[Discuss-gnuradio] freq_xlating filter

[Ben Olsen]

Hello,

I'm trying to use the freq_xlating filter to select a narrowband portion of a wideband signal, but I'm a bit confused as to exactly how much I'm changing the center frequency of the filter from the baseband value.  Could someone break it down for me please: here is where i create the filter - 
 
gr.freq_xlating_fir_filter_ccc(sw_decim,           #decim
                                            chan_coeffs1,      #taps 
                                            ???,                    #center freq 
                                            sw_decim * self._spb) #sampling freq

Suppose I wanted to select a channel (of width determined by chan_coeffs taps) that is 500kHz offset from baseband.  Since we're working with normalized frequency, I would enter the ratio of 500kHz to the sampling frequency as the center freq.  However, in trying to determine the value of sw_decim * self._spb I just put a simple print statement so that it displays, giving me the answer "2".  What are the units of this?

Thanks very much!

Ben