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Jim Lesurf wrote:


The whole idea of devices using RF over the mains under the pretense
that they are "not transmitters" is absurd.

In a way, though, I would argue it's OK. In most cases it causes no
harm to anyone. In a few cases, it does (so I hear, although I've
never seen a properly documented case, only hearsay and foaflore
(friend-of-a-friend)). In those cases the affected person can appeal
to OFCOM to help sort it out.

As far as I know OFCOM's view is that RF-over-mains is for the greater
good, and the relatively small number of problems can usually be
resolved on a case-by-case basis.

It seems like a sensible, pragmatic approach, all things considered.

--
SteveT

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On 07/01/2014 22:04, David Woolley wrote:

The telephone wires are explicitly balanced, by being made as twisted
pairs. That balances them against environmental asymmetries.

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?

--
Mark
Please replace invalid and invalid with gmx and net to reply.

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On Wed, 08 Jan 2014 07:17:05 +0000, Mark Carver
wrote:


The telephone wires are explicitly balanced, by being made as twisted
pairs. That balances them against environmental asymmetries.

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?

You mean parallel wires with constant spacing, like mains cable?

Rod.

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Mark Carver wrote:
On 07/01/2014 22:04, David Woolley wrote:

The telephone wires are explicitly balanced, by being made as twisted
pairs. That balances them against environmental asymmetries.

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?


Yes. Of course balanced RF feeder is not usually twisted and it does
have reasonable immunity to interference. I say 'reasonable'...

Bill

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In article , Steve Thackery
wrote:
Jim Lesurf wrote:


The whole idea of devices using RF over the mains under the pretense
that they are "not transmitters" is absurd.

In a way, though, I would argue it's OK. In most cases it causes no
harm to anyone.

In practice that may mean it *does* cause reception problems for some
people - who have no idea of the reason and so don't raise a complaint
identifying that mains RF devices are a problem.

Hence any 'passively collected' stats on this may well seriously
under-indicate the impact.

As far as I know OFCOM's view is that RF-over-mains is for the greater
good, and the relatively small number of problems can usually be
resolved on a case-by-case basis.

Yes. I'm sure they find that an easy presumtion to make by putting their
fingers in their ears and looking at the cash waved by manufacturers.

It seems like a sensible, pragmatic approach, all things considered.

To them, yes.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

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In article , Roderick
Stewart
wrote:
On Wed, 08 Jan 2014 07:17:05 +0000, Mark Carver
wrote:


The telephone wires are explicitly balanced, by being made as twisted
pairs. That balances them against environmental asymmetries.

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?

You mean parallel wires with constant spacing, like mains cable?

There are various mains cables around our house. They don't all have the
same wire spacing or diameters. Some are three wire, some are two. None, so
far as I know, behave in a balanced way at RF.

I'm no expert on domestic mains wiring but AIUI the wires to the light
fittings tend to only switch one 'arm' of the connection. If so, leaving a
'spur' of a single wire for the RF. Rather more like an antenna than
balanced impedance-matched cable. One per room. Antenna array.

But apparently OfCom have decided the result is not a "transmitter". Wonder
how many of the decision makers ever did Radio 101 at Uni...

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

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In article , Bill Wright
wrote:
Mark Carver wrote:
On 07/01/2014 22:04, David Woolley wrote:

The telephone wires are explicitly balanced, by being made as twisted
pairs. That balances them against environmental asymmetries.

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?


Yes. Of course balanced RF feeder is not usually twisted and it does
have reasonable immunity to interference. I say 'reasonable'...

Yes. Twisting can help in some circumstances. All depends on factors like
what may be 'close' to the wires, upsetting the effect of the balancing.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

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Mark Carver wrote:

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?

That's the old type, and hasn't been in use for some years. By the
way, you might be interested to know that even that type of dropwire is
"twisted". To be more accurate, it has a figure-of-eight
cross-section, but when it's pulled up it is (sorry, was) twisted to
prevent "galloping" when the wind blows.

There was no particular requirement for the number of twists per span,
or metre, or anything. I've no idea how that twist might affect the RF
immunity. To be honest, I would expect it to be pretty good even when
untwisted, the wires only being a tiny fraction of a wavelength apart.


--
SteveT

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On 08/01/2014 08:45, Roderick Stewart wrote:
On Wed, 08 Jan 2014 07:17:05 +0000, Mark Carver
wrote:


The telephone wires are explicitly balanced, by being made as twisted
pairs. That balances them against environmental asymmetries.

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?

You mean parallel wires with constant spacing, like mains cable?

Yep, more or less.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

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On Wed, 08 Jan 2014 04:47:42 -0600, "Steve Thackery"
wrote:

Mark Carver wrote:

All the overhead 'drop wires' I've ever seen close up are 'shotgun'
rather than twisted ?

That's the old type, and hasn't been in use for some years. By the
way, you might be interested to know that even that type of dropwire is
"twisted". To be more accurate, it has a figure-of-eight
cross-section, but when it's pulled up it is (sorry, was) twisted to
prevent "galloping" when the wind blows.

There was no particular requirement for the number of twists per span,
or metre, or anything. I've no idea how that twist might affect the RF
immunity. To be honest, I would expect it to be pretty good even when
untwisted, the wires only being a tiny fraction of a wavelength apart.

Modern 4 wire dropwires have the wires laid parallel with a common
twist (quad). This actually gives better crosstalk immunity than if
each pair had been given their own seperate twist and then laid up
alongside each other (with or without yet another twist).

In a quad, it's the diagonally opposite wires which are used to form
each of the two balanced pairs.
--
Regards, J B Good