[time-nuts] Realistic Tbolt phase noise

John Miles jmiles at pop.net
Tue Mar 9 21:59:48 UTC 2010


I haven't exhaustively tested the ADF4107 but I have played with the ADF4002
recently.  I haven't been able to come within several dBc/Hz of its rated
noise level.  In one test, at 100 Hz from an 80 MHz carrier, I've seen
about -118 dBc/Hz from the ADF4002 when fed by 10 MHz with -145 dBc/Hz at
100 Hz (which would become about -127 dBc/Hz in an ideal 80 MHz multiplier.)
The figure-of-merit equation suggests that -222 + 20*log(8) + 10*log(10 MHz)
= -134 dBc/Hz would be achievable, well below the -127 dBc/Hz limit imposed
by the reference.

ADISimPLL thinks the figure of merit for the ADF4002 is -216 dBc/Hz rather
than -222, so its predicted inband noise of about -122 dBc/Hz is quite a bit
closer to my observation.  The remaining ~4 dB could be partially bridged by
careful tweaking of the drive waveform and input levels to the chip, but the
9 dB needed to get to -127 would be a much bigger leap.

Both the old and newer-style Thunderbolts have been tested at around -145
dBc/Hz at 100 Hz, so I think Bob's right in that you can't take full
advantage of it with an ADF-series chip.  Both the 4002 and 4107 are among
the best-rated parts in the lineup.

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Bob Camp
> Sent: Tuesday, March 09, 2010 9:44 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] Realistic Tbolt phase noise
>
>
> Hi
>
> I think you will find that the noise floor of the ADF4107 (dividers and
> phase detector) is a bit higher than -150 at 100 Hz offset at 10 MHz. It
> should get you past the -120 level though. That's still much
> better than you
> are seeing.
>
> Indeed -120 is not what figure 15 on page 8 of the specification would
> imply. I'm sure that the figure is technically correct. It's just not
> showing the complete picture.
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Christophe Huygens
> Sent: Tuesday, March 09, 2010 12:28 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Realistic Tbolt phase noise
>
> Hi,
>
> I am using an ADF4107 and a Crystek resonator, with a LBW of
> a few 100 Hz. It behaves perfect outside the loop, but inside the
> loop it is too noisy (not too important for my application, but
> just curious).
>
> I ll try to measure the Thunderbolt directly at 10Mhz, but the
> my HP 11729C needs some mods for this.
>
> Christophe
>
>
> On 09/03/10 18:21, Bob Camp wrote:
> > Hi
> >
> > How are you multiplying it to 1 GHz and checking it?
> >
> > I've seen multipliers that have issues beyond about -130 at 100 Hz. It's
> not
> > common, but it can happen.
> >
> > ------------------
> >
> > The supply provided by TAPR is a pretty basic unit. It would
> not surprise
> me
> > if some were better than others. They also may work better on US mains
> > voltage than they do on international voltages. I would rig up another
> > supply and see what happens. That would at least rule out the
> supply as an
> > issue.
> >
> > In a previous post the idea of putting a 7805 and 7812 regulator on the
> > TBolt came up. If you have +14 available that seems like the
> best thing to
> > try.
> >
> > Bob
> >
> > -----Original Message-----
> > From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> > Behalf Of Christophe Huygens
> > Sent: Tuesday, March 09, 2010 7:50 AM
> > To: Discussion of precise time and frequency measurement
> > Subject: Re: [time-nuts] Realistic Tbolt phase noise
> >
> > This is with the power supply as provided by TAPR so should be ok.
> >
> > Xtof.
> >
> >
> > On 09/03/10 13:44, Bob Camp wrote:
> >
> >> Hi
> >>
> >> Power supply noise would be the first thought.
> >>
> >> Next up would be grounding inside the Thunderbolt (card to case,
> >>
> > connectors to case).
> >
> >> Bob
> >>
> >>
> >> On Mar 9, 2010, at 7:32 AM, Christophe Huygens wrote:
> >>
> >>
> >>
> >>> Hi,
> >>>
> >>> I noticed several vendors on Ebay have the t-bolt on sale.
> >>>
> >>> However, the once showing their own PN plots seem to get only
> >>> -115, -120 dBc/Hz at 100Hz. Yet,
> >>> http://www.leapsecond.com/pages/tbolt/noise.htm seems
> >>> to have mucht better results: up to -150 depending on
> >>> power supply.
> >>>
> >>> By multiplying to 1GHz I also seem to be getting something
> >>> like -75 or - 80 rather than -110.
> >>>
> >>> Any thoughts?
> >>>
> >>> Christophe
> >>> on4iy
> >>>
> >>>
> >>>
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