[Elecraft] Observation on new Synthesizers for K3
David Cole
dave at nk7z.net
Wed Jul 8 10:25:06 EDT 2015
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 <dave at nk7z.net> 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
> >
> >
> >
> >
>
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