[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: DIY Low offset Phase Noise Analyzer
Another great post from Bob (as usual). Bob's advice is exactly correct. Unfortunately, the HP 11848 phase noise test set (part of the HP 3048 PN measurement system) is poorly designed, and does not break out the low gain non clipped signal. I modified mine to bring out this signal and it was MUCH easier to use. Follow Bob's advice if you are DIYing. Rick N6RK On 7/4/2022 9:12 AM, Bob kb8tq via time-nuts wrote: Hi If you are running a high gain op-amp to buffer things into a sound card *and* using the same op-amp output to drive the EFC, then you will have problems. Simple answer is to use a couple of op amps. Buffer the mixer with something low noise. Get the output of the mixer up to the point it almost saturates the op amp. Just how much gain that is depends a lot on your parts and power supplies. Running +/- 18V supplies into this op amp is no at all unusual. Since this output is linear, you have the full range of the beat note present. Nothing has been lost (yet). One path off this device goes to the high gain stage to the sound card. If the beat note is present, you will have clipping there. The other path goes to whatever you do to run the EFC. There are *many* approaches that could be used. One of many is a variable gain / variable roll off amp to “set” the PLL corner. That is followed by a simple summing amp to tune out the DC offset on the EFC. Bob ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Is SC the most stable cut for lowest phase noise?
I think there is a severe misunderstanding of this issue. First of all, "rapid warmup" is a red herring. The real issue is "rapid frequency stabilization". The time it takes for the oven to cut back (typically only a minute or two) is a very minor part of the time budget to get to frequency stabilization. You could have an AT cut oscillator that reached "oven warmup" in 1 second, but then you would have something like a 1 hour wait to get frequency stability, due to the thermal stresses. Part of the reason for the misunderstanding is that the problem I have described is basically orthogonal to the proverbial time nut with his master OCXO in an underground bunker running on an uninterruptible power supply, that has been powered up continuously for umpteen years. Rick N6RK On 6/10/2022 6:47 AM, Lux, Jim via time-nuts wrote: On 6/9/22 8:53 PM, Bob kb8tq via time-nuts wrote: Hi There happen to be *some* AT cut based OCXO’s that beat the typical SC cut on warmup … just saying …. :) Bob On the subject of rapid warm up. I suppose if you had a need, one could dump as much power as you need into the heater. Turn on oscillator, lights in room dim for a few moments. But everything is a tradeoff, and I suspect that over time "standard designs" sort of migrate to particular ratios of things like peak vs average heater current, etc. Especially in applications driven by design rules for things like "maximum current per connector pin" or "component derating" - I suspect that drives things more than the fundamental physics, in most cases. Why are diodes rated at 1 or 3 Amps? And not 2? ___ 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: Is SC the most stable cut for lowest phase noise?
On 6/9/2022 10:03 AM, Bruce Hunter via time-nuts wrote: My only experience with SC-cut crystals is that time base oscillators in later EIP/Phase-Matrix counters with SC-cut crystal oscillators seem to warm-up from a cold start and stabilize more quickly than earlier AT-cut versions. I was surprised to see from Jeff Cartwright's paper that SC-cut crystals operate at higher temperatures. Could this rapid warm up characteristic be attributable to oven design rather than crystal cut? Bruce Absolutely not. It is strictly due to thermal stress compensation. 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: Is SC the most stable cut for lowest phase noise?
Yet another interesting time nuts conversation. A few comments: 1 A number of comments stated as a "fact" that higher unloaded Q for the resonator corresponds to lower phase noise. This idea evidentially comes from looking at analysis of a so-called free running oscillator with a simple LC tank or microwave resonator, as published by Edson, Kurakawa, and Cutler/Leeson. However, even in this case, what matters is the LOADED Q, and the drive level to the sustaining amplifier. A given drive level will have a particular phase noise and flicker noise floor associated with it. Incidentally, the resonator should be critically coupled, in which case Ql = 1/2 Qu, for optimum phase noise., 2. With a piezo electric resonator, the intrinsic flicker noise of the resonator dominates, and it isn't related to Q (unloaded to loaded). The sustaining amplifier ordinarily is not a factor. 3. I personally measured the intrinsic phase noise of a free-standing 10811 crystal and compared it to the phase noise of a 10811 oscillator with that same crystal installed. The conclusion was that the oscillator phase noise was basically the same as the intrinsic crystal noise, except at large frequency offsets. 4. The only possible scenario I can see for why an SC cut might have better phase noise is if you don't have a very good oven. Then ADEV at long averaging times starts to go up. In that case, an SC cut might help because of improving tempco. 5. Phase noise at large offsets (>1kHz) depends on the buffer amplifier design. The grounded base design in the 10811 is the optimum first stage. Unfortunately, the 2nd and 3rd stages in the 10811 degrade its phase noise. This has little or nothing to do with the cut of the crystal or anything else about it. (The idea for this was published by U. Rhode and later patented by Burgoon of HP). 6. The primary motivation for the SC cut at the HP Santa Clara division (where I worked) was to be able to put it into a frequency counter used for field maintenance. The idea was that the technician could carry it from his truck into the worksite and plug it, starting from a cold oven. Then, in only 15 minutes, the counter met some accuracy spec. With a 10544, it would take many times longer to get to the same accuracy. Jack Kusters used to say that "SC" actually stood for "Santa Clara" :-) 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: measuring tiny devices
These types of devices have been around so long they can be found in labs wearing the hp badge. Their uselessness 40 years ago compelled me to invent the workarounds in the copper mountain ap note. Rick N6RK Keysight retiree, 2014. On 5/26/2022 12:51 PM, Brooke Clarke via time-nuts wrote: Hi Ed: You might surf the Accessories Catalog for Impedance Measurements. https://www.keysight.com/us/en/assets/7018-06727/brochures/5965-4792.pdf They have a number of SMD fixtures for 4-terminal pair LCR meters. https://prc68.com/I/Z.shtml#KeyDocs ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: measuring tiny devices
This was already SOP for any knowledgeable RF engineer by the 1940's. Somewhere I have a copy of Dishal's paper. I worked for Zeta Labs in the 1970's and we sold lots of microwave filters that were tuned this way. We didn't even have VNA's at Zeta. We just used a directional detector (diode type) and a sweep oscillator. All the techs could do this in their sleep. Recently, I needed a 3 pole VHF bandpass filter for a client requiring only 8% bandwidth. I knew from previous experience that the Dishal method as the ONLY one that would work. And sure enough, it worked perfectly. That's fine, if you want to build a filter, but there are many other cases where you need to measure immitance unrelated to a filter. Rick N6RK On 5/26/2022 10:27 AM, John Lofgren via time-nuts wrote: Bob, You may be thinking of Dishal's method. < https://www.johansontechnology.com/dishal-bandpass-filter-tuning-using-lasertrim-chip-caps> -John -Original Message- From: Bob kb8tq via time-nuts Sent: Thursday, May 26, 2022 10:18 AM To: Discussion of precise time and frequency measurement Cc: Bob kb8tq Subject: [time-nuts] Re: measuring tiny devices EXTERNAL EMAIL: Be careful with attachments and links. Hi The real answer to the problem is to dig into the bowels of 1940’s electronic craft. There are various methods for setting up an L/C filter. You short this / open that sweep to find a dip or a peak. You move it to the “right” place. Just what you do depends very much on the filter design. Many L/C’s got done this way or that way simply because they would fit a known alignment method. While it all sounds very cumbersome and obscure it actually isn’t. Long ago I stumbled upon a gal setting up very complex L/C IF filters this way. The display gyrated this way and that way as she did this or that. I don’t think it took her more than a minute to get the whole thing set up….. to this day, I’m amazed by how fast she was. Do I have any useful links to actually read up on this magic? … sorry about that. Bob On May 26, 2022, at 4:58 AM, Lux, Jim via time-nuts wrote: On 5/25/22 3:16 PM, ed breya via time-nuts wrote: Thanks Mike, for info on LCR alternatives. It's good to know of others out there, if needed. I have an HP4276A and HP4271A. The 4276A is the main workhorse for all part checking, since it has a wide range of LCZ, although limited frequency coverage (100 Hz - 20 kHz). The 4271A is 1 MHz only, and good for smaller and RF parts, but very limited upper LCR ranges. I think it works, so I can use it if needed, but would have to check it out and build an official lead set for it. I recall working on it a few years ago to fix some flakiness in the controls, so not 100% sure of its present condition. The main difficulty I've found in measuring small chokes is more of probing/connection problem rather than instrument limitation. For most things, I use a ground reference converter that I built for the 4276A many years ago. It allows ground-referenced measurements, so the DUT doesn't have to float inside the measuring bridge. The four-wire arrangement is extended (in modified form) all the way to a small alligator clip ground, and a probe tip, for DUT connection, so there is some residual L in the clip and the probe tip, which causes some variable error, especially in attaching to very small parts and leads. When you add in the variable contact resistance too, it gets worse. Imagine holding a small RF can (about a 1/2 inch cube) between your fingers, with a little clip sort of hanging from one lead, and pressing the end of the probe tip against the other lead. All the while, there's the variable contact forces, and effects from the relative positions of all the pieces and fingers, and the stray C from the coil to the can to the fingers. I have pretty good dexterity, and have managed to make these measurements holding all this stuff in one hand, while tweaking the tuning slug with the other. I had planned on making other accessories like another clip lead to go in place of the probe tip, but not yet built. I also have the official Kelvin-style lead set that came with the unit, so that's an option that would provide much better accuracy and consistency, but the clips are fairly large and hard to fit in tight situations, and the DUT must float. Anyway, I can make all sorts of improvements in holding parts and hookup, but usually I just clip and poke and try to get close enough - especially when I have to check a lot of parts, quickly. The other problem is that the 4276A is near its limit for getting measurements below 1 uH, with only two digits left for nH. The 4271A would be much better for this, with 1 nH vs 10 nH resolution. If I get in a situation where I need to do a lot of this (if I should get filter madness, for instance), then I'll have to improve the tools and methods, but I'm OK for now, having slogged through it this time. You might check out the N
[time-nuts] Re: measuring tiny devices
On 5/26/2022 10:24 AM, Lux, Jim wrote: https://www.mwrf.com/technologies/test-measurement/article/21849791/copper-mountain-technologies-make-accurate-impedance-measurements-using-a-vna describes the various approaches I don't know how long these methods have been in use, but I independently (re)-invented them around 40 years ago. At the time I was working for HP and attempted unsuccessfully to interest various HP business units in publishing this as an ap note, as copper mountain has. Meanwhile I taught them to numerous hams, clients, and HP engineers, etc. Fast forward now to 2022 and nearly everyone knows about them. As useful as they are, they have serious limitations: 1. The high-Z workaround requires the DUT to be floating. 2. The low-Z workaround requires the DUT to be grounded. Can anyone suggest workarounds for the workarounds? 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: measuring tiny devices
I have had good results with the LCR Research tweezers. Search "LCR Research" on Amazon. They work great on anything you can pick up or probe with tweezers. The general disclaimer on any kind of component measuring device is: Virtually all of them are ONLY suitable for measuring a free-standing device, not one soldered into a PC board. This is partly for technical reasons, but also for marketing reasons. The vast majority of money to be made in this field is for high speed testers for component manufacturers, not so much for R&D use. The LCR tweezers at first glance would appear to buck the trend by acting as a "free standing analyzer" due to its tiny size. This turns out to be not quite true. A chip capacitor soldered to a ground plane will measure 1/2 pF high, no matter what the value. Trying to make an embedded capacitance measurement of a capacitor in a pi network is completely unsuccessful. The one good thing about the tweezers is that they virtually eliminate the "fixturing" problem with small components, that plagues "big iron" out of Santa Rosa. (Personal note: I worked for HP/Agilent/Keysight for 35 years, including designing network analyzers). The tweezers are in no way a "nanoVNA" at all. They don't work on that principle, which is good. VNA's of any kind (no matter how small their size) don't work well on components that are too far away from 50 ohms, at least if you make a simple minded s11 smith chart measurement. There are complicated work-arounds for these measurements, but they require different configurations depending on what you are measuring, so there is no turn key or universal solution. With the low price of available VNA's, anyone can afford to buy one, but that doesn't mean they know how to use it correctly. Rick N6RK On 5/26/2022 5:58 AM, Lux, Jim via time-nuts wrote: On 5/25/22 3:16 PM, ed breya via time-nuts wrote: Thanks Mike, for info on LCR alternatives. It's good to know of others out there, if needed. I have an HP4276A and HP4271A. The 4276A is the ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
