[time-nuts] Leviton VTP24 Is this Time Accurate enough?
I inquired with Leviton as to the accuracy of the VTP24 24 Hour Programmable Timer with DST. https://www.leviton.com/en/products/vpt24-1pz Don Resor Here is the reply I received: Hello, Thank you for contacting Leviton technical support. According to the code it meets, it is required to have time keeping accuracy within 5 minutes every year. It also uses a crystal to keep time, as it must maintain the time even during power outages. Regards, Virgilio Dominguez Technical Services Representative II Leviton Manufacturing Co., Inc. 201 North Service Road., Melville, NY 11747 ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: General Radio 1105-A Frequency Measuring Equipment, parts wanted.
Stijn, I have a GR unit marked GR-1101 Piezoelectric Oscillator that consists of the quartz bar(broken) and the oscillator. If this is what you are looking for you're welcome to it. Let me know if it can be of use to you. Bill On 8/23/2021 9:15 AM, Stijn wrote: Seems that the pictures got scrubbed: Links: The equipment I am working on: https://www.pe1rks.nl/plaatjes/GR_1105A/IMG_0030.JPG The GR 774 connectors that I am after: https://www.pe1rks.nl/plaatjes/GR_1105A/IMG_0115.JPG The mains connectors that I am looking for need to fit these: https://www.pe1rks.nl/plaatjes/GR_1105A/IMG_0116.JPG The oscillator module that I would like to replace: https://www.pe1rks.nl/plaatjes/GR_1105A/IMG_0013.JPG Sincerely, Stijn Op 23-8-2021 om 15:04 schreef Stijn: Fellow Time-nuts, I have for some time a General Radio 1105-A and I have started to resurrect this two rack Frequency Standard combined with Frequency Measuring Equipment. There are some repairs to be made and some units require some more in depth restoration, but to be able to complete this task and get all working like it once should I need some parts. What I need are some General Radio 774 connectors, 8 to be exact: I am also in need for 6 of the connectors fitting this mains entry: And the worst part is the Piezo Oscillator, the Quartz bar is there and in good condition the oven is also working. But the oscillator circuit has been heavily modified. Instead of the original bridge circuit they have build a totally different oscillator and I can't get this to work. So here are my questions: Does anybody have or know a supplier for the needed connectors? Is there someone out there who has just the Oscillator module for the Piezo-Electric Oscillator and is willing to sell and ship this? Sincerely, Stijn Nestra ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: uncertainty/SNR of IQ measurements
Just to be clear, the shift has to be in phase, not time per se. A 90 deg phase shifter based on a constant delay will not work well at other frequencies. That's why phasing-type SSB exciters got so messy in the audio phase splitter department (in the old days). Nowadays with digital processing, the mathematical transformation required can be done accurately over rather wide bandwidths. Dana On Thu, Aug 26, 2021 at 7:05 PM Graham / KE9H wrote: > I think Dana's explanation is a much clearer way to think of what is going > on in an I-Q receiver. > > Until you are really far down the signal chain, at the demodulator, where > you might process the I and Q signals differently, > there is no 'splitting' or division of the signal into I and Q. > The signal in the I and Q channels is the same, just shifted in time / > phase in one of the channels, relative to the other. > > --- Graham > > == > > On Thu, Aug 26, 2021 at 4:43 PM Dana Whitlow > wrote: > > > Hi Jim, > > > > I think the best way is to view the signal as a phasor, with any > > noise present adding a > > random trajectory (a fuzzball) to the tip of the signal vector. > > Conceptually speaking, > > this eliminates needing to worry about the distribution of power between > I > > & Q, etc. > > It lets you view the whole thing without regard for choice of axes, > > coordinate system, > > and all that. > > > > If the S/N is good, the fuzzball is small in size compared to the length > of > > the phasor, > > and you can immediately see that neither the length nor the angle of the > > sum vector > > is much affected. > > > > But as the SNR is reduced, you eventually reach the point where some of > the > > noise > > peaks almost reach down to the origin, and as the vector tip swings near > > the origin > > the phase angle changes very rapidly by nearly 180 deg, but the effect > is a > > temporary > > glitch of zero area. > > > > But if the noise peak is a little bit bigger, the vector tip swings all > the > > way around the > > origin, yielding an eventual effect of an added 360 deg (a whole extra > > cycle) in phase > > shift. This tends to have a far more deleterious effect on a signal. I > > had a text given > > to me by a friend in which the author used this kind of explanation to > > explain, for > > example, the "threshold effect" of noise in FM demodulation. I just > > looked, but could > > not find the book, else I'd have given you the title and author > > information. > > > > This mode of thought also leads towards an understanding of the "FM > capture > > effect", > > which spec was always highlighted in datasheets of HiFi FM tuners. But > one > > hears > > little of it nowadays, I suspect because the advent of fast ICs has made > it > > so easy > > to very- closely approach the "theoretical limit" that everybody is about > > the same. > > BTW, said "theoretical limit" is not fixed until one specifies other > > parameters, and > > at one time there was a standard test definition so that such a limit > could > > be defined > > and measured against. > > > > In IQ demodulation I find the ATAN2 function a good deal more useful than > > the old > > arctan function, which needs a lot of help in order to work usefully. > The > > ATAN2 > > function takes two arguments (I & Q values) and automatically places the > > angular > > result in the correct quadrant and is not bothered by either of the > > arguments being > > zero. The only place it gets in trouble is if *both* arguments are zero, > > which is an > > infinitely-tough nut to crack in any case. > > > > As with all the inverse trig functions, ATAN2 has a limited angular > range, > > from > > -180 deg through zero to +180 deg, then snaps back to -180 deg again. > > But it's not too difficult to "unwrap" the results so that a continuous > > rotation of a > > phasor leads to a nice smooth phase ramp with no discontinuities at all. > > In many > > cases this presentation makes the picture much clearer, although overly > > high > > noise peaks can create what some will call a false transition. If you're > > really > > interested in the signal alone, yes you have a problem then. But if you > > consider > > the "signal" to be the composite vector sum of some signal and added > noise, > > the unwrap process works correctly. > > > > Whew! > > > > Dana K8YUM > > > > > > > > On Thu, Aug 26, 2021 at 3:52 PM Poul-Henning Kamp > > wrote: > > > > > > > > Lux, Jim writes: > > > > > > >I'm looking for a simplified treatment of the uncertainty of I/Q > > > >measurements. Say you've got some input signal with a given SNR and > you > > > >run it into a I/Q demodulator - you get a series of I and Q > measurements > > > >(which might, later, be turned into mag and phase). > > > > > > > >[...] > > > > > > > >I'm looking for a sort of not super quantitative and analytical > > > >treatment that I can point folks to. > > > > > > Good luck with that :-) > > > > > > Some of the noise processes will be along
[time-nuts] Re: uncertainty/SNR of IQ measurements
I think Dana's explanation is a much clearer way to think of what is going on in an I-Q receiver. Until you are really far down the signal chain, at the demodulator, where you might process the I and Q signals differently, there is no 'splitting' or division of the signal into I and Q. The signal in the I and Q channels is the same, just shifted in time / phase in one of the channels, relative to the other. --- Graham == On Thu, Aug 26, 2021 at 4:43 PM Dana Whitlow wrote: > Hi Jim, > > I think the best way is to view the signal as a phasor, with any > noise present adding a > random trajectory (a fuzzball) to the tip of the signal vector. > Conceptually speaking, > this eliminates needing to worry about the distribution of power between I > & Q, etc. > It lets you view the whole thing without regard for choice of axes, > coordinate system, > and all that. > > If the S/N is good, the fuzzball is small in size compared to the length of > the phasor, > and you can immediately see that neither the length nor the angle of the > sum vector > is much affected. > > But as the SNR is reduced, you eventually reach the point where some of the > noise > peaks almost reach down to the origin, and as the vector tip swings near > the origin > the phase angle changes very rapidly by nearly 180 deg, but the effect is a > temporary > glitch of zero area. > > But if the noise peak is a little bit bigger, the vector tip swings all the > way around the > origin, yielding an eventual effect of an added 360 deg (a whole extra > cycle) in phase > shift. This tends to have a far more deleterious effect on a signal. I > had a text given > to me by a friend in which the author used this kind of explanation to > explain, for > example, the "threshold effect" of noise in FM demodulation. I just > looked, but could > not find the book, else I'd have given you the title and author > information. > > This mode of thought also leads towards an understanding of the "FM capture > effect", > which spec was always highlighted in datasheets of HiFi FM tuners. But one > hears > little of it nowadays, I suspect because the advent of fast ICs has made it > so easy > to very- closely approach the "theoretical limit" that everybody is about > the same. > BTW, said "theoretical limit" is not fixed until one specifies other > parameters, and > at one time there was a standard test definition so that such a limit could > be defined > and measured against. > > In IQ demodulation I find the ATAN2 function a good deal more useful than > the old > arctan function, which needs a lot of help in order to work usefully. The > ATAN2 > function takes two arguments (I & Q values) and automatically places the > angular > result in the correct quadrant and is not bothered by either of the > arguments being > zero. The only place it gets in trouble is if *both* arguments are zero, > which is an > infinitely-tough nut to crack in any case. > > As with all the inverse trig functions, ATAN2 has a limited angular range, > from > -180 deg through zero to +180 deg, then snaps back to -180 deg again. > But it's not too difficult to "unwrap" the results so that a continuous > rotation of a > phasor leads to a nice smooth phase ramp with no discontinuities at all. > In many > cases this presentation makes the picture much clearer, although overly > high > noise peaks can create what some will call a false transition. If you're > really > interested in the signal alone, yes you have a problem then. But if you > consider > the "signal" to be the composite vector sum of some signal and added noise, > the unwrap process works correctly. > > Whew! > > Dana K8YUM > > > > On Thu, Aug 26, 2021 at 3:52 PM Poul-Henning Kamp > wrote: > > > > > Lux, Jim writes: > > > > >I'm looking for a simplified treatment of the uncertainty of I/Q > > >measurements. Say you've got some input signal with a given SNR and you > > >run it into a I/Q demodulator - you get a series of I and Q measurements > > >(which might, later, be turned into mag and phase). > > > > > >[...] > > > > > >I'm looking for a sort of not super quantitative and analytical > > >treatment that I can point folks to. > > > > Good luck with that :-) > > > > Some of the noise processes will be along the "vector" and distributed > > between I & Q components depending on the phase, while other noise > > processes affect the components individually. > > > > To make matters worse, both kinds of noise processes may depend on the > > phase, usually because of cross-talk and/or insufficient isolation. > > > > Low-resolution ADC's are a particular nasty problem, because they add > > +/-1 count jitter independent of the phase, and that causes very > > large arctangent errors. > > > > Counterintuitive as it may sound, it is easier to process the bits from > > ADC's where the low two bits are pure noise, than ADC's where all bits > > are good... > > > > -- > > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > >
[time-nuts] Re: uncertainty/SNR of IQ measurements
Hi Jim, I think the best way is to view the signal as a phasor, with any noise present adding a random trajectory (a fuzzball) to the tip of the signal vector. Conceptually speaking, this eliminates needing to worry about the distribution of power between I & Q, etc. It lets you view the whole thing without regard for choice of axes, coordinate system, and all that. If the S/N is good, the fuzzball is small in size compared to the length of the phasor, and you can immediately see that neither the length nor the angle of the sum vector is much affected. But as the SNR is reduced, you eventually reach the point where some of the noise peaks almost reach down to the origin, and as the vector tip swings near the origin the phase angle changes very rapidly by nearly 180 deg, but the effect is a temporary glitch of zero area. But if the noise peak is a little bit bigger, the vector tip swings all the way around the origin, yielding an eventual effect of an added 360 deg (a whole extra cycle) in phase shift. This tends to have a far more deleterious effect on a signal. I had a text given to me by a friend in which the author used this kind of explanation to explain, for example, the "threshold effect" of noise in FM demodulation. I just looked, but could not find the book, else I'd have given you the title and author information. This mode of thought also leads towards an understanding of the "FM capture effect", which spec was always highlighted in datasheets of HiFi FM tuners. But one hears little of it nowadays, I suspect because the advent of fast ICs has made it so easy to very- closely approach the "theoretical limit" that everybody is about the same. BTW, said "theoretical limit" is not fixed until one specifies other parameters, and at one time there was a standard test definition so that such a limit could be defined and measured against. In IQ demodulation I find the ATAN2 function a good deal more useful than the old arctan function, which needs a lot of help in order to work usefully. The ATAN2 function takes two arguments (I & Q values) and automatically places the angular result in the correct quadrant and is not bothered by either of the arguments being zero. The only place it gets in trouble is if *both* arguments are zero, which is an infinitely-tough nut to crack in any case. As with all the inverse trig functions, ATAN2 has a limited angular range, from -180 deg through zero to +180 deg, then snaps back to -180 deg again. But it's not too difficult to "unwrap" the results so that a continuous rotation of a phasor leads to a nice smooth phase ramp with no discontinuities at all. In many cases this presentation makes the picture much clearer, although overly high noise peaks can create what some will call a false transition. If you're really interested in the signal alone, yes you have a problem then. But if you consider the "signal" to be the composite vector sum of some signal and added noise, the unwrap process works correctly. Whew! Dana K8YUM On Thu, Aug 26, 2021 at 3:52 PM Poul-Henning Kamp wrote: > > Lux, Jim writes: > > >I'm looking for a simplified treatment of the uncertainty of I/Q > >measurements. Say you've got some input signal with a given SNR and you > >run it into a I/Q demodulator - you get a series of I and Q measurements > >(which might, later, be turned into mag and phase). > > > >[...] > > > >I'm looking for a sort of not super quantitative and analytical > >treatment that I can point folks to. > > Good luck with that :-) > > Some of the noise processes will be along the "vector" and distributed > between I & Q components depending on the phase, while other noise > processes affect the components individually. > > To make matters worse, both kinds of noise processes may depend on the > phase, usually because of cross-talk and/or insufficient isolation. > > Low-resolution ADC's are a particular nasty problem, because they add > +/-1 count jitter independent of the phase, and that causes very > large arctangent errors. > > Counterintuitive as it may sound, it is easier to process the bits from > ADC's where the low two bits are pure noise, than ADC's where all bits > are good... > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: uncertainty/SNR of IQ measurements
Lux, Jim writes: >I'm looking for a simplified treatment of the uncertainty of I/Q >measurements. Say you've got some input signal with a given SNR and you >run it into a I/Q demodulator - you get a series of I and Q measurements >(which might, later, be turned into mag and phase). > >[...] > >I'm looking for a sort of not super quantitative and analytical >treatment that I can point folks to. Good luck with that :-) Some of the noise processes will be along the "vector" and distributed between I & Q components depending on the phase, while other noise processes affect the components individually. To make matters worse, both kinds of noise processes may depend on the phase, usually because of cross-talk and/or insufficient isolation. Low-resolution ADC's are a particular nasty problem, because they add +/-1 count jitter independent of the phase, and that causes very large arctangent errors. Counterintuitive as it may sound, it is easier to process the bits from ADC's where the low two bits are pure noise, than ADC's where all bits are good... -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: uncertainty/SNR of IQ measurements
Now, re-reading my response and thinking a little longer, I understand your question a little better, maybe. I see where you are coming from if RF and LO are the same frequency, and it's not totally clear to me yet what happens as the phase changes. My quick back of the napkin (yes, I actually used one!) suggested outputs from a single DBM at zero phase difference of 0 * Flo, and the input noise plus the LO noise would seem to me to be additive, not multiplied. Basically a phase detector. But then I recalled that for PN measurements, the LO and test signal have to be maintained at 90 degrees shift for there to be a zero volts DC component to use for steering but the noise sidebands are then what is measured. I guess I really need to go play in the lab a bit. Tom Holmes, N8ZM -Original Message- From: Tom Holmes Sent: Thursday, August 26, 2021 2:27 PM To: 'Discussion of precise time and frequency measurement' Subject: [time-nuts] Re: uncertainty/SNR of IQ measurements HI Jim... >From my admittedly limited understanding of IQ demodulators, the first thing >done is to split the signal power (signal, noise, and all) evenly between two paths, which then ideally feed identical double balanced mixers (I'm thinking of a hardware implementation, obviously) whose only difference is the quadrature phase of the LO. So both paths are seeing the same SNR at that point. So my first guess would be that the relative phase of the LO to the input signal would only affect the phase of the output from each path, but the noise content ( or modulation if there is any) would not be any different between the two paths. I'm not aware that a single DBM used as a downconverting mixer shows any preference to the phase angle of the input to the LO. Tom Holmes, N8ZM -Original Message- From: Lux, Jim Sent: Thursday, August 26, 2021 1:37 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] uncertainty/SNR of IQ measurements This is sort of tangential to measuring time, really more about measuring phase. I'm looking for a simplified treatment of the uncertainty of I/Q measurements. Say you've got some input signal with a given SNR and you run it into a I/Q demodulator - you get a series of I and Q measurements (which might, later, be turned into mag and phase). If the phase of the input happens to be 45 degrees relative to the LO (and at the same frequency), then you get equal I and Q values, with (presumably) equal SNRs. But if the phase is 0 degrees, is the SNR of the I term the same as the input (or perhaps, even, better), but what's the SNR of the Q term (or alternately, the sd or variance) - Does the noise power in the input divide evenly between the branches? Is the contribution of the noise from the LO equally divided? So the I is "input + noise/2" and Q is "zero + noise/2" If one looks at it as an ideal multiplier, you're multiplying some "cos (omega t) + input noise" times "cos (omega t) + LO noise" - so the noise in the output is input noise * LO + LO noise *input and a noise * noise term. I'm looking for a sort of not super quantitative and analytical treatment that I can point folks to. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: uncertainty/SNR of IQ measurements
Hi Once you get things down to baseband, you (likely) shove the I and Q into some sort of arc tangent math. Depending on just how you do that math, there can be some bumps in the road. It’s implementation dependent so I don’t know of a “generic” answer. I’m not all knowing so there may be one … :) Bob > On Aug 26, 2021, at 2:27 PM, Tom Holmes wrote: > > HI Jim... > > From my admittedly limited understanding of IQ demodulators, the first thing > done is to split the signal power (signal, noise, and all) evenly between two > paths, which then ideally feed identical double balanced mixers (I'm thinking > of a hardware implementation, obviously) whose only difference is the > quadrature phase of the LO. So both paths are seeing the same SNR at that > point. So my first guess would be that the relative phase of the LO to the > input signal would only affect the phase of the output from each path, but > the noise content ( or modulation if there is any) would not be any different > between the two paths. I'm not aware that a single DBM used as a > downconverting mixer shows any preference to the phase angle of the input to > the LO. > > Tom Holmes, N8ZM > > -Original Message- > From: Lux, Jim > Sent: Thursday, August 26, 2021 1:37 PM > To: Discussion of precise time and frequency measurement > > Subject: [time-nuts] uncertainty/SNR of IQ measurements > > This is sort of tangential to measuring time, really more about > measuring phase. > > I'm looking for a simplified treatment of the uncertainty of I/Q > measurements. Say you've got some input signal with a given SNR and you > run it into a I/Q demodulator - you get a series of I and Q measurements > (which might, later, be turned into mag and phase). > > If the phase of the input happens to be 45 degrees relative to the LO > (and at the same frequency), then you get equal I and Q values, with > (presumably) equal SNRs. > > But if the phase is 0 degrees, is the SNR of the I term the same as the > input (or perhaps, even, better), but what's the SNR of the Q term (or > alternately, the sd or variance) - Does the noise power in the input > divide evenly between the branches? Is the contribution of the noise > from the LO equally divided? So the I is "input + noise/2" and Q is > "zero + noise/2" > > If one looks at it as an ideal multiplier, you're multiplying some "cos > (omega t) + input noise" times "cos (omega t) + LO noise" - so the noise > in the output is input noise * LO + LO noise *input and a noise * noise > term. > > I'm looking for a sort of not super quantitative and analytical > treatment that I can point folks to. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: uncertainty/SNR of IQ measurements
HI Jim... >From my admittedly limited understanding of IQ demodulators, the first thing >done is to split the signal power (signal, noise, and all) evenly between two >paths, which then ideally feed identical double balanced mixers (I'm thinking >of a hardware implementation, obviously) whose only difference is the >quadrature phase of the LO. So both paths are seeing the same SNR at that >point. So my first guess would be that the relative phase of the LO to the >input signal would only affect the phase of the output from each path, but the >noise content ( or modulation if there is any) would not be any different >between the two paths. I'm not aware that a single DBM used as a >downconverting mixer shows any preference to the phase angle of the input to >the LO. Tom Holmes, N8ZM -Original Message- From: Lux, Jim Sent: Thursday, August 26, 2021 1:37 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] uncertainty/SNR of IQ measurements This is sort of tangential to measuring time, really more about measuring phase. I'm looking for a simplified treatment of the uncertainty of I/Q measurements. Say you've got some input signal with a given SNR and you run it into a I/Q demodulator - you get a series of I and Q measurements (which might, later, be turned into mag and phase). If the phase of the input happens to be 45 degrees relative to the LO (and at the same frequency), then you get equal I and Q values, with (presumably) equal SNRs. But if the phase is 0 degrees, is the SNR of the I term the same as the input (or perhaps, even, better), but what's the SNR of the Q term (or alternately, the sd or variance) - Does the noise power in the input divide evenly between the branches? Is the contribution of the noise from the LO equally divided? So the I is "input + noise/2" and Q is "zero + noise/2" If one looks at it as an ideal multiplier, you're multiplying some "cos (omega t) + input noise" times "cos (omega t) + LO noise" - so the noise in the output is input noise * LO + LO noise *input and a noise * noise term. I'm looking for a sort of not super quantitative and analytical treatment that I can point folks to. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] uncertainty/SNR of IQ measurements
This is sort of tangential to measuring time, really more about measuring phase. I'm looking for a simplified treatment of the uncertainty of I/Q measurements. Say you've got some input signal with a given SNR and you run it into a I/Q demodulator - you get a series of I and Q measurements (which might, later, be turned into mag and phase). If the phase of the input happens to be 45 degrees relative to the LO (and at the same frequency), then you get equal I and Q values, with (presumably) equal SNRs. But if the phase is 0 degrees, is the SNR of the I term the same as the input (or perhaps, even, better), but what's the SNR of the Q term (or alternately, the sd or variance) - Does the noise power in the input divide evenly between the branches? Is the contribution of the noise from the LO equally divided? So the I is "input + noise/2" and Q is "zero + noise/2" If one looks at it as an ideal multiplier, you're multiplying some "cos (omega t) + input noise" times "cos (omega t) + LO noise" - so the noise in the output is input noise * LO + LO noise *input and a noise * noise term. I'm looking for a sort of not super quantitative and analytical treatment that I can point folks to. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
