Al, Let me pose a set of conditions, and see if I understand this...
Is the smearing caused mostly by the phase noise sidebands, as a resultant of phase flicker? i.e. If the phase noise were reduced on a transmitting VFO, then the smearing would also be reduced, because the sidebands would no longer reflect the wide band phase noise, as-- well-- sidebands? Is this correct? If so, then does that mean that as a station gets stronger, one picks up more of the phase noise, (a function of how far from center one is), and that is why a signal gets wider as it gets stronger? It occurs to me that the the the RX VFO phase noise would be less influencing, (on phase noise sidebands), than the transmit VFO phase noise... Is that correct? If so, then that would explain why the largest change occurred when K7OLN got his new synthesizer, as opposed to me getting my new synthesizer, as shown in the difference between photos 2 and 3. Is my understanding correct? -- Thanks and 73's, For equipment, and software setups and reviews see: www.nk7z.net For MixW support see; http://groups.yahoo.com/neo/groups/mixw/info For Dopplergram information see: http://groups.yahoo.com/neo/groups/dopplergram/info For MM-SSTV see: http://groups.yahoo.com/neo/groups/MM-SSTV/info On Wed, 2015-07-08 at 05:14 +0000, Al Lorona wrote: > We like to think that a VFO exists only at one frequency -- the > frequency on the receiver display. > > > But in reality every VFO has width, and it occupies not only it's > nominal frequency but is "smeared" both lower and higher in frequency, > too. This is because of the phase noise of the synthesizer or VFO. > > > Because of the smearing effect of this phase noise, received signals > can also appear wider than they are. The noise floor on either side > rises in direct proportion to the synthesizer's phase noise. Dave's > screenshots of the P3 spectrograms show this smearing clearly. > > > An oscillator with less phase noise looks more like that ideal picture > we all have in our heads -- of a signal that's infinitely narrow. In > the third of Dave's screenshots you can see how the new synths are > closer to an ideal oscillator-- the CW signal's width on the > spectrogram is much narrower. > > > If a signal has lower noise sidebands (whether the sidebands are > generated in the transmitter or the receiver... each of them has a > synthesizer) then you can enjoy less interference from an adjacent > signal. You will also *cause* less interference to your neighbors on > the band. > > > I have no idea of the design of the new synths, but in general to > design a synthesizer with low phase noise you have to start with very > low noise devices, pay really careful attention to the parts of the > phase-locked loop like the Q, feedback, the numeric dithering, the > loop filter and various other aspects of the circuit. It's a real art. > It appears from Dave's observations that there is a significant and > measurable difference. > > > > > Al W6LX > > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
