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BS67BW Fourier frequency labels are mis-scaled and off by one bin #16
Description
BS67BW uses Fs=4*Fc instead of 4*Fc/3, and its negative FFT window starts at Nz/2 instead of Nz/2+1. A known transmit delay is therefore compensated with the wrong frequency. On current dev, this MWE leaves −90.35°; expected 0°.
Paste into MATLAB from the repository root (no GPU/MEX):
addpath(genpath('echoframe/matlab/core'));
fc = 1e6; dt = 1/(8*fc);
P = struct('pitch',3e-4,'nElements',8);
T = struct('c0',1540,'steer',0,'apodization',ones(8,1), ...
'transmitDelays',dt*ones(8,1));
R = struct('samplingMode','BS67BW','nBuffers',1,'nSamples',512, ...
'nSamplesIQ',256,'nTransmissions',1);
[~,~,~,R] = get_system_parameters( ...
struct('Parameters',struct('numRcvChannels',128)), ...
struct('frequency',1,'numelements',8),T,R);
S = echoframe_setup_fourier(P,T,R,struct('c0',1540,'nx',128,'nz',256));
t = (0:511)'*3/(4*fc);
pack = @(x) complex(x(1:2:end),-x(2:2:end));
a = fft(pack(cos(2*pi*fc*t)));
b = fft(pack(cos(2*pi*fc*(t-dt))));
[~,k] = max(abs(a));
q = b(k)/a(k)*exp(1i*double(S.frequencyAxis(k))*double(S.planewaveDelays(1,2)));
fprintf('Residual phase: %.6f degrees\n',angle(q)*180/pi);
assert(abs(q-1)<1e-5,'BS67BW transmit-delay compensation failed');
Activity
sdiebolt commentedon Oct 7, 2026
To demonstrate in Effusive (VSX simulation mode), this is what the L35-16vX sequence (using BS67W) would give with the current release of EchoFrame:
And after the fix in #17