You can blow out a candle but you can't blow out a fire... 2008/12/11 Mike Feher <[EMAIL PROTECTED]>: > 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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" <[EMAIL PROTECTED]> > Sent by: [EMAIL PROTECTED] > 12/10/2008 09:06 PM > Please respond to > Discussion of precise time and frequency measurement > <[email protected]> > > > To > "'Discussion of precise time and frequency measurement'" > <[email protected]> > 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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 > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >
-- Steve Rooke - ZL3TUV & G8KVD Omnium finis imminet _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
