Re: [Discuss-gnuradio] atsc_cpll finally works

[Eric Blossom]

On Fri, May 23, 2008 at 06:54:16AM -0400, Charles Swiger wrote:
> On Thu, 2008-05-22 at 22:35 -0700, Eric Blossom wrote:
> > On Thu, May 22, 2008 at 10:53:12PM -0400, Achilleas Anastasopoulos wrote:
> > >
> > > So the signal u(t) needs to be sampled at 6 Complex-Msps, which is what 
> > > you 
> > > do (sampling it at 6.4 Complex-Msps, or as Eric wants at 8 complex-Msps).
> > >
> > 
> > I'm worried about the roll off at the edges of the passband at 6.4 MS/s.
> > We're only flat to about 70% of Fs, which is 4.5 MHz at 6.4 MS/s.  
> > If it can be made to work well at 6.4 MS/s, that's great.
> > 
> 
> Your right, it would probably work better at 8Msps - however, with a
> decent signal it *does* work at 6.4Msps. It's an engineering trade-off,
> you want it fast or good? For now I want to squeeze out all the fat just
> to get it to work at all in real time, then when we get enough
> effeciency / cpu horsepower make it work well for marginal signals. 

For my part, I want it good, then fast.
Marginal signals are all you'll ever get with an indoor antenna ;)

There's plenty of stuff we can do to make it fast.  We haven't even
begun to scratch the surface.  We only need to carry the 8 MS/s
through the first couple of blocks, then we'll be running at the 10.76
symbol rate.

Eric