RS232 long distance cable termnation

[munromh]

I have a 16F886 that I'd like to send 9600 baud RS232 half duplex data to a monitoring laptop setup with a terminal program. The distance is 1000'. I made a test setup with 1000' of un-terminated unshielded 26awg twisted pair wire and it works just fine. I took a look at the signal with a scope and it looks pretty good. I think that proper termination might help to clean it up just a bit but I'm having a hard time determining what the proper termination should be. A 100 ohm load on the receiving end? Empirical testing? I've searched the forum and the web but have not come up with a definitive answer. Can someone point me in the direction of a useful reference.

I should note that I plan to go RS485 but at this point I'd like to work with what I have.

Thanks,
Mark

At output of 16F886:



At input to test terminal: