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Re: [Discuss-gnuradio] Bandswitch and rf gain added to HF Explorer
From: |
Matt Ettus |
Subject: |
Re: [Discuss-gnuradio] Bandswitch and rf gain added to HF Explorer |
Date: |
Wed, 29 Jun 2005 17:30:36 -0700 |
User-agent: |
Mozilla Thunderbird 1.0 (X11/20041206) |
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