Is this the same application as you were considering ERF transceivers for? - the outdoor large scale model railway? If so, perhaps one should steer you straight away towards RS485 rather than the less noise-resistance and less-transmission range of the RS232. Hippy asks if you are actually using RS232 or are you proposing the serial output of a PICAXE? RS232 requires drivers and is usually operated at +/-12 volts against the PICAXE 0 to +5 volts. If you are thinking of long-distance outdoor cabling and want reliable operation in an environment that is in any way electrically noisy (I presume your locomotives are electric?) then start off by looking at RS485 drivers. Think of RS485 being like the ARF modules, RS232 being XRF modules and PICAXE serial being ERF modules and you may get my drift.
Do your really need 9600 baud? Perhaps if you could let us know precisely what type of control signals you are trying to transmit and for what purpose we could be of more help. (If you can slow down your data-rate then you can achieve much longer range; that applies generally to radio transmission as well as cable-linking).
It is the same project, just thinking of alternatives.
other thought is to use a 'reverse sma extension cable' for the aerial instead.
not electric locos, live steam.
I was originally asking for max length of rs232 from picaxe, without adding other circuitry.
I now have an ARF ciesco module, to use as a master. it's 3.3v so will need make a pcb to add a 3.3 voltage regulator and a 'level logic shifter', not a great problem.
it's a matter of covering all the bases when I install the 'master' unit. extending aerial or extending rs232, or both.
To keep it simple, as I understand,
15M of standard cable (2500pf) gives me 15M at 9600baud rate.
utp cat5 cable gives longer range.
TOF