> Mike > > It actually measures the additive phase noise of components > (amplifiers, splitters, transformers etc.). > Since it uses a cross correlation technique it can easily achieve a > noise floor below the thermal noise. > Cancellation of the carrier in the interferometer/bridge allows use of a > source with a phase noise well above that of the measurement system. > > In is possible to build lower phase noise oscillators using very low > phase noise sustaining amplifiers. > Such amplifiers can be implemented using feedforward correction techniques. > An RF bridge/interferometer is used to null the carrier at the input to > the low noise figure correction amplifier, so that only the phase noise > and other error components produced by the main amplifier are seen by > the correction amplifier the output of which is combined with (correct > delay and gain) the output of the main amplifier to reduce the composite > amplifier phase noise. Phase noise is absent when a carrier is not > present, so the phase noise contribution of the correction amplifier > will be very small if the interferometer/bridge is well balanced. This > technique has been used to reduce the phase noise of microwave > oscillators. In principle there's no reason it cannot be used at lower > frequencies. > > Bruce > Addendum/Correction
Use of the cross correlation technique and cancellation of the carrier in the interferometer/bridge allows use of a source with a phase noise well above that of the measurement system. The test signal phase noise is common to both correlator inputs and is rejected by the cross correlation technique. Bruce _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
