Happy New Year!   More photos and updates are coming soon…. and in fact this update has been over a year in the making.   Here’s two “then and now” photos of Union Switch’s Carrier Telephone equipment – the office carrier phone and a portable field phone.    Union Development –  Number 252 explains the history and application of this equipment.     Both require 110V AC as they contain tubes and operate at a frequency of 35 kilocycles.    When clipped onto a DC code line, clicking can be heard during a code cycle.    When clipped onto a carrier code line (such as US&S 507), I can barely hear the 15.3 kilocycle transmitting frequency switching on and off during a control code.     The indication frequency of 24kHz is too high for a  human ear – however it probably drives the local dogs crazy.  🙂