[Discuss-gnuradio] Halfband filter,etc.

[Sebastiaan Heunis]

Hi people

Can I please ask a question or two about the HBF?  So I know that it
is has 31 taps and what the coefficients look like from reading a bit.
 Is it just a lowpass decimation filter from Goodman and Carey's list?
 How does it work?  Is it just like a standard FIR filter where the
input gets convolved with the filter taps?  Is the decimation achieved
because every second tap is 0?  I know that we receive an input value
every 64e6/(decimation/2) from the CIC filter.  I know for a
decimation of 16 the hb_strobe is supposed to be 4MHz.  I just don't
know where the last clocking down by 2 is done.  I've seen this bit of
Verilog:

always @(posedge clock)
     begin
        start_d1 <= #1 start;
        start_d2 <= #1 start_d1;
        start_d3 <= #1 start_d2;
        start_d4 <= #1 start_d3;
        start_d5 <= #1 start_d4;
        start_d6 <= #1 start_d5;
        start_d7 <= #1 start_d6;
        start_d8 <= #1 start_d7;
        start_d9 <= #1 start_d8;
        start_dA <= #1 start_d9;
        start_dB <= #1 start_dA;
        start_dC <= #1 start_dB;
        start_dD <= #1 start_dC;
     end // always @ (posedge clock)

   reg    mult_en, mult_en_pre;
   always @(posedge clock)
     begin
        mult_en_pre <= #1 phase!=8;
        mult_en <= #1 mult_en_pre;
     end

   assign clear = start_d4; // was dC
   wire   latch_result = start_d4; // was dC
   assign strobe_out = start_d5; // was dD

Can anyone please help?

Thank you in advance.

Sebastiaan

-- 
Sebastiaan Heunis
Radar and Remote Sensing Group, University of Cape Town
Tel:  +27 83 305 5667