# Tag Info

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1Meg ohm. Voltage divider: output=input(R1/(R1+R2)) You've got the 1M of the meter being the R1 and R2 is the external series R. 1/1+1 or 0.5 of your input is the output voltage.

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Thinking about it some more, I think it'd be hard to get a large enough inductor to counteract the capacitance, but still keep it small enough to not degrade the USB signal, especially at USB 2.0 data rates (480 Mbit.) For long USB runs, if you can't alter the physical construction of the cable sufficiently, then active amplification is needed. And, yes, it ...

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The impedance of the data line is determined by capacitance between wires and inductance of the pair of wires. It's a simple formula and I've used it to make custom cables for high speed data links in circumstances where the wires and overall covering needed to be made from PTFE material to suit high temperature applications. The formula is Zo = ...

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Well, normal USB cables have these shielding to decrease line capacitive effect. My initial guess: Why don't you try to shield them at first to see if the capacitance is the result of the physical cabling. Also having a twisted pair in USB cable might help to decrease the capacitance in between lines, see USB cable construction.

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Q3: Termination is needed at the far end to stop reflections, especially for high data rates and long cables. The termination should be from the receiving end to ground.

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I understand you asking these sort of questions and I've tried to answer in the format that you presented the questions. Please forgive if I have misconstrued something. Q1 - cable length when transmitting high data rate: - (1) Impedance of the transmission line is independent of cable length (2) Source impedance is independent of cable length (3) ...

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The 50Ω standard is basically just convention. There are various stories about how 50Ω came to be chosen. The article Anindo linked is good. There is also The History of 50 Ω or There’s Nothing Magic About 50 Ohms. But the long and short of it is that it is a compromise between low attenuation and power handling. But it became the standard impedance when ...

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50 ohms is used because it is the impedance of the coaxial cable, except audiovisual applications is 75ohms, and so we avoid having to use an impedance matching circuit to connect the PCB to the outside.

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Since the current through R2 is zero, Vo = Vx. You can calculate Vo (and Vx) just using the known expression of a voltage divider: $$V_o = V_x = \frac{\frac{1}{sC}}{\frac{1}{sC} + R_1} V_i= \frac{1}{R_1Cs + 1} V_i.$$

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Drop your inputs with a resistive net (10K-ish) and a DC block, maybe a 104 cap, then once the signals are down, mix it all back out with an op amp like a TL072 with whatever -gain you want out of it, or you can use the opamp as a buffer if the attenuation is ok. The point is that the opamp will give you a really high impedance and a really low output ...

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