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]
