On Thu, 18 Jul 2013 10:46:03 +0100, tony sayer wrote:

In article o.uk, Dave
Liquorice scribeth thus
On 18 Jul 2013 07:45:58 GMT, mick wrote:

As for cat5 being balanced, look at it this way: both wires in the
pair are being moved up and down in voltage at 50Hz by mains hum. Data
is carried in the difference between the voltage on the pairs.

Agreed.

At some point the 1s and 0s become 1s and 1s, as the hum voltage
overcomes the differential voltage at the top and bottom ends of the
50Hz waveform.

How? Show the maths.


Have you ever tried this in practice?..

We have, and the only place where we had a problem, now fixed, was
running some CAT 5 right next (within 4 foot) on a radio mast to some
transmitting dipoles radiating some 100 watts in the FM band!..

That caused a problem for some microwave link units connected to the CAT
5 cable but we now have replaced that with Ubiquity screened cable which
BTW is excellent mechanical stuff as well and that cured that
completely.,

I rather doubt that any domestic situation would have such a problem
somehow;!...


I know of other installations where power cables are right next to
bundles of CAT 5 cables and all is well running at 100 and gigabit
rates.

I think you'll find that balanced line working such as what CAT 5 is to
be very immune to external interferer's...

In fact some 10 years ago I put a SWA cable into my shed some 100 feet
away from the house chucked in the same trench as the SWA were a couple
of bits of CAT 5 cable (temporary use of course!). One was in use for
the phone the other a PC point. Never a moments trouble even when using
arc welders and the like;!...


I think the problem only really appears where the hum level is quite high
and there is liable to be mains noise on top of that. Quite typical in,
say, engineering works where there is a relatively high load and plenty
of noise from SMPS and motor speed controllers. It becomes very relevant
where the bandwidth of the network is important as speed is definitely
compromised. Nowadays it's almost as cheap to go fibre instead of cat5e
on any long lengths between buildings anyway.

Of course, you don't see the network slowing down unless you monitor it
over a period of time. Bursts of noise slow it down, but it speeds up
again between the bursts!

As you say, in domestic applications it probably isn't so important. In
the OP's case I'd be tempted to bury cat5e or cat6 in hosepipe as I said
earlier. The distance isn't great, the pipe gives some protection and
also a little bit of spacing from the SWA. The more spacing, the more
consistent the network speed will be. Best results would probably be with
utp at about 1' away. Perfectly acceptable results would probably be with
ftp at a couple of inches away, but the cable is more expensive.