You mgiht want to check-out a post I am about to write: "The Day the Fort Bragg PsyWar Center Audio/Radio Section controlled the SAL Main Line

[daveklepper]

This srory was submitted to Trains for publication a long time ago, with no response any way, and a short version may have been posted here sevferal yeaers ago.  I am going into some more detail, because it is relevant to some technical discussions concerning oil trains on the Trrains forum, alathoutht he date of the efvents are in the year 1956.

I was given the job of testing an air-to ground parachute supported droppable message repeating psywar public address sysem, consisting of a copact shock-proof tape playback maching, amplifiaiion and effiicent horn-loudspeaker and driver, all solid state and battery powered..  The plane would take off from Pope Airforce Base, cross our base Fort Bragg, and drop the bright red bomb-looking device over Camp McCall, an Army-controlled area for maneuvers and training, between Ft. Bragg andd  Southern Pines, with the western edge along the SAL main line.   Spaced around the target point for dropping the system in a hezgon pattern were six Altec 21B concenser microphone systems, powered with ac from an ac generator in our 1-1/2ton truck, which also housed the six Magnecorders that would record the signals from the six microphones.  Ordinary field wire would power the microphone preamplifiers and bias supply for the microphnes, and the voltage drop over 1000 feet was calculated not a problem.  We expected to use microphone cable, two-conductor plus shield, between the Altecs and the Magnecorders.  The prerecorded tape in the device had random words, test listeners would listen to the tapes we made, and the experiment would be a success if most of the words they wrote matched the list of the words in the device.

The microphone cable never arrived.  I was ORDERED to try to make the setup work with field wire used for microphone cable.  Of course unshielded wire running such  a distance and in parallel with the AC power line produced hum, buzz, and hiss, all at the same time.  But Eureka, I really earned by MIT degree by solving the problem.  At the microphone line input to each Magnecorder, I installed a regular volume control across the incoming two wires of the field wire pair, wirh the control output connected to the Magnecorer ground.   And I could tune out completely, below tap-hiss, all the hum, buss, and hiss, by adjusting the control.

But on one test, wind came up, the device blew off couse, and landed smack dab in the middle of the SAL main line, and I had visions of the Silver Meteor or whatever zipping into it at 100mph.  But I got on my walkie-talkie, called the Fort Bragg message chief, and was specific to call the SAL Hamlet Dispatcher with the information, and that I would call back when the track was clear.  He called me and to my great relief said no trains were scheduled for the next two hours.   So  we meneurvered our truck to the side of the track, hooked our cable onto the device, manage to guide it over the near rail without damaging it or the rail, and it slid nicely up the loading ramp as usual to a secure spot in the truck.  I called the Message Center Chief, and possession of the track reverted to the railroad.