From 9458a881601016c81e12c273a83183f7cae04371 Mon Sep 17 00:00:00 2001
From: Erik Kooistra <kooistra@astron.nl>
Date: Thu, 30 Nov 2017 10:40:37 +0000
Subject: [PATCH] Use fir_wb_reverse to try effect of wrong wideband factor P
order of the FIR coefficients.
---
applications/apertif/matlab/run_pfir_coeff.m | 37 ++++++++++++++++----
1 file changed, 30 insertions(+), 7 deletions(-)
diff --git a/applications/apertif/matlab/run_pfir_coeff.m b/applications/apertif/matlab/run_pfir_coeff.m
index 107686f199..cff3d954f0 100644
--- a/applications/apertif/matlab/run_pfir_coeff.m
+++ b/applications/apertif/matlab/run_pfir_coeff.m
@@ -65,16 +65,16 @@ close all;
fig=0;
%% Select application
-%application = 'lofar_subband'; % load LOFAR subband filterbank coefficients from file
-application = 'apertif_subband'; % calculate Apertif subband filterbank coefficients using fir1 or fircls1
-application = 'apertif_channel'; % calculate Apertif channel filterbank coefficients using fir1 or fircls1
+application = 'lofar_subband'; % load LOFAR subband filterbank coefficients from file
+%application = 'apertif_subband'; % calculate Apertif subband filterbank coefficients using fir1 or fircls1
+%application = 'apertif_channel'; % calculate Apertif channel filterbank coefficients using fir1 or fircls1
%application = 'arts_channel'; % calculate Arts channel filterbank coefficients using fir1 or fircls1
%application = 'test_bypass'; % create bypass pfir coefficients with 1 in first tap and 0 in remaining taps
%application = 'test_incrementing'; % create incrementing pfir coefficients 1:L*N for PFIR implementation verification purposes
%% - Application specific settings
-% Default settings
+% Default settings (will get overruled dependend on application)
config.hp_factor = 1;
config.hp_adjust = false;
config.dc_adjust = false;
@@ -91,15 +91,19 @@ elseif strcmp(application, 'test_incrementing')
L = 8;
coeff_w = 16;
%coeff_w = 9;
+ q_full_scale = 2^(coeff_w-1);
coeff = [1:L*N]'; % row
+ coeff = coeff / q_full_scale; % or use coeff = coeff / (max(coeff)+1);
config.design = 'incrementing';
elseif strcmp(application, 'lofar_subband')
% Load the quantized FIR coefficients of the subband filterbank in a LOFAR station
N = 1024;
L = 16;
coeff_w = 16;
+ q_full_scale = 2^(coeff_w-1);
coeff = load('data/Coeffs16384Kaiser-quant.dat'); % column
coeff = coeff'; % row
+ coeff = coeff / q_full_scale;
config.design = 'lofar_subband';
else
if strcmp(application, 'apertif_subband')
@@ -126,15 +130,16 @@ else
end
% Enable or disable adjustment of the PFIR coefficients. Uncomment to
- % overrule default:
+ % overrule application default for test purposes:
%config.hp_adjust = true;
- config.hp_adjust = false;
+ %config.hp_adjust = false;
%config.dc_adjust = true;
%config.dc_adjust = false;
% Select FIR filter design method (fircls1 yields better results than
- % fir1 regarding stop band suppression). Uncomment to overrule default:
+ % fir1 regarding stop band suppression). Uncomment to overrule
+ % application default for test purposes:
%config.design = 'fircls1';
%config.design = 'fir1';
@@ -163,6 +168,24 @@ else
end
NL = N*L; % Total number of FIR filter coefficients (taps)
+% Try effect of wrong wideband factor P order of the FIR coefficients.
+% It is noticable in the FIR transfer function as about factor 2 in dB
+% less attenuation outside the passband for bins that are multiples of
+% about N/P. For P = 4 the attenuation spikes occur at:
+% . bin 255.6
+% . bin 256.4
+% . bin 511.6
+% In a time domain simulation a CW at those bins will then also show in
+% the DC bin.
+fir_wb_reverse = true;
+%fir_wb_reverse = false; % default
+if fir_wb_reverse
+ P = 4;
+ coeff = reshape(coeff, P, NL/P);
+ coeff = flipud(coeff);
+ coeff = reshape(coeff, 1, NL);
+end
+
% Scale to actual frequency
fs = 200e6; % Lofar ADC sample rate = 200.0 MHz
fs = 200e6/1024; % Lofar subband sample rate = 200.0 MHz
--
GitLab