On Mon, Nov 18, 2013 at 10:56 AM, Paul B. Huter [email protected]
Thanks, Tom. I do intend to decimate the 50MHz input by 50 to have 1MHz. Is
Yes, decimating by a factor of 50 will give you 1 Msps. Remember to
define your filter for a sampling rate of 50 Msps and a bandwidth of
500 kHz to achieve what you want.
Paul B. Huter
I should have asked this with your other question. What do you mean by
center frequency? Don’t confuse that with samp_rate. The center
frequency is where you’ve tuned your receiver to. GNU Radio deals with
complex baseband, so the frequency you’ve tuned your front-end (e.g.,
USRP) to is viewed by GNU Radio as 0 Hz.
The samp_rate in your example above should be set to the sampling rate
of the receiver: that is, 50 Msps. The bandwidth of your filter is
determined based off this.
Remember that you are /just/ filtering your signal but not affecting
the sampling rate at all. So if you set up your filter like this:
taps = firdes.low_pass(1, 50e6, 15e6, 500e3)
And your filter block as:
lpf = filter.fft_filter_ccc(1, taps)
Then you are not changing the sampling rate at all. You will remove
anything between 30 - 50 MHz but your sampling rate is still 50 MHz.
Also, I see you have a sampling rate of 50 Msps but a transition width
of 100 Hz. That’s going to be one gigantic filter! You don’t need that
tight of a transition band.
Run gr_filter_design. You can set up the parameters there and look at
the shape of the filter. It will also tell you the size of your