Quite a lot actually, professional RF engineer for 40 odd years here. Coupling between different signals can be problematic, I assume that the cable people have a whole variety of kit to fix these issues. Jim has had a fairly long time with the same ISP I think, so he may have a relatively old installation that is a bit more sensitive to the exact topology around and inside his house. It's not easy when you are constrained in what can be fitted, cable internet is quite after-market in nature certainly 25 years ago when a lot of it was initially fitted.
Sometimes TNP I see what makes so many cam.misc regulars find you abrasive. This is one such occasion.
And Jim, you've suckered me into a cross-post to uk.d-i-y you old sod.
Well, surely the whole idea is to try to remove your transmitted signal from the modem or anything connected to it. So for a start are you sure of the mechanism its getting into? Generally, it seems if you live next door to a ham and are on BT then its far more difficult than on virgin unless its fibre to the home, I would leave the Virgin hub where it is, make it into a modem only then buy yourself a nice shine router and stick that on the end of a good quality network cable. The wireless will be better and from tests someone I know did, very little is getting back to the hub. It seems as you deduce that the main problem is that the hub is fed by coax, and it is the sheath of this which is picking up the signals. Its counter intuitive I know that bits of open wire in a plastic bundle seem better than a screened cable, but proof of pudding and eating, and you may have other issues, even the length of the coax can cause issues if its a quarter wave at the transmitting frequency, I'd imagine. Back in the old CB days one used to use braid breakers on tvs, but I do not know what effect that kind of device might have on a broadband signal, as by definition it is,um broad band!
Unfortunately, because the theory and the on the ground result often do not match, I'd imagine. Like balanced aerials and unbalanced tuners can work well but using a balun often makes stuff worse. Its the great mystery of life, or at least one of them. No I do not have a licence, but my late Father was friends with quite a few.
I wonder what sort of Earth the guy has on his system. Brian
The merit of your ethernet solution is that it already has galvanic isolation. Unless you use shielded ethernet cable, which is often counterproductive unless the whole system is designed for it.
The point is, that people who do electronics professionally, as I did for many years, have been there, done that, got the T shirt and automatically, simply as a way of reducing fault calls, isolated their domestic kit that plugs into long lines, from any hard LF connection to the ground. In ADSL it is conventional to have a ferrite balun IIRC. IN CAR5 ethernet its all balanced mode anyway.
Look at Jims post. The term 'galvanic isolator' is misspelt for a start. Secondly it is never used outside of a marine context where the point is not to have boats floating in sea water 'earthed' to the earth and to each other, to avoid *galvanic* corrosion.
It is never ever used by normal engineers to refer to not earthing equipment for the avoidance of ground loops which are only relevant anyway in the audio band. At RF there are a lot more weird effects that come in, but earthing stuff doesn't normally make any difference.
So there are 3 solid hard reasons bound up with experience why Jim is in fact talking through his arse.
1/. A 'galvanic isolator' is irrelevant outside of a marina.
2/. Ground loop seldom if ever have any effect at RF and above, which is where cable operates.
3/. Despite their desire to make profits, manufacturers of electronic kit in general make sure it works without the need for ancillary plug in items.
Oh FFS. Intelligent lives matter. Do we have to pander to idiocy everywhere, all the time?
If wannabe electronics engineers were just to actually learn the theory and do some design, perhaps their little knowledge wouldn't be such a dangerous thing.
And gold plated speaker wires, red sharpies to reduce CD distortion and the like wouldn't be on sale.
I must say I assumed that Jim's "galvanic isolator" was something supplied by (and named by!) Virgin Cable. I don't think he would have thought of it for himself. Equally, I assumed the earth voltages were affecting the low level digital circuits in his equipment rather than the RF parts. Obviously ICBW!
And generally it works. But twisted pair lines are more sensitive to environment than coax, and are built to higher standards in general. Especially in comparison with pre-2000 cable TV systems.
I will admit that when I saw Jim's post, I did have to have a quick look to see what he was referring to. As I said, braid breaker is the term that is used in RF circles, and is mainly intended to avoid current flowing on the outside of coax getting anywhere it's not wanted, obviously the internal currents on coax matter but you rarely want the outside current involved except in coax baluns.
Have a look here:
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and here:
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See above. Terminology might not be to our taste, but it's what the industry calls these things.
Depending on what is going on, it is possible for cable lengths to cause notches within the desired passband if the grounding is imperfect or if there is unintended inductance in ground paths. Cable TV is notorious for this sort of effect.
Yes, but as I said in after-market equipment there are always a few odds and sods that need mopping up. I would love to say that you're right and nothing is needed, but then I've seen enough cable TV cabinets with broken doors on the streets, and what lies within is quite horrifying to anyone with even a faint interest in tidiness. The F connector, usually screw on, is the absolute cheapest and nastiest RF connector in existence.
No, but if someone is asking about something that exists, and why it might be problematic if disturbed, they deserve a fair hearing.
Jim is against professionals having radio as a hobby, so his preference is not to be too technical. Amateur radio is a broad church.
Don't hold with any of those. All nonsense as you well know.
Yes. I owe Jim an apology. The idiot here is not Jim, but Virgin, who have
(a) deigned to supply kit that was not fit for purpose ,
(b) added in a 'ground breaker' and called it by a misleading name presumably for 'marketing purposes'
(c) not supplied simple instructions on where to put it.,
It is sad reflection when you look on approaching death with equanimity, because at least the frightful incompetence you sought to eradicate in every thing you did,and has achieved dominance in professional areas, will be something you no longer have to deal with...
...Except no doubt St Peter will require two factor authorisation and a printed electricity bill before letting me in the pearly gates, but the computer system will be down and the backup system gone to the Devil.
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