Unboxing and checking my new LCR meter!

I was told by a VU ham friend that in order to experiment with loaded coil dipole antennas, it is essential to have an LCR meter. It was during the discussion on my recently homebrewed loaded coil 80m antenna which would not resonate on 80m. The coil which I had wound myself probably did not have the needed inductance due to wider spacing of winding than in the design. This is the new LCR meter which arrived today after an online purchase a few days back.

This digital inductance, capacitance, resistance meter, that is LCR meter, came with a couple of red and black test leads with crocodile clips, a calibration certificate, instruction leaflets and a 9V battery. There was a nice carrying pouch with zip fastener as well. Everything came packed in a cardboard carton, which I have just removed. First I went through the calibration certificate and instruction leaflets quickly before proceeding further.

Now I have removed the polythene cover of the LCR meter and the 9V battery as well as attached the test leads on the corresponding input terminals. You can see that the test leads are quite short unlike the multimeter, possibly to reduce stray capacitance and inductance.

Now I have removed the test leads and kept the LCR meter inverted to see the rear side and removed the screw from the battery cover using a star edged screwdriver. The connectors for the 9V battery can be seen inside the battery compartment.

Battery has been connected to the connector and the battery inserted inside the battery compartment and it is fitting well inside it.

Now the LCR meter has been kept back in the correct position and the power switched on by a long press of the power button. LCD display has been lit up and shows ‘1’ which is the default out of range display. Measuring range of this LCR meter is 200 picofarad to 2000 microfarad for capacitance, 200 microhenry to 20 henry for inductance, and 200 ohms to 2 mega ohms for resistance. There is also an option for checking the forward voltage drop of a diode. There are few safety precautions to be borne in mind. Do not give any alternating or direct current voltage to the input terminals. While measuring capacitance, make sure that the capacitor has been fully discharged prior to testing. While changing switching function, test leads should be removed from the test points. Make sure that the correct function has been selected prior to testing.

Here I have attached a 1000 microfarad electrolytic capacitor after discharging it, to the test leads. I had also tried inserting it into the slots, which also showed same value, but there was loose contact and fluctuation of value when the pressure on the capacitor was changed. Testing using test leads may introduce some stray capacitance. Short leads have to be used for lower values of capacitors to reduce errors. If ‘1’ is displayed as the reading, the next higher range should be selected. If zeros are seen, then the next lower level has to be selected. There is provision for zero correction using the rotary knob. If zero is seen for all ranges, the capacitor is probably open circuit. If the reading is unstable, it may indicate a leaky capacitor.

A 470 microfarad capacitor is being tested here and the value seen is 446. This test and the previous test were done in the 2000 microfarad range of the selector switch.

Now a 470 picofarad capacitor is being tested in the 20 nanofarad range. It is shown as 0.49. Zero suggests that it is not the correct range for testing. 471J written on the capacitor indicates the capacitance and tolerance. J indicates 5% tolerance, meaning that the actual value may be within 5% above or below the nominal value.

This testing is done in the 200 nanofarad range and we see two zeros, meaning the range is much above the needed one.

Now testing is being done in the 200 picofarad range and it shows ‘1’, indicating that the value is beyond the measurable range for the selection. All these are not the recommended methods to test.

This test is in the 2 nanofarad range and the value is shown as .479 without any preceding zeros. That means this is the correct selection for testing the value of this capacitor.

Now a one kilo ohm resistor is being tested in two kilo ohm range and the value shown is 995, which is within the 5% tolerance limit.

This is a demo of shorting the test leads for a short period before measuring values below 200 ohms to find the resistance of the leads. Shorting for long periods can drain the battery and may cause internal damage to the LCR meter and should be avoided. Resistance of the test leads should be subtracted from the measured value of low value resistors.

330 ohms resistor being tested in the two kilo ohms range of the selector switch.

Here is a 5.6 ohm resistor being tested in the 200 ohms range. Though a zero is shown before the measured value of 4.8, I have no option in this LCR meter to reduce the range below 200 ohms for higher accuracy. May be I have to use another meter with higher resolution at lower range.

Now I will proceed with testing inductances with my new LCR meter or inductance, capacitance, resistance meter. I had already posted testing capacitors and resistors with this LCR meter yesterday. Brought down the recently constructed 80m antenna which did not resonate on 80m and took out the loading coils for testing. When the antenna did not resonate on 80m, I had calculated the inductance using an online calculator and found it to be around 52 microhenries as against the 118 microhenries in the design.

As instructed by VU2XPZ today morning during a contact on amateur radio, I first shorted the lead to check the inductance of the leads. VU2XPZ had mentioned that while testing inductors, the inductance of test leads have to be checked after shorting the leads while they have to be kept open circuit for testing stray capacitance. Here you can see that the range selected is 200 microhenries, which is the lowest available in this LCR meter. The meter shows a value of -03.1. For highly accurate calculations, the inductance of the leads have to subtracted from the inductance of the coil measured as a correction. I presume that the leading zero would also mean that the selected measurement range is high for the low inductance being measured. But I have no lower range available in this LCR meter.

For a curiosity I tested it at the next higher range available, of 2 millihenry. As expected, it showed a value of -.001. So the range selected in the LCR meter is way beyond the range to be selected for testing such a small inductance as the inductance of the test leads.

Next I tested the inductance of one loading coil, and it is seen as 62 millihenry, with the range of 200 millihenry selected in the meter. That is 10 millihenries higher than the value which I had calculated. Still much below the 118 millihenry needed for the 80m loaded coil dipole antenna by VU2XTO design. The design is an upgrade of a 20m antenna and needs a lot of inductance for tuning off the extra capacitance of the shortened dipole. If it was an upgrade of a 40m antenna, lower inductance would have been enough. But I will not be able to mount such an antenna due to space constraints.

Inductance of the second loading coil for the 80m antenna was also similar, at 61.5 millihenry. I am happy that there was not much of a difference between the two hand wound coils, which was my first attempt at making loading coils by manual winding.

Just for practical learning of the concept of inductance of coils, I stretched out the coil and placed it like a slinky, the toy being used by kids. Incidentally there is also a shortened slinky dipole antenna made like this! As expected, when the coil was stretched, the inductance came down to 29.2 millihenry. If you recall the formula shown earlier, length of the coil comes in the denominator and when the length is increased for a given number of turns, inductance comes down, as is well illustrated in this simple experiment.

As winding had been loosened for the last experiment, I thought of rewinding the coil again as close as possible for me. Took a lot more time and effort than the initial winding and made the turns a bit more closer. It was rewarding to see that the inductance has gone up from 61.5 millihenry to 68.3 millihenry. I had also thought of making it a shorter multilayer winding which would increase the inductance further. I shall try that later after discussing with my friends on the band. My concern is that a multilayer coil might not dissipate heat as well as a single layer coil. Loading coils are known to heat up with higher transmission powers. My friends have had the experience of the PVC former melting with higher power and the antenna coming down in the middle of a contact, suddenly raising the SWR. I wish to thank VU3TBU who introduced me to the concept of loaded coil dipoles couple of years back. I hope to make my 80m loaded coil inverted V dipole antenna functional soon.