% Now plot the signal minus the noise
figure(3);
N = 1; % down-sample the FFT 
BANDDIV = 2.5; % take this fraction of the bandwidth 
fft_freq_sub = linspace(1, 1/T_samp/2/BANDDIV, fft_length/2/N/BANDDIV);
fft_signal_sub = downsample(fft_signal, N);
fft_noise_sub = downsample(fft_noise, N);
fft_domain_sub = 1:(fft_length/2/N/BANDDIV);
semilogy(fft_freq_sub, abs(fft_signal_sub(fft_domain_sub) - fft_noise_sub(fft_domain_sub)) );
title('Signal Minus Noise Spectrum');
xlabel('Frequency (MHz)');
ylabel('Magnitude (Volts)');
print -djpg 'signal_minus_noise_spectrum.jpg'