controlling cross talk in a 50 lines digital slic based intercom

[89c52]

Now here is a issue that is really confusing me these days. I have got a simple 50 lines pulse dailing intercom system. For this system 8816 and microcontroller 89c52 is used. I have practically done its cabling using the common wire thing but there is lot of cross talk coming in this system.
I have used multi pair {10 pairs , 7 pairs } cable and some where single pair cable. In case of single pair cable there is no cross talk issue but where i have used multi pair there is cross talk coming. Now the only solution is to change the multipair cable with single pair cable for each user but as i have done the cabling it will be too costly to change the cables again..
So if any one has any kind of solution please let me know how to over come this problem.

 

[392]

Is this twisted pair or regular cable? I would venture to guess it's like thermostat or security cable with no conductor twisting at all, in which case it will crosstalk forever until replaced.

 

[executone]

Crosstalk is a common problem with low grade cable. Isolate your probem areas and upgrade cable to a higher grade twisted pair cable. I bet your most problem areas are your longer runs. Good Luck!!

 

[pansophic]

As the previous posts state, you really need to move to a twisted pair cable. Telephone cable is twisted for this very reason, and each pair in a cable has a different twist rate so that you get away from differential mode noise.

You'll commonly find telephone cable in 2, 3, 4 and 25 pair cable formats. There are other configurations that can be purchased, but these are the most common station cables, and they are inexpensive compared to other configurations.

When you buy it, you will probably be asked questions about things like:

CAT x: an industry standard for rating the performance of the cable. 1 is low, 5 is high. For your purposes, a CAT 2 cable would be fine, but you will probably have difficulty finding anything less than CAT 3. CAT 5 is capable of supporting 100 Mb/s ethernet (low capacitance and high velocity of propgation).

Article 800: a National Electric Code rating that determines where a given cable type can be installed. CM can be installed in non-plenum areas, or dead air spaces. CMR can be installed in cable risers and dead air spaces. CMP can be installed in plenum areas (air returns for air conditioning systems).

If you have unused conductors in the existing cable, you may try grounding all unused conductors. This will help to drain off some of the RFI/EMI loose in your cable, but I wouldn't expect miracles.

Also, if your existing cable is actually twisted pair, ensure that each independent audio path is traveling over a pair that is twisted.

Good luck!

pansophic