Signal Package pwelch

[Thomas D. Dean]

I have a application using the signal package pwelch function that seems 
to produce an incorrect plot.

[s, f] = pwelch(iq,[], overlap=0, NFFT=2048, Fs=sample_rate, 
detrend='none', range='shift', plot_type = 'dB')

iq is read from an rtl-sdr

knowing the location of some signals, like the Hydrogen line, and, 
comparing this to python, pwelch puts the "hydrogen bump" about .3MHz 
too high.

pwelch(iq,[], overlap=0, NFFT=2048, Fs=sample_rate, detrend='none', 
range='shift', plot_type = 'dB');

How do I upload an image to show this?

Tom Dean