Re: [time-nuts] Reverse isolation
Didier Yes it is, and it can only usually be justified if one has an antenna array to distribute low phase noise RF to. One then also needs to add a means of compensating for fiber delay tempco, which adds yet more cost. A cleanup PLL using an ultra low noise OCXO locked to each photomixer output is usually advisable as well. Achieving more than about 120 dB of isolation at 10MHz is difficult without shielding. NIST claimed about 144dB of reverse isolation for one of their designs. Bruce Didier wrote: > All this sounds quite a bit more expensive and expansive than 3 ECL gates, > even if one uses 3 packages to improve isolation... > > Didier > > >> -Original Message- >> From: time-nuts-boun...@febo.com >> [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths >> Sent: Monday, March 09, 2009 9:08 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Reverse isolation >> >> Didier >> >> A 10-1000mW of single mode ECDL helps. >> But then you need a modulator. >> You would also need to avoid frying any photomixer at the other end. >> >> Bruce >> >> Didier wrote: >> >>> But not necessarily lowest noise >>> >>> Didier >>> >>> >>> >>>> -Original Message- >>>> From: time-nuts-boun...@febo.com >>>> [mailto:time-nuts-boun...@febo.com] On Behalf Of Don Latham >>>> Sent: Sunday, March 08, 2009 8:48 PM >>>> To: Discussion of precise time and frequency measurement >>>> Subject: Re: [time-nuts] Reverse isolation >>>> >>>> Best isolation is via a piece of fiber optics. >>>> Don >>>> >>>> > > > ___ > 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] Reverse isolation
All this sounds quite a bit more expensive and expansive than 3 ECL gates, even if one uses 3 packages to improve isolation... Didier > -Original Message- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Bruce Griffiths > Sent: Monday, March 09, 2009 9:08 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Reverse isolation > > Didier > > A 10-1000mW of single mode ECDL helps. > But then you need a modulator. > You would also need to avoid frying any photomixer at the other end. > > Bruce > > Didier wrote: > > But not necessarily lowest noise > > > > Didier > > > > > >> -Original Message- > >> From: time-nuts-boun...@febo.com > >> [mailto:time-nuts-boun...@febo.com] On Behalf Of Don Latham > >> Sent: Sunday, March 08, 2009 8:48 PM > >> To: Discussion of precise time and frequency measurement > >> Subject: Re: [time-nuts] Reverse isolation > >> > >> Best isolation is via a piece of fiber optics. > >> Don > >> ___ 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] Reverse isolation
Didier A 10-1000mW of single mode ECDL helps. But then you need a modulator. You would also need to avoid frying any photomixer at the other end. Bruce Didier wrote: > But not necessarily lowest noise > > Didier > > >> -Original Message- >> From: time-nuts-boun...@febo.com >> [mailto:time-nuts-boun...@febo.com] On Behalf Of Don Latham >> Sent: Sunday, March 08, 2009 8:48 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Reverse isolation >> >> Best isolation is via a piece of fiber optics. >> Don >> >> Bruce Griffiths >> >>> Lux, James P wrote: >>> >>>>> Actually, it depends on the distance from the hot carrier, the >>>>> amplitude of the hot carrier and the particular VNA in >>>>> >> question. My >> >>>>> VNA allows me to change filters as well as integration time. >>>>> >>>>> >>>> And especially, where is the selectivity in the VNA's >>>> >> receiver? You >> >>>> might have a 10 Hz filter, but if the receiver's front end is wide >>>> open, then the dynamic range requirement might be a challenge to >>>> meet. >>>> >>>> Consider a 30 dB gain amplifier claiming 120dB reverse isolation.. >>>> >>>> You put in -30dBm and get 0dBm out in the forward direction. >>>> Meanwhile, you inject 0dBm into the output of the >>>> >> amplifier (from the >> >>>> VNA) and you expect to see -120dBm appearing at the input. >>>> >> Depending >> >>>> on how good the directional coupler/bridge is that feed the port 1 >>>> reflected power receiver, you might be facing measuring a -120dBm >>>> signal next to a -30dBm signal, which is challenging... >>>> >>>> Assuming the DUT is linear (hah!) one could just apply load with >>>> different reflection coefficients to it when measuring S11. This >>>> might even be harder, though... With -120dBm reverse isolation, >>>> you're basically looking at seeing the effect of adding a coherent >>>> signal 90 dB down to the signal you're already measuring for S11. >>>> That's not going to result in a huge change in amplitude or phase >>>> (e.g. About 1 part in 1E4 or 1E5).. >>>> >>>> Maybe for this list, though.. Measuring phase shifts of >>>> >> 1E-5 radian.. >> >>>> Walk >>>> in the park, as it were. >>>> >>>> Jim >>>> >>>> >>>> ___ >>>> 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. >>>> >>>> >>>> >>> Jim >>> >>> Its even more challenging when the isolation amplifier has >>> >> a nominal >> >>> gain of 0dB coupled with a reverse isolation of 120dB or more. >>> In this case one would be looking at measuring phase shifts on the >>> order of 1urad or less. >>> >>> In this case one could try applying say a +10dBm signal to >>> >> the input, >> >>> modulate the load reflection coefficient and look for a modulation >>> frequency related sideband at the input port. >>> >>> Bruce >>> >>> ___ >>> 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. >>> >>> >> -- >> Dr. Don Latham AJ7LL >> Six Mile Systems LLP >> 17850 Six Mile Road >> POB 134 >> Huson, MT, 59846 >> VOX 406-626-4304 >> www.lightningforensics.com >> www.sixmilesystems.com >> >> >> ___ >> 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 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] Reverse isolation
But not necessarily lowest noise Didier > -Original Message- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Don Latham > Sent: Sunday, March 08, 2009 8:48 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Reverse isolation > > Best isolation is via a piece of fiber optics. > Don > > Bruce Griffiths > > Lux, James P wrote: > >>> Actually, it depends on the distance from the hot carrier, the > >>> amplitude of the hot carrier and the particular VNA in > question. My > >>> VNA allows me to change filters as well as integration time. > >>> > >> > >> And especially, where is the selectivity in the VNA's > receiver? You > >> might have a 10 Hz filter, but if the receiver's front end is wide > >> open, then the dynamic range requirement might be a challenge to > >> meet. > >> > >> Consider a 30 dB gain amplifier claiming 120dB reverse isolation.. > >> > >> You put in -30dBm and get 0dBm out in the forward direction. > >> Meanwhile, you inject 0dBm into the output of the > amplifier (from the > >> VNA) and you expect to see -120dBm appearing at the input. > Depending > >> on how good the directional coupler/bridge is that feed the port 1 > >> reflected power receiver, you might be facing measuring a -120dBm > >> signal next to a -30dBm signal, which is challenging... > >> > >> Assuming the DUT is linear (hah!) one could just apply load with > >> different reflection coefficients to it when measuring S11. This > >> might even be harder, though... With -120dBm reverse isolation, > >> you're basically looking at seeing the effect of adding a coherent > >> signal 90 dB down to the signal you're already measuring for S11. > >> That's not going to result in a huge change in amplitude or phase > >> (e.g. About 1 part in 1E4 or 1E5).. > >> > >> Maybe for this list, though.. Measuring phase shifts of > 1E-5 radian.. > >> Walk > >> in the park, as it were. > >> > >> Jim > >> > >> > >> ___ > >> 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. > >> > >> > > Jim > > > > Its even more challenging when the isolation amplifier has > a nominal > > gain of 0dB coupled with a reverse isolation of 120dB or more. > > In this case one would be looking at measuring phase shifts on the > > order of 1urad or less. > > > > In this case one could try applying say a +10dBm signal to > the input, > > modulate the load reflection coefficient and look for a modulation > > frequency related sideband at the input port. > > > > Bruce > > > > ___ > > 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. > > > > > -- > Dr. Don Latham AJ7LL > Six Mile Systems LLP > 17850 Six Mile Road > POB 134 > Huson, MT, 59846 > VOX 406-626-4304 > www.lightningforensics.com > www.sixmilesystems.com > > > ___ > 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] Reverse isolation
You¹re thinking that the fiber optic transmitter and receiver pair provide good reverse isolation? Maybe.. At least you could separate them by 100s of meters, so leakage isn't as big an issue. But what you gain in isolation, you might lose in other uncertainties. TANSTAAFL Jim On 3/8/09 6:47 PM, "Don Latham" wrote: > Best isolation is via a piece of fiber optics. > Don > > Bruce Griffiths >> Lux, James P wrote: Actually, it depends on the distance from the hot carrier, the amplitude of the hot carrier and the particular VNA in question. My VNA allows me to change filters as well as integration time. >>> >>> And especially, where is the selectivity in the VNA's receiver? You >>> might >>> have a 10 Hz filter, but if the receiver's front end is wide open, then >>> the >>> dynamic range requirement might be a challenge to meet. ___ 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] Reverse isolation
Best isolation is via a piece of fiber optics. Don Bruce Griffiths > Lux, James P wrote: >>> Actually, it depends on the distance from the hot carrier, the >>> amplitude >>> of the hot carrier and the particular VNA in question. My VNA allows me >>> to change filters as well as integration time. >>> >> >> And especially, where is the selectivity in the VNA's receiver? You >> might >> have a 10 Hz filter, but if the receiver's front end is wide open, then >> the >> dynamic range requirement might be a challenge to meet. >> >> Consider a 30 dB gain amplifier claiming 120dB reverse isolation.. >> >> You put in -30dBm and get 0dBm out in the forward direction. Meanwhile, >> you >> inject 0dBm into the output of the amplifier (from the VNA) and you >> expect >> to see -120dBm appearing at the input. Depending on how good the >> directional coupler/bridge is that feed the port 1 reflected power >> receiver, >> you might be facing measuring a -120dBm signal next to a -30dBm signal, >> which is challenging... >> >> Assuming the DUT is linear (hah!) one could just apply load with >> different >> reflection coefficients to it when measuring S11. This might even be >> harder, though... With -120dBm reverse isolation, you're basically >> looking >> at seeing the effect of adding a coherent signal 90 dB down to the >> signal >> you're already measuring for S11. That's not going to result in a huge >> change in amplitude or phase (e.g. About 1 part in 1E4 or 1E5).. >> >> Maybe for this list, though.. Measuring phase shifts of 1E-5 radian.. >> Walk >> in the park, as it were. >> >> Jim >> >> >> ___ >> 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. >> >> > Jim > > Its even more challenging when the isolation amplifier has a nominal > gain of 0dB coupled with a reverse isolation of 120dB or more. > In this case one would be looking at measuring phase shifts on the order > of 1urad or less. > > In this case one could try applying say a +10dBm signal to the input, > modulate the load reflection coefficient and look for a modulation > frequency related sideband at the input port. > > Bruce > > ___ > 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. > -- Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ 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] Reverse isolation
Lux, James P wrote: >> Actually, it depends on the distance from the hot carrier, the amplitude >> of the hot carrier and the particular VNA in question. My VNA allows me >> to change filters as well as integration time. >> > > And especially, where is the selectivity in the VNA's receiver? You might > have a 10 Hz filter, but if the receiver's front end is wide open, then the > dynamic range requirement might be a challenge to meet. > > Consider a 30 dB gain amplifier claiming 120dB reverse isolation.. > > You put in -30dBm and get 0dBm out in the forward direction. Meanwhile, you > inject 0dBm into the output of the amplifier (from the VNA) and you expect > to see -120dBm appearing at the input. Depending on how good the > directional coupler/bridge is that feed the port 1 reflected power receiver, > you might be facing measuring a -120dBm signal next to a -30dBm signal, > which is challenging... > > Assuming the DUT is linear (hah!) one could just apply load with different > reflection coefficients to it when measuring S11. This might even be > harder, though... With -120dBm reverse isolation, you're basically looking > at seeing the effect of adding a coherent signal 90 dB down to the signal > you're already measuring for S11. That's not going to result in a huge > change in amplitude or phase (e.g. About 1 part in 1E4 or 1E5).. > > Maybe for this list, though.. Measuring phase shifts of 1E-5 radian.. Walk > in the park, as it were. > > Jim > > > ___ > 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. > > Jim Its even more challenging when the isolation amplifier has a nominal gain of 0dB coupled with a reverse isolation of 120dB or more. In this case one would be looking at measuring phase shifts on the order of 1urad or less. In this case one could try applying say a +10dBm signal to the input, modulate the load reflection coefficient and look for a modulation frequency related sideband at the input port. Bruce ___ 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] Reverse isolation
> > > Actually, it depends on the distance from the hot carrier, the amplitude > of the hot carrier and the particular VNA in question. My VNA allows me > to change filters as well as integration time. And especially, where is the selectivity in the VNA's receiver? You might have a 10 Hz filter, but if the receiver's front end is wide open, then the dynamic range requirement might be a challenge to meet. Consider a 30 dB gain amplifier claiming 120dB reverse isolation.. You put in -30dBm and get 0dBm out in the forward direction. Meanwhile, you inject 0dBm into the output of the amplifier (from the VNA) and you expect to see -120dBm appearing at the input. Depending on how good the directional coupler/bridge is that feed the port 1 reflected power receiver, you might be facing measuring a -120dBm signal next to a -30dBm signal, which is challenging... Assuming the DUT is linear (hah!) one could just apply load with different reflection coefficients to it when measuring S11. This might even be harder, though... With -120dBm reverse isolation, you're basically looking at seeing the effect of adding a coherent signal 90 dB down to the signal you're already measuring for S11. That's not going to result in a huge change in amplitude or phase (e.g. About 1 part in 1E4 or 1E5).. Maybe for this list, though.. Measuring phase shifts of 1E-5 radian.. Walk in the park, as it were. Jim ___ 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] Reverse isolation
Didier Juges skrev: > As long as one is not trying to measure extremely low signals (or extremely > high isolation), the conventional method works, and I have used it many > times, I am not sure that the method would scale when dealing with very high > levels of isolation. > > I certainly would not trust a conventional VNA for isolation of 100dB or > more, simply because such isolation is difficult to achieve in an instrument > that is supposed to be able to switch its source and receivers between the > two ports. > > The HP 8722D which we use at work is only specified with 100dB dynamic > range, and I am not sure how that applies to reverse isolation. Notice that the VNA does not have to handle all the dynamics by itself. You could use an external output amp which can be made sufficiently isolated from the input side as well as a LNA to gain the receiver side. By measuring the amps gain in a calibration setup you can get correct measures in the total setup. If you have a 60 dB of total amplifier gain the VNA would see a remaining 60 dB dynamics on its output-to-input. That is more along the lines of what we trust. What remains an issue is how we ensure more than 120 dB isolation between input and output of the DUT and also the output of measurement amp and input. I agree with you that I would not entierly trust the VNA for 120 dB... directly. Additional amp stages near the DUT can give the VNA dynamic range the necessary boost. > Using a slightly offset test frequency while driving the device at its > normal operating frequency would only work when using a spectrum analyzer as > receiver. Most VNAs don't have the capability of rejecting large signals > close in, and separating the frequencies too much would make the test > invalid with a narrow band amplifier. I have used that method to measure the > hot output VSWR of a TWT amplifier for instance (that was interesting). Of > course, the spectrum analyzer does not give you the phase, but it's better > than nothing. Actually, it depends on the distance from the hot carrier, the amplitude of the hot carrier and the particular VNA in question. My VNA allows me to change filters as well as integration time. So, I agree that not all VNAs is well suited for it and that is indeed a good warning. Cheers, Magnus ___ 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] Reverse isolation
Didier NIST have measured reverse isolation as high as -144dB @ 10MHz for one of their isolation amplifier designs but they gave no measurement system details. Bruce Didier Juges wrote: > As long as one is not trying to measure extremely low signals (or extremely > high isolation), the conventional method works, and I have used it many > times, I am not sure that the method would scale when dealing with very high > levels of isolation. > > I certainly would not trust a conventional VNA for isolation of 100dB or > more, simply because such isolation is difficult to achieve in an instrument > that is supposed to be able to switch its source and receivers between the > two ports. > > The HP 8722D which we use at work is only specified with 100dB dynamic > range, and I am not sure how that applies to reverse isolation. > > Using a slightly offset test frequency while driving the device at its > normal operating frequency would only work when using a spectrum analyzer as > receiver. Most VNAs don't have the capability of rejecting large signals > close in, and separating the frequencies too much would make the test > invalid with a narrow band amplifier. I have used that method to measure the > hot output VSWR of a TWT amplifier for instance (that was interesting). Of > course, the spectrum analyzer does not give you the phase, but it's better > than nothing. > > Didier KO4BB > > >> -Original Message- >> From: time-nuts-boun...@febo.com >> [mailto:time-nuts-boun...@febo.com] On Behalf Of John Day >> Sent: Sunday, March 08, 2009 5:47 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Reverse isolation >> >> At 06:14 PM 3/8/2009, Didier wrote: >> >>> This question is directed at Bruce, but if anyone else has a >>> contribution, feel free to speak. >>> >>> Bruce, >>> >>> What is the best way to measure the reverse isolation of an >>> >> amplifier >> >>> (particularly a buffer amplifier for a 10 MHz reference), when it is >>> expected to be in the order of 100 dB or more? >>> >>> Feeding the output with a known signal and measuring at the >>> >> input with >> >>> a spectrum analyzer comes to mind, but I am sure there must be >>> something wrong with that technique, it sounds too simple. >>> >> No, not really. How else would you measure it? Reverse >> isolation is basically the reverse gain - S12 - of the >> amplifier. How does a VNA measure S12? Essentially inject a >> signal at port 2 and see how much comes out of port 1. >> >> If you want to get so picky as to determine S12 with a signal >> in the forward direction then you have a problem. Because the >> forward gain - >> S21 - is going to effectively swamp the signal going the other way. >> So this is almost impossible to measure if the signals are at >> the same frequency. In this case measure the S-parameters of >> the amplifier in its 'normal ' configuration, then de-embed >> the S-parameters of the device. Assuming the device is the >> only non-linear element you are dealing with then from the >> S12 & S22 values you can also figure out how the device >> reacts in the reverse direction. >> >> Then if you don't mind solving a large matrix you can figure >> out how the device might react to passing a signal in both >> directions. The reality is however that if the device is >> within its linear range, which it is likely to be if you want >> to distribute a reference or some such, the reverse behaviour >> of the well terminated amplifier will approach the nominal >> S12 value. The difficult part is to determine what happens >> when the amplifier is not nicely terminated! >> >> John >> >> >> >>> The presence of a signal at the input (or not) may affect >>> >> the operating >> >>> point of the amplifier, so measuring from output to input >>> >> without such >> >>> signal may not give a true result. >>> >>> Didier >>> >>> >>> >>> >>> ___ >>> 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. >>> >>> >>> -- >>> No virus found in this incoming message. >>> Checked b
Re: [time-nuts] Reverse isolation
Probably does not mean a lot for an amplifier, but it would for a mixer :) Generic terms need sometimes to be put in the proper context :) In fact, it's a negative number, now that I think of it :) Didier KO4BB > -Original Message- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of Mike S > Sent: Sunday, March 08, 2009 5:43 PM > To: Discussion of precise time and frequency measurement > Cc: 'Discussion of precise time and frequency measurement' > Subject: Re: [time-nuts] Reverse isolation > > At 06:14 PM 3/8/2009, Didier wrote... > >What is the best way to measure the reverse isolation of an amplifier > > Now I'm curious. What would "forward isolation" be in an amplifier? > ___ 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] Reverse isolation
As long as one is not trying to measure extremely low signals (or extremely high isolation), the conventional method works, and I have used it many times, I am not sure that the method would scale when dealing with very high levels of isolation. I certainly would not trust a conventional VNA for isolation of 100dB or more, simply because such isolation is difficult to achieve in an instrument that is supposed to be able to switch its source and receivers between the two ports. The HP 8722D which we use at work is only specified with 100dB dynamic range, and I am not sure how that applies to reverse isolation. Using a slightly offset test frequency while driving the device at its normal operating frequency would only work when using a spectrum analyzer as receiver. Most VNAs don't have the capability of rejecting large signals close in, and separating the frequencies too much would make the test invalid with a narrow band amplifier. I have used that method to measure the hot output VSWR of a TWT amplifier for instance (that was interesting). Of course, the spectrum analyzer does not give you the phase, but it's better than nothing. Didier KO4BB > -Original Message- > From: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On Behalf Of John Day > Sent: Sunday, March 08, 2009 5:47 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Reverse isolation > > At 06:14 PM 3/8/2009, Didier wrote: > > > >This question is directed at Bruce, but if anyone else has a > >contribution, feel free to speak. > > > >Bruce, > > > >What is the best way to measure the reverse isolation of an > amplifier > >(particularly a buffer amplifier for a 10 MHz reference), when it is > >expected to be in the order of 100 dB or more? > > > >Feeding the output with a known signal and measuring at the > input with > >a spectrum analyzer comes to mind, but I am sure there must be > >something wrong with that technique, it sounds too simple. > > No, not really. How else would you measure it? Reverse > isolation is basically the reverse gain - S12 - of the > amplifier. How does a VNA measure S12? Essentially inject a > signal at port 2 and see how much comes out of port 1. > > If you want to get so picky as to determine S12 with a signal > in the forward direction then you have a problem. Because the > forward gain - > S21 - is going to effectively swamp the signal going the other way. > So this is almost impossible to measure if the signals are at > the same frequency. In this case measure the S-parameters of > the amplifier in its 'normal ' configuration, then de-embed > the S-parameters of the device. Assuming the device is the > only non-linear element you are dealing with then from the > S12 & S22 values you can also figure out how the device > reacts in the reverse direction. > > Then if you don't mind solving a large matrix you can figure > out how the device might react to passing a signal in both > directions. The reality is however that if the device is > within its linear range, which it is likely to be if you want > to distribute a reference or some such, the reverse behaviour > of the well terminated amplifier will approach the nominal > S12 value. The difficult part is to determine what happens > when the amplifier is not nicely terminated! > > John > > > >The presence of a signal at the input (or not) may affect > the operating > >point of the amplifier, so measuring from output to input > without such > >signal may not give a true result. > > > >Didier > > > > > > > > > >___ > >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. > > > > > >-- > >No virus found in this incoming message. > >Checked by AVG. > >Version: 7.5.557 / Virus Database: 270.11.9/1989 - Release Date: > >3/7/2009 6:43 PM > > > ___ > 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. > > > -- > No virus found in this incoming message. > Checked by AVG. > Version: 7.5.557 / Virus Database: 270.11.9/1989 - Release > Date: 3/7/2009 6:43 PM > ___ 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] Reverse isolation
I've been learning a little bit about this lately from my friend who is an Agilent network analyzer apps engineer. He tells me that "hot S12" tests can be done with modern network analyzers. The key is being able to offset the frequencies enough so the front end of the analyzer doesn't get creamed. For example, you put +10dBm at 11 MHz on the input, and +10dBm at 10 MHz on the output. Then measure S12 using a narrow bandwidth in the analyzer. Hopefully the DUT frequency response is flat enough for that to be meaningful. In any event, it's a challenging measurement. John Didier said the following on 03/08/2009 06:14 PM: > > This question is directed at Bruce, but if anyone else has a contribution, > feel free to speak. > > Bruce, > > What is the best way to measure the reverse isolation of an amplifier > (particularly a buffer amplifier for a 10 MHz reference), when it is > expected to be in the order of 100 dB or more? > > Feeding the output with a known signal and measuring at the input with a > spectrum analyzer comes to mind, but I am sure there must be something wrong > with that technique, it sounds too simple. > > The presence of a signal at the input (or not) may affect the operating > point of the amplifier, so measuring from output to input without such > signal may not give a true result. > > Didier > > > > > ___ > 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] Reverse isolation
Didier skrev: > > This question is directed at Bruce, but if anyone else has a contribution, > feel free to speak. > > Bruce, > > What is the best way to measure the reverse isolation of an amplifier > (particularly a buffer amplifier for a 10 MHz reference), when it is > expected to be in the order of 100 dB or more? > > Feeding the output with a known signal and measuring at the input with a > spectrum analyzer comes to mind, but I am sure there must be something wrong > with that technique, it sounds too simple. > > The presence of a signal at the input (or not) may affect the operating > point of the amplifier, so measuring from output to input without such > signal may not give a true result. If you are concerned about that issue, then you can apply a signal of a different frequency on the input and then use your network analyser to sweep the range. To be able to sweep the full range apply two different frequencies so you can make partial sweeps of the other range. Otherwise the buffer amplifier should see the 50 Ohm termination of the network analysers as you run the buffer amplifier in reverse. I suspect that isolational amplifiers often is analysed in sections. If you have -120 dB reverse gain it can be a bit hard to measure. Notice that a network analyser is automatically synchronous to the source, which makes detection of modulated frequency more sensitive. Cheers, Magnus ___ 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] Reverse isolation
At 06:14 PM 3/8/2009, Didier wrote: > >This question is directed at Bruce, but if anyone else has a contribution, >feel free to speak. > >Bruce, > >What is the best way to measure the reverse isolation of an amplifier >(particularly a buffer amplifier for a 10 MHz reference), when it is >expected to be in the order of 100 dB or more? > >Feeding the output with a known signal and measuring at the input with a >spectrum analyzer comes to mind, but I am sure there must be something wrong >with that technique, it sounds too simple. No, not really. How else would you measure it? Reverse isolation is basically the reverse gain - S12 - of the amplifier. How does a VNA measure S12? Essentially inject a signal at port 2 and see how much comes out of port 1. If you want to get so picky as to determine S12 with a signal in the forward direction then you have a problem. Because the forward gain - S21 - is going to effectively swamp the signal going the other way. So this is almost impossible to measure if the signals are at the same frequency. In this case measure the S-parameters of the amplifier in its 'normal ' configuration, then de-embed the S-parameters of the device. Assuming the device is the only non-linear element you are dealing with then from the S12 & S22 values you can also figure out how the device reacts in the reverse direction. Then if you don't mind solving a large matrix you can figure out how the device might react to passing a signal in both directions. The reality is however that if the device is within its linear range, which it is likely to be if you want to distribute a reference or some such, the reverse behaviour of the well terminated amplifier will approach the nominal S12 value. The difficult part is to determine what happens when the amplifier is not nicely terminated! John >The presence of a signal at the input (or not) may affect the operating >point of the amplifier, so measuring from output to input without such >signal may not give a true result. > >Didier > > > > >___ >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. > > >-- >No virus found in this incoming message. >Checked by AVG. >Version: 7.5.557 / Virus Database: 270.11.9/1989 - Release Date: >3/7/2009 6:43 PM ___ 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] Reverse isolation
At 06:14 PM 3/8/2009, Didier wrote... >What is the best way to measure the reverse isolation of an amplifier Now I'm curious. What would "forward isolation" be in an amplifier? ___ 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] Reverse isolation
Didier wrote: > > This question is directed at Bruce, but if anyone else has a contribution, > feel free to speak. > > Bruce, > > What is the best way to measure the reverse isolation of an amplifier > (particularly a buffer amplifier for a 10 MHz reference), when it is > expected to be in the order of 100 dB or more? > > Feeding the output with a known signal and measuring at the input with a > spectrum analyzer comes to mind, but I am sure there must be something wrong > with that technique, it sounds too simple. > > The presence of a signal at the input (or not) may affect the operating > point of the amplifier, so measuring from output to input without such > signal may not give a true result. > > Didier > Didier Network analysers like the Agilent E5071C can be limited by the fixture used, to around S22 (fixture) ~ -120dB@ 10MHz. In principle one just feeds a signal into the output and measures the resultant signal that appears at the input. However when attempting to measure reverse isolation of 120dB or more cable leakage, leakage from connectors (non screw mount connectors like BNC can be quite leaky) need to be considered. Also if one isn't careful with the grounding system this can limit the measured attenuation. Leakage from the test source also needs to be considered. The HP journal article on achieving 120dB attenuation with an attenuator is informative on some of the issues involved. The other major consideration is that unless one is making the measurements within a shielded room the ambient RF signals may make such measurements difficult. Bruce ___ 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.
