Transmission line emulation.

Isn't that what a real line is? I mean, continuous, not made of sections?

Cheers

I think the incuctors should be discrete, not coupled.

That's right. The telegraph equations assume separate LC elements, with constant L/C ratio and infitesimally small elements.

The OP never indicated if the original test had the proper L/C ratio (being square of the characteristic impedance).

That corresponds to the classical LCL sub-segment design of a transmission line/ delay line. Available via DigiKey, Mouser, etc.

The L was guestimated from the C and an assumed propagation velocity, I can't actually measure it. Then the Z0 is calculated, again, it can't be measured.

I know the usual method is separate LCR sections, but surely in reality the L is not discrete sections, neither is the C of course, but there's nothing I can do about that. In this particular case, the L and R can be readily made with a long air-cored helix of resistance wire and there are multiple Cs at taps.

Again, I know this isn't the usual method, and I suppose for most lines it would be more difficult to do it this way, but why would this be a worse approximation to reality than separate sections?

Cheers

You should do the other way round: The characteristic impedance of a coaxial cable depends on the ratio of outer and inner diameters, and on the dielectric constant of the insulation, assuming no ferromagnetic enhancments on the cable. You could get the dimensions, diameter of the inside of the outer conductor and diameter of the outside of the inner conductor.

The propagation velocity is by far more difficult to guess right, and it will be off for your simulator anyway.

A discrete simulation should be good up till a frequency which is a significant fraction of the low-pass corner frequency of an element.

You can handle the line attenuation by a suitable constant-impedance attenuator at either or both ends of the line.

If it's coax, with conductors and dielectrics, and you know the dimensions then you should be able to guesstimate C and L and R. And the coupling... which I'd guess to be small, unless there is some magnetic material involved.

George H.

Exactly. Due to the inverse logarithmic relation of the diameter ratio, the impedance cannot be very far from the customary 50 ohms.

What exactly are you trying to emulate ?

A several thousand kilometer 50/60 Hz EHT transmission line ?

Some HF coaxial lines ?

Some microwave PCB microstrip constructions ?

For all of these there are more appropriate calculation tools.

Apparently you have some impedance discontinuations in the form of open/shorted stubs etc, since a matched (flat) line should not require much analysis apart from some loss calculations. Or are you running a large diameters coaxial at such high frequencies that it is entering the circular waveguide mode ?

The hard part is the R calculation, since after all, the EM field propagates in the dielectric between the outside of the center connector inside of the shield. Thus the insulation material losses are material and frequency dependent. Even when air is used as dielectric, you have to consider skin dept of the conductor, which is also material and frequency dependent.

Commercial coaxial cables are available to at least 93 ohms.

In my vocabulary, 93 ohms is not very far from 50 ohms, SWR not even 2:1.

The cable has an extermely thin inner conductor. IBM liked to use it as network cable.

Tauno Voipio wrote in news:q9kqv3$s0k$ snipped-for-privacy@dont-email.me:

TV broadcast interconnect jumpers were 90 Ohm IIRC. That was at least what we were using at General Instrument on some links.

• Propagation velocity and Zo CAN be measured, maybe not as accurately as you might please, but try TDR open and short for calculating propagation velocity VS length. Zo from reflections seen in TDR measurements; start at 300 ohms max termination and go down

• Why in the heck use resistive wire, that is counter-productive; adds loss, adds noise, and just plain silly.

That's out by over 100 times.

Cheers

I'm emulating something with resistive loss, so I figured using resistance was the way to go. I did consider using dried Aardvark pelts, but soon dismissed that as plain silly.

Cheers

In which direction?

Please locate the nearest coaxial cable impedance formula, plug in the dimensions (for starters, you can guess epsilon-r and mu-r both at 1), and do the calculation.

Even vith a hair as center conductor in an oli barrel, you cannot get off 100 fold (500 milliohms or 5 kilo-ohms?).

Asking for help on a secret and unspecified system is kinda silly too.

Yes, 5k is impossible. But 500m is easy. You can try it with your nearest etc.

It's not RG6. It is coaxial.

Cheers