Do I really need an LC meter?

"notbob" schreef in bericht news: snipped-for-privacy@nbleet.hcc.net...

A LC-meter is a usefull piece of equipment - at least for me. I build Phil Rices LC meter

though a designed my owm PCB. It's very good for measuring capacitances and I get at least an idea about coils. But measuring coils is tricky. Except for air core types, inductance depends highly on the frequency which may not be the frequeny used by the LC meter. So for measuring inductance accurately it's better to use a griddipper or similar and measure in the frequency range the coil is intended for to be used. Measuring toroids require some additional tricks as the magnetic field of it hardly radiates.

petrus bitbyter

It's a neat gadget, but people lived without them in the past. And while you can get a DMM for ten dollars and definitely get value out of it (especially considering that analogue meters in the old days were pretty awful at that low a price), the ones that measure inductance are in a different price range. The standalone are obviously better, but will cost money.

It's important to note that many DMMs above the cheapest price now measure capacitance, one reason I bought a new DMM about 1996. But they are biased towards larger values, since the built in capacitance is larger than some small value capacitors that you'd use in RF.

People always used to wind coils without an inductance meter. They'd wind it according to a chart, or the math, or just follow what someone had described in the magazine. Generally, it was okay. But no matter what, often you'd have to make adjustment anyway, so coils were wound on forms that had a core that could be adjusted to tune the coil, or a variable capacitor was in parallel with the coil. With toroids, the variable capacitor would have to be used. Note that a lot of construction articles will never tell you the inductance of the coil, they'll just tell you how to wind them.

You'd need some sort of test equipment, a signal generator or something makedo to peak the coil for the desired frequency, but often one could makedo with something rather than buy an expensive LC meter or signal generator.

Michael

The Peak Atlas LCR meter isn't too pricey at about 4-5x the price of a cheapo DMM.

Maybe. You can use a DMM that measures capacitance to also measure inductance. Google for how to do that. But you need to realize that just measuring inductance that way is not necessarily what you need. Why? Because the effective inductance value, in many cases, depends on the current going through the inductor and the frequency of use (inductors have capacitance too). So you need to understand more than simple inductance. Google around for more tutorials on types of inductors (core material, capacitance) then decide what you need to measure.

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You could learn to do it the old fashioned way. Measure the impendence at the operating frequency, measure the DC resistance, and use some light math. It will get you close. But then you would need equipment to do that. I'll see if I have a spare LC meter in the shed.

Tom

I second the motion for a grid dip meter -- because it's useful for so many other things, too.

Or a signal generator and a demodulator probe -- you can usually get a nice sharp dip with a series LC and the right resistance.

Or -- just wind your coils. I've had good luck with winding toroids on Amidon cores. Unless you're trying to use some toroid made out of mystery material, you can pretty much build it to print and expect it to work.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

e

Do you have a 'scope and function generator? (If not I might put those on my 'wish list' first.) If you do then I lived for years without an LCR meter. An RC and a voltage step can give you the C. (And John L had a neat trick of looking at the very small DC offset to get the ESR.) Then you can resonate an LC to find L. As someone said do a few different frequencies.

George H.