Re: [Discuss-gnuradio] saturation with multi_fft.py

[ematlis]

Ok, that works in principle, but I'm finding that I cannot sustain the 
same data rate as before on a fast dual core machine.

I'm acquiring all 4 channels, and I'm doing both low-pass and high-pass 
filtering on all of them.  I am also displaying 5 sinks simultaneously; 1 
fft and 4 scopes.

I set the decimation in the fpga to 128, and in the host to a further 10 
for an effective data sampling rate of 50 kHz, and while the gain problem 
is gone I'm seeing some uO errors.

With the decimation set to 250 in the fpga, as I was doing previously, I 
can sustain data rates of 128 kHz without a problem while having all 5 
sinks going, albeit with the gain problem.

So, in the long term it would help to have this sorted out in the fpga if 
that's possible; is that impossible as things stand now, or is there 
sufficient space in the 4rx no hb fpga?

thanks,
eric

On Wed, 10 Oct 2007, Eric Blossom wrote:

> On Wed, Oct 10, 2007 at 04:54:10PM -0400, address@hidden wrote:
> > Well, this seems logical, and if so then we've finally stumbled on the
> > point of the matter.  So what's the fix? Is it a simple matter of
> > extending the "definitions" to other decimations in the file Brian cites?
> >
> > thanks Brian and Eric,
> >
> > eric
>
> > > > Also-  this fix you are proposing- is it a simple scaling of gain that
> > > > would be independent of decimation?  Because as you can see from the
> > > > following figure, the amplitudes scale directly with the decimation for
> > > > values above 128 on the 4 rcv rbf.
> > > >
> > > > www.nd.edu/~ematlis/z.gnuradio/Amplitude_vs_decimation.jpg
> > > >
> > > > Both rbf's produce a flat response below 128 decimation; greater than this
> > > > is where the change occurs.  The standard half-band rbf does have a couple
> > > > of dips but is basically flat.
>
> OK.  In the interest of expediency, use the decimation values that
> work, then complete the decimation in the host.  The reason that
> there's a version that DOESN'T have the halfband is to save space.
> Making anything bigger (e.g., width of CIC) is contraindicated ;)
>
> Eric