Re: Noise in receivers
Hi, folks,
Yes, I have read of the phase noise phenomenon - that it is due to phase noise in the local oscillator interacting with phase noise in the signal with low-amplitude inputs.
...and that it can be greatly reduced by using a coherent/low phase noise local oscillator.
OK, so I got my HP synthesised sig gen and a transistor set using a separate local oscillator (i.e., not an autodyne).
The set uses emitter injection, so I disabled the LO and injected a volt of LO frequency (the injection level implied by the circuit schematic) from the sig gen to the emitter of the converter.
I could not get much/any improvement in the noise-level-rise-with-weak-signal effect.
So....
1 - is the LO phase noise thesis just a Furphy? (Australian English - a fanciful or false tale)
2 - is it likely that the HP generator's output contains just as much phase noise as my old-fashioned, valve-equipped, Advance sig gen?
3 - Has *anyone* actually tried to solve this mystery OR had/built a radio that does not exhibit the effect?
(really wann'a nail this one down before I shuffle off my mortal coil, folks)
p.s. Furphy - said to derive from soldiers' chatter while standing around a Furphy water barrel - see Scuttlebutt for the Naval derivation.
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