Re: [Patch-gnuradio] Re: assert (dac_rate () == 128000000);

[Matt Ettus]

The reason for the limit is that the DAC outputs have a sin(x)/x 
rolloff, which puts a big null around multiples of 1/2 of the sampling 
frequency.  Thus, 44-84 MHz is not really very useful.

Matt

On 12/12/2009 07:54 AM, Alexander Chemeris wrote:
> Hi Erik,
>
> Could you give me some insight why high value is set to 44e6?
> Coarse modulator can be set to 128e6/4=32e6 and docs says
> that fine modulation has range of 128e6/4=32e6 too. Thus it should
> be possible to get as much as 32e6+32e6=64e6 offset. Was 44e6
> chosen because of interpolation filtering limits or smth like that?
>
>
> On Sat, Dec 5, 2009 at 17:34, Eric Blossom<address@hidden>  wrote:
> > On Thu, Dec 03, 2009 at 12:09:02AM +0300, Alexander Chemeris wrote:
> > > Hi all,
> > >
> > > Anyone to apply this one-liner?
> >
> > Alexander,
> >
> > The hard-coded magic numbers below the assert need to be corrected to
> > to be a function of the clock rate.  You're not seeing the problem
> > because of the daughterboard you're using, but if you're using a Basic
> > Tx, they come into play.
> >
> > The existing magic numbers are particular percentages of 128e6.
> > The replacements, f(clock_rate), should be the same percentages.
> > They control when and which "coarse modulator" is used in the AD9862.
> >
> > Can you please submit a slightly bigger patch?
> >
> > I apologize for not writing earlier about what the problem was.
> >
> > Thanks,
> > Eric
> >
> >
> > > On Tue, Nov 3, 2009 at 01:01, Alexander Chemeris
> > > <address@hidden>  wrote:
> > > > Hi all,
> > > >
> > > > This assert is not valid, because you may use re-clocked USRP.
> > > > And we indeed do ;)
> > > >
> > > > Patch to remove it is in attachment.
> > > >
> > > > --
> > > > Regards,
> > > > Alexander Chemeris.