My experience, too, has found all the detectors on the Primary Road Frequency for that Railroad. All trains must monitor that frequency while operating on the mainline. Around here, the Norfolk Southern uses 160.95 for a Road Frequency and all the detectors are there, too. These detectors operate with relatively low power...just enough for the train passing by to hear the report after they pass. I live about 3 miles from a detector and can hear it clearly with a handheld scanner. Another detector, located about 12 miles north of me can only be heard on my base scanner connected to an antenna up about 40 ft. In recent years, these devices are fully automated and speak with a computerized voice.
A "Typical" detector message might sound like this:
"Norfolk Southern---milepost 87 dot 8, no defects" REPEATS
or, if there is a problem with a train, it will sound something like this:
"Norfolk Southern--Detector Alarm (Loud Tone) Repeats...Then something like "Hotbox Alarm, Left Side, Axle Number 42 (Repeats)"
An alarm message repeats several times to be sure the engineer hears it. Railroad regulations require the train must stop and the conductor investigate the problem before moving the train further.
I know that Norfolk Southern operates in your area, but may use a different road frequency than what is used around here. These detectors are located about every 10-15 miles along the mainline of the NS here in Central KY. On lesser used lines, they may not be found as close together.
