In 1939, the Department of the Navy contracted with RCA to build the ultimate military communications receiver.
This 82 pound RBC receiver covers 4 to 27 MHz in 4 bands. The RBC-1 is a single conversion 19 tube set, with a separate power supply
The RBB is a very similar superhet companion radio covering 500 KHz to 4 MHz.
The audio/ IF section is the same for both the RBB and RBC. The 400 KHz IFs are electrically designed to provide three switchable levels of selectivity. Further selectivity is provided through excellent audio filters and a 300 hz narrow band pass filter.