[time-nuts] Re: Ublox NEO-M8T-0-10​as a LO question

[Andy Talbot]

More to do with amateurs using narrow band modulations, and the LB GPSDO
being moderately good close in.   Phase noise out beyond a few kHz goes
more or less unnoticed on SSB

Andy
www.g4jnt.com



On Wed, 31 Mar 2021 at 13:35, Dana Whitlow <k8yumdoober at gmail.com> wrote:

> Chris,
>
> It may be that the modulation and subsequent demodulation scheme used for
> satellite TV and the
> like is rather more robust than many people give it credit for.
>
> Dana
>
>
> On Wed, Mar 31, 2021 at 7:09 AM Chris Wilson <chris at chriswilson.tv> wrote:
>
> > Hello everyone
> >
> >  Monday, March 29, 2021
> >
> >  Thanks for the replies, some went a little over my head, which is not
> > hard :) I am wondering how people successfully use a Leo Bodnar
> > programmable GPS source to provide an external LO for an LNB as opposed
> to
> > its internal xtal. What is different, in simple terms please, between my
> > Ublox output and the Leo Bodnar one?
> >
> >
> > Best regards,
> >  Chris        mailto:chris at chriswilson.tv
> >
> >
> > LJ> On 3/29/21 10:14 AM, John Ackermann N8UR wrote:
> > >> That's probably a really bad idea.  The phase noise from the TIMEPULSE
> > >> output is pretty bad compared to a "real" RF source, and by the time
> > >> it's multiplied up to 10 GHz you'll have more noise than signal.
> > >> Attached are some phase noise plots and a couple of spectrum analyzer
> > >> captures to give you some idea what to expect.
> >
> > >> BTW, even the Bodnar unit may not look too good at 10 GHz -- remember
> > >> that you increase phase noise by 20 dB for 10 times multiplication.
> >
> > >> John
> >
> > LJ> What's the signal bandwidth from Es'Hail?
> >
> > LJ> The optimum strategy is a *very quiet* crystal oscillator that you
> > LJ> discipline with the 1pps, and choose that oscillator so its frequency
> > is
> > LJ> what you need.
> >
> > LJ> What we've done in the past is use the reference to clock a NCO in
> > FPGA,
> > LJ> and use one of the well known spur reduction techniques that pushes
> the
> > LJ> spurs away from the center before running it to the DAC. This
> degrades
> > LJ> the performance at, say, 100kHz away, but improves the performance
> > LJ> within 1 kHz. This relies on knowing what the loop bandwidth is in
> your
> > LJ> 10GHz LO PLL, since inside that bandwidth it's the reference, but
> > LJ> outside it's the DRO or GaAs oscillator.
> >
> >
> > LJ> There might be some DDS chips that implement this kind of thing - the
> > LJ> latest chips from ADI are pretty sophisticated.
> >
> >
> >
> >
> >
> > >> On 3/29/21 12:25 PM, Chris Wilson wrote:
> >
> >
> > >>>    29/03/2021 17:20
> >
> > >>> Can I use my Ublox NEO-M8T-0-10​  as a LO for  a  modified satellite
> > >>> LNB on 10 GHz? It needs 25 MHz and the Ublox is my only GPS locked
> > >>> source for such a frequency. I want to receive the Es Hail downlink
> > >>> with excellent stability. I can lock the receiver to 10 MHz which is
> > >>> available from my Trimble Thunderbolt. If the Ublox would do I would
> > >>> not have to buy something like the Leo Bodnar GPS. Thanks.
> >
> >
> > >> _______________________________________________
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> >
> > LJ> _______________________________________________
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