ALL RC radios in the United States are Narrow Band. This was mandated by the FCC years ago and all RC radios in the 72 Mhz range must comply. This is what moved this hobby from 5 available channels to the 50 that we have now.


Actually, this should read; "All RC TRANSMITTERS in the United States are Narrow Band". There are some FCC requirements for receivers but they have nothing to do with bandwidth, and bandwidth requirements for them do not exist.
NB receiver requirements are an AMA recommendation (ONLY) and can actually only be enforced at AMA controlled fields and events. AMA does not have the federal authority that FCC has. Double conversion, though not mentioned goes hand in hand with receiver design, but again it is not mandated by anyone - it is a manufacturers method of achieving narrow band. Actually, ONE of the methods. For example, JR receivers with their unexplained "ABC&W" circuitry are single conversion, though touted as being narrow band.