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RS-232 is primarily an electrical signal interface standard. It is a moderately high source impedance, unbalanced, and unterminated system. Unbalanced means ground or common is used as a reference for the signal. Unterminated means that the load impedance at the end of the transmission line does not match the characteristic impedance of the transmission line. Unterminated transmission lines cause reflected signals (reflected energy).
Read my web site page
http://www.beta-a2.com/cat-5e_photo.html for some useful information so I do not have to repeat the same thing here. This is titled CAT-5E Waveforms, does not directly relate to use at Ethernet speeds, but the discussion is related to its use for RS-232 because of its low capacitance per foot.
The original RS-232 specification had a dead band in the range of +/-3 V at the destination. This meant a voltage in this range was indeterminate. At the receiving end any voltage above +3 was one state, and anything below -3 was the other state. If the driving point voltage swung between + and - 12 V, then whatever attenuation or distortion of the waveform occurred over the transmission line the signal at the destination had to be of the correct polarity and outside of the +/- 3 V band.
If you look at my photo P-9 you see that a steady state condition exists after about 60 microseconds when the transmission line is driven by a standard RS-232 driver. If you operated at 10,000 baud that would be 100 microseconds between bits and that would probably work with CAT-5E cable. However, there could be major noise problems over this distance. If Belden 8723 with its much higher capacitance per foot was used then at 1000 ft the baud rate might be limited to about 2400 or less baud, or 9600 baud would work with 200 ft.
If you want to work at 115.2 kbaud, then the cable lengths need to be about 1/12 as long.
Do not assume these distances represent real world usable distances. There are other factors and major noise problems. Then there is also the problem of damage to components at both ends resulting from ground voltage differences.
Our I232 Isolator System can provide 4000 ft range with short time 2000 V peak isolation and at 115.2 kbaud. Maybe 8000 ft at 9600 baud. Very high noise conditions will reduce the distance.
I believe the greatest problem with direct connection of RS-232 ports relates to noise and component damage.
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