Hi That’s one of the methods. There are others for various filter topologies. Some are more practical than others …
Bob > On May 26, 2022, at 9:27 AM, John Lofgren <[email protected]> > 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 <[email protected]> > Sent: Thursday, May 26, 2022 10:18 AM > To: Discussion of precise time and frequency measurement > <[email protected]> > Cc: Bob kb8tq <[email protected]> > 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 >> <[email protected]> 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 NanoVNA - people have made a variety of novel >> fixtures for measuring small parts (i.e. 0604 SMTs) >> >> It certainly has the measurement frequency range you need. The trick is >> figuring out whether you want to do a series or shunt measurement, and that >> sort of depends on the reactance of your device at the frequency of interest. >> _______________________________________________ >> time-nuts mailing list -- [email protected] To unsubscribe send >> an email to [email protected] > _______________________________________________ > time-nuts mailing list -- [email protected] To unsubscribe send an > email to [email protected] > THIS MESSAGE, ANY ATTACHMENT(S), AND THE INFORMATION CONTAINED HEREIN MAY BE > PROPRIETARY TO LAIRD CONNECTIVITY, LLC. AND/OR ANOTHER PARTY, AND MAY FURTHER > BE INTENDED TO BE KEPT CONFIDENTIAL. IF YOU ARE NOT THE INTENDED RECIPIENT, > PLEASE DELETE THE EMAIL AND ANY ATTACHMENTS, AND IMMEDIATELY NOTIFY THE > SENDER BY RETURN EMAIL. THIS MESSAGE AND ITS CONTENTS ARE THE PROPERTY OF > LAIRD CONNECTIVITY, LLC. 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