Perhaps you have a dc offset in the test_audio.wav data which would
result in the presence of the carrier after the modulate step?
Nick, g4jnx.
raymonda58 wrote:
>The lower sideband signal file is useful as a test source as it
>exists, however I discovered an anomaly that I am trying to track
>down.
>
>The signal contained in the .wav file is a LSB signal with carrier
>inserted. I generated the signal utilizing the Matlab modulate.m
>function. At first I thought the presence of the carrier was a
>function of the Matlab function. Further testing (including coding my
>own SSB generation code from first principles) showed a definite
>presence of an unsuppressed carrier that shouldn't be there. Further
>investigation has shown the undesired carrier is not present if I
>generate test tones mathematically. Whenever I input an audio signal
>either by way of a .wav file or directly from the microphone through
>the sound card the undesired carrier appears.
>
>Inspection of the spectra of the generated signal within Matlab using
>an FFT shows the same spectral characteristics as displayed in
>SDRadio.
>
>So it seems that the undesired carrier is somehow caused by the
>sampling associated with the sound-card and/or .wav file. I'm going to
>try running the audio through a 300Hz to 3kHz BPF before applying it
>to the modulator to see if I can eliminate the carrier.
>
>Once I solve this issue I'll generate some proper LSB, USB, DSB, AM
>and FM test files.
>
>
>-Ray WB6TPU
>
>
>
>
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