Re: [time-nuts] NIST isolation amplifiers
A single 2N or equivalent transistor in a suitable circuit dissipating about 200mW or so can achieve a reverse isolation of 35dB with distortion of around -40dBc (output +13dBm) with a gain of unity, and an output impedance of 50 ohms with a PN floor of around -180dBc/Hz or so. Bruce On Wednesday, 26 November 2014 9:13 PM, Charles Steinmetz csteinm...@yandex.com wrote: Bruce wrote: Another issue is that if even one output needs high reverse isolation and low crosstalk, then even those outputs that arent so critical will also need high reverse isolation and low crosstalk to avoid degrading the crosstalk to the critical output. This brings up the distinction between *isolation* amplifiers and *distribution* amplifiers. Most of us need a dozen or three feeds for various test equipment, radios, etc. These feeds should have 50 ohm output impedance, moderate isolation (35dB or more), and should not noticeably degrade the noise, PN, distortion, or xDEV of the source. That is the job of a distribution amp. I would generally not use anything like one of the NIST circuits for this, but rather some version of a two- or three-transistor Class A buffer amplifier. There are lots of circuits to choose from. Many are transformer (or autoformer) coupled, some are not (the JPL circuits come to mind) and can also be used to distribute lower frequencies. You can get build-out the NIST way (buffer amp input impedance high so you parallel a bunch of them at the input connector), or by using one stage with low output impedance to drive a number of output amplifiers in parallel, or by using an amplifier with very low output impedance (perhaps a high-current monolithic amplifier) to drive a number of 50 ohm build-out resistors, or by fanning out with CMOS logic and following each CMOS final buffer with a Tee network to generate sine waves. Then there are the times when you are making measurements of oscillators and must absolutely ensure that there is no interaction between them. That is the job of an isolation amp. Rarely will you need more than two or three feeds per oscillator, so what you need are several, one-to-three iso amps (one for each oscillator). Here, something like the NIST amplifiers makes sense. Note that I'm advocating distributing sine waves exclusively, NOT square waves or pulse trains. You will find that it is hard enough keeping 1, 5, or 10 MHz from getting into everything in the shop (and radio room), without adding the much-increased difficulty of keeping all of the harmonics under control. Also, you would like the harmonic content to be rather lower than is often thought because (i) even harmonics cause asymmetry, which can cause phase modulation when the signal is AC coupled or feeds a comparator-type zero-cross detector, and (ii) variations in the phase of harmonics in relation to the fundamental cause phase modulation (this is harmonic dispersion, which is caused by temperature changes and other circuit variations such as modulation of semiconductor capacitances by low frequecies). NIST published a paper on this (see Walls and Ascarrunz, The Effect of Harmonic Distortion on Phase Errors in Frequency Distribution and Synthesis). 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. ___ 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] NIST isolation amplifiers
Bruce wrote: Another issue is that if even one output needs high reverse isolation and low crosstalk, then even those outputs that arent so critical will also need high reverse isolation and low crosstalk to avoid degrading the crosstalk to the critical output. This brings up the distinction between *isolation* amplifiers and *distribution* amplifiers. Most of us need a dozen or three feeds for various test equipment, radios, etc. These feeds should have 50 ohm output impedance, moderate isolation (35dB or more), and should not noticeably degrade the noise, PN, distortion, or xDEV of the source. That is the job of a distribution amp. I would generally not use anything like one of the NIST circuits for this, but rather some version of a two- or three-transistor Class A buffer amplifier. There are lots of circuits to choose from. Many are transformer (or autoformer) coupled, some are not (the JPL circuits come to mind) and can also be used to distribute lower frequencies. You can get build-out the NIST way (buffer amp input impedance high so you parallel a bunch of them at the input connector), or by using one stage with low output impedance to drive a number of output amplifiers in parallel, or by using an amplifier with very low output impedance (perhaps a high-current monolithic amplifier) to drive a number of 50 ohm build-out resistors, or by fanning out with CMOS logic and following each CMOS final buffer with a Tee network to generate sine waves. Then there are the times when you are making measurements of oscillators and must absolutely ensure that there is no interaction between them. That is the job of an isolation amp. Rarely will you need more than two or three feeds per oscillator, so what you need are several, one-to-three iso amps (one for each oscillator). Here, something like the NIST amplifiers makes sense. Note that I'm advocating distributing sine waves exclusively, NOT square waves or pulse trains. You will find that it is hard enough keeping 1, 5, or 10 MHz from getting into everything in the shop (and radio room), without adding the much-increased difficulty of keeping all of the harmonics under control. Also, you would like the harmonic content to be rather lower than is often thought because (i) even harmonics cause asymmetry, which can cause phase modulation when the signal is AC coupled or feeds a comparator-type zero-cross detector, and (ii) variations in the phase of harmonics in relation to the fundamental cause phase modulation (this is harmonic dispersion, which is caused by temperature changes and other circuit variations such as modulation of semiconductor capacitances by low frequecies). NIST published a paper on this (see Walls and Ascarrunz, The Effect of Harmonic Distortion on Phase Errors in Frequency Distribution and Synthesis). 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] NIST isolation amplifiers
Bruce wrote: A single 2N or equivalent transistor in a suitable circuit dissipating about 200mW or so can achieve a reverse isolation of 35dB with distortion of around -40dBc (output +13dBm) with a gain of unity, and an output impedance of 50 ohms with a PN floor of around -180dBc/Hz or so. For those wondering, I suspect Bruce had in mind something like the attached (he posted the basic design a few years ago). I built 8 channels using toroids on FT37-61 cores. I think the Mini-Circuits T622 should work, but I have not tried it. The analyses are from my simulation, and the constructed unit performed similarly. The Miller effect limits fan-out to about 10 for a 10MHz distribution amp. [Note: the 50 ohm resistors on the outputs represent the external loads, and are not part of the amplifier.] 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] NIST isolation amplifiers
Almost. 1:1:2 (turns ratio) transformers used in each stage and 1:1 transformer on input. This allows a lower power supply voltage to be used. One thing to watch with minicircuits transformers is core saturation due to dc flowing in the windings. Bruce On Wednesday, November 26, 2014 08:52:14 AM Charles Steinmetz wrote: Bruce wrote: A single 2N or equivalent transistor in a suitable circuit dissipating about 200mW or so can achieve a reverse isolation of 35dB with distortion of around -40dBc (output +13dBm) with a gain of unity, and an output impedance of 50 ohms with a PN floor of around -180dBc/Hz or so. For those wondering, I suspect Bruce had in mind something like the attached (he posted the basic design a few years ago). I built 8 channels using toroids on FT37-61 cores. I think the Mini-Circuits T622 should work, but I have not tried it. The analyses are from my simulation, and the constructed unit performed similarly. The Miller effect limits fan-out to about 10 for a 10MHz distribution amp. [Note: the 50 ohm resistors on the outputs represent the external loads, and are not part of the amplifier.] 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] NIST isolation amplifiers
Bruce wrote: Almost. 1:1:2 (turns ratio) transformers used in each stage and 1:1 transformer on input. This allows a lower power supply voltage to be used. I spent a little time (emphasis on little) fiddling with the simulation, and I did not immediately find any solution with 1:1:2 and 1:1 transformers that I liked as well as the design with 1:1:1 and 1:2 transformers. For those who are winding their own transformers (which I recommend, partly for the reason given below), the simplicity of three equal windings may, by itself, outweigh any potential advantage of using a lower power supply voltage. Each constructor should evaluate this for him- or herself. One thing to watch with minicircuits transformers is core saturation due to dc flowing in the windings. Good point, I too have found that some MCL transformers have skimpy cores. I have no idea whether the MCL T622 (1:1:1) or T613 (1:1:2) would work in this circuit. They are both specified for 30mA, and I had the 3904s biased at 20mA -- but I'm not sure what MCL means by 30mA. In this circuit, 20mA flows in the same direction in two of the windings. If the 30mA applies only if one winding has DC flowing (or more generally, if the allowable net DC is equal to 30mA through just one winding), then the core would not be adequate. 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] NIST isolation amplifiers
The magnetic field in the core due to the current in the windings is proportional to current times number of turns. If there are more than one winding, add the currents. Yes, 2 x 20mA certainly exceeds 30mA. The core will be driven closer or into saturation and the inductance will be decreased. Dave Original message From: Charles Steinmetz csteinm...@yandex.com Date:2014/11/26 12:54 PM (GMT-08:00) To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] NIST isolation amplifiers Bruce wrote: Almost. 1:1:2 (turns ratio) transformers used in each stage and 1:1 transformer on input. This allows a lower power supply voltage to be used. I spent a little time (emphasis on little) fiddling with the simulation, and I did not immediately find any solution with 1:1:2 and 1:1 transformers that I liked as well as the design with 1:1:1 and 1:2 transformers. For those who are winding their own transformers (which I recommend, partly for the reason given below), the simplicity of three equal windings may, by itself, outweigh any potential advantage of using a lower power supply voltage. Each constructor should evaluate this for him- or herself. One thing to watch with minicircuits transformers is core saturation due to dc flowing in the windings. Good point, I too have found that some MCL transformers have skimpy cores. I have no idea whether the MCL T622 (1:1:1) or T613 (1:1:2) would work in this circuit. They are both specified for 30mA, and I had the 3904s biased at 20mA -- but I'm not sure what MCL means by 30mA. In this circuit, 20mA flows in the same direction in two of the windings. If the 30mA applies only if one winding has DC flowing (or more generally, if the allowable net DC is equal to 30mA through just one winding), then the core would not be adequate. 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. ___ 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] NIST isolation amplifiers
Dave wrote: The magnetic field in the core due to the current in the windings is proportional to current times number of turns. If there are more than one winding, add the currents. Yes, 2 x 20mA certainly exceeds 30mA. The core will be driven closer or into saturation and the inductance will be decreased. Right, that's how you calculate ampere-turns. But the question is, when MCL says DC: 30mA with no elaboration, does that mean 30mA through one winding, 30mA in the same direction through two windings, or 30mA in the same direction through all three windings? (Whereas, 30mA through one winding and 30mA through another equal winding in the *opposite* direction creates no net magnetic field because the flux cancels. This is the case, for example, if two windings are used as a CT primary for a push-pull amplifier with Vcc applied to the CT. No net field presupposes perfect matching -- in practice, there will be some residual imbalance.) 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] NIST isolation amplifiers
Hi Run in common base ( with things done properly) you can get well over 60 db isolation on a single stage. Bob On Nov 26, 2014, at 2:59 AM, Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: A single 2N or equivalent transistor in a suitable circuit dissipating about 200mW or so can achieve a reverse isolation of 35dB with distortion of around -40dBc (output +13dBm) with a gain of unity, and an output impedance of 50 ohms with a PN floor of around -180dBc/Hz or so. Bruce On Wednesday, 26 November 2014 9:13 PM, Charles Steinmetz csteinm...@yandex.com wrote: Bruce wrote: Another issue is that if even one output needs high reverse isolation and low crosstalk, then even those outputs that arent so critical will also need high reverse isolation and low crosstalk to avoid degrading the crosstalk to the critical output. This brings up the distinction between *isolation* amplifiers and *distribution* amplifiers. Most of us need a dozen or three feeds for various test equipment, radios, etc. These feeds should have 50 ohm output impedance, moderate isolation (35dB or more), and should not noticeably degrade the noise, PN, distortion, or xDEV of the source. That is the job of a distribution amp. I would generally not use anything like one of the NIST circuits for this, but rather some version of a two- or three-transistor Class A buffer amplifier. There are lots of circuits to choose from. Many are transformer (or autoformer) coupled, some are not (the JPL circuits come to mind) and can also be used to distribute lower frequencies. You can get build-out the NIST way (buffer amp input impedance high so you parallel a bunch of them at the input connector), or by using one stage with low output impedance to drive a number of output amplifiers in parallel, or by using an amplifier with very low output impedance (perhaps a high-current monolithic amplifier) to drive a number of 50 ohm build-out resistors, or by fanning out with CMOS logic and following each CMOS final buffer with a Tee network to generate sine waves. Then there are the times when you are making measurements of oscillators and must absolutely ensure that there is no interaction between them. That is the job of an isolation amp. Rarely will you need more than two or three feeds per oscillator, so what you need are several, one-to-three iso amps (one for each oscillator). Here, something like the NIST amplifiers makes sense. Note that I'm advocating distributing sine waves exclusively, NOT square waves or pulse trains. You will find that it is hard enough keeping 1, 5, or 10 MHz from getting into everything in the shop (and radio room), without adding the much-increased difficulty of keeping all of the harmonics under control. Also, you would like the harmonic content to be rather lower than is often thought because (i) even harmonics cause asymmetry, which can cause phase modulation when the signal is AC coupled or feeds a comparator-type zero-cross detector, and (ii) variations in the phase of harmonics in relation to the fundamental cause phase modulation (this is harmonic dispersion, which is caused by temperature changes and other circuit variations such as modulation of semiconductor capacitances by low frequecies). NIST published a paper on this (see Walls and Ascarrunz, The Effect of Harmonic Distortion on Phase Errors in Frequency Distribution and Synthesis). 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. ___ 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] NIST isolation amplifiers
Hi I very much would not implement that circuit these days. A logic buffer based design beats it on pretty much ever (useful) spec in the book. Bob On Nov 26, 2014, at 7:52 AM, Charles Steinmetz csteinm...@yandex.com wrote: Bruce wrote: A single 2N or equivalent transistor in a suitable circuit dissipating about 200mW or so can achieve a reverse isolation of 35dB with distortion of around -40dBc (output +13dBm) with a gain of unity, and an output impedance of 50 ohms with a PN floor of around -180dBc/Hz or so. For those wondering, I suspect Bruce had in mind something like the attached (he posted the basic design a few years ago). I built 8 channels using toroids on FT37-61 cores. I think the Mini-Circuits T622 should work, but I have not tried it. The analyses are from my simulation, and the constructed unit performed similarly. The Miller effect limits fan-out to about 10 for a 10MHz distribution amp. [Note: the 50 ohm resistors on the outputs represent the external loads, and are not part of the amplifier.] Best regards, Charles Distribution_amp_one_stage_CE_2N3904_after_Griffiths.gif___ 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] NIST isolation amplifiers
Hi If you look at some of the wire that they use, the rating may be as much a wire rating as a core rating. They use *small* wire !!! I’ve always assumed that if you go over 30 ma anywhere on any winding you are in trouble. I suspect that DC through the entire winding (ignoring the center tap) is a “legal” thing to do. Bob On Nov 26, 2014, at 6:39 PM, Charles Steinmetz csteinm...@yandex.com wrote: Dave wrote: The magnetic field in the core due to the current in the windings is proportional to current times number of turns. If there are more than one winding, add the currents. Yes, 2 x 20mA certainly exceeds 30mA. The core will be driven closer or into saturation and the inductance will be decreased. Right, that's how you calculate ampere-turns. But the question is, when MCL says DC: 30mA with no elaboration, does that mean 30mA through one winding, 30mA in the same direction through two windings, or 30mA in the same direction through all three windings? (Whereas, 30mA through one winding and 30mA through another equal winding in the *opposite* direction creates no net magnetic field because the flux cancels. This is the case, for example, if two windings are used as a CT primary for a push-pull amplifier with Vcc applied to the CT. No net field presupposes perfect matching -- in practice, there will be some residual imbalance.) 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. ___ 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] NIST isolation amplifiers
Hi Charles, Thanks a bunch for the comments and the article reprints. This is just what I was looking for to get started on my distribution amplifier. Regards...Bill -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Charles Steinmetz Sent: Tuesday, November 25, 2014 11:35 AM To: TimeNuts Subject: [time-nuts] NIST isolation amplifiers A couple of people were asking about NIST isolation amplifiers recently. I'm attaching circuit diagrams of the 5-10 MHz amp from 1997 and the 1-200 MHz amp from 1990. I think Bruce has the papers linked at his ko4bb.com pages. I built some of the 5-10 MHz amps with minor variations and they work very well (I used a separate capacitance multiplier for the base divider string, and changed the first 4.3k resistor to 6.65k to achieve symmetrical clipping and a small increase in headroom). I used 2N3904s for the two lower transistors and a 2N2219A for the top transistor, which dissipates over 300mW. I tried some fancy transistors with very low base spreading resistance, which reduced the noise -- but the increased junction capacitance made the AM to PM conversion worse, so the overall residual PM was worse. On the other hand, GHz transistors had higher noise due to lower gain. So the 3904/2219A combination appears to be just about optimum. (Note that the 200 ohm resistor at the input contributes about half of the circuit's noise, and you can't use the Norton trick because it would ruin the isolation.) The transistor stack draws 32mA and the base divider stack draws ~1.5mA. The amplifiers have an input impedance of 250 ohms, so paralleling the inputs of 5 sections creates an overall 50 ohm input impedance. When a circuit has reverse isolation of well over 150dB, as this one does, you need to pay very careful attention to shielding. 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] NIST isolation amplifiers
Hi For a modern build, the PZT3904’s and PZT’s are a pretty good way to go with this amp. For normal distribution to instruments, there’s really no need to do anything this complex. Bob On Nov 25, 2014, at 2:34 PM, Charles Steinmetz csteinm...@yandex.com wrote: A couple of people were asking about NIST isolation amplifiers recently. I'm attaching circuit diagrams of the 5-10 MHz amp from 1997 and the 1-200 MHz amp from 1990. I think Bruce has the papers linked at his ko4bb.com pages. I built some of the 5-10 MHz amps with minor variations and they work very well (I used a separate capacitance multiplier for the base divider string, and changed the first 4.3k resistor to 6.65k to achieve symmetrical clipping and a small increase in headroom). I used 2N3904s for the two lower transistors and a 2N2219A for the top transistor, which dissipates over 300mW. I tried some fancy transistors with very low base spreading resistance, which reduced the noise -- but the increased junction capacitance made the AM to PM conversion worse, so the overall residual PM was worse. On the other hand, GHz transistors had higher noise due to lower gain. So the 3904/2219A combination appears to be just about optimum. (Note that the 200 ohm resistor at the input contributes about half of the circuit's noise, and you can't use the Norton trick because it would ruin the isolation.) The transistor stack draws 32mA and the base divider stack draws ~1.5mA. The amplifiers have an input impedance of 250 ohms, so paralleling the inputs of 5 sections creates an overall 50 ohm input impedance. When a circuit has reverse isolation of well over 150dB, as this one does, you need to pay very careful attention to shielding. Best regards, Charles NIST_200_iso.pngNIST_5_10_iso_amp.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] NIST isolation amplifiers
On 25 Nov 2014 23:10, Bob Camp kb...@n1k.org wrote: Hi For a modern build, the PZT3904’s and PZT’s are a pretty good way to go with this amp. For normal distribution to instruments, there’s really no need to do anything this complex. Bob I am also thinking about the construction of a distribution amplifier with 15 or so outputs. One thing that came to my mind, is that there may be some point in having one or two outputs where more money is spent. Then if one thinks an item might be particularly sensitive to some aspect of the reference, one can use that. One could for example have one or two outputs which have harmonics suppressed 100 dB, without going to unnecessary expensive on all outputs. Dave ___ 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] NIST isolation amplifiers
Hi Dave, That's exactly the approach I'm going to use. Outputs that go to instruments that might see the low noise and then outputs that go to devices that aren't phase noise sensitive like counters, scopes, pulse generators and others. Regards...Bill -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Dr. David Kirkby (Kirkby Microwave Ltd) Sent: Tuesday, November 25, 2014 3:46 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] NIST isolation amplifiers On 25 Nov 2014 23:10, Bob Camp kb...@n1k.org wrote: Hi For a modern build, the PZT3904’s and PZT’s are a pretty good way to go with this amp. For normal distribution to instruments, there’s really no need to do anything this complex. Bob I am also thinking about the construction of a distribution amplifier with 15 or so outputs. One thing that came to my mind, is that there may be some point in having one or two outputs where more money is spent. Then if one thinks an item might be particularly sensitive to some aspect of the reference, one can use that. One could for example have one or two outputs which have harmonics suppressed 100 dB, without going to unnecessary expensive on all outputs. Dave ___ 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] NIST isolation amplifiers
An alternative is to use a Norton style amp (or other low noise high linearity amp without stellar reverse isolation) to boost the signal level and drive a set of high isolation output stages. A relatively simple discrete current feedback amp may suffice. For higher reverse isolation a cascode arrangement may suffice. Alternatively the input amp could drive a passive splitter each output of which drives a high reverse isolation stage. Even a series shunt feedback stage with a low noise bias circuit can have low PN. Just avoid the design error in the HP3048 option K22 where the bias circuit is more susceptible to power supply noise than it needs to be. Bruce On Tuesday, November 25, 2014 11:45:47 PM Dr. David Kirkby wrote: On 25 Nov 2014 23:10, Bob Camp kb...@n1k.org wrote: Hi For a modern build, the PZT3904’s and PZT’s are a pretty good way to go with this amp. For normal distribution to instruments, there’s really no need to do anything this complex. Bob I am also thinking about the construction of a distribution amplifier with 15 or so outputs. One thing that came to my mind, is that there may be some point in having one or two outputs where more money is spent. Then if one thinks an item might be particularly sensitive to some aspect of the reference, one can use that. One could for example have one or two outputs which have harmonics suppressed 100 dB, without going to unnecessary expensive on all outputs. Dave ___ 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] NIST isolation amplifiers
Am 25.11.2014 um 20:34 schrieb Charles Steinmetz: A couple of people were asking about NIST isolation amplifiers recently. I'm attaching circuit diagrams of the 5-10 MHz amp from 1997 and the 1-200 MHz amp from 1990. I think Bruce has the papers linked at his ko4bb.com pages. I have built _this_ version of the NIST preamp 6 or seven years ago. It is quite ok and feeds the signal generators, counters, SAs and VNA in my lab without issues. There is 1 successor that corrects the awful S11 and has no output transformer but it still awaits characterisation. Maybe over the holiday season to come. Noise on the base voltage string is attenuated by transistor beta in the cascode, so there is not too much to gain here. The next 2 versions use even more current to support 13 dBm without transformer, they run pretty hot ( 2 BFG31 chains/channel). http://www.hoffmann-hochfrequenz.de/downloads/downloads.html regards, 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] NIST isolation amplifiers
Hi Harmonics are (in general) the least of your issues on a distribution amp. There is very little difference in ADEV or instrument performance at -20 dbc versus -120 dbc. Since filtering is relatively easy, adding another inductor or two is about all it takes. ——— If you are going with the NIST approach rather than gates, remember that there are a few issues: 1) These circuits tend to “sing like a bird” at UHF if built from leaded parts. Often it’s tough to spot due to the output filter. 2) Past a handful of outputs, the input impedance of the circuit will become an issue. You will need a more complex approach. 3) The isolation you achieve is far more dependent on the layout than on the circuit. You need a *very* good layout to achieve the numbers commonly tossed around for the circuit. That’s much easier to do with SMT parts. 4) Any (hopefully) low noise circuit needs a quiet supply. This one is no different. That’s not just the regulator, the rest of the feed (ground loops etc) matters as well. 5) There is a tradeoff between filter bandwidth and temperature induced ADEV issues. Going crazy on filtering will likely degrade your ADEV. 6) The amp(s) as shown are not matched either at the input or the output. That may or may not be an issue to you. If it is, you will need to do some mods to the circuit. I’d suggest at least a 3 to 6 db pad on the input and output. Bob On Nov 25, 2014, at 6:45 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 25 Nov 2014 23:10, Bob Camp kb...@n1k.org wrote: Hi For a modern build, the PZT3904’s and PZT’s are a pretty good way to go with this amp. For normal distribution to instruments, there’s really no need to do anything this complex. Bob I am also thinking about the construction of a distribution amplifier with 15 or so outputs. One thing that came to my mind, is that there may be some point in having one or two outputs where more money is spent. Then if one thinks an item might be particularly sensitive to some aspect of the reference, one can use that. One could for example have one or two outputs which have harmonics suppressed 100 dB, without going to unnecessary expensive on all outputs. Dave ___ 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] NIST isolation amplifiers
Hi I’ve built that one as well. It’s a bit easier with +/- supplies. It has the same “you need a good layout” issues as any of the other versions. It’s got a bit higher input impedance than the others so it’s better choice for 4 outputs. Bob On Nov 25, 2014, at 6:53 PM, Gerhard Hoffmann dk...@arcor.de wrote: Am 25.11.2014 um 20:34 schrieb Charles Steinmetz: A couple of people were asking about NIST isolation amplifiers recently. I'm attaching circuit diagrams of the 5-10 MHz amp from 1997 and the 1-200 MHz amp from 1990. I think Bruce has the papers linked at his ko4bb.com pages. I have built _this_ version of the NIST preamp 6 or seven years ago. It is quite ok and feeds the signal generators, counters, SAs and VNA in my lab without issues. There is 1 successor that corrects the awful S11 and has no output transformer but it still awaits characterisation. Maybe over the holiday season to come. Noise on the base voltage string is attenuated by transistor beta in the cascode, so there is not too much to gain here. The next 2 versions use even more current to support 13 dBm without transformer, they run pretty hot ( 2 BFG31 chains/channel). http://www.hoffmann-hochfrequenz.de/downloads/downloads.html regards, 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. ___ 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] NIST isolation amplifiers
Another issue is that if even one output needs high reverse isolation and low crosstalk, then even those outputs that arent so critical will also need high reverse isolation and low crosstalk to avoid degrading the crosstalk to the critical output. Bruce On Tuesday, November 25, 2014 07:54:02 PM Bob Camp wrote: Hi Harmonics are (in general) the least of your issues on a distribution amp. There is very little difference in ADEV or instrument performance at -20 dbc versus -120 dbc. Since filtering is relatively easy, adding another inductor or two is about all it takes. ——— If you are going with the NIST approach rather than gates, remember that there are a few issues: 1) These circuits tend to “sing like a bird” at UHF if built from leaded parts. Often it’s tough to spot due to the output filter. The small resistors in series with each CB stage emitter are useful in suppressing such parasitics as is a low inductance ground connection for each base. 2) Past a handful of outputs, the input impedance of the circuit will become an issue. You will need a more complex approach. A low noise input amp driving a splitter can be useful in resolving that issue. 3) The isolation you achieve is far more dependent on the layout than on the circuit. You need a *very* good layout to achieve the numbers commonly tossed around for the circuit. That’s much easier to do with SMT parts. Shielding each individual amp from the others (SMT or not) may be necessary. 4) Any (hopefully) low noise circuit needs a quiet supply. This one is no different. That’s not just the regulator, the rest of the feed (ground loops etc) matters as well. 5) There is a tradeoff between filter bandwidth and temperature induced ADEV issues. Going crazy on filtering will likely degrade your ADEV. 6) The amp(s) as shown are not matched either at the input or the output. That may or may not be an issue to you. If it is, you will need to do some mods to the circuit. I’d suggest at least a 3 to 6 db pad on the input and output. ' Input pads will increase the PN floor. With slight modifications up to 6 such isolation amp inputs can be driven by a single 50 ohm source. Bob On Nov 25, 2014, at 6:45 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 25 Nov 2014 23:10, Bob Camp kb...@n1k.org wrote: Hi For a modern build, the PZT3904’s and PZT’s are a pretty good way to go with this amp. For normal distribution to instruments, there’s really no need to do anything this complex. Bob I am also thinking about the construction of a distribution amplifier with 15 or so outputs. One thing that came to my mind, is that there may be some point in having one or two outputs where more money is spent. Then if one thinks an item might be particularly sensitive to some aspect of the reference, one can use that. One could for example have one or two outputs which have harmonics suppressed 100 dB, without going to unnecessary expensive on all outputs. Dave ___ 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] NIST isolation amplifiers
Hi The reverse isolation of a “typical” pc layout for this sort of thing is maybe 60 db. Getting to 120 is far from simple. Achieving the 160 (or whatever) numbers you see in some papers is “isolation nuts” territory. The circuit its self can do great numbers. Coming up with a box that has 17 100’ long coax cables into it that isolates well …. good luck if you haven’t done is before. Good luck even if you have and you can’t afford to tool a fancy enclosure. So back to the “what do you need” rant. If: 1) You are running signals into the reference inputs on the back of test gear. 2) You are using BNC connectors and using something like RG-58 or RG-59 3) Your gear is all on one bench or a bench plus a rack 4) The longest run of cable is 20’ 5) Nothing much ever gets unplugged from the distribution line (or if it does you don’t care about a 100 ps burp). Then reverse isolation is not all that big a deal. I’ve seen people run this kind of setup with passive power splitters. If they had 30 db of isolation I’d be amazed. The power splitter might not even be the weak link isolation wise. I’ve seen some really rotten cables and connectors being used. Now, if you have “many hundreds of feet” type runs, you stop talking to Mars when a 100 ps bump hits, or you routinely measure phase noise on 20 day runs with this setup - yes that’s different. Hopefully you have a lot of money in your wallet. Bob On Nov 25, 2014, at 8:57 PM, Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: Another issue is that if even one output needs high reverse isolation and low crosstalk, then even those outputs that arent so critical will also need high reverse isolation and low crosstalk to avoid degrading the crosstalk to the critical output. Bruce On Tuesday, November 25, 2014 07:54:02 PM Bob Camp wrote: Hi Harmonics are (in general) the least of your issues on a distribution amp. There is very little difference in ADEV or instrument performance at -20 dbc versus -120 dbc. Since filtering is relatively easy, adding another inductor or two is about all it takes. ——— If you are going with the NIST approach rather than gates, remember that there are a few issues: 1) These circuits tend to “sing like a bird” at UHF if built from leaded parts. Often it’s tough to spot due to the output filter. The small resistors in series with each CB stage emitter are useful in suppressing such parasitics as is a low inductance ground connection for each base. 2) Past a handful of outputs, the input impedance of the circuit will become an issue. You will need a more complex approach. A low noise input amp driving a splitter can be useful in resolving that issue. 3) The isolation you achieve is far more dependent on the layout than on the circuit. You need a *very* good layout to achieve the numbers commonly tossed around for the circuit. That’s much easier to do with SMT parts. Shielding each individual amp from the others (SMT or not) may be necessary. 4) Any (hopefully) low noise circuit needs a quiet supply. This one is no different. That’s not just the regulator, the rest of the feed (ground loops etc) matters as well. 5) There is a tradeoff between filter bandwidth and temperature induced ADEV issues. Going crazy on filtering will likely degrade your ADEV. 6) The amp(s) as shown are not matched either at the input or the output. That may or may not be an issue to you. If it is, you will need to do some mods to the circuit. I’d suggest at least a 3 to 6 db pad on the input and output. ' Input pads will increase the PN floor. With slight modifications up to 6 such isolation amp inputs can be driven by a single 50 ohm source. Bob On Nov 25, 2014, at 6:45 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 25 Nov 2014 23:10, Bob Camp kb...@n1k.org wrote: Hi For a modern build, the PZT3904’s and PZT’s are a pretty good way to go with this amp. For normal distribution to instruments, there’s really no need to do anything this complex. Bob I am also thinking about the construction of a distribution amplifier with 15 or so outputs. One thing that came to my mind, is that there may be some point in having one or two outputs where more money is spent. Then if one thinks an item might be particularly sensitive to some aspect of the reference, one can use that. One could for example have one or two outputs which have harmonics suppressed 100 dB, without going to unnecessary expensive on all outputs. Dave ___ 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
