Google (other search engines are available :-) DISHAL Filter Tuning Very neat and quick way to tune up a filter using just return loss. Doesn't even require a VNWA.
Andy www.g4jnt.com On Thu, 26 May 2022 at 16:40, Bob kb8tq via time-nuts < [email protected]> wrote: > 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] _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]
