Bruce Griffiths wrote: > John Miles wrote: > >> Hmm, I didn't know that. Wouldn't that effect have suppressed the 2nd lobe >> almost entirely on the baseband measurement, though, rather than making it >> appear 6 dB too high? I should probably repeat that measurement to make >> sure of what I'm doing. >> >> Much appreciate the advice, by the way! >> >> -- john, KE5FX >> >> >> > John > > In a linear system the corresponding USB and LSB sideband component > amplitudes are identical so that on translation to baseband by the phase > detector all the even harmonics cancel and the odd harmonics add. > However in a non linear system the USB and LSB components will not have > equal amplitudes. Assymmetric filter passband response will also > attenuate one sideband with respect to the other. > > If the phase detector LO phase shift isnt exactly 90 degrees wrt to the > carrier the even harmonics no longer cancel exactly. > > In an I + Q demodulator FM USB and LSB components have the following > characteristics: > > I channel: > > for odd harmonics (of the modulation frequency) USB and LSB components add > > for even harmonics (of the modulation frequency) USB and LSB components > cancel. > > Q channel: > > for odd harmonics (of the modulation frequency) USB and LSB components > cancel > > for even harmonics (of the modulation frequency) USB and LSB components add. > > Bruce > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > Whoops reverse that:
Q channel: (phase detector) for odd harmonics (of the modulation frequency) USB and LSB components add for even harmonics (of the modulation frequency) USB and LSB components cancel. I channel: (AM detector) for odd harmonics (of the modulation frequency) USB and LSB components cancel for even harmonics (of the modulation frequency) USB and LSB components add. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
