Many thanks for the kind replies,

Stubs are relatively short(varies around 1-2 meter), the cable I have used is Cat5 and unshielded. Terminating resistors are 120R and resistive(I also tried 100R) and located at the extreme ends. RS485 chips used at nodes are of 1/4 UL.

Now, the interesting points I want to mention that may help to figure out the problem.

- If I cancel the terminating resistors or if I use a larger resistors, distance drops dramatically to 100-150 meter.

- If I use my converter with its external power, result is even worser than that of powerless(port powered) mode.
This implies that bus needs biassing, but every overture I made resulted with no any good..

- Even though I use a single node on the bus, I still couldn't provide a distance farther that 400 meter. This stops me thinking that I am suffering from overloading.

- I had omitted the unused cables in cat5 that should have been ended with 100R resistors to GND. I will do it soon.
Do you think it is that why such a poor result I got?

And I planning to descrease the data rate to 9.6Kbps from 19.2K
and see if it will do any use.

I will let you know if I get further.

Regards.

Rustu Kaya