[time-nuts] Re: dual supplies Re: Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi I seem to recall TI having similar parts. The big gotcha is tossing large chunks of C onto the ground to rail connections. A typical op amp is not at all happy with this. Bob > On Jul 10, 2022, at 5:48 PM, Richard (Rick) Karlquist via time-nuts > wrote: > > > > On 7/10/2022 10:14 AM, Lux, Jim via time-nuts wrote: >> Yeah, but that virtual ground brings with it it's own set of problems. For >> instance, it has to both sink and source current, so you can't just use a 3 >> terminal regulator to create the midpoint, although I've seen schemes with a >> resistor from virtual ground to negative supply, but that's not very power >> efficient - the resistor needs to see, say, 10x the maximum sink current. > > You might look at the LT1118-2.85 "Supply Splitter". It is able to do > either sink or source, as needed, unlike an ordinary regulator. > > Rick N6RK > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: dual supplies Re: Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On 7/10/2022 10:14 AM, Lux, Jim via time-nuts wrote: Yeah, but that virtual ground brings with it it's own set of problems. For instance, it has to both sink and source current, so you can't just use a 3 terminal regulator to create the midpoint, although I've seen schemes with a resistor from virtual ground to negative supply, but that's not very power efficient - the resistor needs to see, say, 10x the maximum sink current. You might look at the LT1118-2.85 "Supply Splitter". It is able to do either sink or source, as needed, unlike an ordinary regulator. Rick N6RK ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: What about the frequency discrimination method? (offshoot from DIY PN analyzer)
Hi Ed, On 7/10/22 20:26, ed breya via time-nuts wrote: Hi Magnus, I know what you mean about not needing a quadrature splitter - if you have a very wide phase or delay tuning range - but I'm picturing getting most of the way to quadrature with a fixed structure for a given frequency, and only fine-tuning the phase over a narrow range, in order to minimize the PLL's overall noise contribution. This should also keep it monotonic - too wide a range may let it get stuck on the humps. Well, the traditional method is to lock it up. When you do that Quadrature (PM) comes for free, but In-phase (AM) does not. The lock require either oscillator to be frequency steerable to achieve lock. If that is not what you want to do, well then you can use a non-synchronous method and then a quadrature splitter is the way to go. This is essentially what the modern oversampling measurement devices do anyway. They just sample the waveforms, convert the IQ into amplitude and phase, and then decimate down from that. Comparison with reference is then done in that context after the fact. Frequency errors can be handled within some fairly flexible range. Similarly, just mixing unlocked sources with I/Q setup produces some beat-note and if you get that as I/Q you can do more or less the same thing. For amplitude calibration, I'm picturing rearranging the splitter ports or guts somehow (as simply as possible) to present the DUT signal to the mixer at 0 or 180 degrees, which should give a maximum DC out. For amplitude measurement, you want the in-phase component rather than the quadrature component, if they are locked that is. Using a normal lock, the direct lock phase-detector actually gives you the quadrature, so you need the splitter to get the In-phase too. For non-synchronous receivers, you need to track the beat-note to sort out what is the in-phase and quadrature for AM and PM respectively. An abs/arctan function (such as CORDIC) will convert I/Q samples nicely and the frequency error will be just a phase-ramp on the detected phase. BTW I had never heard of the Tayloe detector, but it appears to be the method (4x f multiplier then digital quadrature divide) used in lock-in analyzers, and I have used the same in a number of projects. Yes. It is fairly widely used these days. Seems to have good enough properties for many things. Azelio wrote: "How can you measure something, any type of measure, not only PN, without a reference? Voltmeters need voltage references, "timemeters" (and frequency meters) need time references." Azelio, this is a well known technique - I haven't described anything new, just a particular implementation I've been pondering. Indeed. There is many ways to measure without an actual reference. There might be other oscillators, but they are not "reference" in the way of a voltage reference for instance. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: What about the frequency discrimination method? (offshoot from DIY PN analyzer)
Hi If you dig into the various books on phase noise, they do go into other ways to measure it. The bottom line is that things like frequency discriminators are quite noisy (floor wise) compared to a single mixer. Bob > On Jul 10, 2022, at 10:26 AM, ed breya via time-nuts > wrote: > > Hi Magnus, > > I know what you mean about not needing a quadrature splitter - if you have a > very wide phase or delay tuning range - but I'm picturing getting most of the > way to quadrature with a fixed structure for a given frequency, and only > fine-tuning the phase over a narrow range, in order to minimize the PLL's > overall noise contribution. This should also keep it monotonic - too wide a > range may let it get stuck on the humps. > > For amplitude calibration, I'm picturing rearranging the splitter ports or > guts somehow (as simply as possible) to present the DUT signal to the mixer > at 0 or 180 degrees, which should give a maximum DC out. > > BTW I had never heard of the Tayloe detector, but it appears to be the method > (4x f multiplier then digital quadrature divide) used in lock-in analyzers, > and I have used the same in a number of projects. > > > Azelio wrote: > "How can you measure something, any type of measure, not only PN, > without a reference? Voltmeters need voltage references, "timemeters" > (and frequency meters) need time references." > > Azelio, this is a well known technique - I haven't described anything new, > just a particular implementation I've been pondering. > > Ed > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: dual supplies Re: Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
I've ALWAYS used an op-amp to nail down the half rail supply, I never use the two resistors and cap idea directly unless the whole thing is quite basic Just don't put bulk capacitance on the output ! like I have seen in some bad designs. ROFL. Some op-amps are better at this than others- IE dead zones in the source-sink changeover curve. On 11/07/2022 3:14 am, Lux, Jim via time-nuts wrote: On 7/10/22 9:07 AM, Bob kb8tq via time-nuts wrote: Hi Yes it is a pain to implement dual supplies. I ponder that issue every time I build one of these setups. I’ve ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Erik, On 7/10/22 17:52, Erik Kaashoek via time-nuts wrote: I've updated the schematic to include the latest additions and added some new measurements Schematic: http://athome.kaashoek.com/time-nuts/PNA/Simple_PNA.pdf The resistor values (many 18k) are a bit weird but I happen to have a big box of 18k resistors. The value of the low pas filter after the mixer (C2,C3,L1) are probably wrong. Calculate yourself for the corner frequency you want. I get 22,5 kHz which isn't completely off the charts. Sure helps to eat the 20 MHz and higher, as well as stray 10 MHz. For the 20 MHz it will in ideal have -180 dB damping, but in practice it will leak over but probably not too bad. The elco's in the PI_controller and the input of the Audio_LNA are probably going to explode due to reverse polarity. You want the resistor and capacitor to be in series and not in parallel in that negative feedback. As you put a resistor in parallel you will drain the state of the capacitor and loose performance. You can choose to either locate a 1 uF non-polar cap, or shift the values a bit to get into plastic caps such as polypropylene. 100 nF and 220 nF should be easy enough to get hold off. You could even put a pair of 470 nF in parallel. A generic note: Most if not all op-amps tends to operate better in terms of offset behavior as they see about the same resistance DC on both + and - inputs. The output of the REF_Buffer acts as the virtual ground so care was taken (almost) not to draw any current, except for the input of the Audio_LNA. The supply of the opamps is not drawn but its from Ground and Vcc (+12V) I've tested symmetric supply but the combination of the REF output voltage from the DOCXO and the REF_Buffer provided the least noise. The audio_LNA has a gain of 1 for DC and increasing to 100 for for 1Hz and above The R/C values around the PI_Controller have not been optimized but they work. As the Summer OPAMP inverts to 5-10V the Inverter OPAMP brings it back to 0-5V for the Vtune of the DOCXO You could do away with the Summer and Inverter op-amps if you fed the TUNING into the + input of the inverter. By skewing the PI-controller balance the output will be suitably offset. The benefit will be that you avoid noise contribution from two op-amps and their resistors. The LED's provide visual feedback on the tuning. IF both are just on the PLL is in lock. It may be better to have two LED's in series at each side to increase the dimming. I would advice moving those LEDs off-board. Let that run on separate "dirty" power. I love the direct observation aspect, but I fear it just add noise to the measurement. Keep up the good work! Cheers, Magnus Some measurements.: All indicated levels are 40dBc/Hz higher compared to actual. The noise floor: http://athome.kaashoek.com/time-nuts/PNA/PN_baseline_3.JPG This is measured without DUT input. Rigol signal generator generating 10MHz Phase modulated with 60 degrees noise at -80dBc/Hz: http://athome.kaashoek.com/time-nuts/PNA/ Rigol signal generator generating 10MHz phase modulated with 0.006 degrees at 220Hz : http://athome.kaashoek.com/time-nuts/PNA/PN_Rigol_3_0.006.JPG The 220Hz is under the cursor at -27dBc, at 0.006 degrees modulation it should be at -88dBc, so there must still be a big mistake somewhere. AR60 Rubidium reference: http://athome.kaashoek.com/time-nuts/PNA/PN_Rb_3.JPG All seems OK, a bit of 50Hz and harmonics. OCXO : http://athome.kaashoek.com/time-nuts/PNA/PN_OCXO_3.JPG very weird spurs between 40 and 50 Hz The famous cheap Chines TCXO: http://athome.kaashoek.com/time-nuts/PNA/PN_TCXO_3.JPG Not too bad for offsets of 100Hz and higher but at 10Hz and lower its 20dB worse. A home designed/build arduino GPSDO: http://athome.kaashoek.com/time-nuts/PNA/PN_GPSDO_3.JPG The GPSDO has a good ADEV but is clearly very noisy! I also measured a Marconi 2022 signal generator and it was possible to lock but the phase noise was terrible with strong factional PLL spurs. I also tried to measure the phase noise of an old Philips analog 10Hz to 12MHz signal generator but it was impossible to get a lock because the generator output is jumping around several Hz at 10MHz output. The noise floor of the simple PNA leaves a lot to improve (from -140dBc/Hz at 10kHz to -180dBc/Hz with better OCXO, LNA and correlation) but it proved to be able to do a first assessment of some not too good oscillator performance. Feedback welcome as these are my first baby steps on phase noise nuttery. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] What about the frequency discrimination method? (offshoot from DIY PN analyzer)
Hi Magnus, I know what you mean about not needing a quadrature splitter - if you have a very wide phase or delay tuning range - but I'm picturing getting most of the way to quadrature with a fixed structure for a given frequency, and only fine-tuning the phase over a narrow range, in order to minimize the PLL's overall noise contribution. This should also keep it monotonic - too wide a range may let it get stuck on the humps. For amplitude calibration, I'm picturing rearranging the splitter ports or guts somehow (as simply as possible) to present the DUT signal to the mixer at 0 or 180 degrees, which should give a maximum DC out. BTW I had never heard of the Tayloe detector, but it appears to be the method (4x f multiplier then digital quadrature divide) used in lock-in analyzers, and I have used the same in a number of projects. Azelio wrote: "How can you measure something, any type of measure, not only PN, without a reference? Voltmeters need voltage references, "timemeters" (and frequency meters) need time references." Azelio, this is a well known technique - I haven't described anything new, just a particular implementation I've been pondering. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi There’s really no need to use the Vref out of the OCXO at all. Since many devices don’t have one, you will need a “replacement” at some point. Simply pulling the “set reference” off of a cleaned up output of your main supply(s) is typically how it is done. The most basic reason to not hard wire a specific device into the circuit is to allow a A to B / B to C / C to A swap process to be done. That is about the only way to get close to working out the numbers on this or that reference. Without that data, you are flying blind as you get close to the limits of the reference. Given the characteristics of the mixer and the other stuff involved, with a roughly +7 dbm input, anything past -174 dbc / Hz is suspect. -180 dbc / Hz is significantly better than what you likely can do with this approach. Indeed, it also is quite a bit better than what you will find your signal sources doing so that’s not a major constraint. Yes there is a wonderful “bet a beer” / after work conversation to be had about the ultimate phase noise of a +7 dbm signal. More or less, the bet is won by postulating a 1 ohm source impedance. For real world sources …. not so much …. Bob > On Jul 10, 2022, at 7:52 AM, Erik Kaashoek via time-nuts > wrote: > > I've updated the schematic to include the latest additions and added some new > measurements > > Schematic: http://athome.kaashoek.com/time-nuts/PNA/Simple_PNA.pdf > > The resistor values (many 18k) are a bit weird but I happen to have a big box > of 18k resistors. > The value of the low pas filter after the mixer (C2,C3,L1) are probably > wrong. Calculate yourself for the corner frequency you want. > The elco's in the PI_controller and the input of the Audio_LNA are probably > going to explode due to reverse polarity. > The output of the REF_Buffer acts as the virtual ground so care was taken > (almost) not to draw any current, except for the input of the Audio_LNA. > The supply of the opamps is not drawn but its from Ground and Vcc (+12V) > I've tested symmetric supply but the combination of the REF output voltage > from the DOCXO and the REF_Buffer provided the least noise. > The audio_LNA has a gain of 1 for DC and increasing to 100 for for 1Hz and > above > The R/C values around the PI_Controller have not been optimized but they work. > As the Summer OPAMP inverts to 5-10V the Inverter OPAMP brings it back to > 0-5V for the Vtune of the DOCXO > The LED's provide visual feedback on the tuning. IF both are just on the PLL > is in lock. It may be better to have two LED's in series at each side to > increase the dimming. > > Some measurements.: > All indicated levels are 40dBc/Hz higher compared to actual. > The noise floor: http://athome.kaashoek.com/time-nuts/PNA/PN_baseline_3.JPG > This is measured without DUT input. > > Rigol signal generator generating 10MHz Phase modulated with 60 degrees noise > at -80dBc/Hz: http://athome.kaashoek.com/time-nuts/PNA/ > > Rigol signal generator generating 10MHz phase modulated with 0.006 degrees at > 220Hz : http://athome.kaashoek.com/time-nuts/PNA/PN_Rigol_3_0.006.JPG > The 220Hz is under the cursor at -27dBc, at 0.006 degrees modulation it > should be at -88dBc, so there must still be a big mistake somewhere. > > AR60 Rubidium reference: http://athome.kaashoek.com/time-nuts/PNA/PN_Rb_3.JPG > All seems OK, a bit of 50Hz and harmonics. > > OCXO : http://athome.kaashoek.com/time-nuts/PNA/PN_OCXO_3.JPG > very weird spurs between 40 and 50 Hz > > The famous cheap Chines TCXO: > http://athome.kaashoek.com/time-nuts/PNA/PN_TCXO_3.JPG > Not too bad for offsets of 100Hz and higher but at 10Hz and lower its 20dB > worse. > > A home designed/build arduino GPSDO: > http://athome.kaashoek.com/time-nuts/PNA/PN_GPSDO_3.JPG > The GPSDO has a good ADEV but is clearly very noisy! > > I also measured a Marconi 2022 signal generator and it was possible to lock > but the phase noise was terrible with strong factional PLL spurs. > I also tried to measure the phase noise of an old Philips analog 10Hz to > 12MHz signal generator but it was impossible to get a lock because the > generator output is jumping around several Hz at 10MHz output. > > The noise floor of the simple PNA leaves a lot to improve (from -140dBc/Hz at > 10kHz to -180dBc/Hz with better OCXO, LNA and correlation) but it proved to > be able to do a first assessment of some not too good oscillator performance. > > Feedback welcome as these are my first baby steps on phase noise nuttery. > Erik. > > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] dual supplies Re: Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On 7/10/22 9:07 AM, Bob kb8tq via time-nuts wrote: Hi Yes it is a pain to implement dual supplies. I ponder that issue every time I build one of these setups. I’ve built a lot of them …. If you are going to do a single supply, setting up a “virtual ground” is probably the best way to go. Do it with a drive circuit to provide very clean 15V off of a 30V supply then tack everything ( including *all* the mixer grounds to that 15V supply. Yeah, but that virtual ground brings with it it's own set of problems. For instance, it has to both sink and source current, so you can't just use a 3 terminal regulator to create the midpoint, although I've seen schemes with a resistor from virtual ground to negative supply, but that's not very power efficient - the resistor needs to see, say, 10x the maximum sink current. Now that I think about it, some sort of op amp driven appropriately (or a complementary PNP/NPN pair?) might work - but then you're concerned about the output Z of the op amp, and how it varies over frequency. And, of course, the bias current. We face this in designing low noise instruments for space. You're running off a DC bus of some sort, and DC/DC inverters tend to be noisier than straight out buck converters or linear regulators. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Pretty much the best mixer to use for this in a basement / DIY basis is a Mini Circuits RPD-1 or one of it’s siblings. It has a 500 ohm output on the mix port instead of 50 ohms. Yes, you open circuit terminate it ( so 5K ) but as noted, it’s the Zout of the mixer that likely sets what the op amp sees. With it’s higher output impedance, you are even less driven to nutty low noise op amps and 4 ohm feedback resistors. The good old OP-27 / OP-37 sitting in the dusty back of your parts drawer from back in 1993 will do just fine. Yes, this all gets back to being nutty as you get close to carrier. If you are after -150 dbc / Hz at 1 Hz offset, you will need go a bit crazy. If you head this way, there are a lot of posts back in the archives leading you down various paths to get it done. While others have indeed fried expensive setups while loosing a supply leg, I’ve never run into that problem. It most certainly can happen. I’ve never taken any special precautions and have yet to “get bit” by the issue. As a rough guess, I’d say I’ve powered up various implementations these setups a couple thousand times over the years. Bob > On Jul 10, 2022, at 6:32 AM, Gerhard Hoffmann via time-nuts > wrote: > > Am 2022-07-09 22:06, schrieb Erik Kaashoek via time-nuts: > >> Ultra low noise opamps have been ordered to hopefully reduce the internal >> noise of the PNA but the reference OCXO may already be the limiting factor. >> The REF voltage output of the OCXO turned out to be rather clean. Much >> cleaner than a 7805 voltage regulator > > The existence of my own ultra-low noise amplifiers was originally triggered > by this problem but has turned into a sport of it's own. Don't yield to the > temptation of driving this too far. A single AD797, LT1028, or ADA4898-2 > all deliver an input noise density of abt. 1nV/rtHz which is the thermal > noise of a 60 Ohm resistor. ADA4898 has goof price/performnce. > > The diodes in the mixer can easily feature RS = 20 Ohms, and the 2 conducting > diodes then show 40 Ohms, which is not much less than the 60 Ohm equiv of the > opamps. > RS is ohmic resistance of silicon and contacts, not the differential > slope resistance of the diode which is only half-thermal IIRC. > > High level mixers often have additional resistors in series to the diodes. > It's no wonder then that high level mixers are usually not the winners in > dynamic range. Maybe an array of low-level mixers that are Wilkinsoned > together on RF and LO, with the IF ports in series would give good results. > > 1. Stephan R. Kurtz, Watkins-Johnson: Mixers as Phase Detectors > 2. Bert C. Henderson, W-J: Mixers: Part 2 Theory and Technology > Copyright © 1981 Watkins-Johnson Company > Vol. 8 No. 3 May/June 1981 > Revised and reprinted © 2001 WJ Communications, Inc. > > cheers, Gerhard > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Yes it is a pain to implement dual supplies. I ponder that issue every time I build one of these setups. I’ve built a lot of them …. If you are going to do a single supply, setting up a “virtual ground” is probably the best way to go. Do it with a drive circuit to provide very clean 15V off of a 30V supply then tack everything ( including *all* the mixer grounds to that 15V supply. Keeping the signal undistorted before you check the beat note and use it to drive the EFC does keep you out of various issues. You do not want to deal with possible clipping / saturation artifacts getting into either process. With devices having positive side EFC, negative side EFC, and “both sides” EFC, it’s hard to get around a dual supply in any sort of general purpose device. A 15V center point is not going to fit any EFC that I’ve seen :). Struggling with the ground loop problem is always the big deal in any setup. Trying to rule out / take out line noise is usually the final straw in any series of tests. Doing that with everything at “real ground” is just a bit easier. Part of the calibration is measuring the beat note as it goes past zero. The ’scope gets cranked up and you look at a bit of the crossing right at ground. Keeping the device happy while doing this is much easier if the chassis does not need to float at 15V. Whatever is used as a supply turns out to be a dedicated device. The same ground loop / isolation stuff get in here. An old style non-switching design is just about mandatory. Keeping switching artifacts out of things is almost impossible. All of this makes a “build from scratch” approach less and less crazy. Old style three terminal regulators ( so 78x18 / 79x18 ) are not as easy to find these days. They do fine if you happen to have a pair …. There’s really not much power used by any of this. The need for anything massive. 100 ma out of each side is overkill …. As you build things up, you eventually come to the realization that a big sheet of brass is a good idea for the ground. Tie this and that to the sheet. Keep everything non-essential away and likely keep it turned off. Tying a dedicated supply to that sheet along with the amp and EFC stuff is not at all unusual. Bob > On Jul 9, 2022, at 11:11 PM, Erik Kaashoek wrote: > > Hi Magnus, > Yes, and it works very well, locking is easier as once locked it nicely > stay's in lock, , even with a slow drift of either the DUT or the reference. > As I could not find a bipolar capacitor the tuning potmeter has to be kept at > the low side to avoid blowing the integration capacitor. Maybe a back to back > series capacitor with pull down resistor is safer to use. > Will need to update the schematic to show the small improvements. > > @Bob, > You mentioned "dual supplies with high voltage" for the first gain opamp. How > much impact would dual voltage bring as its a pain to implement. > I understand everything gets ground reference and you loose the noise of the > buffer opamp but as the first gain opamp is in differential mode for its > input it does not see the noise of the buffer opamp. Or am I making a mistake? > > On 10-7-2022 2:02, Magnus Danielson via time-nuts wrote: >> Have you attempted doing a PI-loop as I've suggested? > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
I've updated the schematic to include the latest additions and added some new measurements Schematic: http://athome.kaashoek.com/time-nuts/PNA/Simple_PNA.pdf The resistor values (many 18k) are a bit weird but I happen to have a big box of 18k resistors. The value of the low pas filter after the mixer (C2,C3,L1) are probably wrong. Calculate yourself for the corner frequency you want. The elco's in the PI_controller and the input of the Audio_LNA are probably going to explode due to reverse polarity. The output of the REF_Buffer acts as the virtual ground so care was taken (almost) not to draw any current, except for the input of the Audio_LNA. The supply of the opamps is not drawn but its from Ground and Vcc (+12V) I've tested symmetric supply but the combination of the REF output voltage from the DOCXO and the REF_Buffer provided the least noise. The audio_LNA has a gain of 1 for DC and increasing to 100 for for 1Hz and above The R/C values around the PI_Controller have not been optimized but they work. As the Summer OPAMP inverts to 5-10V the Inverter OPAMP brings it back to 0-5V for the Vtune of the DOCXO The LED's provide visual feedback on the tuning. IF both are just on the PLL is in lock. It may be better to have two LED's in series at each side to increase the dimming. Some measurements.: All indicated levels are 40dBc/Hz higher compared to actual. The noise floor: http://athome.kaashoek.com/time-nuts/PNA/PN_baseline_3.JPG This is measured without DUT input. Rigol signal generator generating 10MHz Phase modulated with 60 degrees noise at -80dBc/Hz: http://athome.kaashoek.com/time-nuts/PNA/ Rigol signal generator generating 10MHz phase modulated with 0.006 degrees at 220Hz : http://athome.kaashoek.com/time-nuts/PNA/PN_Rigol_3_0.006.JPG The 220Hz is under the cursor at -27dBc, at 0.006 degrees modulation it should be at -88dBc, so there must still be a big mistake somewhere. AR60 Rubidium reference: http://athome.kaashoek.com/time-nuts/PNA/PN_Rb_3.JPG All seems OK, a bit of 50Hz and harmonics. OCXO : http://athome.kaashoek.com/time-nuts/PNA/PN_OCXO_3.JPG very weird spurs between 40 and 50 Hz The famous cheap Chines TCXO: http://athome.kaashoek.com/time-nuts/PNA/PN_TCXO_3.JPG Not too bad for offsets of 100Hz and higher but at 10Hz and lower its 20dB worse. A home designed/build arduino GPSDO: http://athome.kaashoek.com/time-nuts/PNA/PN_GPSDO_3.JPG The GPSDO has a good ADEV but is clearly very noisy! I also measured a Marconi 2022 signal generator and it was possible to lock but the phase noise was terrible with strong factional PLL spurs. I also tried to measure the phase noise of an old Philips analog 10Hz to 12MHz signal generator but it was impossible to get a lock because the generator output is jumping around several Hz at 10MHz output. The noise floor of the simple PNA leaves a lot to improve (from -140dBc/Hz at 10kHz to -180dBc/Hz with better OCXO, LNA and correlation) but it proved to be able to do a first assessment of some not too good oscillator performance. Feedback welcome as these are my first baby steps on phase noise nuttery. Erik. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Am 2022-07-10 9:11, schrieb Erik Kaashoek via time-nuts: @Bob, You mentioned "dual supplies with high voltage" for the first gain opamp. How much impact would dual voltage bring as its a pain to implement. I think is was Rubiola who wrote that he exploded a costly microwave mixer with a LT1028 that had lost one of its power rails. If you go AC coupling, don't forget that the input capacitor must not be selected for f-3dB but that it must be much bigger to short the thermal noise of the bias network to pV levels through the low impedance source. Otherwise you see a noise rise towards 0 Hz that is MUCH steeper than 1/f. Scott Wurzer (designer of ad797) saw that immediately on my 20 * ada4898 220pV/rtHz amplifier. Wish he was more explicit. It took me some time to get it. :-) I had 10K/100u foil, ended up with 10k/4700uF wet tantalum, which opens another can of worms. I have converted to FETs now. A few pVrtHz more, but much less noise current. In cross correlation setups, the noise current of both amplifiers produces a common voltage drop in the (common) source resistance, and that does not average away. (May apply only to voltage measurements from a single source.) Gerhard ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: What about the frequency discrimination method? (offshoot from DIY PN analyzer)
How can you measure something, any type of measure, not only PN, without a reference? Voltmeters need voltage references, "timemeters" (and frequency meters) need time references. On Sun, Jul 10, 2022 at 1:47 AM ed breya via time-nuts wrote: > > I've been following the thread about Erik's DIY PN analyzer, and > wondering if it might be easy enough to use a frequency discrimination > method. I'm opening this in a different thread to avoid muddying the > water on the original (and long) one. > > What I'm picturing is putting the DUT's output into a quadrature power > splitter that optionally has a voltage-tuned slight phase shift feature. > The I and Q outputs would go into the DBM and produce the nearly-zero DC > plus baseband signal for analysis as in the original story. > > If the quadrature is precise and stable enough, the DC out should be > close to zero, and since the baseband is ultimately AC coupled to the > analyzer, small offset should be OK, within reason. > > If this is not sufficient, then having a phase tuning feature could be > used to form a PLL to hold the DC at zero. The big difference here is > that instead of locking a separate reference source to the DUT, the > relative phase at the mixer just has to be fine tuned to maintain the > output DC. The same sorts of PLL requirements are encountered to get the > results, but no external reference (and its noise and lock range etc > issues) is needed. > > The downside is that a different quadrature splitter would probably be > needed for each DUT frequency to be applied - I'm picturing ones for 5 > and 10 MHz initially. Those 90 degree broadband splitters that Mike > mentioned seem very interesting too. > > There is still the necessity of calibration, either way. > > Ed > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: To much test equipment...
Dear Time-Nuts, many thanks for the amazing amount of interest! My son will draw lots today and I´ll notify the "winners". Have a nice Sunday, Matthias Am 09.07.2022 um 14:59 schrieb Matthias Jelen via time-nuts: Dear Time-Nuts, I need to generate some space in my basement... I have three items I´d like to give to good hands: 1. HP5370A. Working fine *most* of the time. Sometimes the noise of the time measurements rises from ~20ps to a few hundred ps after some hours or so. Random activities with the switches on the input bring it back to the good state normally. I always wanted to dive into this, but since I own the TAPR tic I don´t feel the need for this huge and loud instrument any more. I also have a box of spare boards for the 5370. I´d like to keep the 10811 from this one as a spare, but if you really need the OCXO, we might find a solution. 2. HP5335A. Working fine, no further options. Both instruments are available in Munich for pick-up free of charge. If I find a suitable box, shipping might be possible as well, but I´d prefer pick-up of course. Best regards, Matthias ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi Magnus, Yes, and it works very well, locking is easier as once locked it nicely stay's in lock, , even with a slow drift of either the DUT or the reference. As I could not find a bipolar capacitor the tuning potmeter has to be kept at the low side to avoid blowing the integration capacitor. Maybe a back to back series capacitor with pull down resistor is safer to use. Will need to update the schematic to show the small improvements. @Bob, You mentioned "dual supplies with high voltage" for the first gain opamp. How much impact would dual voltage bring as its a pain to implement. I understand everything gets ground reference and you loose the noise of the buffer opamp but as the first gain opamp is in differential mode for its input it does not see the noise of the buffer opamp. Or am I making a mistake? On 10-7-2022 2:02, Magnus Danielson via time-nuts wrote: Have you attempted doing a PI-loop as I've suggested? ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: What about the frequency discrimination method? (offshoot from DIY PN analyzer)
Ed, On 7/9/22 22:26, ed breya via time-nuts wrote: I've been following the thread about Erik's DIY PN analyzer, and wondering if it might be easy enough to use a frequency discrimination method. I'm opening this in a different thread to avoid muddying the water on the original (and long) one. What I'm picturing is putting the DUT's output into a quadrature power splitter that optionally has a voltage-tuned slight phase shift feature. The I and Q outputs would go into the DBM and produce the nearly-zero DC plus baseband signal for analysis as in the original story. If the quadrature is precise and stable enough, the DC out should be close to zero, and since the baseband is ultimately AC coupled to the analyzer, small offset should be OK, within reason. If this is not sufficient, then having a phase tuning feature could be used to form a PLL to hold the DC at zero. The big difference here is that instead of locking a separate reference source to the DUT, the relative phase at the mixer just has to be fine tuned to maintain the output DC. The same sorts of PLL requirements are encountered to get the results, but no external reference (and its noise and lock range etc issues) is needed. The downside is that a different quadrature splitter would probably be needed for each DUT frequency to be applied - I'm picturing ones for 5 and 10 MHz initially. Those 90 degree broadband splitters that Mike mentioned seem very interesting too. There is still the necessity of calibration, either way. There is no need for it. Using the PI loop, it will drive the phase detector into quadrature and as it does this, the DC component of the detector is cancelled as it is integrated into the integrator path I. There is however use for quadrature splitter as you do a Costas loop, which is needed for some modulation schemes. Then again, you really do not need to use a quadrature splitter to achieve the needed quadrature pair, but there is other tricks to achieve the same thing. The Tayloe detector comes to mind, which uses a frequency 4 times higher, divides it down and then drive the detector for a S/H style of mixer. See for instance Elecraft KX3. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Erik, On 7/9/22 22:06, Erik Kaashoek via time-nuts wrote: Getting the simple PNA to lock was a bit difficult due to the overly simplistic translation of the mixer output to the Vtune of the OCXO To get some more flexibility I added a summing opamp that summed the mixer output with the output of the coarse tuning potmeter. As the summing causes inversion one extra inverting opamp was added. This made the loop gain constant To ensure the mixer is in quadrature another opamp was added that amplified the mixer output into two LEDs. One LED on when below zero ouput from mixer, the other on when above zero and both dim when zero output. This made tuning the coarse frequency simple. Turn till the blinking stops and both LED's light up dim. The fine frequency potmeter was no longer needed and the frequency counter is also no longer needed to get into lock With the summing opamp it is also possible to add an integrator but this has not been done yet. So, this is where you should attempt the PI loop. In theory, you have one proportional path P and one integrating path I that sums to form the EFC. You can imagine this as two op-amps having inverted gain and then a summing amp to sum these two up. Thus, you have for the P path a resistor in the negative feedback path and for the I path a capacitor in the negative feedback path. Such a setup is nice for testing, but a bit excessive as one progresses. One can actually reduce this to a single op-amp with the resistor and capacitor of the negative feedback to be in series, having a common input resistor. The integrator part will hold the state that ends up being the DC part of EFC. The proportional path will provide the AC path and set the damping factor for the PLL, you want it well damped. This would replace your normal loop filter. You would still want a filter to reject the sum-frequency out of the mixer. The P gain is proportional to the PLL bandwidth time damping factor. The I gain is proportional to the PLL bandwidth squared. The capture range is for all practical purposes infiinte (it's wide enough). The capture time depends to the cube on the PLL bandwidth, so altering the PLL bandwidth between unlocked and locked conditions have proven very useful approach to speed things up if one has a need for larger lock-in frequencies. Rough-tuning with a trimmer can reduce it significantly. The lock-detection is very simple detection of the presence of beat-notes or not, that AC component dies away as it locks. Anyway, the benefit of the PI loop filter is that you can be rather brutal with parameters, it will lock. So, it can be worth experimenting with it. I've found that one can ball-park things fairly quickly knowing how to change the P and I for wished PLL bandwidth and damping. Very experimentally friendly. I should advice you that any PLL will provide a low-pass filter of the reference input, and a high-pass filter on the noise inside the loop, which includes that of the oscillator. This can help you identify likely sources of disturbances as per their frequency in relation to the PLL loop bandwidth. Cheers, Magnus Shielding is now the biggest problem as any nearby coax connected to a 10MHz source will cause a huge amount of spurs when not at exactly the same 10MHz Ultra low noise opamps have been ordered to hopefully reduce the internal noise of the PNA but the reference OCXO may already be the limiting factor. The REF voltage output of the OCXO turned out to be rather clean. Much cleaner than a 8705 voltage regulator Erik ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On Sonntag, 10. Juli 2022 01:24:49 CEST djl via time-nuts wrote: > I checked the Hittite/AD part at Mouser, $21 and change. Problem is, > they have a few, but it is marked obsolete/discontinued. Also, a > devilish package to work with. . . For a one-off project, lifetime doesn't really matter, does it? The package is QFN, even with center pad. That is inconvenient, but not too bad. It's just kind of small, 4mm edge length. You'd certainly need a microscope and hot air to solder it or a quite fine soldering tip if you would want to deadbug it. Were I to use it, and wanted to breadboard a prototype, I'd certainly make a suitable breakout board for easier handling. > On 2022-07-08 22:19, Mike Monett via time-nuts wrote: > > To Bob kb8tq. You wrote: > >> Hi > >> > >> The noise floor of the double balanced mixer (used as a phase > >> detector at 100 MHz) is in the -165 go -170 dbc / Hz range. I've > >> used the parts you are talking about. Their floor is *way* higher. > >> > >> Bob > > > > I stated the MC100EP140 would not match the Hittite HMC984LP4E. It has > > -231 dBc/Hz noise. > > > > -231 dBc is *way* lower than -170 dbc. About 60 dB lower. > > > > You might be interested in trying it. Only $13.25 at Arrow: > > > > https://octopart.com/search?q=HMC984LP4E > > > > Thanks, > > > > Mike > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe send an email to time-nuts-le...@lists.febo.com > > > When in trouble, when in doubt, > Run in circles, scream and shout. > (Naval War College Football Team) > -- > Dr. Don Latham AJ7LL > PO Box 404, Frenchtown, MT, 59834 > VOX: 406-626-4304 > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
