Help - Hardware advice required

[Ulrich Behrenbeck]

this is the problem:

connect two stations via a shielded 2 wire line of approx 6 km length.

RS485 won't work that length - any other ideas ?

the protocol used may be special/self programmed as it - i guess - will have to be halfduplex anyway



the problems background:
connect two PCs that are located on two tunnel portals and the 2 wire already exists inside the tunnel

any idea welcome  - thx

[Jesper Hansen]

It will probably work at 6 km, but not at maximum speed.

/Jesper

[Ulrich Behrenbeck]

while browsing newsgroups, i found a related problem and an interesting solution:

they suggested to simply use 2 modems (and to pretend to have a postal line in between;-)) - so we even get full duplex at 19.200 or so at a std RS232 (from pc's view) - the only remaining problem is how to get the things to work without switching center - some modems with a permanent ("leased line") option are said to work without and ring/dial/power etc ...

[Scout]

not sure if you guys have them there or not, but a pair of nokia papl modems would do the trick. BBN2M's iirc, also pair gain make some..  try this link... ( watch te wrap)
http://www.nokia.com/networks/product_catalog/pc_product_datasheet/1,5562,,00.html?prod_id=00T67000

They are NOT cheap. but they work. I used to own a pair... This may be an overkill for what you are trying / looking for, but it's all perspective.
enjoy...

[Gall]

Many modems work well without a phone line (just directly connected). If they don't, just add a DC power supply for the line to imitate a phone line. You may have to use special AT commands combinations in order to initiate modem handshake.