Re: [Discuss-gnuradio] Bandswitch and rf gain added to HF Explorer

[Matt Ettus]

John Ackermann N8UR wrote:
> Thanks, Chuck -- sounds like useful new features.  I will download and play.
> 
> I meant to mention earlier in reference to the filter and the tradeoff
> between skirts and CPU usage -- have you looked at the filtering scheme
> used in the Flex-Radio SDR-1000 software?  I don't recall the exact
> details right now, but it works something along the lines of doing an
> FFT to convert the baseband signal back into the frequency domain, and
> implementing the filter as a mask against the FFT bins, and then an
> inverse FFT back to the time domain.  (I'm an idiot about this stuff, so
> probably got some component of that wrong).  The end result is almost
> "brick wall" filter skirts without using up too much CPU.

We do that already.  Instead of using gr.fir_filter_ccc use
gr.fft_filter_ccc.  We should have the fff version in there soon, too.
Probably when Eric gets back.

Even without that, you should be able to do multi-thousand tap filters
on a reasonable machine at the rates you are talking about here.

On the other hand, if you are using a filter with more than a few
hundred taps, you're doing something wrong, IMHO.  In the case of a
decimating filter, you can split the decimation into multiple stages,
thus greatly easing the requirements.

Matt