How to preserve base band signal's bandwidth
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I am using a baseband signal with bandwidth 100 kHz, which I then multiply with a local oscillator of frequency 1.5 MHz. Now, when I see the output after the up-conversion, the base band signal is up-converted to 1.5 MHz frequency, but, the original bandwidth of 100 kHz is not preserved. Rather, the bandwidth is also stretched to 1.5 MHz (the same as the local oscillator's frequency).
How can I up-convert my signal while keeping the original bandwidth of 100 kHz?
I have been trying to look into a lot of things, but couldn't find any solution.
Any help or guidance would be valuable.
Puneet Rana 2014-12-2
For up-conversion you typically need to first increase the sample rate of your input through (multistage) interpolation and then multiply by local oscillator. See the example: http://www.mathworks.com/help/dsp/examples/digital-up-and-down-conversion-for-family-radio-service.html