a given threshold, then the signal is detected,
otherwise it is not. What must be the detection threshold for the detector if A = 5;K = 20? What must
it be if A = 3;K = 75?
What does this say about the notion of \bandwidth?" What do we mean by bandwidth? Does a system
have a bandwidth? Consider bandwidth from the perspective of someone who is trying to send a signal
through a \channel" of a particular \bandwidth" to a detection system. Lets double the amplitude of the
transmitted signal. Does this change the range of frequencies that can be detected? Discuss all of this in
no more than two pages.

#### Papabravo

##### Well-Known Member
Bandwidth is a way of describing the frequency dependant characteristics of a system. There is usually both an upper bound and a lower bound on the frequencies that will pass through a system. The bandwidth is defined as:
Code:
(upper bound) - (lower bound)
On either side of the bounds we speak of the stop band, a place where signals of those frequencies do not pass through the system. In between the bounds we speak of the pass band, where signals are allowed to pass through without appreciable loss of amplitude.

That said, your system has a non-linear threshold element. What you need to determine is if the threshold detector effects the frequency response of the system. I won't do the work for you, but this should stimulate the grey cells.

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