Mike Feher wrote: > Well, I must admit I did not read the referenced article, but, he is talking > about dBc, or relative to the carrier and not kT. So, if the carrier power > is high enough I suppose it could be done. Even suppose you could measure > it, what would it take to generate such a pure carrier. That may even be > more difficult. - > > > > Mike B. Feher, N4FS > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 > 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 _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
