Back in the April 1980 issue of MR there was an article by Andy Sperandeo where seven command control systems were reviewed. These systems were by Alphatronics, Dynatrol, EMS, Onboard Control, Rail-Command, RFPT, and Salota. In addition, in the following May issue there was a review of an MRC command control system called Protrac R/C I. Of course, none of these systems would interface with another. Each of these systems utilized a receiver which was also not compatible with anyone else’s system. So far as I know, none of those first seven companies are viable today. And MRC, while still viable, probably does not offer any support for the Protrac. So anyone who had invested any amount of money in those systems is out of luck.
Actually, Rail-command, made by CVP Products, is still fully supported by them.
http://www.cvpusa.com/railcmd_system.php
They are also in the DCC business with their Easy DCC product line, and in the large scale direct radio with their AirWire900 and have now introduced a small scale version of that system for smaller scales.
http://www.cvpusa.com/mini_airwire_convrtr.php
Be it track powered or battery, there are a number of advantages to direct radio. The obvious one is reduced under layout electronics - especailly for large layouts, which with DCC can require numerous boosters, circuit breakers, reversers, radio throttle repeaters, etc.
Battery power reduces that under layout infrastructure even more.
All comments about Crest or other recievers fitting in locos are a straw man - not every loco easily accepts a DCC sound decoder and speaker. The sizes of the CVP and Crest recievers are similar to most DCC decoders - batteries are the other part of the story.
BUT, even track powered, direct radio uses simple filtered DC - becaue it is just the power,