Vic, The reason for not detecting dialtone is cost. The equipment involve is intended to be cheap. As we know all to well if there is any way to cut costs some companies will go to any length. I personally don't like blind dialing. The time delay before dialing is required to be 10 seconds minimum. I used to cheat and use 7 seconds. We never had any complaints of mis-dialing because CO wasn't ready by the time dialing started.
I re-read Bell Technical Reference Pub 47001. I stand corrected on ground start, it does use dialtone. I now remember the equipment design I did for a ground start network. It was in the late 1960's for a mine in South America. They had a ground start system in a very extensive mining operation. It was an alert system used to detect methane and carbon dioxide levels in a mine. The detection circuits flagged an emergency ventilation system and turn on alarms very quickly. This Ground start system didn't have dialtone. It just looked for the presence of loop current, waited 200 mS, then began alerting the ventilation and alarm system via DTMF. All quipment was inside gas tight housings to eliminate the possibility of an explosion when relays arced during opening and closing. Duane
