Re: [time-nuts] Thunderbolt Harmonics
hello to all, to put things right into perspective please note that the famous OCXO hp10811 is "only" specified with harmonics <25 dB (see page 11 of manual https://www.febo.com/pages/hp10811/HP10811AB-Manual.pdf). This device is but still often felt to be useful. Goetz Am 22.01.2017 um 09:21 schrieb Rhys D: Bill, No offence taken at all. On the contrary, I really appreciate a great deal the effort you have gone to straightening out my misconceptions and blunders! This forum is such a great learning opportunity. I usually work with digital systems, so my RF and analog knowledge is sketchy at best. Half the reason I bought a spectrum analyser is to have an excuse to learn a bit about RF in a hands on way. It's funny you mentioned the overly precise numbers. After I wrote them I thought, well that's ridiculous, but I left them as is. That'll teach me! Cheers, Rhys ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Bill, No offence taken at all. On the contrary, I really appreciate a great deal the effort you have gone to straightening out my misconceptions and blunders! This forum is such a great learning opportunity. I usually work with digital systems, so my RF and analog knowledge is sketchy at best. Half the reason I bought a spectrum analyser is to have an excuse to learn a bit about RF in a hands on way. It's funny you mentioned the overly precise numbers. After I wrote them I thought, well that's ridiculous, but I left them as is. That'll teach me! Cheers, Rhys On Sat, 21 Jan 2017 at 2:37 PM, Bill Byrom wrote: > I'm trying to be gentle, Rhys. :) I work with these issues every day at > > work. Here are a few more comments. I assume you have the preamplifier > > in the spectrum analyzer turned off. > > > > > > The term "X harmonic" (such as 2nd or 3rd harmonic) means a > > multiplication of the fundamental signal by the given factor. So the > > term "1st harmonic" isn't used -- that's the fundamental. The 2nd > > harmonic is 2X the fundamental, and the 3rd harmonic is 3X the > > fundamental. So in your examples you should have said "2nd and 3rd > > harmonics): > > > > > > 15 dB attenuation: 2nd harmonic is (-49.13 - +11.40)= -60.53 dBc > > > > 20 dB attenuation: 2nd harmonic is (-48.84 - +11.40)= -60.24 dBc > > > > 25 dB attenuation: 2nd harmonic is (-48.32 - +11.28)= -59.60 dBc > > > > > > > > In nearly all cases it's silly to compare RF powers to 0.01 dB > > resolution. The uncertainty of the signal powers being measured, > > cable/connector loss, and instrumentation errors is in nearly all cases > > larger than 0.1 dB. Your spectrum analyzer doesn't have separate > > amplitude log linearly error specifications, but the total amplitude > > error with 20 dB of attenuation is specified as +/- 0.7 dB. So the 2nd > > harmonic values are not significantly changing as you change the > > attenuation, so the source you are measuring probably has about -60 dBc > > 2nd harmonic output. > > > > > > The 3rd harmonic results are going to cause me to wave my hands and make > > uncomfortable assumptions. The 20 dB 3rd harmonic level seems to be an > > outlier, but there is a possibility that a small amount of instrument > > distortion is out of phase with the source signal so that they partially > > null. RF measurements ARE magic in some cases. > > > > > > The use of the external 20 dB attenuator means that the spectrum > > analyzer return loss is isolated from the signal source. What does that > > mean? Any RF signal traveling down a cable is slightly reflected by > > cable defects, connectors, filters, mixers, and imperfect attenuators or > > terminators. The reflected signal is called "return loss" and in some > > cases "VSWR" or just "SWR". If you had a perfect 50 ohm termination > > (load) at the end of a perfect 50 ohm cable, all of the power sent into > > the cable would be absorbed by the load and the return loss would be > > infinite. The phase of the reflected signal at the source output > > connector depends on the round-trip electrical length of the cable and > > the nature of the reflection. The reflection from a short is 180 degrees > > different from an open, and other types of load can produce different > > reflected phases. By the time the reflection gets back to the source > > connector, the phase of the reflected signal can cause the impedance to > > appear to be nearly anything (greater or less than 50 ohms and probably > > capacitive or inductive). If you change the source frequency there is a > > different phase round-trip delay due to the wavelength changing, so in > > general the RMS voltage at the source will have some ripple vs > > frequency. If you place that 20 dB attenuator directly on the source > > output connector, the return loss that the source "sees" is nearly > > completely controlled by the quality of the attenuator. Even if the > > cable had an open or short at the end, the signal passes both ways > > though the attenuator so the return loss must be >40 dB (assuming a very > > high quality attenuator). This is the same as saying that the VSWR > > (Voltage Standing Wave Ratio) is close to 1. A 40 dB return loss > > corresponds to a VSWR of 1.02. If an RF filter doesn't see a low VSWR > > load, it may not produce the desired filtering behavior. > > -- > > > > Bill Byrom N5BB > > > > > > > > > > > > > > > > On Thu, Jan 19, 2017, at 10:48 PM, Rhys D wrote: > > > > > Thanks for the detailed post Bill, > > > > > > > > > > I'm learning a lot here! > > > > > So the spectrum analyser is indeed a "trap for young players" > > > > > As you guessed, it is a Siglent SSA3000X series analyzer. > > > > > > > > > > I just looked at the same signal again with varied attenuations > > > dialed in > > > on the instrument (I am using an external 20dB attenuator from > > > > > minicircuits > > > > > as well) > > > > > > > > > > Here is what I saw: > > > > > > > > > > Attenuation - Fundamental -
Re: [time-nuts] Thunderbolt Harmonics
I'm trying to be gentle, Rhys. :) I work with these issues every day at work. Here are a few more comments. I assume you have the preamplifier in the spectrum analyzer turned off. The term "X harmonic" (such as 2nd or 3rd harmonic) means a multiplication of the fundamental signal by the given factor. So the term "1st harmonic" isn't used -- that's the fundamental. The 2nd harmonic is 2X the fundamental, and the 3rd harmonic is 3X the fundamental. So in your examples you should have said "2nd and 3rd harmonics): 15 dB attenuation: 2nd harmonic is (-49.13 - +11.40)= -60.53 dBc 20 dB attenuation: 2nd harmonic is (-48.84 - +11.40)= -60.24 dBc 25 dB attenuation: 2nd harmonic is (-48.32 - +11.28)= -59.60 dBc In nearly all cases it's silly to compare RF powers to 0.01 dB resolution. The uncertainty of the signal powers being measured, cable/connector loss, and instrumentation errors is in nearly all cases larger than 0.1 dB. Your spectrum analyzer doesn't have separate amplitude log linearly error specifications, but the total amplitude error with 20 dB of attenuation is specified as +/- 0.7 dB. So the 2nd harmonic values are not significantly changing as you change the attenuation, so the source you are measuring probably has about -60 dBc 2nd harmonic output. The 3rd harmonic results are going to cause me to wave my hands and make uncomfortable assumptions. The 20 dB 3rd harmonic level seems to be an outlier, but there is a possibility that a small amount of instrument distortion is out of phase with the source signal so that they partially null. RF measurements ARE magic in some cases. The use of the external 20 dB attenuator means that the spectrum analyzer return loss is isolated from the signal source. What does that mean? Any RF signal traveling down a cable is slightly reflected by cable defects, connectors, filters, mixers, and imperfect attenuators or terminators. The reflected signal is called "return loss" and in some cases "VSWR" or just "SWR". If you had a perfect 50 ohm termination (load) at the end of a perfect 50 ohm cable, all of the power sent into the cable would be absorbed by the load and the return loss would be infinite. The phase of the reflected signal at the source output connector depends on the round-trip electrical length of the cable and the nature of the reflection. The reflection from a short is 180 degrees different from an open, and other types of load can produce different reflected phases. By the time the reflection gets back to the source connector, the phase of the reflected signal can cause the impedance to appear to be nearly anything (greater or less than 50 ohms and probably capacitive or inductive). If you change the source frequency there is a different phase round-trip delay due to the wavelength changing, so in general the RMS voltage at the source will have some ripple vs frequency. If you place that 20 dB attenuator directly on the source output connector, the return loss that the source "sees" is nearly completely controlled by the quality of the attenuator. Even if the cable had an open or short at the end, the signal passes both ways though the attenuator so the return loss must be >40 dB (assuming a very high quality attenuator). This is the same as saying that the VSWR (Voltage Standing Wave Ratio) is close to 1. A 40 dB return loss corresponds to a VSWR of 1.02. If an RF filter doesn't see a low VSWR load, it may not produce the desired filtering behavior. -- Bill Byrom N5BB On Thu, Jan 19, 2017, at 10:48 PM, Rhys D wrote: > Thanks for the detailed post Bill, > > I'm learning a lot here! > So the spectrum analyser is indeed a "trap for young players" > As you guessed, it is a Siglent SSA3000X series analyzer. > > I just looked at the same signal again with varied attenuations > dialed in > on the instrument (I am using an external 20dB attenuator from > minicircuits > as well) > > Here is what I saw: > > Attenuation - Fundamental - 1st Harmonic - 2nd Harmonic > 15 dB - 11.40 dB - 49.13 dB- 51.12 dB > 20 dB - 11.40 dB - 48.84 dB- 56.48 dB > 25 dB - 11.28 dB - 48.32 dB- 49.15 dB > > I guess these numbers mean I can't really trust what I can see on the > instrument screen? > > By the way, I should just you know that I am not trying to solve a > specific > timing problem here, I'm more using it as learning opportunity > and making > sure that my setup is the best it can be. > > Thanks again for the input. > > On 20 January 2017 at 12:26, Bill Byrom wrote: > >> You can't trust such low harmonic spurious measurements from a >> spectrum >> analyzer unless you know how the spurs change with input level. The >> second harmonic spur created in an amplifier or mixer inside the >> spectrum analyzer input will typically increase by 2 dB for >> every 1 dB >> of input level increase. Anytime you see a frequency converting RF >> component
Re: [time-nuts] Thunderbolt Harmonics
Hi > On Jan 20, 2017, at 11:22 AM, Tom Miller wrote: > > > - Original Message - From: "jimlux" > To: > Sent: Friday, January 20, 2017 8:34 AM > Subject: Re: [time-nuts] Thunderbolt Harmonics > > >> On 1/19/17 8:48 PM, Rhys D wrote: >>> Thanks for the detailed post Bill, >>> >>> I'm learning a lot here! >>> So the spectrum analyser is indeed a "trap for young players" >>> As you guessed, it is a Siglent SSA3000X series analyzer. >>> >>> I just looked at the same signal again with varied attenuations dialed in >>> on the instrument (I am using an external 20dB attenuator from minicircuits >>> as well) >>> >>> Here is what I saw: >>> >>> Attenuation - Fundamental - 1st Harmonic - 2nd Harmonic >>> 15 dB - 11.40 dB - 49.13 dB- 51.12 dB >>> 20 dB - 11.40 dB - 48.84 dB- 56.48 dB >>> 25 dB - 11.28 dB - 48.32 dB- 49.15 dB >>> >>> I guess these numbers mean I can't really trust what I can see on the >>> instrument screen? >> >> Actually, that's fairly good. Most spectrum analyzers are good to about 1/2 >> dB with a moderate level signal (your fundamental). >> >> The variation you're seeing is probably some combination of: >> 1) the mismatch between the source impedance and the spectrum analyzer input >> impedance - the latter of which almost certainly changes with attenuation >> setting >> 2) The calibration of the step attenuator. >> 3) maybe some change in harmonic production in the SA front end... in your >> case, though the harmonic levels go DOWN as the attenuation is decreased, >> which is the opposite of what happens with harmonics >> > > If you want to see the levels of the harmonics you should notch out the > fundamental. ….. and use a notch filter that does not miss-terminate the output amplifier (as most notch filters do …) Bob > > Regards, > Tom > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Hi > On Jan 19, 2017, at 11:48 PM, Rhys D wrote: > > Thanks for the detailed post Bill, > > I'm learning a lot here! > So the spectrum analyser is indeed a "trap for young players" > As you guessed, it is a Siglent SSA3000X series analyzer. > > I just looked at the same signal again with varied attenuations dialed in > on the instrument (I am using an external 20dB attenuator from minicircuits > as well) > > Here is what I saw: > > Attenuation - Fundamental - 1st Harmonic - 2nd Harmonic > 15 dB - 11.40 dB - 49.13 dB- 51.12 dB > 20 dB - 11.40 dB - 48.84 dB- 56.48 dB > 25 dB - 11.28 dB - 48.32 dB- 49.15 dB > > I guess these numbers mean I can't really trust what I can see on the > instrument screen? Like any instrument, there are limits to it’s performance. There are ways to check if you are at these limits. It’s not a matter of trust. It’s a matter of trust but verify …. Bob > > By the way, I should just you know that I am not trying to solve a specific > timing problem here, I'm more using it as learning opportunity and making > sure that my setup is the best it can be. > > Thanks again for the input. > > On 20 January 2017 at 12:26, Bill Byrom wrote: > >> You can't trust such low harmonic spurious measurements from a spectrum >> analyzer unless you know how the spurs change with input level. The >> second harmonic spur created in an amplifier or mixer inside the >> spectrum analyzer input will typically increase by 2 dB for every 1 dB >> of input level increase. Anytime you see a frequency converting RF >> component (such as the mixer in the input of a spectrum analyzer), it is >> nonlinear and will generate harmonics and intermodulation products. All >> you need to do is to keep the input level low enough so that the >> distortion products generated in the analyzer are below the signals you >> are measuring. The best and easiest technique is to increase the input >> attenuation by the smallest step available (such as 5 dB or 10 dB) and >> checking how the spurious components change. >> ** If the harmonic or other spurious signal is coming from an external >> source, it should not change as the input attenuation changes. >> ** If the harmonic or other spurious signal is generated inside the >> analyzer, it should change relative to the fundamental signal as the >> input attenuation changes. >> ** I'm talking about the harmonics or other spurious signals relative to >> the fundamental frequency being displayed. If you remove the input >> signal and still see the spur, it's a residual spur created inside the >> analyzer unrelated to the input signal. >> >> >> If you graph fundamental signal displayed amplitude vs changing input >> level, you will typically see the following for spurious signals created >> by most mixers or amplifiers: >> (1) Fundamental signal = slope of 1 >> >> (2) Second harmonic signal = slope of 2 >> >> (3) Third order intermodulation (sum or different frequencies caused by >>mixing of two signals) = slope of 3 >> >> >> For more background, see: >> >> https://en.wikipedia.org/wiki/Third-order_intercept_point >> >> >> >> If that is a SiglentSSA3000X series analyzer, here are the spurious >> specifications from the datasheet: >> ** Second harmonic distortion: -65 dBc (above 50 MHz input with >> preamplifier off) >> >> >> Note that the second harmonic distortion is only specified at 50 MHz >> input and above and at a -30 dBm input power level with the preamplifier >> off. For comparison, here are the specifications of a Tektronix RSA507A >> portable spectrum analyzer. Disclosure: I work for Tektronix. >> ** Second harmonic distortion: - 75 dBc (above 40 MHz input, >> preamplifier OFF) >> ** Second harmonic distortion: - 60 dBc (above 40 MHz input, >> preamplifier ON) >> >> >> I'm sure that the reason for a lower limit on the second harmonic >> specification is that the results are worse at lower frequencies. So >> it's quite possible that the harmonics you see are mainly coming from >> the spectrum analyzer input mixer or preamplifier. As I suggested >> earlier, try lowering the input level by 5 or 10 dB and see if the >> harmonics go down linearly. >> -- >> >> Bill Byrom N5BB >> >> >> >> >> >> On Tue, Jan 17, 2017, at 08:40 PM, Rhys D wrote: >> >>> Hi all, >> >>> >> >>> Before I start, let me say I'm rather a newbie at this sort of >>> stuff so >>> please be gentle. >> >>> >> >>> I was looking at the output of my Trimble Thunderbolt GPSDO and >>> was rather >>> surprised to see really "loud" harmonics in there. ~ 60dB down >>> from the >>> 10Mhz signal. >> >>> >> >>> Can anyone here shed some light on what I am seeing here? >> >>> Surely this isn't what it is supposed to look like? Should I be >>> trying to >>> filter these before going to my distribution amplifier? >> >>> >> >>> Thanks for any light you can shed. >> >>> >> >>> R >> >>> >> >>> >> >>>
Re: [time-nuts] Thunderbolt Harmonics
- Original Message - From: "jimlux" To: Sent: Friday, January 20, 2017 8:34 AM Subject: Re: [time-nuts] Thunderbolt Harmonics On 1/19/17 8:48 PM, Rhys D wrote: Thanks for the detailed post Bill, I'm learning a lot here! So the spectrum analyser is indeed a "trap for young players" As you guessed, it is a Siglent SSA3000X series analyzer. I just looked at the same signal again with varied attenuations dialed in on the instrument (I am using an external 20dB attenuator from minicircuits as well) Here is what I saw: Attenuation - Fundamental - 1st Harmonic - 2nd Harmonic 15 dB - 11.40 dB - 49.13 dB- 51.12 dB 20 dB - 11.40 dB - 48.84 dB- 56.48 dB 25 dB - 11.28 dB - 48.32 dB- 49.15 dB I guess these numbers mean I can't really trust what I can see on the instrument screen? Actually, that's fairly good. Most spectrum analyzers are good to about 1/2 dB with a moderate level signal (your fundamental). The variation you're seeing is probably some combination of: 1) the mismatch between the source impedance and the spectrum analyzer input impedance - the latter of which almost certainly changes with attenuation setting 2) The calibration of the step attenuator. 3) maybe some change in harmonic production in the SA front end... in your case, though the harmonic levels go DOWN as the attenuation is decreased, which is the opposite of what happens with harmonics If you want to see the levels of the harmonics you should notch out the fundamental. Regards, Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
On 1/19/17 8:48 PM, Rhys D wrote: Thanks for the detailed post Bill, I'm learning a lot here! So the spectrum analyser is indeed a "trap for young players" As you guessed, it is a Siglent SSA3000X series analyzer. I just looked at the same signal again with varied attenuations dialed in on the instrument (I am using an external 20dB attenuator from minicircuits as well) Here is what I saw: Attenuation - Fundamental - 1st Harmonic - 2nd Harmonic 15 dB - 11.40 dB - 49.13 dB- 51.12 dB 20 dB - 11.40 dB - 48.84 dB- 56.48 dB 25 dB - 11.28 dB - 48.32 dB- 49.15 dB I guess these numbers mean I can't really trust what I can see on the instrument screen? Actually, that's fairly good. Most spectrum analyzers are good to about 1/2 dB with a moderate level signal (your fundamental). The variation you're seeing is probably some combination of: 1) the mismatch between the source impedance and the spectrum analyzer input impedance - the latter of which almost certainly changes with attenuation setting 2) The calibration of the step attenuator. 3) maybe some change in harmonic production in the SA front end... in your case, though the harmonic levels go DOWN as the attenuation is decreased, which is the opposite of what happens with harmonics By the way, I should just you know that I am not trying to solve a specific timing problem here, I'm more using it as learning opportunity and making sure that my setup is the best it can be. You can have a lot of fun with a couple signal generators, or a sig gen and a discrete oscillator, a box of filters and pads ,a mixer or two, and an amplifier. You can look at mixer output spurs, compression in an amplifier, spurs created inside the test equipment, etc. An inexpensive clock oscillator (like used everywhere..get one of those 16 Mhz ones for an arduino or something) and a signal generator some resistors and a T connector is fascinating. You can see what happens when a signal goes "in" on the oscillator output and causes issues with the oscillator output buffer, or when you put some RF on the power supply. Thanks again for the input. On 20 January 2017 at 12:26, Bill Byrom wrote: You can't trust such low harmonic spurious measurements from a spectrum analyzer unless you know how the spurs change with input level. The second harmonic spur created in an amplifier or mixer inside the spectrum analyzer input will typically increase by 2 dB for every 1 dB of input level increase. Anytime you see a frequency converting RF component (such as the mixer in the input of a spectrum analyzer), it is nonlinear and will generate harmonics and intermodulation products. All you need to do is to keep the input level low enough so that the distortion products generated in the analyzer are below the signals you are measuring. The best and easiest technique is to increase the input attenuation by the smallest step available (such as 5 dB or 10 dB) and checking how the spurious components change. ** If the harmonic or other spurious signal is coming from an external source, it should not change as the input attenuation changes. ** If the harmonic or other spurious signal is generated inside the analyzer, it should change relative to the fundamental signal as the input attenuation changes. ** I'm talking about the harmonics or other spurious signals relative to the fundamental frequency being displayed. If you remove the input signal and still see the spur, it's a residual spur created inside the analyzer unrelated to the input signal. If you graph fundamental signal displayed amplitude vs changing input level, you will typically see the following for spurious signals created by most mixers or amplifiers: (1) Fundamental signal = slope of 1 (2) Second harmonic signal = slope of 2 (3) Third order intermodulation (sum or different frequencies caused by mixing of two signals) = slope of 3 For more background, see: https://en.wikipedia.org/wiki/Third-order_intercept_point If that is a SiglentSSA3000X series analyzer, here are the spurious specifications from the datasheet: ** Second harmonic distortion: -65 dBc (above 50 MHz input with preamplifier off) Note that the second harmonic distortion is only specified at 50 MHz input and above and at a -30 dBm input power level with the preamplifier off. For comparison, here are the specifications of a Tektronix RSA507A portable spectrum analyzer. Disclosure: I work for Tektronix. ** Second harmonic distortion: - 75 dBc (above 40 MHz input, preamplifier OFF) ** Second harmonic distortion: - 60 dBc (above 40 MHz input, preamplifier ON) I'm sure that the reason for a lower limit on the second harmonic specification is that the results are worse at lower frequencies. So it's quite possible that the harmonics you see are mainly coming from the spectrum analyzer input mixer or preamplifier. As I suggested earlier, try lowering
Re: [time-nuts] Thunderbolt Harmonics
Thanks for the detailed post Bill, I'm learning a lot here! So the spectrum analyser is indeed a "trap for young players" As you guessed, it is a Siglent SSA3000X series analyzer. I just looked at the same signal again with varied attenuations dialed in on the instrument (I am using an external 20dB attenuator from minicircuits as well) Here is what I saw: Attenuation - Fundamental - 1st Harmonic - 2nd Harmonic 15 dB - 11.40 dB - 49.13 dB- 51.12 dB 20 dB - 11.40 dB - 48.84 dB- 56.48 dB 25 dB - 11.28 dB - 48.32 dB- 49.15 dB I guess these numbers mean I can't really trust what I can see on the instrument screen? By the way, I should just you know that I am not trying to solve a specific timing problem here, I'm more using it as learning opportunity and making sure that my setup is the best it can be. Thanks again for the input. On 20 January 2017 at 12:26, Bill Byrom wrote: > You can't trust such low harmonic spurious measurements from a spectrum > analyzer unless you know how the spurs change with input level. The > second harmonic spur created in an amplifier or mixer inside the > spectrum analyzer input will typically increase by 2 dB for every 1 dB > of input level increase. Anytime you see a frequency converting RF > component (such as the mixer in the input of a spectrum analyzer), it is > nonlinear and will generate harmonics and intermodulation products. All > you need to do is to keep the input level low enough so that the > distortion products generated in the analyzer are below the signals you > are measuring. The best and easiest technique is to increase the input > attenuation by the smallest step available (such as 5 dB or 10 dB) and > checking how the spurious components change. > ** If the harmonic or other spurious signal is coming from an external > source, it should not change as the input attenuation changes. > ** If the harmonic or other spurious signal is generated inside the > analyzer, it should change relative to the fundamental signal as the > input attenuation changes. > ** I'm talking about the harmonics or other spurious signals relative to > the fundamental frequency being displayed. If you remove the input > signal and still see the spur, it's a residual spur created inside the > analyzer unrelated to the input signal. > > > If you graph fundamental signal displayed amplitude vs changing input > level, you will typically see the following for spurious signals created > by most mixers or amplifiers: > (1) Fundamental signal = slope of 1 > > (2) Second harmonic signal = slope of 2 > > (3) Third order intermodulation (sum or different frequencies caused by > mixing of two signals) = slope of 3 > > > For more background, see: > > https://en.wikipedia.org/wiki/Third-order_intercept_point > > > > If that is a SiglentSSA3000X series analyzer, here are the spurious > specifications from the datasheet: > ** Second harmonic distortion: -65 dBc (above 50 MHz input with > preamplifier off) > > > Note that the second harmonic distortion is only specified at 50 MHz > input and above and at a -30 dBm input power level with the preamplifier > off. For comparison, here are the specifications of a Tektronix RSA507A > portable spectrum analyzer. Disclosure: I work for Tektronix. > ** Second harmonic distortion: - 75 dBc (above 40 MHz input, > preamplifier OFF) > ** Second harmonic distortion: - 60 dBc (above 40 MHz input, > preamplifier ON) > > > I'm sure that the reason for a lower limit on the second harmonic > specification is that the results are worse at lower frequencies. So > it's quite possible that the harmonics you see are mainly coming from > the spectrum analyzer input mixer or preamplifier. As I suggested > earlier, try lowering the input level by 5 or 10 dB and see if the > harmonics go down linearly. > -- > > Bill Byrom N5BB > > > > > > On Tue, Jan 17, 2017, at 08:40 PM, Rhys D wrote: > > > Hi all, > > > > > > Before I start, let me say I'm rather a newbie at this sort of > > stuff so > > please be gentle. > > > > > > I was looking at the output of my Trimble Thunderbolt GPSDO and > > was rather > > surprised to see really "loud" harmonics in there. ~ 60dB down > > from the > > 10Mhz signal. > > > > > > Can anyone here shed some light on what I am seeing here? > > > Surely this isn't what it is supposed to look like? Should I be > > trying to > > filter these before going to my distribution amplifier? > > > > > > Thanks for any light you can shed. > > > > > > R > > > > > > > > > > > > > > > _ > > > time-nuts mailing list -- time-nuts@febo.com > > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nut
Re: [time-nuts] Thunderbolt Harmonics
You can't trust such low harmonic spurious measurements from a spectrum analyzer unless you know how the spurs change with input level. The second harmonic spur created in an amplifier or mixer inside the spectrum analyzer input will typically increase by 2 dB for every 1 dB of input level increase. Anytime you see a frequency converting RF component (such as the mixer in the input of a spectrum analyzer), it is nonlinear and will generate harmonics and intermodulation products. All you need to do is to keep the input level low enough so that the distortion products generated in the analyzer are below the signals you are measuring. The best and easiest technique is to increase the input attenuation by the smallest step available (such as 5 dB or 10 dB) and checking how the spurious components change. ** If the harmonic or other spurious signal is coming from an external source, it should not change as the input attenuation changes. ** If the harmonic or other spurious signal is generated inside the analyzer, it should change relative to the fundamental signal as the input attenuation changes. ** I'm talking about the harmonics or other spurious signals relative to the fundamental frequency being displayed. If you remove the input signal and still see the spur, it's a residual spur created inside the analyzer unrelated to the input signal. If you graph fundamental signal displayed amplitude vs changing input level, you will typically see the following for spurious signals created by most mixers or amplifiers: (1) Fundamental signal = slope of 1 (2) Second harmonic signal = slope of 2 (3) Third order intermodulation (sum or different frequencies caused by mixing of two signals) = slope of 3 For more background, see: https://en.wikipedia.org/wiki/Third-order_intercept_point If that is a SiglentSSA3000X series analyzer, here are the spurious specifications from the datasheet: ** Second harmonic distortion: -65 dBc (above 50 MHz input with preamplifier off) Note that the second harmonic distortion is only specified at 50 MHz input and above and at a -30 dBm input power level with the preamplifier off. For comparison, here are the specifications of a Tektronix RSA507A portable spectrum analyzer. Disclosure: I work for Tektronix. ** Second harmonic distortion: - 75 dBc (above 40 MHz input, preamplifier OFF) ** Second harmonic distortion: - 60 dBc (above 40 MHz input, preamplifier ON) I'm sure that the reason for a lower limit on the second harmonic specification is that the results are worse at lower frequencies. So it's quite possible that the harmonics you see are mainly coming from the spectrum analyzer input mixer or preamplifier. As I suggested earlier, try lowering the input level by 5 or 10 dB and see if the harmonics go down linearly. -- Bill Byrom N5BB On Tue, Jan 17, 2017, at 08:40 PM, Rhys D wrote: > Hi all, > > Before I start, let me say I'm rather a newbie at this sort of > stuff so > please be gentle. > > I was looking at the output of my Trimble Thunderbolt GPSDO and > was rather > surprised to see really "loud" harmonics in there. ~ 60dB down > from the > 10Mhz signal. > > Can anyone here shed some light on what I am seeing here? > Surely this isn't what it is supposed to look like? Should I be > trying to > filter these before going to my distribution amplifier? > > Thanks for any light you can shed. > > R > > > > > _ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
On 1/18/17 8:04 PM, Gerhard Hoffmann wrote: Am 18.01.2017 um 22:12 schrieb Bob Camp: Yeah, but it's easier (cheaper if you're paying for labor) just to buy a box of 10 filters at $30/each and stack them Be *very* careful cascading those Min-Circuits filters without putting some sort of isolation between them. You can get all sorts of wonky results as the reactances in one mis-terminates the reactances in another. Bob But you can be quite lucky: 1 SLP15+ filter (15 MHz Low pass): < https://www.flickr.com/photos/137684711@N07/31554251684/in/album-72157662535945536/ 3 filters cascaded < https://www.flickr.com/photos/137684711@N07/32019253490/in/album-72157662535945536/ And the SLP10.7+ is very similar, except the 3dB down is around 13.5 MHz, and it's down 33 dB at 20 MHz. As a practical matter, a chain of two SLP10.7 knocks the harmonics from a Wenzel streamline down below the broadband noise floor when measured with a system with 4 dB NF. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
On 1/18/17 6:25 PM, Tom Holmes wrote: Jim Lux... Note that the Keysight 33622 is basically an ARB, and not really intended to be an RF signal generator. Yes, but it has performance that is as good as the run of the mill signal generator. The big defect in the 33600 series is that it cannot be phase locked to an external reference. If you feed it a 10 MHz ref, it has a frequency locked loop that pushes the internal oscillator around to match the external reference. It's output is DAC based, not oscillator based. Hence it will tend to have higher distortion products than a good RF generator. As good as, if not better, than an inexpensive generator (e.g. the low end Keysight sig gens) phase noise at non-harmonic frequencies is not as good. As you point out, a suitable filter for the intended frequency certainly can clean that up, of course. Tom Holmes, N8ZM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Yeah, but it's easier (cheaper if you're paying for labor) just to buy a box of 10 filters at $30/each and stack them Be *very* careful cascading those Min-Circuits filters without putting some sort of isolation between them. You can get all sorts of wonky results as the reactances in one mis-terminates the reactances in another. that's what a VNA is for. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Am 18.01.2017 um 22:12 schrieb Bob Camp: Yeah, but it's easier (cheaper if you're paying for labor) just to buy a box of 10 filters at $30/each and stack them Be *very* careful cascading those Min-Circuits filters without putting some sort of isolation between them. You can get all sorts of wonky results as the reactances in one mis-terminates the reactances in another. Bob But you can be quite lucky: 1 SLP15+ filter (15 MHz Low pass): < https://www.flickr.com/photos/137684711@N07/31554251684/in/album-72157662535945536/ > 3 filters cascaded < https://www.flickr.com/photos/137684711@N07/32019253490/in/album-72157662535945536/ > Not bad. 73, Gerhard ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Jim Lux... Note that the Keysight 33622 is basically an ARB, and not really intended to be an RF signal generator. It's output is DAC based, not oscillator based. Hence it will tend to have higher distortion products than a good RF generator. As you point out, a suitable filter for the intended frequency certainly can clean that up, of course. Tom Holmes, N8ZM -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of jimlux Sent: Wednesday, January 18, 2017 9:45 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt Harmonics On 1/18/17 4:33 AM, Artek Manuals wrote: > R > > Is what your seeing a harmonic (2nd? 3rd?) or a spur i.e what frequency > is the "harmonic" ? > > How are you measuring this ? (Spectrum analyzer ? make/model?) > > More importantly and at the risk of displaying my naivety, what is the > application that you are using the 10MHz source to feed and why if this > harmonic is 60db down (or even only 40db down, the quoted spec) why > would one care? What is the predicted error you will get in your > application as a result? > One application that needs low harmonic content is where you are measuring the harmonic generating (or lack thereof) of a downstream component. I have an application where we're measuring the performance of a RF chain followed by a digitizer. An easy test is to feed in a nice sine wave (at a frequency that is NOT a submultiple of the samplerate) and look for harmonics in the power spectrum of the sampled data stream. the first time we ran the test (using a Keysight 33622 signal generator) we saw significant 2nd and 3rd harmonics (50-60 dB down, but easily detectable). A quick review of the data sheet.. Oh, the signal generator spec is only -43 dBc for frequencies above 10 MHz. Another case where low harmonic content is when doing two tone IMD tests - if the sources have significant harmonic content, you might be seeing intermod between the harmonics of the source, rather than intermods between the fundamental of the source. For 10 MHz, you can get minicircuits filters for 10.7 MHz that are fairly wideband and work pretty well... about 20-30 dB of harmonic suppression per filter I'd use the low pass flavor SBP-10.7 loss at 20MHz is 26.84 loss at 40MHz is 41.22 loss at 50MHz is 46 est loss at 30 is 35? SLP-10.7 loss at 10 is 0.65 spec loss at 20 is 31.35 specmeasured -33 loss at 30 measured -60 loss at 34 is 47.26 spec loss at 40 measured -77 loss at 67.5 is 69.85 spec Yeah, they might have a significant tempco, but you're running all this stuff in an underground lair with small temperature variations, right? It only looks like a small volcano from the outside. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Thanks all for the extremely educational replies. On 19 January 2017 at 07:08, jimlux wrote: > On 1/18/17 8:56 AM, Bob Camp wrote: > >> HI >> >>> >>> the first time we ran the test (using a Keysight 33622 signal >>> generator) we saw significant 2nd and 3rd harmonics (50-60 dB down, >>> but easily detectable). A quick review of the data sheet.. Oh, the >>> signal generator spec is only -43 dBc for frequencies above 10 >>> MHz. >>> >> >> So even a pretty expensive signal generator still has “loud” >> harmonics if judged at the -60 dbc level …. >> >> that's actually an inexpensive ($7.4k) function generator (with good > performance for a function generator that does a lot of stuff, except > generate chirps at the right rate).. > > A $8k Keysight N9310 is -30dBc > > A R+S SMA100 specs -30dBc (actually does better) > > A $23k Keysight 8663D specs -55dBc (at 1 GHz) > > > > > >>> Another case where low harmonic content is when doing two tone IMD >>> tests - if the sources have significant harmonic content, you might >>> be seeing intermod between the harmonics of the source, rather than >>> intermods between the fundamental of the source. >>> >> >> Which is one of the reasons a lot of IMD test setups have a variety >> of filters in them. >> >> >> These also are a pretty common item on eBay, at ham fest, and in your >> typical RF junk box. 10.7 MHz IF filter cans can fairly easily be >> tuned down to 10 MHz to custom roll bandpass filters. >> > > Yeah, but it's easier (cheaper if you're paying for labor) just to buy a > box of 10 filters at $30/each and stack them > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Hi > On Jan 18, 2017, at 1:08 PM, jimlux wrote: > > On 1/18/17 8:56 AM, Bob Camp wrote: >> HI >>> >>> the first time we ran the test (using a Keysight 33622 signal >>> generator) we saw significant 2nd and 3rd harmonics (50-60 dB down, >>> but easily detectable). A quick review of the data sheet.. Oh, the >>> signal generator spec is only -43 dBc for frequencies above 10 >>> MHz. >> >> So even a pretty expensive signal generator still has “loud” >> harmonics if judged at the -60 dbc level …. >> > that's actually an inexpensive ($7.4k) function generator (with good > performance for a function generator that does a lot of stuff, except > generate chirps at the right rate).. > > A $8k Keysight N9310 is -30dBc > > A R+S SMA100 specs -30dBc (actually does better) > > A $23k Keysight 8663D specs -55dBc (at 1 GHz) > > > > >>> >>> Another case where low harmonic content is when doing two tone IMD >>> tests - if the sources have significant harmonic content, you might >>> be seeing intermod between the harmonics of the source, rather than >>> intermods between the fundamental of the source. >> >> Which is one of the reasons a lot of IMD test setups have a variety >> of filters in them. >> >> >> These also are a pretty common item on eBay, at ham fest, and in your >> typical RF junk box. 10.7 MHz IF filter cans can fairly easily be >> tuned down to 10 MHz to custom roll bandpass filters. > > Yeah, but it's easier (cheaper if you're paying for labor) just to buy a box > of 10 filters at $30/each and stack them Be *very* careful cascading those Min-Circuits filters without putting some sort of isolation between them. You can get all sorts of wonky results as the reactances in one mis-terminates the reactances in another. Bob > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
On 1/18/17 8:56 AM, Bob Camp wrote: HI the first time we ran the test (using a Keysight 33622 signal generator) we saw significant 2nd and 3rd harmonics (50-60 dB down, but easily detectable). A quick review of the data sheet.. Oh, the signal generator spec is only -43 dBc for frequencies above 10 MHz. So even a pretty expensive signal generator still has “loud” harmonics if judged at the -60 dbc level …. that's actually an inexpensive ($7.4k) function generator (with good performance for a function generator that does a lot of stuff, except generate chirps at the right rate).. A $8k Keysight N9310 is -30dBc A R+S SMA100 specs -30dBc (actually does better) A $23k Keysight 8663D specs -55dBc (at 1 GHz) Another case where low harmonic content is when doing two tone IMD tests - if the sources have significant harmonic content, you might be seeing intermod between the harmonics of the source, rather than intermods between the fundamental of the source. Which is one of the reasons a lot of IMD test setups have a variety of filters in them. These also are a pretty common item on eBay, at ham fest, and in your typical RF junk box. 10.7 MHz IF filter cans can fairly easily be tuned down to 10 MHz to custom roll bandpass filters. Yeah, but it's easier (cheaper if you're paying for labor) just to buy a box of 10 filters at $30/each and stack them ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Harmonic traps are another avenue to explore since the frequency is "fixed" at well below ppm. Which leaves the fundamental untouched. On Wed, Jan 18, 2017 at 5:21 AM, Charles Steinmetz wrote: > Rhys wrote: > > I was looking at the output of my Trimble Thunderbolt GPSDO and was rather >> surprised to see really "loud" harmonics in there. ~ 60dB down from the >> 10Mhz signal. >> > > Welcome to the world of RF. Loudest harmonic at ~ -60dBc (dB with respect > to carrier) is actually pretty good for a commercial product. Very few > distribution amplifiers do this well. For that matter, many good > laboratory RF generators are specified with harmonics only below -35 to -45 > dBc. We do not generally expect RF sources or amplifiers to get down to > the -80 to -90 dBc range (although amplifiers with harmonics < -80dBc at > 10MHz/1Vrms/50 ohms are possible), and certainly not the -100 to -120dBc > that we expect from high fidelity audio sources and amplifiers. > > Even harmonics (which make the carrier asymmetrical) can cause phase > errors that are harmful in high-precision systems [1], so I am a vocal > supporter of distribution amplifiers with harmonics < -80dBc. > > Note that cleaning up the Tbolt output to < -80dBc would probably require > a crystal filter (a filter with a sharp corner very close to 10MHz, in any > case), which means its phase response changes very rapidly with the filter > frequency. Sharp filters shift frequency with temperature, which causes > temperature-dependent phase shifts. Unless the filter is maintained in an > isothermal environment (like a good oven), this can cause problems in > sensitive applications. > > Best regards, > > Charles > > > [1] F.L. Walls (NIST), F.G. Ascarrunz (SpectraDynamics), The Effect of > Harmonic Distortion on Phase Errors in Frequency Distribution and Synthesis > (year unknown, probably late '90s). > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Is what your seeing a harmonic (2nd? 3rd?) or a spur i.e what frequency is the "harmonic" ? The OP attached a spectrum analyzer screen shot to his initial post -- go back and have a look. It shows the harmonic series from 1 to 7, with H6 close to the noise level. Loudest harmonic is H2 at ~ -60dBc. Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
HI > On Jan 18, 2017, at 9:44 AM, jimlux wrote: > > On 1/18/17 4:33 AM, Artek Manuals wrote: >> R >> >> Is what your seeing a harmonic (2nd? 3rd?) or a spur i.e what frequency >> is the "harmonic" ? >> >> How are you measuring this ? (Spectrum analyzer ? make/model?) >> >> More importantly and at the risk of displaying my naivety, what is the >> application that you are using the 10MHz source to feed and why if this >> harmonic is 60db down (or even only 40db down, the quoted spec) why >> would one care? What is the predicted error you will get in your >> application as a result? >> > > One application that needs low harmonic content is where you are measuring > the harmonic generating (or lack thereof) of a downstream component. > > I have an application where we're measuring the performance of a RF chain > followed by a digitizer. An easy test is to feed in a nice sine wave (at a > frequency that is NOT a submultiple of the samplerate) and look for harmonics > in the power spectrum of the sampled data stream. > > the first time we ran the test (using a Keysight 33622 signal generator) we > saw significant 2nd and 3rd harmonics (50-60 dB down, but easily detectable). > A quick review of the data sheet.. Oh, the signal generator spec is only -43 > dBc for frequencies above 10 MHz. So even a pretty expensive signal generator still has “loud” harmonics if judged at the -60 dbc level …. > > Another case where low harmonic content is when doing two tone IMD tests - if > the sources have significant harmonic content, you might be seeing intermod > between the harmonics of the source, rather than intermods between the > fundamental of the source. Which is one of the reasons a lot of IMD test setups have a variety of filters in them. > > For 10 MHz, you can get minicircuits filters for 10.7 MHz that are fairly > wideband and work pretty well... about 20-30 dB of harmonic suppression per > filter I'd use the low pass flavor > > SBP-10.7 > loss at 20MHz is 26.84 > loss at 40MHz is 41.22 > loss at 50MHz is 46 > est loss at 30 is 35? > > SLP-10.7 > loss at 10 is 0.65 spec > loss at 20 is 31.35 spec measured -33 > loss at 30 measured -60 > loss at 34 is 47.26 spec > loss at 40 measured -77 > loss at 67.5 is 69.85 spec These also are a pretty common item on eBay, at ham fest, and in your typical RF junk box. 10.7 MHz IF filter cans can fairly easily be tuned down to 10 MHz to custom roll bandpass filters. Bob > > > > Yeah, they might have a significant tempco, but you're running all this stuff > in an underground lair with small temperature variations, right? It only > looks like a small volcano from the outside. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
On 1/18/17 4:33 AM, Artek Manuals wrote: R Is what your seeing a harmonic (2nd? 3rd?) or a spur i.e what frequency is the "harmonic" ? How are you measuring this ? (Spectrum analyzer ? make/model?) More importantly and at the risk of displaying my naivety, what is the application that you are using the 10MHz source to feed and why if this harmonic is 60db down (or even only 40db down, the quoted spec) why would one care? What is the predicted error you will get in your application as a result? One application that needs low harmonic content is where you are measuring the harmonic generating (or lack thereof) of a downstream component. I have an application where we're measuring the performance of a RF chain followed by a digitizer. An easy test is to feed in a nice sine wave (at a frequency that is NOT a submultiple of the samplerate) and look for harmonics in the power spectrum of the sampled data stream. the first time we ran the test (using a Keysight 33622 signal generator) we saw significant 2nd and 3rd harmonics (50-60 dB down, but easily detectable). A quick review of the data sheet.. Oh, the signal generator spec is only -43 dBc for frequencies above 10 MHz. Another case where low harmonic content is when doing two tone IMD tests - if the sources have significant harmonic content, you might be seeing intermod between the harmonics of the source, rather than intermods between the fundamental of the source. For 10 MHz, you can get minicircuits filters for 10.7 MHz that are fairly wideband and work pretty well... about 20-30 dB of harmonic suppression per filter I'd use the low pass flavor SBP-10.7 loss at 20MHz is 26.84 loss at 40MHz is 41.22 loss at 50MHz is 46 est loss at 30 is 35? SLP-10.7 loss at 10 is 0.65 spec loss at 20 is 31.35 specmeasured -33 loss at 30 measured -60 loss at 34 is 47.26 spec loss at 40 measured -77 loss at 67.5 is 69.85 spec Yeah, they might have a significant tempco, but you're running all this stuff in an underground lair with small temperature variations, right? It only looks like a small volcano from the outside. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
On 1/18/17 2:21 AM, Charles Steinmetz wrote: Rhys wrote: [1] F.L. Walls (NIST), F.G. Ascarrunz (SpectraDynamics), The Effect of Harmonic Distortion on Phase Errors in Frequency Distribution and Synthesis (year unknown, probably late '90s). 9th Euro Freq & Time Forum 1995 Besancon http://tf.nist.gov/general/pdf/1437.pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
I suppose I should have said that Trimble specifies the Tbolt with harmonics -40dBc max, according to the User Guide v.5.0 (2003). Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
R Is what your seeing a harmonic (2nd? 3rd?) or a spur i.e what frequency is the "harmonic" ? How are you measuring this ? (Spectrum analyzer ? make/model?) More importantly and at the risk of displaying my naivety, what is the application that you are using the 10MHz source to feed and why if this harmonic is 60db down (or even only 40db down, the quoted spec) why would one care? What is the predicted error you will get in your application as a result? Dave manu...@artekmanuals.com On Jan 17, 2017, at 9:40 PM, Rhys D wrote: Hi all, Before I start, let me say I'm rather a newbie at this sort of stuff so please be gentle. I was looking at the output of my Trimble Thunderbolt GPSDO and was rather surprised to see really "loud" harmonics in there. ~ 60dB down from the 10Mhz signal. Can anyone here shed some light on what I am seeing here? Surely this isn't what it is supposed to look like? Should I be trying to filter these before going to my distribution amplifier? Thanks for any light you can shed. R <10MhzRef.png>___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Dave manu...@artekmanuals.com www.ArtekManuals.com --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Rhys wrote: I was looking at the output of my Trimble Thunderbolt GPSDO and was rather surprised to see really "loud" harmonics in there. ~ 60dB down from the 10Mhz signal. Welcome to the world of RF. Loudest harmonic at ~ -60dBc (dB with respect to carrier) is actually pretty good for a commercial product. Very few distribution amplifiers do this well. For that matter, many good laboratory RF generators are specified with harmonics only below -35 to -45 dBc. We do not generally expect RF sources or amplifiers to get down to the -80 to -90 dBc range (although amplifiers with harmonics < -80dBc at 10MHz/1Vrms/50 ohms are possible), and certainly not the -100 to -120dBc that we expect from high fidelity audio sources and amplifiers. Even harmonics (which make the carrier asymmetrical) can cause phase errors that are harmful in high-precision systems [1], so I am a vocal supporter of distribution amplifiers with harmonics < -80dBc. Note that cleaning up the Tbolt output to < -80dBc would probably require a crystal filter (a filter with a sharp corner very close to 10MHz, in any case), which means its phase response changes very rapidly with the filter frequency. Sharp filters shift frequency with temperature, which causes temperature-dependent phase shifts. Unless the filter is maintained in an isothermal environment (like a good oven), this can cause problems in sensitive applications. Best regards, Charles [1] F.L. Walls (NIST), F.G. Ascarrunz (SpectraDynamics), The Effect of Harmonic Distortion on Phase Errors in Frequency Distribution and Synthesis (year unknown, probably late '90s). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
Hi If you look at the FCC transmitter regs, -60 dbc is “ok” for many transmitters. Bob > On Jan 17, 2017, at 9:40 PM, Rhys D wrote: > > Hi all, > > Before I start, let me say I'm rather a newbie at this sort of stuff so > please be gentle. > > I was looking at the output of my Trimble Thunderbolt GPSDO and was rather > surprised to see really "loud" harmonics in there. ~ 60dB down from the > 10Mhz signal. > > Can anyone here shed some light on what I am seeing here? > Surely this isn't what it is supposed to look like? Should I be trying to > filter these before going to my distribution amplifier? > > Thanks for any light you can shed. > > R > > > > <10MhzRef.png>___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt Harmonics
I'm not sure what the Thunderbolt specs state for harmonics, but -60 dB seems quite good to me. From: Rhys D To: Discussion of precise time and frequency measurement Sent: Tuesday, January 17, 2017 6:40 PM Subject: [time-nuts] Thunderbolt Harmonics Hi all, Before I start, let me say I'm rather a newbie at this sort of stuff so please be gentle. I was looking at the output of my Trimble Thunderbolt GPSDO and was rather surprised to see really "loud" harmonics in there. ~ 60dB down from the 10Mhz signal. Can anyone here shed some light on what I am seeing here? Surely this isn't what it is supposed to look like? Should I be trying to filter these before going to my distribution amplifier? Thanks for any light you can shed. R ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Thunderbolt Harmonics
Hi all, Before I start, let me say I'm rather a newbie at this sort of stuff so please be gentle. I was looking at the output of my Trimble Thunderbolt GPSDO and was rather surprised to see really "loud" harmonics in there. ~ 60dB down from the 10Mhz signal. Can anyone here shed some light on what I am seeing here? Surely this isn't what it is supposed to look like? Should I be trying to filter these before going to my distribution amplifier? Thanks for any light you can shed. R ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
