[time-nuts] Sub Pico Second Phase logger (Posting Style)

Steve Rooke sar10538 at gmail.com
Thu Dec 11 03:52:14 UTC 2008


You can blow out a candle but you can't blow out a fire...

2008/12/11 Mike Feher <mfeher at eozinc.com>:
> I do not give a shit about a fight or Wiki. I was only stating my
> position. BTW, good thing you stated your post on top, otherwise I would
> not have seen it :). - Mike
>
>
>
> Mike B. Feher
> EOZ Inc.
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
> 908-902-3831 - cell
>
>
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Joseph M Gwinn
> Sent: Wednesday, December 10, 2008 9:27 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Sub Pico Second Phase logger (Posting Style)
>
> Let's have a top-posting versus bottom-posting fight!
>
> But we're too late, it's already been done:
>
> <http://en.wikipedia.org/wiki/Posting_style>
>
> <http://allmyfaqs.net/faq.pl?Top-posting_or_bottom-posting>
>
> And so on.  Many times.
>
> Joe
>
>
>
>
> "Mike Feher" <mfeher at eozinc.com>
> Sent by: time-nuts-bounces at febo.com
> 12/10/2008 09:06 PM
> Please respond to
> Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
>
>
> To
> "'Discussion of precise time and frequency measurement'"
> <time-nuts at febo.com>
> cc
>
> Subject
> Re: [time-nuts] Sub Pico Second Phase logger
>
>
>
>
>
>
> I am now, and actually have been, at the point where I just do not read
> bottom line post/replies. Bruce has a lot of good information to share,
> but, now, if I click on a post, and do not immediately see a response it
> is just deleted. Maybe it will be my loss, but, technology as well as
> the internet is evolving, and bottom line replies totally suck. - Mike
>
>
> Mike B. Feher
> EOZ Inc.
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
> 908-902-3831 - cell
>
>
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Bruce Griffiths
> Sent: Wednesday, December 10, 2008 8:38 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Sub Pico Second Phase logger
>
> Joe
> Joseph M Gwinn wrote:
>> Bruce,
>>
>>
>>> Reflecting the sum frequency back into the mixer is actually
> necessary
>>> to reduce the noise at the IF port.
>>> I believe that one of Agilent's simulation application notes mentions
>>> this effect but I don't recall the actual application note number.
>>> This will affect the mixer RF and IF port impedance so adding a
> series
>>> resistor may be required to improve the SWR.
>>>
>>
>> How big an effect is this?  Is the absolute noise decreased, or does
> it
>> remain the same while the signal increase?
>>
>>
> With the same difference frequency IF port termination impedance,  noise
> is actually decreased along with the mixer conversion loss.
> However if the sound card input noise dominates reducing the mixer
> effective output noise wont help.
>> If I'm understanding Walls and Stein (paper 112) correctly, the
> advantage
>> is because with the capacitor load the beatnote waveform approaches
>> square, thus increasing the zero-crossing speed and therefor the phase
>
>> sensitivity.  This is no doubt true, but the question was if this also
>
>> caused a small everything-dependent phase shift, something that would
> not
>> have mattered in the measurement of phase noise.  The object of paper
> 112
>> was to remedy a 10 to 20 dB error in phase noise measurements.  The
>> critical words are in the lower left column of page 337, in the
> paragraph
>> beginning "If the mixer is terminated ...".
>>
>>
>>
> Saturating the RF port has a similar effect.
> If one is time stamping the zero crossings an increased zero crossing
> slope is an advantage.
> For relative phase measurements a trapezoidal beat frequency waveform
> may be less useful.
>>>> MiniCircuits AN-41-001 "FAQ about Phase Detectors" has on page 2 a
> 500
>>>>
>> ohm
>>
>>>> resistor to ground and a 5000 ohm resistor to the first filter
>>>>
>> capacitor,
>>
>>>> so the capacitor is isolated from the IF port by the resistors.
>>>>
>>>>
>>>>
>>> I wouldn't take too much notice of that recommendation as I have
> little
>>> confidence in the author's experience/knowledge.
>>>
>>
>> Well, OK, but:
>>
>> Stephen Kurtz says the same thing on the third column of the third
> page, a
>> bit above Figure 6.
>>
>
> Off course with a capacitive IF port termination matching the RF and LO
> ports becomes more critical as does the reverse isolation of the various
> amplifiers driving the RF and LO ports.
> It may be simpler in fact to use a level 17 mixer with high LO to RF and
> LO to IF isolation with the RF port unsaturated as it relaxes the
> reverse isolation specs for the isolation amplifiers.
>> Nelson and Walls (paper 971), Figure 4, also shows the low pass filter
>
>> arranged to absorb the sum signal, not allowing it to be reflected
> back
>> into the mixer.
>>
>>
>>
>>>>> Supposedly an SRA-1, but some caution is in order as some
>>>>>
>>> statements as
>>>
>>>>> to the effect of the input offset of an opamp based IF preamp in
> the
>>>>> same application note were of dubious veracity unless one
>>>>>
>>> were to use an
>>>
>>>>> inverting opamp input stage.
>>>>>
>>>>>
>>>> This issue was mentioned in another app note, but their main issue
>>>> appeared to be that the opamp bias currents could cause an offset.
>>>>
>>>>
>>>>
>>>>
>>> But the circuit they suggest has no effect on bias current induced
>>> offset, the same current flows into the mixer and termination
> impedance
>>> independent of the series resistance.
>>>
>>
>> You're right that the proposed remedy didn't make sense.  I don't know
>
>> that this is a big problem with modern opamps, especially FET input
> ones
>> (if needed).
>>
>>
> The only configuration for which it makes any sense is an inverting
> input amplifier with a finite input voltage offset.
>>> Yes, I should have said that when the 2 input signals are in
> quadrature,
>>> any capacitive crosstalk will have little effect on the phase shift.
>>>
>>
>> Ah.  Because the capacitor coupling adds a second 90 degree shift,
>> bringing the total to 180 degrees.
>>
>> But crosstalk by ground coupling will be unaffected.  As will
> crosstalk by
>> transformer action.  Those boards are pretty crowded.
>>
>>
>>
> Yes its better to measure it rather than relying too much on conjecture.
>>> The AP192 has a somewhat higher interchannel isolation than that, the
>>> interchannel crosstalk spec is about -120dB.
>>> With a sufficiently large number of samples the its easy to see
>>> artifacts as low as -140dBFS.
>>>
>>
>> Yep.  Seems like a very good card.
>>
>>
>>
>>
>>
>>> It's hard to find such Firewire systems without such unnecessary
> frills
>>> (for this application) as high gain preamps.
>>>
>>
>> The AP192 has high-level inputs, but I don't know if this bypasses the
>
>> preamps, or attenuates.  Given their target market, I'd bet it
> bypasses.
>>
>>
> There are no preamps other than an external differential input amplifier
> that translates the 4 Vrms FS inputs at the input connector to a level
> that the ADC can handle.
> The ADC chip itself has no preamps built in.
> There have been numerous complaint about this by some audio nuts,
> however for this application not having such amplifiers is ideal.
>>
>>> The gain tempco and linearity of some variable gain audio preamps is
>>> somewhat suspect.
>>>
>>
>> I would think that none of these cards has a good tempco of anything,
>> given the lack of necessity in their market.
>>
>> I would think that linearity would be quite good, given the horsepower
>
>> competitions on linearity.
>>
>>
> Since the 2 ADCs share the same reference their gain tracking tempco
> should be quite good given that they use capacitors rather than
> resistors within the ADCs.
>>
>>>>> Other cards using AKM 24 bit ADCs should also be suitable.
>>>>>
>>>>>
>>>> Who is AKM?
>>>>
>>>>
>>>>
>>> Asahi Kasei EKM
>>>
>>> http://www.asahi-kasei.co.jp/akm/en/
>>>
>>> http://www.asahi-kasei.co.jp/akm/en/product/proaudio.html
>>>
>>>
>>
>> Thanks.  I'll look into their data.
>>
>>
>>
>>>> 20 Log[ 2^24 ] = 144 dB, so something else will be the limit.
>>>>
>>>>
>>>>
>>>>
>>> Actual ENOB ~ 19 to 20 bits.
>>>
>>
>> Makes sense.  20 Log [ 2^19 ] = 114 dB.  Still plenty good enough.
>>
>>
>>
>>>>> Ideally an external sound card with balanced  XLR inputs would be
>>>>>
>> best.
>>
>> Yes.
>>
>>
>>
>>
>>>>> HP produced a number of different phase comparators each with a
>>>>> different type of phase detector.
>>>>>
>>
>> OK.  And the PLL folk must have a million designs.
>>
>>
>>
>>>
>>> Can alleviate it to some extent by driving a pair of such phase
>>> detectors so that their outputs are in quadrature.
>>> One just selects the phase detector output that is in the linear
> range.
>>> The quadrature outputs also allow unambiguous assignment of the sign
> of
>>> any phase change.
>>>
>>
>> The Symmetricom 5120A does something very clever to alleviate this
>> problem.  Explained in US patent 7,227,346 and "Direct-Digital
> Phase-Noise
>> Measurement"; J. Grove, J. Hein, J. Retta, P. Schweiger, W. Solbrig,
> and
>> S.R. Stein; 2004 IEEE International Ultrasonics, Ferroelectrics, and
>> Frequency Control Joint 50th Anniversary Conference, pages 287-291.
>>
>> Joe
>>
>>
> I've read the patent.
>
> Bruce
>
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
Omnium finis imminet



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