Talk:Characteristic impedance/Archive 2

more surge impedance

I only yesterday saw surge impedance used, in the article on UHF connectors. I changed the link to use the redirect, as we are supposed to do, but then wonder why surge impedance? As far as I can tell, the UHF connector was named when UHF was what is now VHF, so the name is old. I also suspect, then, that surge impedance is the old name for characteristic impedance. That would be before nice sine oscillators were readily available. Maybe more like we might call pulse impedance today? If other articles use it, and maybe if they don't, this one should expain the reasoning for the name. (Maybe just that it is the old fashioned name for it.) Gah4 (talk) 23:23, 28 September 2021 (UTC)

Is not the passage beginning "A surge of energy on a finite transmission line..." sufficient explanation already? I thought surge impedance was only used in power distribution, I had never seen it anywhere else. But searching for "surge impedance" UHF in gbooks turns up a lot of hits from the 1950s. Similar results for "surge impedance" VHF and "surge impedance" radio except also used in some quite modern books. So maybe a bit dated in telecomms, but still out there. There's no doubt these are simply synonyms, they just refer to two different attributes of the same thing. Characteristic because it is a property of the line regardless of its length and surge becasue that is the impedance seen by a voltage surge. SpinningSpark 09:53, 29 September 2021 (UTC)

OK, but why surge impedance instead of characteristic impedance for UHF connector? And more specifically, UHF connectors are commonly used on HF and low VHF radio transceivers. Is it surge for a pulse, and characteristic for a sine? Gah4 (talk) 12:15, 29 September 2021 (UTC)

That would make sense, but I think it's actually more a matter of author preference as far as I can tell. SpinningSpark 12:20, 29 September 2021 (UTC)

Oh, like US English vs. British English, and not ancient vs. modern? Gah4 (talk) 20:42, 29 September 2021 (UTC)

A search in Google Books suggest that the term surge impedance is almost entirely peculiar to the field of power distribution. Moreover, it seem that surge impedance is specifically the characteristic impedance neglecting line resistance (i.e. the characteristic impedance at frequencies higher than the mains frequency). The etymology given in the article, namely: A surge of energy on a finite transmission line will see an impedance of Z prior to any reflections returning (which was also my interpretation) is probably incorrect. More likely, it refers to the impedance seen by an abrupt step in the current due to a fault. catslash (talk) 21:51, 29 September 2021 (UTC)

Not entirely power. This is a relatively modern book on microwave and radio simply stating they are synonyms. As does this one. I don't think "neglecting line resistance" is part of the power engineering definition. It's just that for many purposes it can be neglected. This makes it clear. SpinningSpark 22:37, 29 September 2021 (UTC)

Not entirely clear, as the two consecutive sentences seem to contradict each other. In any case, the second says: The term surge impedance is, however used in connection with surges (due to lightning or switching), where the lines [sic] loss can be neglected such that [eqn], a pure resistance.. This says: When the line resistance is neglected, the characteristic impedance is known as surge impedance. catslash (talk) 23:49, 29 September 2021 (UTC)

differential

There is a recently removed external link to this page. This article specifically describes a common case in PC board design that is the difference between two transmission lines. A line on a PC board with a ground plane is already a transmission line with a characteristic impedance. Common on PC boards now is two such lines close together. Close enough that both the individual L/C and differential L/C are important. Maybe the article should cover that case, but if it doesn't, then the reference is useful. Gah4 (talk) 23:53, 9 February 2022 (UTC)

Hello. Yes, differential lines are used in PCBs. That particular link is low quality. It only has the lecture notes and not the lecture. External links should provide high quality, unique information that cannot be included in the article. There is no information in that EL that could not easily be included in the article. If there is info in that link that can be paraphrased and put into the article, then the link could be used as a reference. As a standalone link, it is just a signpost that says that there may be some useful information here, but the connecting information is not here, so you cannot use it unless you already know the material. Constant314 (talk) 00:02, 10 February 2022 (UTC)

OK, I agree low quality. I actually read through the whole thing, though, and it wasn't so hard to follow. But yes, it is meant for those who already understand ordinary transmission line theory. It is slightly obvious if you think about it enough (and know the theory), but only slightly. I suspect not so easily included in the article, but not so hard, either. It might be that more PC boards keep the lines of a pair far enough apart not to need the extra terms. This should also come in shielded twisted-pair cables, where there is capacitance between wires, and also to the shield. There is, then, a differential and common-mode impedance, likely different. Gah4 (talk) 00:53, 10 February 2022 (UTC)