R2D2 occurs when there is enough signal for the D-STAR receiver to  
detect the digital signal but the signal has degraded to the point  
that error correction cannot recover the original audio stream.  It  
has long been observed that the trained ear may be able to pull the  
audio out of a very weak FM-Analog signal as the brain can "fill in"  
for the missing elements of speech.  If you hear "che-r-le impal-"  
your brain has heard "chevrolet impala" enough times it can "correct"  
the missing elements.  When the vocoder looses lock, it can take a  
little longer to get it back and the intervening sounds (R2D2) have  
little or no relationship to the speech that is being sent, as the  
brain has no frame of reference to rebuild the original phrase.   
Consequently, once the D-STAR signal falls into the thin slice between  
recoverable audio and dead silence, it is generally not useful -  
however as FM-Analog approaches that same signal level, copy becomes  
more and more difficult while the D-STAR signal remains quite clear,  
right up to that threshold..

This is why a potential repeater operator may want to perform specific  
signal tests between the repeater antenna and a typical handheld or  
mobile stations rather than depending on reports from sources that may  
not replicate the conditions that will be experienced in the repeater  
footprint by its users.

On Mar 13, 2009, at 12:44 PM, AB8XA wrote:

> I've been into D-Star almost a week, so take this for what it's worth.

> ...
> I can usually get the gist of what's being said on a noisy FM call,
> but not on one with any significant R2D2. Someone commented that when
> DV is sweet, it's really sweet, but it's more important to me how well
> communication occurs when it isn't sweet. I guess until I learn to
> pick through R2D2, analog seems to do better there for me.
> --
> Moe

John Hays
Amateur Radio: K7VE

[Non-text portions of this message have been removed]

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