Date   : Sun, 03 May 2009 17:18:41 +0100
From   : mfirth@... (Michael Firth)
Subject: Econet over UTP ?

Mike Tomlinson wrote:
> In article <8D14D006E2A3472FAD0795CAAF00F6A4@...>, Mark Haysman
> <jumbos.bazzar@...> writes
>
>   
>> Yes there is....the house mains earth. That's how it's working. Because it's 
>> differential transmission, the induced noise doesn't affect it.
>>     
>
> I understand it works cos of the differential voltages, but still a very
> bad idea in my book.  At the least you're asking for blown line drivers
> as there's no galvanic isolation, like there is with Ethernet.
>
>   
Surely its only likely to become a problem if one or more machine(s) 
lose their mains earth connection?

And, if I understand things correctly, as long as at least one machine 
on each side of the non-earthed UTP link has a good earth, then 
effectively you've got an earth path between the two halves.
> Cat5 cable is so cheap there's no reason to skimp on the job.
>
>   
Cat 5 cable may be cheap, but running a new cable between floors is 
usually non trivial (unless you're doing it while doing other major 
building work.

Another idle thought I had was whether a filter network could be built 
to combine Econet and 100M Ethernet onto the same cables - Econet isn't 
going to have any useful signal components above about 1MHz, and I don't 
think 100M Ethernet is going to have much content down that low, so a 
high pass, low pass filter setup (basically similar to an ADSL 
microfilter, but with a higher crossover point) should allow both on the 
same pairs, giving plenty of spare lines for an Econet earth.

Regards

Michael