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Passive linear circuits

I'm on a search for two types of passive, linear circuits. The first circuit is an amplitude filter. Let me explain. Most filter circuits are designed to filter out certain input signals according to their frequencies. Is there such a thing as an amplitude filter that filters signals according to their amplitude? The circuit that I'm thinking of would be a passive, linear circuit that would carry out this task. It would allow signals of a certain amplitude to pass, while rejecting all other signals. For instance, if the design was set to only allow signals with an amplitude of three to pass, it would allow a sinusoid that swings from -3 to +3, but would reject one that swings from -5 to +5. Is such a circuit possible? Does it already exist? The second circuit that I'm searching for is a circuit that will change the frequency of the input signal. It's basically a linear, passive version of a frequency multiplier, except that it could also be designed to decrease the frequency of the input. The output signal would have a frequency that has been increased, or decreased, by a given factor. This circuit would also be a passive, linear circuit. Does such a circuit already exist? I know that non-linear, active circuits have become quite popular, and it wouldn't surprise me if these two designs could be found in the realm of non-linear, active circuits. But what about as linear, passive circuits? The last thing I want is to try to design something that has already been proven to be impossible, or to redundantly design something that is already accessibly in existence. Therefore, any information, from those of you who have experience in this field, would be extremely helpful.

Reply to
Steven
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It is by definition not linear.

Also not linear.

John

Reply to
John Larkin

"Steven" The last thing I want is to try to design something that has

** You ask for non-linear behaviour from a linear circuit ?

Plus you want it to consume no power ?

Please return to your alternative universe immediately - Mr. Alien

..... Phil

Reply to
Phil Allison

As others have said, the response you require is NOT linear.

Consider a system with a transfer function H and input x and output y

y = H(x)

Say we know that the response to an input X1 is Y1 and the response to an input X2 is Y2. We now want to know the the output, Y, for an input, X, made up from inputs aX1 and bX2, where a and b are constants.

We want to know Y Y = H(X)

Y = H(aX1 + bX2)

If the system is linear then we can simply calculate the output for the two components separately and then add the outputs:

Y = H(aX1 + bX2) = aH(X1) + bH(X2)

Y = aY1 + bY2

For the response you require, this clearly isn't true so your system is by definition non linear.

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Reply to
Gareth

As you have probably learned by now, no such "passive, linear" circuits exist. You might want to Google for "AMSAT Leila" and "AMSAT Transponder" for some practical advice on the state of the art regarding active RF signal level control and frequency translation.

Also this link describes hardware.

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Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

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For if it prosper, none dare call it treason."

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Reply to
RFI-EMI-GUY

By definition something that outputs 3V for a 3V input and 0V for a 5V input isn't linear!

I'm coming into this quite late, though, so you've probably already been told this.

OK, are you sure this isn't a homework problem? Again, check the basic definition of "linear" -- there's no way to change frequencies in a linear system. This is usually the sort of thing discussed in the first handful of weeks of Signals & Systems 101 classes... I remember them giving you a bunch of input and output exercises where you had to determine whether the system was line and time-invariant... most are obvious, but a few are actually a bit tricky.

---Joel

Reply to
Joel Koltner

A PLL comes to mind. of course, this would have to be a case were only one signal is present at a time.. The PLL could lock with in coming signal to track as a reference signal into a summing circuit where the circuit would be balanced to generate a NULL output or very little output when the amplitude and phase are correct.

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Reply to
Jamie
:

Nope, that is not possible. One intrinsic property of linear circuits is superposition, which means the output corresponding to a linear summation of inputs is simply the linear summation of outputs corresponding to each component of the input summation. So for example your circuit wants the response to a 5V sine to be zero, but the response to a 2.5V sine to be a 2.5V sine, then linearity requires the response to 5V=2.5V + 2.5V to be 5V and not 0V.

Again, this is not possible, a violation of superposition, due to the fact that sin(A+B)=sin(A)cos(B)+ sin(B)cos(A) and not sin(A) + sin(B).

Reply to
Fred Bloggs

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