Signal Conditioning

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Is impedance matching needed?

I need to connect


a sensor (output impedance 50 Ohm)


coax BNC cable (2 m, 50 Ohm)


filter (1 M Ohm)


coax BNC cable (1 m, 50 Ohm)


SMB-100 cable (0.6m, 50 Ohm)


NI PCI5105 scope (50 Ohm or 1M Ohm)


I think impedance matching is needed, am I correct?

If yes, how to do it the easiest way? (I don't have electrical electronic background.)


Thank you in advance...

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Impedence matching is required if you are seeing a lot of reflections and the power is damped in the output signal. the easiest way to match any given impedence is by using a transformer. i could give you more details if you can post more information, application,....?

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Hi Ultrasound,


Thank you for your reply. I want to use my instruments for the measurement of dynamic acceleration and ultrasound waves. The frequency range is below 1.5 MHz, and the peak-to-peak of the signal is 10 V.


I have been searching more information about the impedance matching. The information from NI (link) suggests resistive matching, and many other, including you, suggested transformer. Could you please tell me how to determine the specification of the transformer? What other information is needed?


Many thanks!!

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You have not mentioned the Impedance of your Txdr, nevertheless the method for transformer impedance matching is given below:


1. Buy a ferrite core (air core is not suitable) you should be able to get it from RS and its very cheap too.


2. Use this formula to determine the number of primary and secondary turns you will need to match the Txdr:


Z1 / Z2 = (N1/N2)^2


z1= Impedance of the Txdr


z2= the target impedance


N1= primary turns which is to be connected to the Txdr


N2= secondary turns, to be connected to the scope.....


Due to the coiling of wires there is always some stray inductance that will be induced, which might damp the signal.. inorder to get a better SNR use a capacitance of the right value, the value can be determined by simple formula to overcome this.


Hope this helps..




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