[Premium-Rx] Power Line Carrier, Last Mile and xDSL

[Warren Ziegler]

Apparently Scott Adams got wind of your idea Frank -
see today's Dilbert! (www.dilbert.com)

73 Warren

--- "Carcia, Frank A.           HS"
<francis.carcia at hs.utc.com> wrote:
> George,
> You guys are doing it right. The clowns here want to
> run the signal down a
> single bare conductor. Next we will be running
> sewage down a open trench 1/2
> the day and
> fresh water the other half.    fc
> 
> -----Original Message-----
> From: George Georgevits
> [mailto:georgg at bigpond.net.au]
> Sent: Tuesday, August 19, 2003 5:24 PM
> To: Premium Rx
> Subject: [Premium-Rx] Power Line Carrier, Last Mile
> and xDSL
> 
> 
> Guys,
> 
> I am a practicing amateur here in Australia. I am
> also a self-employed
> communications engineer involved in this field. I
> work mainly in the test
> and measurement area and have been involved
> extensively with the design and
> testing of connection hardware and cables for high
> speed balanced line
> applications, including "LOW END" applications such
> as xDSL. I say LOW END
> because most of my work involves components used for
> high speed LAN
> applications where bandwidths (and hence spectrum)
> reaches much higher
> (typically I test to 250MHz). I am not all that
> familiar with Power Line
> Carrier systems, but from what I have read, I tend
> to agree that it sounds
> like a really dumb idea! No doubt if it becomes
> popular in the US, we will
> be lucky enough to get it here too.
> 
> At this stage, I limit myself to xDSL applications
> for the following
> comments. Firstly, the new ADSL2plus standard
> utilises spectrum a little
> further than someone earlier had commented. It
> actually reaches to about
> 4.5MHz, and if anyone is really interested, I have
> the graph from the ITU
> standard to prove it.
> 
> Regarding xDSL applications running on twisted pair
> in the street, I
> initially had similar concerns to those some of you
> have raised in your
> recent postings. I am note sure what you mean by
> Last Mile applications, but
> I think they would fall into this category too.
> 
> Please note the following:
> 
> ADSL and other forms of DSL services are and have
> for some time been in use
> extensively here in Australia. More particularly,
> VDSL has been in use
> extensively on aerial cable in the Canberra region,
> and I have not heard of
> a single complaint about interference from amateurs
> living there. As a
> matter of interest, VDSL uses spectrum to 30MHz and
> the last 300 metres in
> Canberra is delivered by aerial twisted pair Cat 5
> cable.
> 
> These twisted pair technologies rely on cable pair
> balance to keep radiation
> very low. Pair balance is typically 40dB or better
> at the frequencies in
> use. It is only the common mode signal which can
> radiate, and in order to be
> an effective radiator, the cable needs to be a
> significant fraction of a
> wavelength long. What's more, if there was
> significant radiation, the first
> thing it would interfere with is the adjacent pairs
> in the same cable
> sheath. Such interference is known as crosstalk and
> it is one of the main
> limiting factors for the use of such services in
> twisted pair cables.
> 
> Also, street cables are all fitted with either a
> grounded foil screen or (in
> the case of older cables) a lead sheath. Although
> such screening serves
> primarily as a moisture barrier, it also acts as an
> effective screen,
> reducing any radiation out of the cable bundle
> significantly. The power
> levels in cables containing these services sit
> typically around 0dBm or
> lower. By the time you take into account the cable
> pair balance (40dB) and
> the effectiveness of the cable screen (has to be at
> least another 20-30dB),
> its no wonder there are no complaints about
> interference to HF.
> 
> I just thought the above might be useful for
> directing what to and what not
> to worry about.
> 
> Regards,
> George Georgevits
> Power and Digital Instruments Pty Ltd
> Sunny Sydney, Oz
> 
> 
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