🚀 go-pugleaf

In <dE1LrARIBh107h@lorc.eskimo.com> lowen@lorc.eskimo.com (Lamar Owen) writes:

>I'm not.  I'm an EE-turned-computer-freak person.  Thus, I am familiar with what
>VSWR on improper-impedance wiring can do.  At the power levels and wide frequency
>range employed in 10base-T, I would forsee very little problem with wiring that
>is up to half of spec length, even if the wiring varies wildly from the spec.

10BaseT seems to be very forgiving.. we have an istallation between 2
buildings in a botanic garden where they don't like us to dig
between tree roots.

The distance is about 80 meters, 20m from the spec maximum. There
wire is a 24 pair unshielded brand xyz cable, which is installed
for a fire alarm/central heating controls.

The original installation was full of mistakes: there was a 3-8 Volt
common mode 50Hz voltage and about 3 Volts of differential 50Hz in 
a pair, because the pair had only one wire connected.

The line was slow, but not completely dead, packets got through
when the 50Hz was near crossing zero voltage!!

When the loose wire was connected, and some other adjustments were 
made, we had about no differential 50Hz (about 300mV is allowed by
the spec), and we had about 2V peak to peak common mode 50Hz on
the line ( spec allows 4 Volts, i think)

And the line works just fine now.

Probably crosstalk is the worst enemy in 10BaseT, attenuation
and reflections are not so important because there is only one
listener at each pair, something reflecting back disappears
to transmitter termination, and the signal is just attenuated
a little.. the transmitter is 2.5 Volts, and 0.4 Volts
is enough at the other end.

So if you have an unknown cable get some 10BaseT gear and something that
counts errors, and try it !!

might save you $$

--
Vesa Halkka                       -O___/ 
University of Helsinki CC:         (  /   	 vhalkka@helsinki.fi 
Centre for scientific computing:  ~~~~~  	 vhalkka@csc.fi