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Low cost L-C meters
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Folks, as there is a lot of discussion on toroid winding etc, I would like to recommend purchasing a low cost L-C meter to measure your actual values for your various toroids to minimize winding adjustments,? A good inexpensive one, which can be found on EBAY, is the LC-100A. Search EBAY for "Digital LC-100A high precision inductance/capacitance L/C meter tester".? They go for about $15-16.? It works quite well, but it is not mounted in a case.? If you spend more money, I would recommend the LC-200a. Search EBAY for "LC200A inductance inductor capacitance capacitor L/C multimeter Meter Tester"That one costs about $30 comes mounted in a case,? I own both and they both work very well. I have found after designing and testing many toroid-based filters that inductance values can stray considerably from theoretical value based on number of turns.? Some precautions with these: ? ?Zero (calibrate) just before measurement.? Calibrate often for multiple measurements such as for L or C matching
Increasing Inaccuracy for low inductance values (<~500nH) and low capacitance values (~10pF) due to low measurement frequency ~ 750KHz
?Be careful in accepting inductance values of coils with frequency-dependent (and amplitude dependent) permeability, such as most ferrites.
?Measures effective inductance, not actual inductance,? where distributed capacitance is significant.
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I have found, in general that inductance values tend to be on the high side for toroids used in HF filters, compared to theoretical values based on number of turns.? I also found that small inductance values (500 nanohenries or less)? using relatively few turns and low permeability material, tend to be way off due to leakage inductance and really need to be measured to get them right.? These meters are also good for verifying no mislabeled capacitors.
?For best accuracy when measuring low inductance devices, do not use flexible test leads
?You can measure test frequency by pushing the rightmost button (depending on version of software used)
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I would like to recommend purchasing a low cost L-C meter to measure your actual values for your various toroids to minimize winding adjustments,? A good inexpensive one, which can be found on EBAY, is the LC-100A.Steven, I purchased one of these and it was very inaccurate. Unless someone has a way of checking the accuracy this would be very confusing, worse than useless! This one said it was 1% but was actually more like 15%, far more than the variations in inductance that have been reported. I do not recommend anyone to buy an inductance meter unless they are able to verify it's accuracy. 73 Alan G4ZFQ |
¿ªÔÆÌåÓýHi Steven. I have several inductance meters, only one of which is useful. This is an old wyne-kerr bridge. It is the only one that allows measurements at the operating frequency.? I have noticed that if RF toroids are measured at the typically 1khz, or 12khz test frequency, they can show up to 20% error. Sometimes worse. Regards? Alvey Street. On 09/11/17 23:06, Steven Dick wrote:
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This is an old wyne-kerr bridge. It is the only one that allows measurements at the operating frequency.Alvey, What no dip meter? I think carefully done with 1% capacitors a dip meter is quite accurate, an SDR helps to easily measure the exact dip frequency. (Dip meters seem almost unknown these days) I have noticed that if RF toroids are measured at the typically 1khz, or 12khz test frequency, they can show up to 20% error. Sometimes worse.Are these the general purpose multimeter-type testers? Many of the modern L/C meters use 300-500KHz, one I use compares well with normal HF type inductors. But, the problem is that others I've tried are not so good.. 73 Alan G4ZFQ |
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Hi Alan. YMMV but I did verify their accuracy with known accurate inductors and also verified filter performance via measurements with a network analyzer and comparison against LTSPICE simulation of filters, especially with regard to return loss These inexpensive meters are specified as having a measurement accuracy of 1 percent. There are bogus models out there which work poorly and you might have gotten one of those. My LC100A has buttons to the left of the test leads. Look for vendors with large number of buyers of their unit and good reviews. It's a wasteland out there.
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-Steve K1RF -----Original Message-----
From: Alan G4ZFQ Sent: Friday, November 10, 2017 1:40 AM To: [email protected] Subject: Re: [QRPLabs] Low cost L-C meters I would like to recommend purchasing a low cost L-C meter to measure your actual values for your various toroids to minimize winding adjustments, A good inexpensive one, which can be found on EBAY, is the LC-100A.Steven, I purchased one of these and it was very inaccurate. Unless someone has a way of checking the accuracy this would be very confusing, worse than useless! This one said it was 1% but was actually more like 15%, far more than the variations in inductance that have been reported. I do not recommend anyone to buy an inductance meter unless they are able to verify it's accuracy. 73 Alan G4ZFQ |
¿ªÔÆÌåÓýHi Mike. Not familiar with that one.? I never really measured the
LC200 absolute accuracy over a wide range of inductances but it worked well for
me for many verified designs. Most of these designs use the same principal and
their accuracy depends on the quality of their internal inductor. Basic
principal of operation is that they measure the frequency of a square wave
oscillator with an internal reference inductor, then switch in the inductor
under test to put it in series with the reference inductor, then use software to
compute the inductor value under test. They are limited by their test frequency
which is usually pretty low (on the order of 750KHz or so) and the quality of
their reference inductor.
-Steve K1RF
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Hi
Steven I have been looking at the LC200 ~ my concern is how accurate are the measurements? Have you been able to check? There is another low cost meter available on AliExpress ~ any info anyone? 73 Mike G0CVZ |
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I do have a dip meter, but my son has 'borrowed' it.? For a quick, on frequency test, I use a 10m scope across the TC and make it 'ring' by means of a 'gimmik' capacitor fed from the calibration outlet on the front of the scope.? The small pic based LC meter has a 12khz source, feeding an RC (C is item under test) potential divider. The pic measures the voltage.? Another one that I have uses time measurment of the rise time of an inductor to a voltage step-edge. On capacity, it applies a current charge or discharge step edge and measures time to a fixed percentage of the supply voltage.
Alvey Street g4ksy |
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Chuck, K7QO had done some preliminary testing of various LC meters and posted it on his webpage.? I gleaned this info from the yahoo group QRP-tech, in case anyone finds it useful.?? I would stay away from the LC100 that Chuck describes as "Left" terminals, at least from my very limited experience...
"I started the comparison of some LC meters. Using the LC200A from China, the AADE L/C Meter IIB with the famous Preston Douglas, WV2J, cap mod and two LC100A L/C meters. The LC100A's on ebay come in two variations (at least) that I see. One I call Right, as the component terminals are on the right front of the PCB and Left for the terminals on the left side. I have two Rights and found that they have a Rev 4.8 and Rev 4.7 firmware show at startup, so thought it would be interesting to see if there was an effect. None that I can see. OK, before you weigh in on the numbers. This is the first pass and only for discs caps Got a whole set of mono, mylar and electrolytics to do. The AADE fades on the electrolytics. Meaning that the measurements are way off and low. I'll try to get some more done tonight and put in a table. I made a mod to the LC200A. Bought two terminal posts that have a screw down so that I could build a fixture and get exact reproducing measurements. I will come back in a week and redo them to see if there are changes. Good results between all four meters and most within 1% and some points that were off by more than 1% and I will come back and remeasure those later. I just take data..... I have one of the Frog Sounds transceivers ($12) coming to the mailbox today. Some one mentioned they found shorts in som caps and I will measure them all for the heck of it. LC200A - $29.95 on ebay AADE - $99.95 in kit and $149 assembled and no longer available LC100A - about $14 USD on ebay for Left sided terminals If you have an LC100A with the terminals on the left, send me the Rev that you get on power up. Please. The LC200A is Rev 5.5, so it has the same uP processor and just a different PCB and comes with a case." |
There is another way to measure inductance and that if you have an MFJ-259 or similar you can use the method in the manualMike, That would not be low-cost to me, I don't have one! But yes, a way, many do have them. I wonder how accurate measurements can be? The need for the standard, high accuracy inductors (and capacitors) might be a problem. Inductors: 330¦ÌH, 56 ¦ÌH, 5.6 ¦ÌH, .47 ¦ÌH Capacitors: 10 pF, 150 pF, 1000 pF, 3300 pF Best if all were 1%? It strikes me if anyone had that range of standards then maybe a calibration chart could be made up for one of the cheaper testers if they were found to be inaccurate. A set of standards could be made up, what sort of glue should be used to secure the windings of toroids? Then some one with reliable gear could measure them, odd values would not matter. Maybe a Club project? 73 Alan G4ZFQ |
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Ken KM4NFQ
Greetings, I would like to add my two-cents to this discussion.References: |
As a radio-related electronics hobbyist, I also need anKen, I built the original version of this and agree it is surprisingly accurate. But as it is basically an AADE.. The original just needs a 1000pF 1%, I see the new version does not need one in the construction but an accurately known value to calibrate. There are versions of this for sale, the ones I've seen are not particularly cheap, and do they work as well? 73 Alan G4ZFQ |
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Arv Evans
The original AADE LC meter used an LM311 as the oscillator section and derived measured values from counting frequency of oscillation with the PIC16F84.? Now that there are PIC chips that have a built-in equivalent of the LM311 it is possible to build an LC meter that is similar to the AADE unit but with less parts count because the oscillator can be inside the PIC. There are also many instructional articles on-line for building your own LC Meter that is similar to the AADE unit.? If you build your own you will be able to do your own calibration to the accuracy level that you desire. Arv? K7HKL _._ On Sat, Nov 11, 2017 at 9:48 AM, Alan G4ZFQ <alan4alan@...> wrote: As a radio-related electronics hobbyist, I also need an |
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Ken KM4NFQ
I built the kit from and it did not work right after I built it.On Sat, Nov 11, 2017 at 11:48 AM, Alan G4ZFQ <alan4alan@...> wrote: As a radio-related electronics hobbyist, I also need an |
I built the kit fromKen, I'm surprised, yes it looks like that one. My build was as Phil said "surprisingly accurate" checked with 1% components and careful use of a dip meter. Just goes to show that any cheap or home-made meter needs careful testing before using in earnest. 73 Alan G4ZFQ |
¿ªÔÆÌåÓýKen, that was one of the first LC meters I had/built.? It drifted
quite a bit and was no where as stable or accurate as the LC100-A or the LC200-A
that I now use, nor was it as good for measuring low value inductors (on the
order of 500 nanohenries).?? I would also add that 1 percent accuracy
is certainly nice to have but I have found that, depending on material,
frequency of operation, number of turns, spacing, etc they can sometimes be off
as much as 20 percent, so measuring them within 1 or 2 or 3 percent is a helluva
lot better. One other method I use for measuring an LC pair (if it can be
isolated as part of a filter) is to use a return loss bridge/power meter. Take
the parallel LC and add one extra turn through it, and connect this turn to the
return loss bridge unit under test port. You will see a clear peak or dip at the
resonant frequency. If the cap is a precision cap (1%) you will very accurately
set the inductance value by squeezing turns or adding/removing turns as
necessary.? This method is also testing the inductor at the actual
operating frequency.? Sort of like a fancy grid dip meter, but with much
more accurate frequency readout if you are using an accurate freqwuency
reference such as a DDS or SI5351 derived.
Steve K1RF
? From: Ken KM4NFQ
Sent: Saturday, November 11, 2017 1:20 PM
Subject: Re: [QRPLabs] Low cost L-C meters ?
I built the kit from and
it did not work right after I built it.? ?
On Sat, Nov 11, 2017 at 11:48 AM, Alan G4ZFQ <alan4alan@...> wrote: As a radio-related electronics hobbyist, I also need an ?
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This method is also testing the inductor at the actual operating frequency.? Sort of like a fancy grid dip meter, but with much more accurate frequency readout if you are using an accurate freqwuency reference such as a DDS or SI5351 derived.Steve, With a dip meter you can get an accurate frequency readout quickly with an SDR. There's still life in old technology. 73 Alan G4ZFQ |
va3rr
Bob ah7i
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