yesWhat if I put a series 10k resistor on it's output (center lead of the coaxial)?
Will it increase the impedance seen by external devices connected to it, to about 10k?
A resistor has two legs.What if I put a series 10k resistor on it's output (center lead of the coaxial)?
1st case: 50 ohm generator connected to a filterA resistor has two legs.
Your description only tells where you connected one leg .. but what did you do with the other leg?
And if you say "increase" ... this means there are two situations: one with the resistor, one without the resistor. You should give clear informations for both situations..
Where exactly are the "external devices" connected?
As so often... I tiny effort to take a pencil and a paper .. would be so helpful.
Klaus
Your previous question was clear enough, the answer has not changed: yes, the filter will "see" 10kOhm source impedance (10 kOhm + 50 Ohm in series)Will the input of the filter "see" a 10k input impedance?
you surely have more HF experience than me ... so usually I rely on your informations.Your previous question was clear enough, the answer has not changed: yes, the filter will "see" 10kOhm source impedance (10 kOhm + 50 Ohm in series)
This is true if both sides of the cable are matched to the cable impedance. In any case the OP asks for the impedance at filter side that is on the right side of the coax in your simulation, not on the left side where you placed the measurement probe. In the point you measure is correct to see 10k (as per your simulation) since the 50 ohm termination are transferred to the left side (reflection is present but negligible). The 10k impedance, instead, is not transferred to the right side.If the cable is terminated with the same impedance (50 or 75) The cable input appears as Zo = sqrt(L/C) as it gets no reflection.
I disagree.This is true if both sides of the cable are matched to the cable impedance. In any case the OP asks for the impedance at filter side that is on the right side of the coax in your simulation, not on the left side where you placed the measurement probe. In the point you measure is correct to see 10k (as per your simulation) since the 50 ohm termination are transferred to the left side (reflection is present but negligible). The 10k impedance, instead, is not transferred to the right side.
But he does not want to make a cable filter as you suggest. I said the load should be matched to the cable.From the equation of the transmission lines:
Zin = Zo*[(ZL+jZo*tg(beta*length)/(Zo+jZL*tg(beta*length)]
as you can see Zin becomes independent from the length of the cable only if ZL = Zo. Looking into the cable from the termination resistor we have to set ZL = 10k, so the impedance will vary with the length of the cable than at least will not be a constant 10k
As far as I've understood the question is what's the impedance seen by the filter; so we are interested to S22 (right side) and not to S11 (left side). If the the cable is terminated onto Zo, then S11 will be Zo. But we are interested in S22 where the termination on the other side of the cable is 10k. This means the load doesn't match the impedance of the cable, this means the impedance seen by the filter will not be 10k.But he does not want to make a cable filter as you suggest. I said the load should be matched to the cable.
Your previous objection about the source side affecting cable s11 is not valid.
Without 50 ohm termination near the 10 k resistor, you still see constant impedance into the cable as long as it has correct source termination. There are many reasons to implement both side termination for high performance RF and pulse transmission. Source side termination with high impedance load (Zload >> Z0) is however a valid scheme and has the advantage of receiving full generator voltage at load side.Looking into the cable from the termination resistor we have to set ZL = 10k, so the impedance will vary with the length of the cable than at least will not be a constant 10k
This is correct and corresponds to the connection "best case" of my post #6. The post #9, instead, refers to the opposite situation: "worst case". The problem is the transmission line between 10k and load.All I'm saying is if the cable is classic transmission theory. If the cable length is more than 10% wavelength one should match both ends and then transform the impedance on the output after this is correct if it is 10k.
The best case is the coax cable connected to the generator, then the 10k connected as close as possible to the filter.
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