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I think as long as the proper display is there, someone using the 1.2k gmsk modem with analog audio (or echolink with callsign pass-through) won't really be noticed. It will probably require some special tricks somewhere along the line to properly work with the Icom gateway software and such, but that's already taken care of in Jomathan's software.
On Wed, May 23, 2012 7:02 PM EDT John D. Hays wrote:
The argument that analog should never be linked to digital because of white
noise and other artifacts forgets that Vocoders (as opposed to Codecs) like
AMBE and Codec-2 are specifically looking for speech and work hard to
remove background noise. All audio starts and ends as analog and
transitioning from an analog FM to digital voice system using a vocoder
applies the same filtering to the audio. I think the folks the argument
haven't tested their theory. Some who have tested it, can probably show
some issues like drop out, overdrive on CTCSS, etc. that will degrade the
system, however, well conditioned audio from an analog FM source should
encode much like analog voice from a microphone.
The second argument is often that the callsign information isn't there in
an analog signal or incompatible digital voice signal. Rules may vary
around the world, but here in the US the ID is for the transmitter where
the signal originates. It doesn't need to be passed through the network for
identification purposes (other than courtesy or vanity) when it comes to
the regulations. In D-STAR, the callsign is also used as an address for
directed transmissions. In a linked system the only address needed is the
one that identifies the repeater(s) and conference channels, so that the
traffic is properly routed.
Any linking protocol that mixes systems should contain an ability to
identify the type of traffic source (Analog, Digital) and encoding (AMBE,
Codec-2, etc.) and allow the administrator of a repeater to determine which
traffic to accept.
Given these two "non-issues", the rest is just politics. :)
John D. Hays
PO Box 1223, Edmonds, WA 98020-1223