In message , invalid writes
At what frequency ?
At DC, of course you'll get a short circuit. At the working frequency, it will be a completely different matter. Inductive effects only occur with AC not DC (no flames please)
Not necessarily
Sorry, not you Andy, that other bloke
In message , raden writes
You should be more careful with your reading and/or snipping. That is exactly what I said.... the paragraph following the one you quoted (ie where you snipped) said....
"Admittedly there is no signal being passed down it, and to determine what the impedance would be with a sine wave (video, data etc) passed down that same piece of cable is a different matter. The impedance will vary according to the frequency of the signal passed down it."
It will be there on google for any one to check.
I'll post you a sensible reply, when you stop arguing the fact against paragraphs you have snipped. Bill
In message , fred writes
No troll, but I have noticed a tendency in some groups for anyone who disagrees with frequent posters to be labelled as such.
I note that while you're referring to me as a troll (what for, my views?) you do not refer to geoff as a troll too. That's strange, because even though I have discounted his post for gratuitous (sp) snipping, he seems to agree with my view about a sine wave inducing impedance (although he does seem to have missed the fact that DC can be sinusoidal).
It seems I'll have to post some references back to google groups in this thread in order to support my disdain at your unhelpful/non constructive post. Bill
Sorry, this thread seems to have been "A uniform line terminated in its characteristic impedance will have no standing waves, no reflections from the end, and a constant ratio of voltage to current at a given frequency at every point on the line."
Note the part about "constant [...] at a given frequency".
Regarding "no reflections", that is actually a requirement of RG58 and the purpose of the terminator. I would like to read further regarding the term "characteristic impedance" as I am not familiar with it. I would be inclined to suggest that (as I said in an earlier post) it relates to the designed/intended use of the cable and this seems to be supported by your link.
This last statement appears to support my view and that of geoff (the surreptitious snipper) regarding impedance being influenced by frequency of a sinusoidal wave.
It seems our disagreement of opinion/fact/whatever is being hijacked by people throwing personal insults. I would suggest we return to the original point over whether TV Antennae signal could be satisfactorily passed down RG58 thin net cable.
Of that, I still have no idea (as stated in earlier posts) and still recommend the OP tries it himself (I might even go and buy some m/f antenna connectors tomorrow and try it *myself* :-)
If I make it into town to do so, I'll post the findings regardless of the results... even though they could be snipped up and a "troll" label attached too ;-)
Regards Bill
It has a small effect. The impedance depends on both the geometry and the behaviour of the dielectric, and this can have a small variation in its properties with frequency.
But for two solid core polyethylene coax cables, yes you can eyeball which is the 50 and which the 75 ohm.
(for bonus points, why is it 93 ohms ? 8-) )
Probably because IBM wanted to create a market for something incompatible with anything else. They did it with pretty much everything else, although less so now.
.andy
To email, substitute .nospam with .gl
93 ohm coax - RG62 - was around long before IBM used it for networking. I've only ever used in situations where I've simply wanted to minimise shunt capacitance.
So go on Andy D: why 93 ohms? I can explain the logic behind 50 ohms and 75 ohms, but the reason for the existence of 93 ohm coax has always been something of a mystery.
The ratio of voltage and current on the line will be constant over a wide range of frequency if the line is properly terminated.
A Google search for "characteristic impedance" "transmission line" gives
13,600 hits. Happy reading. Otherwise, for books giving a simple introduction, try something like Scroggie's "Foundations of Wireless" or the RSGB or ARRL handbooks.FSVO "satisfactorily". The loss (attenuation) of that cable at UHF will be too high for anything other than very short runs, unless you can afford to throw away a lot of signal. And using a 50 ohm cable in what would normally be a 75 ohm system isn't good practice, although it won't lead to any great disaster.
From RS, the attenuation of RG58 is 7.6dB per 10 metres at 1000MHz.
El cheapo UHF aerial cable is about half that - before any mismatch is taken into consideration.
CT 100 is approx 2 db per 10 metres at 1000MHz.
Are you sure of this? Why do you think that cable is available in a variety of impedance values?
Impedance is NOT the same as resistance. A piece of coaxial cable can be open circuit at DC, but a short circuit at RF.
And using a 50 ohm cable in what
The tilt characteristics of sub standard cable will lead to some interesting signal levels!
We have a problem with a new development that we have trunked. It seems that the dropleads were pre-installed using RG59. Although it offends all my sensibilities, it could be OK(ish), except for the fact that the digital Muxes are at C/D and the analogue down at group A. The dropcable runs are quite long too, so there are some flats that will never have full performance, without spending more developers money. You can imagine that Porcine Aviation will launch first!
93 Ohms is still a cable standard and its use in instrumentation predates networks by some years. For once IBM is not guilty :-).
Cable attenuation is minimum at 77 ohms; the breakdown voltage is maximum at 60 ohms and the power-carrying capacity is maximum at 30 ohms. 50 Ohms is the best compromise between voltage/power handling,
75 Ohms gives the lowest loss (but lower power handling) and 93 Ohms gives the lowest capacitance which reduced loading and allowed for longer cable runs.(75 Ohm rather than 77 Ohm because the diameter ratios could be more easily made with existing tooling for standard cable sizes).
In message , "Andy Luckman (AJL Electronics)" writes
Isn't that impedance at a given frequency (I believe I discussed this in an earlier post). "Intended/designed use". Bill
Andy,
Try this link with two reasonable descriptions of impedance/resistance/reactance etc. For the shortened version, check the very last paragraph which reads...
"The short answer is -- impedance includes reactance, and reactance includes effects which vary with frequency due to inductance and capacitance." Ted Pavlic, Electrical Engineering Undergrad Student, Ohio St.
Regards Bill
In message , "Andy Luckman (AJL Electronics)" writes
I'm getting a bit fed up of this surreptitious snipping. The very next sentence in the paragraph where you have snipped reads...
"Admittedly there is no signal being passed down it, and to determine what the impedance would be with a sine wave (video, data etc) passed down that same piece of cable is a different matter. The impedance will vary according to the frequency of the signal passed down it." Bill
You have fallen into almost the same trap - you are reading snippets of information in isolation, when you don't understand the background.
And whatever the subject may be, you can always find a web page written by someone who doesn't understand it either:
That last sentence is just plain wrong! As Andy is trying to tell you: the characteristic impedance of a transmission line - of which coaxial cable is one example - is in fact *constant* over a very wide range of frequencies.
Do not confuse this with the impedance of an inductor or a capacitor, both of which do vary with frequency, in opposite directions (inversely to each other).
You may have read that a transmission line contains distributed inductance and capacitance; but the salient feature of RF transmission lines is that it contains *both* of these things, and that they combine to produce a characteristic impedance that does *not* vary with frequency.
(Behind that simple basic fact, there are some fine details that do lead to small deviations away from a constant value at very low frequencies and at microwaves; but those really are small details.)
In article , invalid writes
Hi Bill,
I think you are trolling, because you are posting information in an authoritative tone when it is clear you don't have any real knowledge on the subject.
Whatever your knowledge in other fields or even in the field of electronics, you do not appear to have enough knowledge in the area of transmission line theory and characteristic impedance to make a useful input into this thread.
If you don't know the answer, please don't guess.
The original poster's question and his follow-up were answered comprehensively in the first 10 replies to this thread, before your first post, but here we are some 30 replies later and still going. The misinformation in your first post was politely corrected by 2 people, me included, but you continue to post like you are an expert in the subject, which you are not, and which I'm sure will be very confusing for subsequent googlers on this subject.
If you were/are trolling, you have a result, congratulations.
You are IMM and I claim my five pounds . . . . .
Love & Hugs,
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.