Dear All

How I can calculate the impedance of the wire having the length of 4000ft. This cable is using for RS485 communication.

 

Dear All

How I can calculate the impedance of the wire having the length of 4000ft. This cable is using for RS485 communication.

The characteristic impedance of a cable has to do with it's construction type rather then it's length. Normal specification for RS-485 type communication cable is 120 ohms.

Here is a good application document for wiring of RS-485 circuits:

http://www.maxim-ic.com/appnotes.cfm?appnote_number=763&CMP=WP-1

Lefty

 

Thanks a lot leftyretro. I got some useful information.