[time-nuts] Very challenging phase noise measurement, does anyone have an idea??

John Miles jmiles at pop.net
Thu Dec 6 01:24:00 UTC 2012


That would be a good way to do it.  I wouldn't use an XOR gate or other
digital phase detector for this, due to the low slew rate among other
things.  Instead, you could phase lock two of your sources with a
double-balanced mixer, then run the IF through a lowpass filter and a quiet
opamp or other LNA.  The baseband noise can then be viewed on a spectrum
analyzer that goes down to whatever the minimum offset of interest is.  The
analyzer's noise floor doesn't matter, it just needs to be something that
can tune down to the 100 Hz-1 kHz area.  An old-school HP 8566 or 8568 is
ideal.

For calibration details, see the references in the last FAQ entry at
http://www.ke5fx.com/gpib/faq.htm , especially HP 11729B-1. 

Alternatively, I'm not sure where the noise floor of the FSUP is, but if it
is otherwise low enough, you could mix the 125 kHz with an ultra-low-noise
OCXO and measure one of the resulting sidebands.  It might or might not be
necessary to filter the other sideband depending on how the FSUP works. 

You could also build a low-noise 8x active multiplier to get to 1 MHz where
the FSUP can see it, as well.  This would have the advantage of not
requiring a ULN OCXO for mixing, and would also boost the PN by 18 dB for
easier measurement on the FSUP.  However, you'd need to be careful with the
multiplier's residual noise, especially in the first couple of stages.  

If you need to make these measurements over and over, go with the multiplier
or mixer, otherwise I'd use an analog quadrature PLL.

-- john
Miles Design LLC


> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-
> bounces at febo.com] On Behalf Of Adrian
> Sent: Wednesday, December 05, 2012 4:40 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Very challenging phase noise measurement, does
> anyone have an idea??
> 
> You can always use an external mixer / phase detector and the baseband
> input of a HP 3048A or FSUP.
> 
> Just to name a few:
> For low power (+7dBm) you can use a SRA-3 which goes from 25kHz to
> 200MHz
> SRA-3MH +13dBm from 25kHz to 200MHz
> SRA-3H +17dBm from 50kHz to 200MHz
> For high power signals use a RAY-3. It goes from 70kHz to 200MHz.
> The IF must be specified from DC, which for the above is the case.
> 
> Between mixer and baseband input a lowpass filter is required to
> suppress the sum signal (2x f_input) sufficiently.
> 
> Adrian
> 
> 
> Azelio Boriani schrieb:
> > Yes, I have taken a look and the FSUP is 1MHz min at the signal
analyzer.
> > Timepod? No, 500KHz min... an R&S FAM modulation analyzer?
> >
> > On Wed, Dec 5, 2012 at 10:48 PM, Bob Camp <lists at rtty.us> wrote:
> >
> >> Hi
> >>
> >> A "3048" style measurement with the carrier suppressed by lock should
> do
> >> pretty well. If the XOR's are out, there are a lot of mixers available
that
> >> work at 125 KHz. A simple op-amp buffer and a sound card could do what
> you
> >> need to do.
> >>
> >> Bob
> >>
> >> -----Original Message-----
> >> From: time-nuts-bounces at febo.com [mailto:time-nuts-
> bounces at febo.com] On
> >> Behalf Of Adrian
> >> Sent: Wednesday, December 05, 2012 4:33 PM
> >> To: Discussion of precise time and frequency measurement
> >> Subject: Re: [time-nuts] Very challenging phase noise measurement,
> does
> >> anyone have an idea??
> >>
> >> For phase noise the frequency range is 1MHz to 8/26.5/50GHz
> >> The spectrum analyzer works from 20Hz to max.
> >>
> >> Adrian
> >>
> >>
> >> Azelio Boriani schrieb:
> >>> Isn't the FSUP a 110K euros equipment 20Hz-50GHz capable? 125KHz
> >> shouldn't
> >>> be a problem. I had an FSUP for 25 seconds to play with... really
> >>> impressive but too limited test time to appreciate fully.
> >>>
> >>> On Wed, Dec 5, 2012 at 1:14 PM, Bob Camp <lists at rtty.us> wrote:
> >>>
> >>>> Hi
> >>>>
> >>>> Just about any of the high speed CMOS parts should work. A 74AC86 is
> >> about
> >>>> the earliest part I would trust. Any of the fast logic families that
> >> came
> >>>> after that should do equally well.
> >>>>
> >>>> Bob
> >>>>
> >>>> On Dec 5, 2012, at 7:03 AM, Hans Rosenberg <Hrosenberg at catena.nl>
> >> wrote:
> >>>>> Hello Time-nuts,
> >>>>>
> >>>>> I have to do a phase noise measurement and I'm wondering if anyone
> here
> >>>> has any ideas on that. We have to measure the phase noise of a 125kHz
> >>>> carrier (5Vp-p signal level). The measurement system should have a
> noise
> >>>> floor that is -164dBc/Hz at a distance of 1kHz to 8kHz away from the
> >>>> carrier.
> >>>>> Our current plan is to use 2 of these sources, have one in free
running
> >>>> mode and lock the other one to the first one using an XOR gate and
> then
> >> use
> >>>> the output of the XOR gate as an output signal. However, we are
> >> wondering
> >>>> if any of you know a better idea. Maybe there is an off-the-shelf
piece
> >> of
> >>>> equipment that can do that that we could rent. Or maybe we could
> >> increase
> >>>> the frequency to a few megahertz using a pll, which means the signal
> >> comes
> >>>> into the measurement range of our FSUP phase-noise analyzer.
> Problem is,
> >>>> the phase detector would then need to have an insanely low noise-
> floor
> >> (in
> >>>> our idea the XOR also has to have this insanely low noise floor as
well
> >> off
> >>>> course) so does anyone have experience with anything like this? Does
> >> anyone
> >>>> know an XOR with these good specs? I don't have a clue what a
> standard
> >>>> 74lvc1g86 would do. Needless to say the supply of this XOR would have
> to
> >> be
> >>>> ridiculously clean, but I do have a solution for that problem.
> >>>>> Any help is greatly appreciated!
> >>>>>
> >>>>> Best regards,
> >>>>>
> >>>>> Hans Rosenberg
> >>>>> _______________________________________________
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