On Fri, 2006-06-02 at 17:34 -0700, Duane - N9DG wrote:
> --- Bill Tippett <btippett@alum.mit.edu> wrote:
>
> > Corsair's measurements were done long ago before Rob had
> > standardized on his current 10 kHz for phase
> > noise and 2 kHz for IMD.
>
> I will stick by my wish to see it standardized at something
> under 5kHz, much for the same reason as wide spaced IMD
> (>5kHz) measurements don't tell the story for real world
> performance in the IMD dimension.
The 2.5 KHz from carrier out are the frequencies of phase noise that
affect the received signal directly. Further out affects unwanted
signals being phase modulated to spread them into the pass band.
Real world IMD measurements are made at 20 kHz because most radios with
20 kHz wide roofing filters come up with really rotten IMD results
because the first IF and second mixer aren't made to handle the
increased signal level that comes from gain at the first IF before the
second mixer. Its most instruction to see both 5 and 20 and maybe 50 or
100 kHz IMD results.
>
> > Also, Orion's phase
> > noise does not degrade appreciably at closer
> > spacings compared to Omni. (see figure 2-b on
> > page 5 below. I suspect Corsair also degrades
> > more at very close spacings than Omni but do
> > not have any measurements.
>
> I highly doubt that is the case. I suspect that the Corsair
> holds up better as you get closer. From what I can tell the
> first radio that can truly match (I think may even exceed) a
> non synthesized LO for phase noise performance is the Orion.
>
> The big thing that I see with the Omni VI(+) phase noise plot
> in the QST review(s) is that it is somewhat "spikey"
Spikes in the phase noise plot are usually the results of some phase
modulation from the phase detector frequency (and its harmonics) both
from the programmable dividers and from leaks in the loop filter.
> I really
> doubt that the Corsair (or any other PTO/Xtal LO radio) would
> do that. Unfortunately the ARRL made no attempt to measure
> phase noise of the Corsair II when they reviewed it in 1987.
> That said I don't think that the measurements of the TX phase
> noise that they started making a few years later necessarily
> reflects how the RX performs for that parameter either.
Another possible standard of low phase noise should be the Collins S-
line with even better PTO stability than the Corsair II.
>
> One big flaw of the Omni VI that I have (Oct 1992 vintage -
> no option upgrades) is that it is full of spurs on 10M. So
> many in fact that I find it unusable for VHF transverter IF
> duties here. The Corsairs and Pegasi that I run are much
> cleaner. I know that Bob, K4TAX and some others were
> successful at slaying most of the 10M RX spurs by making
> extensive mods to the CPU board. I have not attempted to do
> any of those mods and I'm not likely to do so either because
> I'm focusing my efforts on other technology for my transverter
> IF's. For the very near term I'll just keep using the Pegs
> with Corsair's as sub RX's on VHF.
>
> Duane
> N9DG
>
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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