[plug] phone line interference

[David Campbell]

> Software Engineers..sheesh   :)
> 
> Seriously though David, insulation won't stop radio waves, screening may.
> You could have well hit upon your problem though and I would suggest a
> filter in series with the phone line.  Not sure if you can buy them, supect
> not.  Basically an inductor in series with each wire with 2 caps at each
> end of the inductor. Ground the center connection of the 2 caps.  If there
> are any radio hams in the area talk to them. You may get lucky.

This may or may not work. Assuming that you are trying to achieve 56k, this 
would require a signal of 56+ kHz while your friendly local transmitter will be 
pumping out 700-740 kHz (720[6WF]+/-20kHz). Some calcs will be required to get 
the parameters just right. Any filtering WILL degrade the signal performance.

Possibly a better solution is to borrow a pair of 8 way (UTP) joiners and the 
necessary length of UTP cable. UTP differs from standard phone flex in that the 
wires are twisted together rather than lying flat. The advantage of the flat 
(cheap) cable is that a machine can easily terminate the ends (cut, strip, 
crunch), anyone who has made a UTP or UTP crossover cable will tell you it is 
fiddly trying to get the wires to sit still for long enough to crimp the end.

The twisting of the pairs (send/return) cancels out the bulk of the external 
interference. Telstra does the bulk of its wiring using twisted pair (although 
only Cat 3 not Cat 5) without much noise problem.

I could loan a joiner and a good length of UTP for testing...

David Campbell
=======================================================
campbell at torque.net

Check http://www.torque.net/parport for all Linux parallel port solutions.

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