I am working on a system that gets data from a sensor via a TTL connection. Currently, the data that is gathered from the sensor is sent to another part of the system via a set of modems. The distance between the modems can range anywhere from a few hundred feet to up to 4000 feet or more. I'll try to provide a rough schematic:
------ TTL ----- TTL ------- CARRIER SIGNAL ------- TTL ----- |Sensor|=====|PCB A| =====|MODEM A|======================|MODEM B|=====|PCB B| ------ ----- ------- ------- -----
So, my question is this: what other alternatives are there other than the use of modems to send the data from the sensor to PCB B? To me, it seems using a modem for a single connection is overkill, especially because the modems have to connect to establish a data link (which is time consuming for this application). I had thought of using a Digital to Analog to Digital conversion scheme, but I am not sure what repercussions (if any) there would be to this at distances up to 4000 feet. I imagine a direct TTL connection across that distance would dissipate the signal fairly quickly. Any insight or suggestions (or corrections) are appreciated.
EDIT: Current data rate is 19.2 kbps. As for the modems, we have actually used two types. One was a spread spectrum modem and the other was a standard dial-up modem. There are only two wires (essentially a tip and ring) connecting the two modems as of now and the system is half duplex.