Hi, Thanks, I need to think about this a bit prior to commenting on it. :) -- 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 10:20 -0400, Guy Olinger K2AV wrote: > Hi, Dave. > > > Well, there is one thing you did not do. A fourth condition, which > would be difficult, a lot more work given what you were doing. That > would be changing his syn first and noting the difference. It might be > that the TX change first would create a different middle picture in > the series. But I doubt it... > > > These are not linear additive behaviors, and explaining noise > reduction from various sources is often very complex. The appearance > in the *frequency span* of the heavy continuous noise is cut in half > in the middle picture and then cut in half again in the third. That > would appear that the combining is a multiplicative function. The > difference at a given frequency would then be completely a child of > the shape of the noise curve, rendering the reduction at some > frequencies as an "effectiveness" measure pretty meaningless. > > > Noting that the heavy noise bandwidth is halved and then halved again > presents a better assessment. By that measure the changes are equally > effective. > > > 73, Guy > > On Wed, Jul 8, 2015 at 9:02 AM, David Cole <[email protected]> wrote: > 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:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: > http://www.qsl.net/donate.html > Message delivered to [email protected] > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
