Modulation is information

Produce modulated signals is one the purposes of experiments with DSP included on OMAP-L137. The CODEC included in OMAP-L137 can support sampling (input and output) up to 96 KSPS. This allows for manipulation of signals up to 45 KHz (a little bit more).

So on this experiment I decided to experiment with digital modulations. For this purpose, two signals are synthesised (with samples), both exact divisors of main frequency to have a small number of samples. One of them, of higher frequency, will be the carrier. The other of a lower frequency will be the modulating signal.

This experiment explores techniques used in modulation of AM, DSB, USB/LSB signals. For AM and DSB, simple mathematics are used. For all of them an I/Q (with signlas in quadrature) modulator has been designed.

I/Q is a "complex" matter. Somtimes has a meaning sometimes other. So I plan in the near future add some explanation to the mathematics behind this matter.

¿How to test these signals?. Just connect the "Line-output" of the kit to the "Line-input" of your computer souncard, and use one of the many signal analyzer with spectrogram programs. I've used Spectravue, but others as PowerSdr can be used too.

You must be able to see lines of the spectrum corresponding to each modulation, considering that your soundcard rate and wideband is enough for all the presented signals.

If you have a receiver able to reach the low carrier frequency, inject the signal on receiver (Two twisted wires coupling -antenna receiver, and line out- are enough for receiving de signal). Avoid direct connection unless you can guarantee your receiver can withstand with near 1Vp-p without damage.

Probably you noted no FM modulation has been included, and expect audio modulation. For this we need more complicated processes. In the next entries we will introduce oscillators (for generation of any frequency non related to sampling) and filtering (useful for SSB generation from a real signal).

But now you can experiment with modulations downloading porject for CCSv4 and OMAPL137 KIT from here: http://sites.google.com/site/dspradiol137/downloads/100106a.zip