Talk:Transmission line/Archive 2

Archive 1

Archive 2

Merging Communications cable

Although it uses the more common name, Communications cable is presenting the same subject as Transmission line#Practical types of electrical transmission line and its children. I would suppose that if Communication Cable is turned into a referential list of types of Comms Cables, then it would be useful to have. However, at the moment its existence seems surplus. Your thoughts? Foxhill 07:05, 20 November 2006 (UTC)

Since Communications cable right now redirects to Transmission line, I think it would be a good idea to do as you propose: to have Communications cable mainly as a referential list, and to keep the mathematical stuff on Transmission line. Then Transmission line can be kept scientific, and Communications cable can contain commercial aspects of cable. Note also that there are a lot of aspects on Communications cable that has nothing to do with physics. For example dimension standars, connectors, environmental issues, etc. --HelgeStenstrom 12:52, 31 January 2007 (UTC)

The article is very long and I would be happy to put the signal transmission stuff into a separate article. There are thound and 1 article about communication, but they make the topic look unnecessary complicated. Arnero 16:57, 25 February 2007 (UTC)

Typo or Contradiction ?

Transmission Line page has a confusing aspect. See the following two excerpts within quotes.

"Transmission Line vs Wire ...A common rule of thumb (justified in the input impedance section) is that the cable or wire should be treated as a transmission line if the length is greater than 1/100 of the wavelength.

Input impedance of a transmission line ...This occurs when either the length of the transmission line is at least 100 times smaller than the wavelength.... The physical significance of this is that the transmission line can be ignored (i.e. treated as a wire) in either case."

To me, "at least 100 times smaller" in the second excerpt sounds like the length of the transmission line is *less* than 1/100 of the wavelength. But the first excerpt says "greater than 1/100". Which is correct? 75moore 21:35, 25 May 2007 (UTC)

The first one says that the cable is a transmission line if it's longer than 1/100 of a wavelength. The second one says that the cable is not a transmission line if it's shorter than 1/100 of a wavelength. Sorry about the double negative, but the two statements agree with each other. --Heron 14:11, 26 May 2007 (UTC)

I've just read less than 1/10 of a wavelength one place, and less than a wavelength (1/1) in one or possibly two places, fairly near the 2.98.205.195 (talk) 05:30, 14 March 2013 (UTC)start, at a quick glance thru the first 10% of the article only. And found this page. That's 3 possible Factors. 05:27, 14 March 2013 (UTC)

Merge with Transmission medium: absolutely not

Whoever suggested this has not given a signed proposal, but there is no reason to merge these articles. 'Transmission medium' is a scientific topic in physics which deals with any kind of waves transmitting through any medium and has has very diverse applications in many brances of science and technology, not just the narrow application of a transmission line in telecommunications. Rexparry sydney 02:46, 10 August 2007 (UTC)

Merge with Single-circuit transmission line

The single-circuit transmission line article does not present sufficient information to stand on its own. It should be merged here. Neelix (talk) 20:26, 22 August 2009 (UTC)

Nah, this article is aimed at telecomms (although its principles apply to power transmission as well). You want electric power transmission. The article also has a sister, double-circuit transmission line and they would like to go on a double date together if they are going out anywhere. SpinningSpark 20:57, 22 August 2009 (UTC)

If it is to continue to exist, this article needs to be improved. Spinningspark says it is about communications, but it looks to me as if it is about electric power transmission. Who ever heard of a three-phase communications transmission line? --Jc3s5h (talk) 13:51, 23 August 2009 (UTC)

Clarification. By "this article" I meant the article here transmission line which is indeed slanted to telecomms and is inappropriate for single-circuit transmission line or double-circuit transmission line to be merged into. I am suggesting as a target electric power transmission which is much more suitable. I should have known it was a mistake to try humour on Wikipedia, there's always someone who doesn't understand. Both articles together could be reduced to a few short sentences: something like "pylons commonly carry two circuits" captures the essence of it. SpinningSpark 14:36, 23 August 2009 (UTC)

and waveguides?

I reckon this page may be spreading the definition of transmission line a bit far. Transmission lines are sometimes regarded as waveguides, but waveguides aren't usually described as transmissions lines (lines possibly). The IEEE Standard Dictionary of Electrical and Electronics Terms 6th Ed. has:

"transmission line (1) (A) (data transmission) (signal transmission system) The conductive connections between system elements which carry signal power. A waveguide consisting of two or more conductors [my italics] (B)(data transmision)(electric power) [...etc....]. (C)(data transmission) (electromagnetic wave guidance) A system of material boundaries or structures for guiding electromagnetic waves, in the TEM (transverse electromagnetic) mode [my italics]. Commonly a two-wire or coaxial system of conductors. (2)[...etc....] (3)(waveguide) [...etc....] in the TEM mode [my italics] [...etc....]"

(Sorry that was a bit long). I'm loathe to agree with this publication (it's a bit like finding myself in agreement with Mrs Thatcher), but on this occasion it suits my purpose - so can we lose the waveguides? --catslash (talk) 21:26, 11 November 2009 (UTC)

I think we have to face the fact that many authors do not go along with that definition, examples [1][2][3][4][5]. It might be fair to say that possibly most authors include only pairs of conductors as transmission lines, but even that statement immediately runs into a problem with acoustic transmission lines, a widely used concept in acoustics which are more often than not of the hollow waveguide type, and yet the analysis in acoustics will often proceed by analogy with the electrical transmission line theory. Limiting the scope to only those forms typically included in an electrical analysis textbook (TEM) would suggest a disambiguated title of transmission line (electrical) leaving this title free for a more general discussion. SpinningSpark 10:11, 2 July 2010 (UTC)

You have anticipated my next objection: acoustic transmission lines. These have as section in the body of the article, but it consists of little more than a link to acoustic transmission line, and so could be moved to a hatnote. Incidentally, there is also a waveguide (acoustics) page. As there is no contention for the transmission line title, and as electric transmission line is probably the most common meaning, a dab page or an (electric) qualifier seems unnecessary. The only other common meaning I can think of is specifically electric power transmission lines, but there does not appear to be a page devoted to just the lines themselves overhead power lines. --catslash (talk) 16:00, 2 July 2010 (UTC)

Proposal: Correcting Language in the section "The four terminal model"

In this section there is the statement "Ensuring the source impedance matches Z0 will maximize power transfer from the source to the transmission line". It is correct to say that if the source impedance is fixed, that matching the load (or the transmission line impedance) maximizes the power transferred to the load, but the converse is not true. If the load or input impedance of the transmission line is fixed and the source is a voltage source with a series impedance, then minimizing the source impedance maximizes the power transfer. If the source is a current source with a shunt impedance, then maximizing the source impedance will maximize the power transferred to the load. One reason to match the source to a fixed impedance transmission line is to help control reflections generated at the load end of the transmission line. This is often seen in printed circuit boards where there is one source and one load and the load is high impedance. I think the entire sentence should be removed. Constant314 (talk) 01:03, 5 October 2010 (UTC)

It depends what parameter of the source is held constant as the impedance is varied. If you hold constant the available power (that is, you vary the source impedance by putting a transformer on the source), then the statement is true. However, I expect most readers would assume that the e.m.f. is held constant, and so I have deleted the sentence. --catslash (talk) 09:12, 5 October 2010 (UTC)

Solutions of the Telegrapher's Equations as Circuit Components

Is this standard stuff? I've never heard of it before. Also, why would one want to represent a transmission line by an active circuit? --catslash (talk) 18:18, 18 October 2010 (UTC)

Regarding the question “why”

• 1. You can insert it into your SPICE circuit simulator for robust simulation of the transmission line, its load, its source and all the other circuitry including equalizers, filters, pads, amplifiers and other signal conditioning. It also lets you readily simulate such things as multiple bridge taps, gauge changes, splits, and corroded splices. You can simulate complex structures such as customer wiring which might have bridge taps with bridge taps, on-hook telephones, off- hook telephones, etc. If you can draw it as a circuit, then you can simulate it with SPICE. Check out the link about SPICE simulation for more details.

http://www.eetimes.com/design/microwave-rf-design/4200760/SPICE-Simulation-of-Transmission-Lines-by-the-Telegrapher-s-Method-Part-1-of-3-

• 2. Thanks to Linear Technology Corporation, SPICE is available to almost every one with a very general and free license at

http://www.linear.com/designtools/software/ltspice.jsp

• 3. This is subjective, but I find this diagram to be highly intuitive. If the load side is open, it is obvious that the pulse voltage doubles and is reflected. If the load is shorted, the pulse current doubles and is reflected. If the load is matched, then there is no reflection. For a sanity check, assume that the line is lossless but has delay (T = pure delay) and then try various combinations of impedance at each end (infinite, matched, and zero) and verify that you get the expected behavior. Constant314 (talk) 13:25, 19 October 2010 (UTC)

Regarding the question: “Is this standard stuff?”

• The solutions to the Telegrapher's Equation are, of course, standard stuff.
• Representing the transmission line as a two-port is also standard stuff.
• Using the solutions of the Telegrapher’s equations to derive the two-port parameters is standard stuff.
• Using circuits to implement equations is standard stuff.
• The pararmeters of any of the standard two-ports can be derived from this circiut.Constant314 (talk) 23:23, 19 October 2010 (UTC)

But, is this circuit new? The mathematical equations that the circuit implies have been around for decades. So, is this standard stuff? In my opinion, yes it is because it translates precisely to standard stuff (the Telegrapher’s equations). But representing a transmission line as this circuit instead of a list of equations may be new. Which is to say, I haven’t seen this particular circuit anywhere, although I recall seeing crude equivalent circuits buried in the back of very old (from the 90’s or older) SPICE manuals. Constant314 (talk) 15:28, 19 October 2010 (UTC) Constant314 (talk) 15:32, 19 October 2010 (UTC)

Constant314 (talk) 20:03, 19 October 2010 (UTC)

For use in circuit solvers that don't support transmission lines is a pretty good why, and equivalent circuits (in general) are certainly standard stuff. The 2 in the version on the telegrapher's equations page reminds me that the Thèvenin equivalent for one just end of a transmission line is the characteristic impedance in series with a voltage source equal to twice the arriving signal. This is something I use all the time, and is standard stuff because it can be found in books like this. --catslash (talk) 20:47, 20 October 2010 (UTC)

And of course a ladder is commonly used approximate equivalent for a finite transmission line. --catslash (talk) 21:18, 20 October 2010 (UTC)

Proposal: Change upper case gamma to lower case gamma to conform to references.

I'd like to change the propagation constant from upper case to lower case.

I have two reasons:

1. To conform with the symbols used by the references. I've looked at about 7 sources and all of them use lower case gamma instead of upper case gamma.

2. To free up the upper case gamma for its traditional use as a reflection coefficient which is a section I wish to create. —Preceding unsigned comment added by Constant314 (talk • contribs) 12:32, 21 October 2010 (UTC)

Wrong Schematic

In the schematic , the shunt resistor is labeled G, but everywhere in the article G represents the shunt CONDUCTANCE. So, that resistor should be labeled 1/G. — Preceding unsigned comment added by 129.105.6.129 (talk) 15:38, 25 May 2011 (UTC)

Rocketman768 (talk) 15:39, 25 May 2011 (UTC)

Nah, this is absolutely the conventional representation. There are not separate graphic symbols for resistance and conductance. The symbol G has a conventional meaning of conductance which makes the meaning of the diagram perfectly clear. SpinningSpark 16:32, 25 May 2011 (UTC)

Electric power transmission lines

kindly tell me in detail about technical terms used in transmission line design.

and is there any specifications of transmission line towers? — Preceding unsigned comment added by 115.186.48.194 (talk) 08:14, 17 August 2011 (UTC)

This article is about transmission lines for radio frequency signals. For electric power transmission lines used by electric utilities, ask at the Wikipedia:Reference desk/Science. Or see our article, Electric power transmission. Jc3s5h (talk) 09:35, 17 August 2011 (UTC)

"The four terminal model"'s statement of 3dB loss halving the Power?

I always thought that 3dB loss are equivalent of about 30% loss of power. At least the following formula leads me to that conclusion: P[dB] = 10lg(P[W]); If I'm not right, do tell me. I want to know. — Preceding unsigned comment added by Nikolageneshki (talk • contribs) 14:57, 24 January 2012 (UTC)

Let's do the math. A signal has a power, P₀ of 0 dB which we define in this case as 1 watt. It passes through something that causes a loss of 3 dB, so the new power, P₁ is -3 dB.

P[dB] = 10lg(P[W])

-3 dB = 10 log(P₁ W)

-0.3 B = log(P₁ W)

Using each side of the equation as the exponent of 10 we get

10^-0.3 W = P₁ W

0.501 W = P₁ W

Jc3s5h (talk) 15:55, 24 January 2012 (UTC)

The simple version: you are wrong, and you are making a classic confusion about voltage and power. A 3dB loss halves the power, but it only reduces the voltage by 30%. Power (when the load resistance is fixed) is proportional to the voltage squared (P = I * V = (V/R) * V). Strangely enough, if you lose about 30% of the voltage, then you still 70% of the voltage, and 0.7 * 0.7 = 0.49 -- which is about half the power. The actual fraction is not 0.7 but rather √2/2. Glrx (talk) 21:17, 25 January 2012 (UTC)

that link.

That link to his site that User:Dsbirkett wanted to add, and that User:69.43.65.104 (very likely the same guy or the web site creator, or perhaps the ) tried to re-add (the remove said "no interactive capability", the link no longer claims this, so the reason for the original remove no longer applies), is it completely useless? I mean, it does look suspicious, especially when someone tries to push a link like this (and although the site doesn't seem to sell anything, it still looks like it is promoting these tools (with ugly SEO-gaming); perhaps these tools just aren't sold on the Web and/or the web site but the site helps build up credibility? In any case, the easiest thing for User:Dsbirkett / User:69.43.65.104 to do is to communicate with the other Wikipedia editors. At the very least using edit summaries, ideally here on the talk page. It may turn out that it's all quite harmless after all. Nczempin (talk) 16:06, 29 June 2012 (UTC)

Okay, I only just now noticed the situation on Antenna (radio). This is getting more suspicious, looking increasingly like a spam attempt. Nczempin (talk) 16:14, 29 June 2012 (UTC)

As far as I am concerned, you do not need to provide a reason for removal; that is always the default for external links, the onus is entirely on the person wanting to insert a link to justify it. WP:ELNO#EL1 states that a link that does not provide a unique resource beyond what the article would contain if it became a featured article should not be included. Anything that can be found in reliable sources can be included in the article, and if it can't be found in RS, its hard to see why we should be linking to it. SpinningSpark 17:52, 29 June 2012 (UTC)

Well, in the context of not biting the newbies, it's a little more helpful perhaps to give more accurate reasons. But in any case, the point is moot given the developments that make it very obvious this is/was a COI promotion (perhaps/probably innocently, but that doesn't change the result). Nczempin (talk) 18:46, 29 June 2012 (UTC)

transmission lines

can we get shocked when we touch two transmission lines carrying same potetial? — Preceding unsigned comment added by 117.200.197.167 (talk) 18:40, 12 September 2012 (UTC)

The practical answer is if you don't work for an electrical utility and been through the training to make you a fully qualified linesman, yes, you can get shocked, because something you didn't think of will turn the ideal case to a death. Jc3s5h (talk) 19:30, 12 September 2012 (UTC)

√µ/Ɛ

Amazing that √µ/Ɛ is evaded in the article, even though one section is called "Input impedance of lossless transmission line". I discuss this problem at http://www.ivorcatt.co.uk/x324.htm Ivor Catt — Preceding unsigned comment added by 86.156.252.218 (talk) 17:27, 4 February 2013 (UTC)

What is raised here is the wave-impedance of a plane wave in free space, √(µ0/Ɛ0) or µ0c, which is irrelevant in a page about transmission lines. So there is no 'evasion', whatever that is supposed to mean. 77.96.212.249 (talk) 12:14, 26 October 2014 (UTC)

Wavelength ... is always shorter than the wavelength in free space of the same frequency.

Since they have included waveguides as types of transmission lines, the wavelength inside the waveguide can be longer than in free space.Constant314 (talk) 19:13, 18 June 2013 (UTC)

Yes, I don't see the need for that sentence in the explanation. It is irrelevant to the point being made in that paragraph, which is that as the frequency increases, the wavelength decreases, so transmission lines are only needed at high frequencies. --Chetvorno^TALK 19:27, 18 June 2013 (UTC)

I'm cool with it being removed. I was only trying to restore the original information before it was copyedited. I just did not want it to be lost "by accident". I still feel there is a place for this to be discussed somewhere in the article. We have a lot of mathematical detail of the telegrapher's equation describing the behaviour of lines which most people will probably not read, but a basic property like this is missing. SpinningSpark 21:57, 18 June 2013 (UTC)

It's probably a correct statement if you limit it to the TEM mode, but then you would have to explain that. But then, maybe there should be a section on the TEM mode.Constant314 (talk) 02:25, 20 June 2013 (UTC)

Constant impedance with length

I have trouble with the unsourced "The defining property of a transmission line is that it has a constant impedance along its length, called its characteristic impedance". If the line is not constant Z, then it is not a transmission line? Tapered lines; shock lines. Constant Z is only an approximation. RG 58 isn't a constant impedance for audio. A transmission line carries (transmits) energy (works for power transmission, too). Carrying that energy with fidelity may set a goal of linear delay implicating constant Z line, but it is not clear that constant Z is the defining property. Glrx (talk) 04:35, 19 June 2013 (UTC)

This is an introductory section near the top that will be read by nontechnical people. They will want to know: what is the difference between a transmission line cable and any garden variety electrical cable? This section answers that question. And the difference is commercial transmission line is constructed to have a constant impedance along its length (note it doesn't say constant with frequency). I agree with your caveats: it's an approximation; tapered lines are used occasionally to change the impedance; also transmission line networks may have different impedance sections joined by impedance matching; some transmission lines have deliberate impedance steps. But these are technical details. It seems to me that a good summary of the transmission line concept for nontechnical people is: transmission lines carry RF power without reflections by avoiding (abrupt) impedance changes. I think this idea should either be in this section or in the introduction. --Chetvorno^TALK 10:08, 19 June 2013 (UTC)

Thanks for mentioning sources. I added some. --Chetvorno^TALK 10:08, 19 June 2013 (UTC)

Explanation paragraph: somewhat self-contradictory

I know we have been over the issue of whether a transmission line is a special type of waveguide or a waveguide is a special type of transmission line. I tend to the former because you can use waveguide techniques (solving PDE by separation of variables) to analyze a TEM two conductor transmission line but you cannot use the telegrapher's equations to analyze a hollow (EM) waveguide. But there are arguments for the other way. My problem is with two sentences: "Types of transmission line include parallel line (ladder line), coaxial cable, dielectric waveguide, stripline, optical fiber, and waveguides." and "To conduct energy at frequencies above the radio range, ... transmission line techniques become inadequate and the methods of optics are used". The first sentence says dielectric waveguide, stripline, optical fiber, and waveguides are transmission lines and the other sentence says transmission line techniques are inadequate. It seems to me that if transmission line techniques are inadequate for dielectric waveguide, stripline, optical fiber, and waveguides then dielectric waveguide, stripline, optical fiber, and waveguides should not be called waveguides. Or "transmission line techniques" ought to be called something else, such as "telegrapher's equation methods". Constant314 (talk) 05:05, 4 September 2013 (UTC)

I've never liked that "methods of optics" passage. Solving Maxwell's equations is hardly optical methods in the classical sense of optics, but Maxwell's equations are precisely what are used for analysing waveguides. Optics (lenses, prisms etc) are not used in millimetre wave bands (waveguides), but start to become useful at micrometre bands (fibre-optics). Yes, I know that optics can be explained by Maxwell and that a microwave dish is the analogue of a parabolic mirror and a plane reflector is the analogue of a flat mirror etc but that is all rather esoteric and this article is not the place for that discussion. SpinningSpark 09:01, 4 September 2013 (UTC)

I think "methods of optics" could be changed to "waveguide methods".Constant314 (talk) 12:28, 4 September 2013 (UTC)

I added the "methods of optics" sentence to try to place transmission line theory in its proper place between circuit theory and optics. An AC power cable, an RF transmission line, and an optical system are all transmission structures for electromagnetic waves. Transmission line theory only applies when the length of the guiding structure L is of the same order as a wavelength λ. Electromagnetics is traditionally divided into three regimes:

• Circuit theory (λ>>L) At low frequencies the lumped-component circuit model is used. The phase is approximately constant throughout connecting wires, so transmission line theory is not needed.
• "Microwave theory" (λ≈L) At intermediate frequencies, the phase varies along the transmission structure but only a few modes (sol'ns of Maxwell's eqs) can propagate. So circuit variables R, L, C, current, and voltage are still used but are considered continuous (distributed) functions along the transmission structure. "Optical" parameters: reflection coefficient Γ, refractive index η, permittivity ε, and permeability μ are also used. This is the domain of transmission line and waveguide theory.
  • In two-conductor transmission lines (parallel wire, coaxial cable and stripline) only TEM (transverse electromagnetic) modes can propagate. Since the flow of energy is one-dimensional the full Maxwell's eqs. are not needed and the telegrapher's eqs. are used.
  • In waveguide and dielectric waveguide, other modes (TE and TM) propagate so Maxwell's eqs. must be used.
• Optics (λ<<L) At high frequencies many different modes (millions) can propagate at once, so Maxwell's equations are mostly replaced by the simplified rules of geometrical optics. Circuit variables R, L, C lose meaning, and only optical parameters Γ, η, ε, μ are used to describe the transmission structures.

--Chetvorno^TALK 21:25, 4 September 2013 (UTC)

I like the starting point of comparing "the length of the guiding structure" to the wavelength. But the frequency identifications may be misleading. A single-mode optical fiber is λ≈L ... a radio-wave in free space is λ<<L ... Better to say "geometrical optics" (or "ray optics") than just "optics" because of optical fibers. --Steve (talk) 13:22, 5 September 2013 (UTC)

Yeah, you're probably right about that. Optical fibers are always a confusing point in texts on transmission lines, because they function as waveguides even though they operate at frequencies far above other waveguides and transmission lines. "Optics" refers to traditional optical systems, in which all the dimensions of the system are much larger than the wavelength. --Chetvorno^TALK 14:27, 5 September 2013 (UTC)

What I would like to avoid is the statements of the form "X is a transmission line. X cannot be analyzed by transmission line techniques." It's akin to saying "I have a universal translator but only works for Spanish to English." The article includes X as a transmission line because the non-specialist reader does. But only the specialist knows what transmission line techniques means. It's jargon. If we are going to use that particular bit of jargon, we might as well use transmission line in its jargon sense and exclude waveguides.

Alternately, perhaps, a paragraph could be added after the Explanation paragraph called something like "Methods of analysis" and move any discussion of techniques out of the Explanation paragraph and into that paragraph. That way the Explanation paragraph explains what transmission lines are and the Methods paragraph briefly lists and defines the methods and prepares the reader for the rest of the article, which is almost entirely about transmission line techniques.Constant314 (talk) 05:03, 7 September 2013 (UTC)

I see what you mean. Yes, I agree, an additional paragraph is the way to go. The problem comes because "transmission line" was traditionally the umbrella term; "transmission lines" included waveguides. I think this usage is still common, but the two terms have been getting more separate, and some people think "waveguide" should be the umbrella term. However, the term "transmission line theory" refers specifically to two-conductor line analysis with the Telegrapher's eqs, and doesn't include "waveguide theory", so we have the conflict that you rightly pointed out. However, as long as this article uses "transmission line" to include waveguide (which it does), I think the parts intended for general readers such as the "Explanation" section need to be consistent with this. So I'd like to see the "Explanation" section, which lumps waveguides in with transmission lines, stay as it is. As you suggested, a following section could be added, "Methods of analysis" or "Transmission lines vs waveguides", which explains that two conductor transmission lines are analyzed with a simplified set of equations which is the subject of this article, while waveguides require the full Maxwell's equations treatment, which is not included in this article.

The alternative is to remove all waveguide content from the article, and add a hatnote or introductory paragraph referring to Waveguide (electromagnetism). But I suspect the common engineering usage for "transmission line" still includes waveguides. --Chetvorno^TALK 08:22, 7 September 2013 (UTC)

How about making these changes to the Explanation paragraph.

Types of transmission line include parallel line (ladder line), coaxial cable, stripline, and microstrip. Waveguides, including dielectric waveguides and optical fibers, are sometimes considered transmission lines, but those are analyzed by techniques that are substantially different from the quasi-circuit techniques described in this article. ... . To conduct energy at frequencies above the radio range, such as millimeter waves, infrared, and light, the waves become much smaller than the dimensions of the structures used to guide them, so quasi-circuit techniques become inadequate and the methods of waveguides or optics are used.Constant314 (talk) 15:01, 7 September 2013 (UTC)

You're proposing this as an alternative to an additional paragraph? — Preceding unsigned comment added by Chetvorno (talk • contribs)

I'm proposing it until there is an additional paragragh on methods.Constant314 (talk) 00:40, 8 September 2013 (UTC)

I have never heard of transmission line theory being described as "quasi-circuit techniques". Unless the term is commonly used in RS I don't think we should be using it either. All kinds of difficulties arise if we try and create firm dividing lines. Microstrip in particular cannot firmly be put in the two-conductor camp because its transmission mode is not entirely TEM and this sometimes needs to be taken into account. Stripline, in the rare case where the two boards of a triplate construction have different permittivities, also has this problem. I think a simpler solution is to declare that the scope of the article is limited to two-conductor transmission lines (which in truth is what the contents of the article actually are). SpinningSpark 08:53, 8 September 2013 (UTC)

I can support your proposal.Constant314 (talk) 15:48, 8 September 2013 (UTC)

Yes, so can I, that seems to be more consistent with how the term is used now. However, I liked Constant314's idea for the explanation paragraph, except that I agree with Spinningspark that the nonstandard term "quasi-circuit techniques" should not be used. --Chetvorno^TALK 16:35, 8 September 2013 (UTC)

We can go back to using transmission line techniques if we limit the discussion to two conductor transmission lines. One advantage of limiting it to two conductor transmission lines is that the meaning of two conductor transmission lines is unambiguous. A methods paragraph could still be useful because two conductor transmission lines can support non-TEM modes. The methods would include circuit theory, telegrapher's equations A.K.A. transmission line techniques and waveguide techniques.Constant314 (talk) 18:34, 8 September 2013 (UTC)

How about this for the explanatory paragraph: Types of transmission line include parallel line (ladder line), coaxial cable, stripline, and microstrip. At frequencies in the microwave range and above, transmission lines become excessively lossy and waveguide and dielectric waveguide are used, which function as "pipes" to guide the radio waves. --Chetvorno^TALK 16:52, 8 September 2013 (UTC)

I generally like it, but for the moment I would like to have discussion on the phrases "excessively lossy" and "functions as a pipe". I'm not an expert but I wonder: do transmission lines become excessively lossy which suggests to me that they become unusable or is it that waveguides simply become a better solution? Is the fact that transmission lines become multi-modal a consideration in the choice of waveguide over a transmission line? Regarding pipes: some waveguides look like pipes and are often referred to as pipes or piping, but do the function as pipes? A pipe is a simple thing. It can have bends and wiggles and it can be run from point A to point B without much thought and it doesn't require a special coupling means to get its contents into it or out of it. A waveguide is much more constrained. I'm not sure pipe is the best analogy, but I also don't know any better analogy.Constant314 (talk) 19:10, 8 September 2013 (UTC)

A pipe analogy is reasonable as a qualitative explanation for the non-technical. As always with simplistic analogies, they will start to fail if taken too far. Transmission lines do indeed become very lossy with increasing frequency mainly for two reasons: dielectric losses in the insulator, and increasing resistance of the conductor due to skin effect. In an air filled hollow waveguide there are no dielectric losses to speak of and since transmission is not due to conduction the skin effect problem goes away as well. Losses in waveguide tend to be principally due to currents being induced in the waveguide walls. This can be ameliorated by depositing a thin layer of precious metal on the inside of the waveguide (skin effect is actually helping here by restricting the current to the thin high conductivity region). Choice of mode also has a bearing; before fibre-optics became common, the TE₀₁ mode in circular waveguide was being hawked as a good choice for wide-bandwidth trunk lines. This is particularly low loss due the absence of electric field in the direction of propagation. Multiple modes are generally considered a "bad thing" in waveguide propagation and steps are taken to suppress unwanted modes. However, some devices use multiple modes in order to reduce the size of equipment. SpinningSpark 11:42, 9 September 2013 (UTC)

You should probably be writing this article; I have a feeling you've forgotten more about electromagnetics than I ever knew. Feel free to jump in here with wording. --Chetvorno^TALK 12:40, 9 September 2013 (UTC)

I have no plans for a major rewrite of this article. I am fine with your explanatory paragraph. The only thing I think might be added is to mention that some authors include waveguides as transmission lines but that is not covered in out article. SpinningSpark 17:35, 9 September 2013 (UTC)

I concur. I think it should not only be mentioned in the explanatory paragraph, but should also be in the introduction, to define the scope of the article. --Chetvorno^TALK 03:12, 12 September 2013 (UTC)

Constant314, here are soms sources that use the simile of a "pipe" for waveguide: 1, p.367, 2, p.109, 3, p.409, 4, p.130. These sources confirm that transmission line becomes "lossy" at higher frequencies: 6, p.37, 7, p.3-4. Perhaps my wording above on this was misleading; two conductor transmission line doesn't become lossy because of dissipation in dielectrics, but because when the freq gets high enough that the conductor spacing is a significant fraction of a wavelength the line begins radiating [6]. --Chetvorno^TALK 03:12, 12 September 2013 (UTC)

I'm only asking for my own edification: what if the transmission line is a gold plated solid coax with a vacuum dielectric? Of course there are no dielectric losses and I don't think it will radiate. All modes will cause surface currents down to a skin depth. I do see SpinningSpark's point about multiple modes. You don't want your signal to propagate simultaneously with two modes because of the difference in speed and possible because the coupling is different. You could see interference between the modes. You could see mode hopping which might causes random looking changes in delay and amplitude. Again speculating, perhaps the avoidance of multiple modes is equally or more important than loss issues.Constant314 (talk) 15:01, 14 September 2013 (UTC)

Chetvorno is quite right, a coax (or any kind of two conductor line) will radiate if it is multiple wavelengths long. This is an important loss mechanism and silly of me to forget to mention it. Gold plating the coax screen will not help, it will make things worse if anything; the hollow tube formed by the screen is acting as an antenna. It is extremely difficult to keep this grounded along its entire length, even if it is perfectly grounded at the ends. Think how an impedance transformer works when perfectly short-circuited at one end. The other end is anything but a short circuit impedance. One would have to solidly ground the "screen" every λ/10 or so to entirely suppress radiation. On modes, once the frequency is above the cutoff frequency of the pipe formed by the coax screen, it is quite difficult to suppress waveguide modes, and these will then propagate down the coax completely ignoring the inner conductor. On skin depth, the current in TEM mode is central to the propagation of the wave, but in waveguide modes it is almost a secondary effect: the central conductor is irrelevant and can be removed without any detrimental effects. On air dielectric, yes, air cored coax avoids dielectric losses; this is why coax downleads are made of foam or air-spaced ribs. SpinningSpark 19:09, 14 September 2013 (UTC)

I specified gold plated so that we did not have to worry about surface currents propagating in copper oxide. I wanted to put transmission lines and waveguides on equal footing with regard to surface resistance. Constant314 (talk) 17:32, 15 September 2013 (UTC)

Actually, in the remark about radiating, I was only thinking about parallel-conductor lines; I forgot about coax. SpinningSpark, are you sure that long coax runs with shields grounded at both ends radiate? I hadn't heard that. I would think that would be a problem for cable television systems. --Chetvorno^TALK 20:31, 14 September 2013 (UTC)

Your point about waveguide modes traveling on transmission lines is fascinating, I had no idea. But I'd guess that the dielectric in the coax would tend to attenuate higher modes. By the way, these sources 6, p.37, 7, p.3-4 say that above 100 GHz waveguide becomes lossy because metal is not a good reflector at millimeter wavelengths, so "quasioptical" systems with lenses and mirrors are used. --Chetvorno^TALK 20:59, 14 September 2013 (UTC)

"...grounded at both ends." Yes, sorry, that should be grounded at one end. This is particularly a problem on antenna feeds where the antenna end cannot be grounded and common mode currents can be generated. See [7] amd [8]. SpinningSpark 21:32, 14 September 2013 (UTC)

I see what you mean. I guess that is a problem for all transmission lines of sufficient length when balanced and unbalanced systems are connected without a balun.

What about something like this wording for the explanatory paragraph? The term "pipes" is just being used descriptively for waveguides, to give general readers some idea of how they differ from transmission lines. --Chetvorno^TALK 15:31, 15 September 2013 (UTC)

Types of transmission line include parallel line (ladder line), twisted pair, coaxial cable, stripline, and microstrip. The higher the frequency of electromagnetic waves moving through a given cable or medium, the shorter the wavelength of the waves. Transmission lines must be used when the frequency is high enough that the wavelength of the waves begins to approach the length of the cable used. At microwave frequencies and above, power losses in transmission lines become excessive, and waveguides are used instead, which function as "pipes" to confine and guide the electromagnetic waves. Some sources define waveguides as a type of transmission line; however, this article will not include them. At even higher frequencies, in the terahertz, infrared and light range, waveguides in turn become lossy, and optical methods, (such as lenses and mirrors), are used to guide electromagnetic waves. --Chetvorno^TALK 15:31, 15 September 2013 (UTC)

I think that is a good improvement and it avoids the particular contradiction that concerned me. Do you want to edit the first sentence so that it specifies two conductor transmission lines?Constant314 (talk) 17:25, 15 September 2013 (UTC)

Yes, you and SpinningSpark were right about avoiding combining transmission lines and waveguides in one article. It seems to me that the introduction should have a clear statement of what is and is not included, and the reasons. What do you think about adding sentences along these lines?

This article covers two-conductor transmission line such as parallel line (ladder line), coaxial cable, stripline, and microstrip. Some sources also refer to waveguide, dielectric waveguide, and even optical fiber as "transmission line", however these lines require different analytical techniques and so are not covered by this article; see Waveguide (electromagnetism). --Chetvorno^TALK 00:22, 16 September 2013 (UTC)

That seems fine to me.Constant314 (talk) 02:48, 17 September 2013 (UTC)

Done. --Chetvorno^TALK 07:09, 17 September 2013 (UTC)