Transmission line emulation.

[Clive Arthur]

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to
ground. So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs
much better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is
that a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA
model with the same RLC. Is this a similar effect?

Cheers
--
Clive

 

[John Larkin]

On Fri, 19 Apr 2019 12:53:48 +0100, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to
ground. So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs
much better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is
that a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA
model with the same RLC. Is this a similar effect?

Cheers

Simulate a lossless line with just Ls and Cs... no Rs.

A discrete LC line tends to ring on a fast edge. The number of LC
sections grows as the square of Tr/Td, which gets ugly fast.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Clive Arthur]

On 19/04/2019 14:16, John Larkin wrote:

On Fri, 19 Apr 2019 12:53:48 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to
ground. So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs
much better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is
that a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA
model with the same RLC. Is this a similar effect?

Cheers

Simulate a lossless line with just Ls and Cs... no Rs.

A discrete LC line tends to ring on a fast edge. The number of LC
sections grows as the square of Tr/Td, which gets ugly fast.

It needs R, it's far from lossless and carries significant power too.
(In fact most people in this business don't bother with the Ls, but I
want a better emulation.)

So the question is, would a resistive inductor tapped with multiple Cs
be closer to a real line than multiple discrete RLC stages? I can't
test a real line.

Cheers
--
Clive

 

[John Larkin]

On Fri, 19 Apr 2019 17:20:14 +0100, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

On 19/04/2019 14:16, John Larkin wrote:
On Fri, 19 Apr 2019 12:53:48 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to
ground. So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs
much better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is
that a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA
model with the same RLC. Is this a similar effect?

Cheers

Simulate a lossless line with just Ls and Cs... no Rs.

A discrete LC line tends to ring on a fast edge. The number of LC
sections grows as the square of Tr/Td, which gets ugly fast.


It needs R, it's far from lossless and carries significant power too.
(In fact most people in this business don't bother with the Ls, but I
want a better emulation.)

So the question is, would a resistive inductor tapped with multiple Cs
be closer to a real line than multiple discrete RLC stages? I can't
test a real line.

Cheers

What's the physics that you'd like to emulate?

If you can't test a real line, the sim will be a guess.


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Tim Williams]

What kind of line are you emulating? What bandwidth, delay and impedance
tolerance?

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Clive Arthur" <cliveta@nowaytoday.co.uk> wrote in message
news:q9ccsf$jt3$1@dont-email.me...

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the L.
So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to ground.
So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs much
better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is that
a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA model
with the same RLC. Is this a similar effect?

Cheers
--
Clive

 

[Clive Arthur]

On 19/04/2019 19:13, Tim Williams wrote:

What kind of line are you emulating?  What bandwidth, delay and
impedance tolerance?

Tim

Unfortunately that's all NDA stuff.

But, assuming it's just a very long, very large coax, and I know its
total C and R and can guess the L, the question is, as a generality,
would you expect that a resistive inductor tapped with multiple Cs would
make a better model than multiple discrete RLC stages? I can't test a
real line.

Cheers
--
Clive

 

[George Herold]

On Friday, April 19, 2019 at 2:30:06 PM UTC-4, John Larkin wrote:

On Fri, 19 Apr 2019 17:20:14 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

On 19/04/2019 14:16, John Larkin wrote:
On Fri, 19 Apr 2019 12:53:48 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to
ground. So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs
much better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is
that a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA
model with the same RLC. Is this a similar effect?

Cheers

Simulate a lossless line with just Ls and Cs... no Rs.

A discrete LC line tends to ring on a fast edge. The number of LC
sections grows as the square of Tr/Td, which gets ugly fast.


It needs R, it's far from lossless and carries significant power too.
(In fact most people in this business don't bother with the Ls, but I
want a better emulation.)

So the question is, would a resistive inductor tapped with multiple Cs
be closer to a real line than multiple discrete RLC stages? I can't
test a real line.

Cheers

What's the physics that you'd like to emulate?

If you can't test a real line, the sim will be a guess.

Maybe the trans atlantic cable :^)

George H.

--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Tim Williams]

"Clive Arthur" <cliveta@nowaytoday.co.uk> wrote in message
news:q9d502$7e1$1@dont-email.me...

Unfortunately that's all NDA stuff.

But, assuming it's just a very long, very large coax,

Must be one odd customer to hold their coax so close to their chest.

Warning signs?...

and I know its total C and R and can guess the L, the question is, as a
generality, would you expect that a resistive inductor tapped with
multiple Cs would
make a better model than multiple discrete RLC stages? I can't test a
real line.

Better for what? You've given us no way to tell.

Tapped inductors are generally better, where "better" is measured in terms
of delay per stage.

Filters in general, analyze nicely when symmetry is taken advantage of. For
example, a pi filter should be divided into half-stages of CL and LC, and
those further into RC || CL + LC || CR, where the R's are the source and
load impedance.

The inductor doesn't need to be resistive, but if that's what happens to
give a closer result, so be it. It would seem more inconvenient to use an
inductor of specific loss, until you know how lossy it actually needs to be.

Note that lossy inductance doesn't give complementary lossy capacitance.
This may or may not be correct. In average coax, there's far more ESR than
EPC (equivalent parallel conductance), because typical dielectrics are much
better capacitors than copper an inductor.

If it's, say, ferro(electric|magnetic) loaded line, the equivalent case may
involve some combination.

(The ratio of parallel and series equivalent losses affects dispersion.)

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[Michael Terrell]

On Friday, April 19, 2019 at 2:48:54 PM UTC-4, George Herold wrote:

On Friday, April 19, 2019 at 2:30:06 PM UTC-4, John Larkin wrote:
On Fri, 19 Apr 2019 17:20:14 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

On 19/04/2019 14:16, John Larkin wrote:
On Fri, 19 Apr 2019 12:53:48 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to
ground. So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs
much better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is
that a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA
model with the same RLC. Is this a similar effect?

Cheers

Simulate a lossless line with just Ls and Cs... no Rs.

A discrete LC line tends to ring on a fast edge. The number of LC
sections grows as the square of Tr/Td, which gets ugly fast.


It needs R, it's far from lossless and carries significant power too.
(In fact most people in this business don't bother with the Ls, but I
want a better emulation.)

So the question is, would a resistive inductor tapped with multiple Cs
be closer to a real line than multiple discrete RLC stages? I can't
test a real line.

Cheers

What's the physics that you'd like to emulate?

If you can't test a real line, the sim will be a guess.

Maybe the trans atlantic cable :^)

How are you going to emulate the bidirectional amplifiers?

 

[Clive Arthur]

On 19/04/2019 20:43, Tim Williams wrote:

"Clive Arthur" <cliveta@nowaytoday.co.uk> wrote in message
news:q9d502$7e1$1@dont-email.me...

Unfortunately that's all NDA stuff.

But, assuming it's just a very long, very large coax,

Must be one odd customer to hold their coax so close to their chest.

Warning signs?...

No, it's just very special and very expensive for a specific purpose and
still under development.

and I know its total C and R and can guess the L, the question is, as
a generality, would you expect that a resistive inductor tapped with
multiple Cs would
make a better model than multiple discrete RLC stages?  I can't test a
real line.

Better for what?  You've given us no way to tell.

Better (lower) attenuation at higher frequencies.

If I make a lumped line model in LTspice and compare this with the LTRA
(lossy transmission line) model provided using a simple AC analysis,
after following each other nicely for a while, the lumped line response
goes south at an alarming rate while the LTRA flattens out.

I don't know why this is, and that's why I'm asking here, it's not my
specialism. Is the LTRA model faulty, or is a lumped model not that
representative?

My two physical test lines behave quite differently despite having the
same overall RLC, the 10 section lumped RLC is worse at HF than my long
resistive inductor with Cs on taps. Is the latter behaving more like
the LTRA model?

Tapped inductors are generally better, where "better" is measured in
terms of delay per stage.

For me, delay and phase don't matter, in that they're critical so are
compensated for Attenuation is the issue.

Filters in general, analyze nicely when symmetry is taken advantage of.
For example, a pi filter should be divided into half-stages of CL and
LC, and those further into RC || CL + LC || CR, where the R's are the
source and load impedance.

The inductor doesn't need to be resistive, but if that's what happens to
give a closer result, so be it.  It would seem more inconvenient to use
an inductor of specific loss, until you know how lossy it actually needs
to be.

I do know the total resistance of the line, and my long tapped inductor
is designed to have that resistance and also the total line inductance
as estimated.

Note that lossy inductance doesn't give complementary lossy capacitance.
This may or may not be correct.  In average coax, there's far more ESR
than EPC (equivalent parallel conductance), because typical dielectrics
are much better capacitors than copper an inductor.

There is some parallel conductance too, but at this stage I'm ignoring it.

If it's, say, ferro(electric|magnetic) loaded line, the equivalent case
may involve some combination.

(The ratio of parallel and series equivalent losses affects dispersion.)

Tim

Thanks
--
Clive

 

[Simon S Aysdie]

On Friday, April 19, 2019 at 11:45:28 AM UTC-7, Clive Arthur wrote:

On 19/04/2019 19:13, Tim Williams wrote:
What kind of line are you emulating?  What bandwidth, delay and
impedance tolerance?

Tim

Unfortunately that's all NDA stuff.

But, assuming it's just a very long, very large coax, and I know its
total C and R and can guess the L, the question is, as a generality,
would you expect that a resistive inductor tapped with multiple Cs would
make a better model than multiple discrete RLC stages? I can't test a
real line.

I don't really know. But I know that in all-pass delay network synthesis, a negative inductor will show up. And were that occurs, the negative inductor is resolved by a coupled inductor transformation.

But you're asking, perhaps, more about a low-pass type structure.

Do you recall with the Brune process (Brune cycle or one of the Darlington networks) where coupled inductors result? Maybe some intuition can be sourced there. The structure looks low-pass-ish. See Fig. 6 in:

https://www.adv-radio-sci.net/9/91/2011/ars-9-91-2011.pdf

 

[George Herold]

On Friday, April 19, 2019 at 4:19:00 PM UTC-4, Clive Arthur wrote:

On 19/04/2019 20:43, Tim Williams wrote:
"Clive Arthur" <cliveta@nowaytoday.co.uk> wrote in message
news:q9d502$7e1$1@dont-email.me...

Unfortunately that's all NDA stuff.

But, assuming it's just a very long, very large coax,

Must be one odd customer to hold their coax so close to their chest.

Warning signs?...

No, it's just very special and very expensive for a specific purpose and
still under development.

and I know its total C and R and can guess the L, the question is, as
a generality, would you expect that a resistive inductor tapped with
multiple Cs would
make a better model than multiple discrete RLC stages?  I can't test a
real line.

Better for what?  You've given us no way to tell.

Better (lower) attenuation at higher frequencies.

If I make a lumped line model in LTspice and compare this with the LTRA
(lossy transmission line) model provided using a simple AC analysis,
after following each other nicely for a while, the lumped line response
goes south at an alarming rate while the LTRA flattens out.

I don't know why this is, and that's why I'm asking here, it's not my
specialism. Is the LTRA model faulty, or is a lumped model not that
representative?

My two physical test lines behave quite differently despite having the
same overall RLC, the 10 section lumped RLC is worse at HF than my long
resistive inductor with Cs on taps. Is the latter behaving more like
the LTRA model?

Tapped inductors are generally better, where "better" is measured in
terms of delay per stage.

For me, delay and phase don't matter, in that they're critical so are
compensated for Attenuation is the issue.

Huh, I know nothing of what you do, but attenuation is about resistance.
(I guess you can have an antenna with radiation resistance.)

The difference between the lumped L and tapped L is that the tapped L
has more linkage/ coupling. Is that right?

So how much coupling is in the real cable?

George H.

Filters in general, analyze nicely when symmetry is taken advantage of.
For example, a pi filter should be divided into half-stages of CL and
LC, and those further into RC || CL + LC || CR, where the R's are the
source and load impedance.

The inductor doesn't need to be resistive, but if that's what happens to
give a closer result, so be it.  It would seem more inconvenient to use
an inductor of specific loss, until you know how lossy it actually needs
to be.

I do know the total resistance of the line, and my long tapped inductor
is designed to have that resistance and also the total line inductance
as estimated.

Note that lossy inductance doesn't give complementary lossy capacitance..
This may or may not be correct.  In average coax, there's far more ESR
than EPC (equivalent parallel conductance), because typical dielectrics
are much better capacitors than copper an inductor.

There is some parallel conductance too, but at this stage I'm ignoring it..
If it's, say, ferro(electric|magnetic) loaded line, the equivalent case
may involve some combination.

(The ratio of parallel and series equivalent losses affects dispersion.)

Tim

Thanks
--
Clive

 

[whit3rd]

On Friday, April 19, 2019 at 9:20:25 AM UTC-7, Clive Arthur wrote:

On 19/04/2019 14:16, John Larkin wrote:
On Fri, 19 Apr 2019 12:53:48 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line ...
It didn't perform very well,

So the question is, would a resistive inductor tapped with multiple Cs
be closer to a real line than multiple discrete RLC stages? I can't
test a real line.

There are ferrite beads you can string on a wire, and swage a tube around it...
to make a delay line with real delay (and hundreds of 'sections'). Or, two-hole
beads to make a differential (twinax style) line. How much delay do you
want, and with what signal bandwidth?

Heck, you can buy acoustic (reverb module) lines and couple into 'em with transformers.
Not gonna be a good electrical-resistance model, if you do it that way, but you
get lots of milliseconds for the dollar.

 

[whit3rd]

On Friday, April 19, 2019 at 11:45:28 AM UTC-7, Clive Arthur wrote:

would you expect that a resistive inductor tapped with multiple Cs would
make a better model than multiple discrete RLC stages?

NEVER gonna make that work. An inductor with taps is a MUTUAL
inductor, you need decoupled ones. Looks similar on a diagram,
but not at all the same.

 

[Tim Williams]

"Clive Arthur" <cliveta@nowaytoday.co.uk> wrote in message
news:q9daff$7tu$1@dont-email.me...

Better (lower) attenuation at higher frequencies.

So, reduce R towards zero?

Mind, in a simulation, that depends on the accuracy and integration method.
Accuracy is the various *TOL parameters.

LTSpice claims to have a hacked integration method, that gets losses closer
than original TRAP (which tends to underestimate). It also runs faster, but
has a number of... quirks consequential to that speed. GEAR tends to
overestimate losses, though to a much lesser degree, especially at higher
levels. Of course, it goes much slower at higher levels.

The more precise of a measurement you are trying to make, the more these
will matter. Loss is a subtractive element, so you need an extremely
precise simulation to model it correctly, when it's a small part of the
total.

The model needs to be that much more representative, as well.

If I make a lumped line model in LTspice and compare this with the LTRA
(lossy transmission line) model provided using a simple AC analysis, after
following each other nicely for a while, the lumped line response goes
south at an alarming rate while the LTRA flattens out.

I don't know why this is, and that's why I'm asking here, it's not my
specialism. Is the LTRA model faulty, or is a lumped model not that
representative?

"Goes south" when? At frequencies on the order of 1 / sqrt(L*C)?

I ask again, what delay to risetime ratio are you looking at? Because
that's exactly as important as JL noted!

My two physical test lines behave quite differently despite having the
same overall RLC, the 10 section lumped RLC is worse at HF than my long
resistive inductor with Cs on taps. Is the latter behaving more like the
LTRA model?

Doubt it: the transmission line models are propagating-wave hacks. They are
not built from RLC sections! They should be more accurate, around the
cutoff, than a lumped equivalent.

RTFM for more details? I don't know how exactly the LTRA is built. Finding
the equations used, would be the best reference.

I do know the total resistance of the line, and my long tapped inductor is
designed to have that resistance and also the total line inductance as
estimated.

Sure, but is that the same as the AC resistance? Is that distributed the
same as in the real article?

This seems like a lot of folly, like trying to use the wrong tool for the
job -- it sounds like a proper field solver would be more effective, and
that would get you the parameters of an incremental TL segment, including
correct AC resistance.

Assuming they've been kind enough to give you any mechanical information at
all, of course.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[John Larkin]

On Fri, 19 Apr 2019 19:45:19 +0100, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

On 19/04/2019 19:13, Tim Williams wrote:
What kind of line are you emulating?  What bandwidth, delay and
impedance tolerance?

Tim

Unfortunately that's all NDA stuff.

But, assuming it's just a very long, very large coax, and I know its
total C and R and can guess the L, the question is, as a generality,
would you expect that a resistive inductor tapped with multiple Cs would
make a better model than multiple discrete RLC stages? I can't test a
real line.

Cheers

If it's long enough, just Rs and Cs.


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Fri, 19 Apr 2019 11:48:50 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Friday, April 19, 2019 at 2:30:06 PM UTC-4, John Larkin wrote:
On Fri, 19 Apr 2019 17:20:14 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

On 19/04/2019 14:16, John Larkin wrote:
On Fri, 19 Apr 2019 12:53:48 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I wanted to make a physical device to emulate a long transmission line.
This particular line has lots of C, I know the R and can guestimate the
L. So I built a lumped line using T sections, 10 Rs, 10 Ls and 9 Cs to
ground. So far so standard.

It didn't perform very well, and I think part of the reason was the
impedance being too large - dominated by the first R - so limiting the
power into the line.

So I made another, but this time using 38 Cs and a long helix of
resistance wire wound on a plastic pipe to provide the R and L. It
measures quite close to the other in terms of R, L & C, but performs
much better.

I'm guessing that the reasons for this include the impedance issue, but
maybe also because the L is now one long tapped inductor, ie coupled and
no longer discrete. To my mind, that seems closer to a real line. Is
that a valid assumption?

In addition, simulating (different - we use these a lot) lumped models
using LTspice always shows worse performance than the provided LTRA
model with the same RLC. Is this a similar effect?

Cheers

Simulate a lossless line with just Ls and Cs... no Rs.

A discrete LC line tends to ring on a fast edge. The number of LC
sections grows as the square of Tr/Td, which gets ugly fast.


It needs R, it's far from lossless and carries significant power too.
(In fact most people in this business don't bother with the Ls, but I
want a better emulation.)

So the question is, would a resistive inductor tapped with multiple Cs
be closer to a real line than multiple discrete RLC stages? I can't
test a real line.

Cheers

What's the physics that you'd like to emulate?

If you can't test a real line, the sim will be a guess.

Maybe the trans atlantic cable :^)

George H.

They are all fiber now!


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[George Herold]

On Friday, April 19, 2019 at 7:53:28 PM UTC-4, John Larkin wrote:

On Fri, 19 Apr 2019 19:45:19 +0100, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

On 19/04/2019 19:13, Tim Williams wrote:
What kind of line are you emulating?  What bandwidth, delay and
impedance tolerance?

Tim

Unfortunately that's all NDA stuff.

But, assuming it's just a very long, very large coax, and I know its
total C and R and can guess the L, the question is, as a generality,
would you expect that a resistive inductor tapped with multiple Cs would
make a better model than multiple discrete RLC stages? I can't test a
real line.

Cheers

If it's long enough, just Rs and Cs.

Is that the trans atlantic cable..?
Heaviside figured out how to load it.
https://en.wikipedia.org/wiki/Telegrapher%27s_equations

George H.

--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Fri, 19 Apr 2019 17:27:19 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Friday, April 19, 2019 at 11:45:28 AM UTC-7, Clive Arthur wrote:

would you expect that a resistive inductor tapped with multiple Cs would
make a better model than multiple discrete RLC stages?

NEVER gonna make that work. An inductor with taps is a MUTUAL
inductor, you need decoupled ones. Looks similar on a diagram,
but not at all the same.

One good way to make a delay line is with t-coils.

Take a look at the delay line in the old Tektronix 545 scope. There
are manuals online.




--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[whit3rd]

On Friday, April 19, 2019 at 6:17:00 PM UTC-7, John Larkin wrote:

On Fri, 19 Apr 2019 17:27:19 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

On Friday, April 19, 2019 at 11:45:28 AM UTC-7, Clive Arthur wrote:

would you expect that a resistive inductor tapped with multiple Cs would
make a better model than multiple discrete RLC stages?

NEVER gonna make that work. An inductor with taps is a MUTUAL
inductor, you need decoupled ones.

One good way to make a delay line is with t-coils.

Yeah, but you have to orient them so the alternate ones don't couple, only
the adjacent pairs. Solenoids are a bad way to put together lumped-constant
delays, ferrite beads (toroidal magnet circuit, self-shielding) are easier to work
with when you're stacking a dozen or three. A t-coil is an inductor with A tap, not 'taps'.