[time-nuts] Phase Detectors/Mixers for DMTD and PN measurements

[Bruce Griffiths]

Cross Correlation methods are commonly used with analog mixers.
Most of the high end commercial offerings use it (Holzworth, Anapico, Rhohde & Schwarz, etc.)

Bruce
> On 12 December 2019 at 18:53 Gerhard Hoffmann <ghf at hoffmann-hochfrequenz.de> wrote:
> 
> 
> It seems the mixer noise cannot be ignored.
> 
> 
> I wonder then  why nobody  takes the mixer to cross correlation land, 
> and maybe even the driver amplifier.
> 
> The FFT analyzer can do it anyway, a second AF pre amp costs nothing,  
> and other than that
> 
> there are only another mixer and 2 power dividers on the BOM.
> 
> In addition, each mixer gets 3 dB less power which helps the survival rate.
> 
> One can always crank it up for bragging rights.
> 
> 
> Also, high level mixers (type 2 and 3 in [1] ) have resistors in series 
> to each diode for biasing
> 
> so their lower efficiency should not come as a surprise.  And, the 
> resistors in the ring generate
> 
> AF noise. With DC across them also 1/f, esp. for thick film.
> 
> The usual 1nV/rt Hz op amps (LT1028, AD797, ADA4898) have the voltage 
> noise of a 60 Ohm resistor.
> 
> That probably brings them to the point of diminishing return.
> 
> The diodes in the ring themselves create only half-thermal noise.
> 
> 
> Methinks one would be better off with many low level mixers and power 
> dividers,
> 
> adding up the demodulated AF voltages. There is no point in power 
> matching the AF side.
> 
> Maybe for RF with a RC high pass.
> 
> SMD Wilkinson dividers are $2.50 or so now from Macom, MCL or Pulse and
> 
> low level mixers are also cheap, or even 2 1:4 SMD transformers + diode 
> ring.
> 
> Easily done when one does not have to wind the coils.
> 
> 
> When verifying my links below, I stumbled across M9H  for $333.
> 
> The price for two of them is the number of the beast.  =8-) )
> 
> 
> [1]
> 
> < 
> https://www.jlab.org/uspas11/Reading/RF/Mixers%20-%20phase%20detectors.pdf >
> 
> 
> < 
> https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiu8Zi7pa_mAhUKQUEAHb1pAyAQFjAAegQIAxAJ&url=http%3A%2F%2Fwww.rfcafe.com%2Freferences%2Farticles%2Fwj-tech-notes%2Fmixers-theory-technology-p2-v8-3.pdf&usg=AOvVaw3fc3OZgN2H5jzPx6jXDBh9 
>     >
> 
> 
> Also interesting:
> 
> < 
> https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwiFuqCvpq_mAhVTh1wKHcc2ALQQFjAAegQIAxAJ&url=http%3A%2F%2Fliterature.cdn.keysight.com%2Flitweb%2Fpdf%2F5989-8999EN.pdf&usg=AOvVaw3RFawCNg543QEv1hUsscbY 
>    >
> 
> 
> regards,
> 
> Gerhard,  DK4XP
> 
> 
> 
> 
> Am 11.12.19 um 20:29 schrieb Bob kb8tq:
> > Hi
> >
> > There are some famous name papers showing data taken on the 3048. When
> > asked about the levels involved, the next question inevitably was - “How many
> > mixers did you fry running the test?”.
> >
> > Bob
> >
> >> On Dec 11, 2019, at 10:54 AM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
> >>
> >>
> >> The HP 3048A phase noise system has a phase
> >> detector in the HP 11848A chassis that was
> >> originally a Watkins-Johnson (the original
> >> company) M9H.  The M9H lives on now sold by
> >> MaCom Technology Solutions.  "Someone" (unknown)
> >> established that the Mini-Circuits JMS-5H
> >> is an acceptable substitute, although not
> >> an exact replacement.
> >>
> >> The tradeoff in picking a mixer is the LO
> >> level.  A high LO drive level such as the above
> >> mixer have, gives higher performance, provided
> >> you have a driving amplifier that has both the
> >> necessary output power is itself low phase noise.
> >> Depending on the test set up, some of the driver
> >> amplifier phase noise will common mode out.
> >>
> >> Also, high drive level mixers have a narrow window
> >> between high enough drive to operate vs the damage
> >> level.  So a third requirement on the driver
> >> amplifier is that it's maximum output level is
> >> less than the damage level.  (Don't ask how I
> >> know this :-).  You can always put a pad between the
> >> drive amplifier and the LO input of the mixer used
> >> as phase detector to adjust the maximum possible
> >> drive.
> >>
> >> Rick N6RK
> >>
> 
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