[ARC5] Force Feeding Audio into a T19/ARC-5 to Make It Sing for Its Supper/RM-12 Remote Questions

[Christopher Bowne]

Having fun lately feeding high quality audio into my otherwise stock BC456 
screen modulated T19/ARC-5.  I have been truly amazed as to how good these 
things can sound, and how nice the mod waveform looks on a scope.  Been using an 
old RM-12 remote control unit and feeding audio from a small utility amp with a 
25V  line output onto the RM-12 Line 1 landline input terminals.  Also heavily 
loading the RF output circuit with the KJ4KV RF autotransformer circuit, that 
makes a big difference in the modulation linearity and max positive peaks 
percentages attained vs just coupling  a coax 50 ohm load into the antenna 
terminal via a series cap.  Playing "test audio" in to this setup using a dummy 
load shows really clean low end and highs, a pleasure to listen to on a good 
stereo system fed by the R-392.  Better sounding than some of the local FM 
outlets around here!  Getting about 15 watts carrier out when adjusted for best 
audio quality.

Interested in learning more about how the RM-12s were used in the field.  As far 
as I can tell, the T/R switching must be done locally at the transmitter by an 
operator with it, making it more of a phone patch than a true remote control 
unit. How was the true remote operation, including the T/R switching from a 
remote location done, was there another unit besides the RM-12 used in the RC-?? 
system, or was there some DC switching voltage carried over the twisted pair 
feeding into the RM-12? Is there an RM-12 TM or  other documentation out in 
cyberspace?