locked #Beacons Q65 generated by direct upconversion #Beacons


Andy TALBOT
 

16F1827 PIC generating Q65B-15  from a pre-stored set of symbols via I/Q upconverter at 3.4GHz. 

Two pulse width modulators on the chip generate  0° and 90° sines from a numerically controlled oscillator sampled at 31250Hz, frequency determined by the symbol set read out at the symbol period.

Tones are upconverted in an ADL5375 quad upconverter chip direct from baseband to RF - the chip works over the frequency range 400 - 6000MHz

As the NCO generates an I/Q output, it is perfectly in order to programme negative frequencies; here the 854Hz frequency span is covered by generating tones from -433Hz to +420Hz.

The unchanging carrier at the centre of the screen at about -20dBc is carrier leakage.   NO attempt was made to null this out any more.    The nice thing about baseband upconversion is that leakage and image response fall on top of the wanted signal, so provided they are 17dB down or more, go unnoticed by any demodulator.

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