Talk:Distributed-element filter
Latest comment: 15 years ago by Spinningspark in topic Prose comments by Cryptic C62
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Rewrote the lead
The old lead had some problems.
- A distributed element filter is an electronic filter designed for frequencies above the VHF band or thereabouts. At these frequencies the wavelengths of the operative signals are shorter than the size of the device being constructed and it is no longer possible to use the more familiar lumped element model. Filters and other passive circuitry are instead designed using the distributed element model in which the components of the circuit are treated as being transmission lines, which indeed, they effectively are.
Note that at the top of VHF band the wavelength in air is ~1 meter. Lumped elements crap out about here but clearly "wavelengths of the operative signals" are not "shorter than the size of the device being constructed". I've also added some helpful wikilinks. I think the new language flows a bit better as well but YMMV. JPatterson (talk) 20:34, 15 February 2010 (UTC)
Things to improve
- Front figure: "for suppressing non-TEM modes of transmission" needs a cite. Adding a note on image width would help understanding the size - not everyone knows this connector type. Image file needs a better description, preferably explaining why rubber seal (moisture ?).
- I have addressed the "through holes for TEM mode" issue. Image size is a bit problematic; it is not my image so I cannot retake it with a rule included. It would, of course, be possible to estimate the size from some of the circuit structures, but that is almost the definition of OR. I am against explaining the rubber seal (it is to give the enclosure an IP rating because the product is intended for outdoor use) - this is going way off-topic; there are any number of features that could be explained here. The only one mentioned, the through holes, are only described because they can easily be mistaken for a filter structure. SpinningSpark 20:48, 8 April 2010 (UTC)
- Regarding the via fences: there will be an internal metal lid cast with a pattern of walls on the underside, which corresponds to the pattern of via-fences. This lid is clamped down tightly onto the circuit by a large number of bolts - notice all the screw holes associated with the via fences (it can't have been screwed down very well in this example as the walls have not made a visible indentation in the metallization). The via fences connect the base of the walls to the ground-plane, so forming a number of near perfectly isolated enclosures, communicating only where the microstrip passes through a notch in the cast walls. This internal lid is in addition to a simple external lid which makes a seal with the rubber gasket.--catslash (talk) 10:41, 29 April 2010 (UTC)
- Regarding the photo: I've just put a more close-up view of a (just) a filter at File:Microstrip-bandpass-filter.jpg. I was going to use this to illustrate edge-coupling on the microstrip page, but never got around to writing about it. I haven't put the picture on this page, as you may feel that the existing one is better - take a look and see what you think. --catslash (talk) 16:35, 29 April 2010 (UTC)
- Nice picture. That would be great for the parallel-coupled lines section. I don't think we should expand on via fences in this article, it is only mentioned for clarification purposes. I have red-linked it with the intention that an article should go there someday. SpinningSpark 07:35, 30 April 2010 (UTC)
- OK. I just felt that the phrase for suppressing non-TEM modes of transmission though strictly speaking true, is rather misleading. --catslash (talk) 11:55, 30 April 2010 (UTC)
- Nice picture. That would be great for the parallel-coupled lines section. I don't think we should expand on via fences in this article, it is only mentioned for clarification purposes. I have red-linked it with the intention that an article should go there someday. SpinningSpark 07:35, 30 April 2010 (UTC)
- There is some imbalance between figure captions - one cites references and others don't. I probably understand why, but this could be picked up at FAC.
- There is usually no need to give citations to image captions unless they introduce facts not in the main text. All the figures here are described in the text where a citation is given. I have made an exception for figure 2 because it is a composite from a number of different sources and I wished to make it clear which filter structure came from which source. SpinningSpark 20:30, 9 April 2010 (UTC)
- Add history subsection?
- I am actively looking into this. The history of the various technologies (co-ax, stripline, microstrip, waveguide etc) is well documented, mostly of them starting in radar in WWII and the filters in these technologies followed shortly after their first use. However, sources dealing with distributed element filtering as a general topic are a bit harder to find and I need to see if enough material can be gathered to write a worthwile section. SpinningSpark 20:30, 9 April 2010 (UTC)
- I have now started a history section. There is still a bit more that could go in, but I think the point is now addressed. SpinningSpark 18:13, 11 April 2010 (UTC)
- Need to clarify or wikilink "quarter wavelength stubs", "LC (anti-)resonators" (even LC needs some wikilink at first appearance), "impedance or admittance transformers" Materialscientist (talk) 04:21, 6 April 2010 (UTC)
Prose comments by Cryptic C62
Resolved comments
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Unresolved comments
Here are some comments on the article's prose intended to help make the article accessible and precise:
- "...inductance and capacitance (and resistance, but that rarely features in filter designs) are distributed along the length of conductors, and the two..." It seems contradictory to have a parenthetical comment (intended to give "extra" details) in the lead (intended to give a broad overview of the topic). Unless you can think of a way to work it into the sentence without adding a huge amount of clunky commas, I suggest dropping the parenthetical altogether. Also, this seems somewhat contradictory with the opening sentence. Perhaps the opening sentence could be reworded to "in which capacitance, inductance and sometimes resistance" to avoid implying that all three are equally important.
- Decline to do this. All three are equally important and resistance absolutely has to be mentioned. The filter designer does not want it: it is parasitic to his design as they say in the terminology, but he is going to get it anyway. It does not feature in the design in the sense that the designer has deliberately introduced capacitance and inductance, but resistance has crept aboard uninvited like a ship's rat. I might also mention that there are some rare filter designs that do deliberately incorporate resistance, see this patent by Hendrik Bode for instance. The lede should be readable by anybody, as reviewers never cease to remind me, and we should not assume prior technical knowledge. Equally, we should not assume that the reader does not know what the basic three passive elements are and feel we are free to leave one out thinking it will not be missed. In fact, a reader who has come to this article probably will know this, and almost everybody has at least heard of resistance and knows that it is an element of electrical circuits. To not mention resistance will leave the reader asking what has happened to it. I will, of course, welcome rewording to make it less clunky. SpinningSpark 21:58, 17 June 2010 (UTC)
- Very well explained. The question now is how to make it less clunky. I think the phrase "but that rarely features in filter designs" does not adequately explain what you've just told me, nor would it even be possible to concisely explain the matter without cluttering up the lead. Why not just "...inductance, capacitance and resistance are distributed..."? --Cryptic C62 · Talk 01:51, 18 June 2010 (UTC)
- Because the lede has already opened with "capacitance, resistance, inductance". It then goes on to say LE filters usually consist of capacitors and inductors. The secondary point is that resistance is not usually "designed in" with filter circuits. To not say this leaves the reader wondering where it has gone in this story. SpinningSpark 18:03, 18 June 2010 (UTC)
- Two options that have not been explored: First is to use a footnote, which would allow you to explain the matter in more sufficient detail without clogging the lead. The second would be to simply add another sentence after the end of this one. The sentence that currently follows it, ("There is no precise frequency above...") doesn't seem closely related to this sentence, so the flow of the paragraph wouldn't be lost. --Cryptic C62 · Talk 19:51, 18 June 2010 (UTC)
- I have tried restating this in a way which I think addresses your point. SpinningSpark 11:31, 26 June 2010 (UTC)
- "The increasing miniaturisation of electronics means that circuits which were once large compared to λ no longer are." This (quite wrongly) implies that an individual circuit will physically shrink over time. Perhaps "The increasing miniaturisation of electronics means that, unlike their older counterparts, modern circuit elements are generally not large compared to λ." ?
- I sincerely doubt that anyone will put that reading into the sentence, but I have no objection to a rewording in principle. Your suggestion, however, is confusing components/elements/circuits and it is also incorrect that "modern circuits are generally not large compared to λ." There is a trend, but there is still a point (implementation technology dependant) beyond which DE is still required. SpinningSpark 23:05, 18 June 2010 (UTC)
- My suggestion was merely an attempt to make it clearer that it is not the individual circuits themselves that are shrinking, but instead the designs for the circuits. Since I'm quite evidently not an expert on the subject, do you have any ideas for how to make this distinction clearer? Also, it would be nice to rid the sentence of the awkward ending "no longer are." --Cryptic C62 · Talk 15:31, 22 June 2010 (UTC)
- Reworded to get rid of the ugliness. The idea that this could be misread as circuits physically shrinking is pedantic nonsense. "The increasing streamlining of automobiles" would be understood by no one as meaning the "sit up and beg" radiator grille of ones Rolls-Royce Silver Shadow has slowly been worn away by air resistance over the years. SpinningSpark 12:24, 26 June 2010 (UTC)
- "The generic term stripline in modern usage usually refers to the form then known as triplate" Let me just check to see if I'm reading this correctly: Barrett invented something which he called "stripline". That particular technology received competition from another technology called "triplate". Today, the term "stripline" no longer refers to Barrett's technology but to triplate instead. Correct?
- Not quite as clear cut as that. Stripline has become a generic term in the same way as hoover refers to vacuum cleaners and xerox machine means a photocopier regardless of who the manufacturer really is. Most of the time triplate would be meant in modern usage but it still could be applied to Barrett's original form, or some other variant. SpinningSpark 23:23, 20 June 2010 (UTC)
- I see. Such subtleties are often difficult to accurately convey in an article. How about Replacing the aforementioned sentence with the more general "In modern literature, stripline has become a generic term to describe several variations of the technology"?
- While that is true, I would still like to say that stripline unqualified most often means the triplate form. Some authors use stripline and triplate interchangeably, some will use a qualifying adjective where distinction is necessary, such as air stripline, triplate stripline or dual stripline for instance. SpinningSpark 21:25, 22 June 2010 (UTC)
- "Such applications are part of large capital investment programs. However, mass-production..." The use of "however" should set up a contrast between two ideas or two time periods. I fail to see such a contrast between these sentences.
- The contrast was supposed to be between the initial applications where cost was not the overriding issue (the major costs of setting up a telecommunications network are getting all that kit to the top of obscure hills in inaccessible places and building towers to house it all. A piddling little electronics gadget does not really enter the economics, even if it is not made in the most cost effective way) and equipment for the consumer market where shaving fractions of a penny from unit costs can be significant for profitability because of the high volumes. SpinningSpark 21:25, 22 June 2010 (UTC)
- Then I think "are" should be changed to "were" in the first sentence, yes? --Cryptic C62 · Talk 13:18, 24 June 2010 (UTC)
- "The simplest structure that can be implemented is a step in the characteristic impedance of the line" Suggest adding "in a distributed element filter" after "implemented", unless you meant that an impedance step is literally the single simplest structure ever in the history of the universe.
- I'm not really convinced that is necessary given the context of the article, but it is not objectionable. SpinningSpark 18:45, 24 June 2010 (UTC)
- "(often quarter wavelength)" I'm thinking that this can be replaced with "(0.25λ)" to make it consistent with the General comments section.
- it can be, although some reviewers might prefer it in words. I would write it as "(often λ/4)"; stating as a fraction is more normal for mutiples of λ/4 and make the function clearer; "often" is still needed because other lengths can have a useful function as well. SpinningSpark 18:45, 24 June 2010 (UTC)
- "These multiple element filters can implement any of the filter families..." I'm confused. The lead explicitly states that all filter classes can be implemented using a distributed element approach. This is the only instance of "multiple element filters" in the entire article, leading me to believe that "these multiple element filters" refers to the "hybrid mixture" in the previous sentence.
- You are confused because element is not being used with the same meaning here. This is bad, let me think of a better way of writing this. I guess component will have to be used but I don't entirely like that because stripline circuits are made as a single piece, not from components joined together. SpinningSpark 18:45, 24 June 2010 (UTC)
More to come. As you make changes in the article, please respond below individual concerns so I know which are done and which need further discussion. Thanks! --Cryptic C62 · Talk 00:52, 15 June 2010 (UTC)