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#1620547 - 17/05/2018 18:05 Re: Computer doesn't work well with the WiFi [Re: JKD]
barnacle Offline
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Registered: 17/12/2005
Posts: 31807
Loc: Hemel in the Hempstead
Damned if I know. Probably the early coax - single conductor - networking used wireless too.

Oh, wait. It didn't. And neither does Powerline.
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#1620548 - 17/05/2018 18:20 Re: Computer doesn't work well with the WiFi [Re: barnacle]
GrahamL Offline
I need some sleep

Registered: 17/12/2005
Posts: 3487
Loc: Pothole City
Originally Posted By barnacle
Oh, wait. It didn't. And neither does Powerline.


Then how does it work perfectly when there is no physical connection between the 2 devices? Is that not the definition of "wireless" communication?

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#1620551 - 17/05/2018 20:37 Re: Computer doesn't work well with the WiFi [Re: JKD]
DaveG Offline
Club member 311
Forum is my life

Registered: 16/12/2005
Posts: 6818
Loc: Lightwater, Surrey, UK
Maybe I should do a test? I have a UPS that I could plug a Powerline thingummy in to, with another on the mains, and I could wander around the house with the UPS / Powerline / and ethernet laptop...somewhat cumbersome however...
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#1620552 - 17/05/2018 21:19 Re: Computer doesn't work well with the WiFi [Re: DaveG]
Wishy Offline
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Registered: 05/01/2006
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Loc: Sunny Darlo
The only slight flaw with that method is that would just be the same in principle as that shown in the video. In other words, not proof. Without a network analyser in the loop I don't see anything other than interference causing trouble with a susceptible system and cross-talk (forgive the slight bending of the dictionary definition) serving an unintended purpose.

Mind you, now that I've actually watched those videos, if the powerline adaptors wind up short wave radio enthusiasts that much I'm going to start buying loads and plugging them in everywhere.
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#1620559 - 18/05/2018 09:47 Re: Computer doesn't work well with the WiFi [Re: JKD]
DaveG Offline
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Registered: 16/12/2005
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Loc: Lightwater, Surrey, UK
How would you use a network analyser to work out what's going on? I don't have the faintest idea how to use one...
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#1620565 - 18/05/2018 11:15 Re: Computer doesn't work well with the WiFi [Re: DaveG]
Wishy Offline
Forum is my life

Registered: 05/01/2006
Posts: 5911
Loc: Sunny Darlo
As this is way more interesting than the work I'm supposed to be doing this morning I'll give it a shot at explaining what I mean. laugh

Couple of bits of reading material, this on network analysers themselves and this on s-parameters but read the next paragraph before diving into them.

Ignoring that the presentation in the first link is 135 slides long ( :o), the first 4 slides explain the general purpose of a network analyser and the diagram in slide 5 shows exactly what I would like to see measured. This is normally in terms of s-parameters of which there is some explanation on slides 27~29 and in the other link. The other 127 slides are not necessary for the purposes of this discussion.

Starting with slide 5, in particular the diagram with incident, reflected and transmitted waves, what the videos are showing are the reflected waves bouncing out into the air. This can be measured with a spectrum analyser as shown in the videos but, without knowing how much power is transmitted in the first place (incident wave) or how much is coming out the other end of the mains wire (transmitted wave), there is no context and it doesn't tell me anything other than the fact that some power is lost to the air. This is the main crux to my scepticism of the videos as it comes as no shock to me that pumping relatively high frequency signals down an unshielded cable designed to carry 50Hz results in lots of reflected waves large enough to be measured in the air with a spectrum analyser. This is also a reason why I don't like powerline adaptors.

Where a network analyser comes in is that it can measure the reflected and incident waves giving the ratio of power lost over power sent. This is the S11 parameter. The other thing that could be measured is the ratio of power received over power sent (this is the S21 parameter). It does this by sweeping frequencies into whatever is being measured and is capable of measuring the reflections back into the device itself as well as transmitted waves if the other end is also connected (it wouldn't have to be as, putting it simplistically, we are just looking at incident = transmitted + reflected so either measure would do).

The easiest way that I see this being set up is by first measuring whatever frequency the powerline device is transmitting (a spectrum analyser or network analyser could do this) and then mimicking these frequencies with a network analyser connected to some mains cable. That would give a proper measure and cynical me suggests that the ratio going through the wire would be the lions share.

I can't be arsed to watch those videos again but IIRC the frequency coming out into the air was centered at around 100HMz which will be able to transmit either significant distance (relative to higher frequencies such as 2.4 or 5GHz) or alternatively a short distance with relatively little power which is what I suspect is going on here. The fact the that video shows an inverter powering one of them down the garden is of no relevance as the mains wire ends are still both in the same room. The invertor could be in Timbuktoo and I would still expect the same result.

Of course I could still completely wrong as what I would like to see measured hasn't been yet so I'm still open to a proper proof. evil


Edited by Wishy (18/05/2018 11:58)
Edit Reason: Thanks Dave for doing my proofreading!
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#1620566 - 18/05/2018 11:16 Re: Computer doesn't work well with the WiFi [Re: DaveG]
Wishy Offline
Forum is my life

Registered: 05/01/2006
Posts: 5911
Loc: Sunny Darlo
Originally Posted By DaveG
How would you use a network analyser to work out what's going on? I don't have the faintest idea how to use one...

Now that I've seen how long my reply is you may regret asking that but hopefully not. smile
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#1620569 - 18/05/2018 11:48 Re: Computer doesn't work well with the WiFi [Re: JKD]
DaveG Offline
Club member 311
Forum is my life

Registered: 16/12/2005
Posts: 6818
Loc: Lightwater, Surrey, UK
Yes, I think I do regret asking, and I should be working on my day job...

I will read in detail later, but please confirm that you meant to say

Originally Posted By Wishy
...pumping relatively high frequency signals down an unshielded cable designed to carry 50Hz results in lots of reflected waves...
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#1620570 - 18/05/2018 11:59 Re: Computer doesn't work well with the WiFi [Re: DaveG]
Wishy Offline
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Registered: 05/01/2006
Posts: 5911
Loc: Sunny Darlo
I did indeed, now corrected.
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#1620577 - 18/05/2018 13:39 Re: Computer doesn't work well with the WiFi [Re: JKD]
DaveG Offline
Club member 311
Forum is my life

Registered: 16/12/2005
Posts: 6818
Loc: Lightwater, Surrey, UK
Well to do a test it seems like I would need some expensive gadget, it's not just a case or running some fancy software?

What it seems to boil down to is that yes, the earth conductor is used to send and receive network signals, but an undesired side-effect is to generate SW radiation which it just so happens can be received by an isolated powerline adaptor and turned back into network signals?
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#1620585 - 18/05/2018 16:58 Re: Computer doesn't work well with the WiFi [Re: DaveG]
Wishy Offline
Forum is my life

Registered: 05/01/2006
Posts: 5911
Loc: Sunny Darlo
They certainly aren't cheap bits of kit. The inner workings of these things are way beyond my comprehension but I am understood to believe that the main bit of trickery needed is being able to read the reflected waves back on the same port so I'm not sure if there's a fancy software way round this. I've been out of the industry a few years now though.

Originally Posted By DaveG
... an undesired side-effect is to generate SW radiation which it just so happens can be received by an isolated powerline adaptor and turned back into network signals?


Yep. this is pretty much the crux of what I think is happening.


Edited by Wishy (19/05/2018 22:14)
Edit Reason: are r argghhh
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