[time-nuts] Re: measuring tiny devices

[Andy Talbot]

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 <
time-nuts at lists.febo.com> 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 <
> time-nuts at lists.febo.com> 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.
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