Pre VARA , the average data interface , used transformer coupling and served to limit the bandwidth and introduce
various oddities , fine for psk rtty etc, but conveying a complex signal, probably was not to common place , yes the modem can work around the problem, but it consumes resources , often, deployments, unwittingly, had narrow b/w selected , and it still functioned , during testing 50% b/w reduction , served only to reduce the rate .
So if usb direct link is available , then , that's optimum, if the mode wider , then its obviously not , the ic7100 has a 12 KHz b/w option, described as IF-out to enable DRM signals to be monitored , never used it , assume it uses the cal-usb link , there is also a data tx bandwidth setting, that is not documented , that allows to 3.5 Khz b/w but for some reason, the filter is centered on 1.5 KHz ..
video showing use of the ic7100 IF feed , but , may be time lag issue ..have to check
also >> You don't have to go to this complex level to use DSD with a IC-7100, you can decode direct from the IC-7100 either via USB AF out or the DATA 2 port using the 9600 pin to the Line in or Mic port on a PC. Just remember to select 9600 in the Connectors menu and FM-D as the mode and away you go. Mike G1ZRN.
Two ways then ...
Its not immediately clear as to the 5100 facilities , the manual indicates a data in/out for accessing the DV mode, two models , one with and one without ? and the cv-i address is listed , as is the com port settings , rig control is not too well detailed