When the input to the phase detector consists of the OCXO signal plus another frequency offset from the first i.e.
Vi(t) = A1*cos( w1*t) + A2*cos(w2*t) Where w1 = 2*PI*(OCXO frequency) the observed signal at the output of the phase detector is: Vo(t) = Vi(t)*sin(w1*t) Vo(t) = A1*cos(w1*t)*sin(w1*t) + A2*cos(w2*t)*sin(w1*t) Vo(t) = (A1/2)*sin(2*w1*t) + (A2/2)*[sin((w1+w2)t) + sin((w1-w2)t)] After low pass filtering Vo(t) = (A2/2)*sin((w1-w2)t) Thus the amplitude of the discrete spur related component in the low pass filtered phase detector output is 1/2 (6dB) the amplitude of the discrete spur itself. This result is independent of any additional calculations that may be done to derive L(f) from the observed spectrum. The conclusion is independent of any arbitrary phase for the spur signal. It is also independent of the exact phase detector characteristic. If the phase detector characteristic isnt sinusoidal the the phase detector output baseband signal is unchanged. Bruce _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
