inductance meter question

[m23585]

Hi guys, noobish question here. As I'm going to try to build a coil for either Troy X3 or White's Classic IIISL I have, I bought an inductance meter. Same model as on picture below:


It came without any manual.

Now, I have tested 7" X3 coil with it and gave me results for Tx: 1.15mH and Rx: 6.95mH as I remember. When I tested White's BM950 coil i could only have a result of Rx: 35mH. From browsing on this forum I know that Tx should be 540uH (which is equal to 0.54mH). So, is that inductance meter not good enough? Thanks

[WM6]

It is good enough for your needs, dont worry.
You do not need space precision, but comparable and repeatable results in first line.
It is more important how you tune/balance your coil, than absolute precision in L measurements.

[m23585]

Yes, but how can I make a Tx coil if can't measure 540uH? I thought this is more important, to have inductances as close to factory settings as possible.

[WM6]

It is more important what are tolerances of your instrument than number of digits after decimal point.

In general 0.54mH is the same value as 540uH.

You can (and have to) always correct TX frequency using proper C in TX LC tank circuit (don't forget that capacitors have tolerances too).

Put your energy in good balancing of coil and don't worry, if your TX L is somewhere between 530 and 550uH. Use proper C in TX LC tank circuit to reach right TX frequency.

For VLF/IB measurement you can get more proper results with cheaper Chinese L-meter with working frequency at 10kHz, than with high precise and expensive L-meter workig at say 300kHz of measurement frequency (self parasitic capacitance of coil do not imply to results so much at VLF working frequency of L-meter, so we can take such results as more real for our VLF/IB needs)..

[m23585]

I see, will have to rely on coil calculator then. Thanks WM6

Regards

Greg

[WM6]

I see, will have to rely on coil calculator then.

Yes it can be very usefull, especially if you don't have frequency meter (for TX frequency measurement).

You have RLC meter, so in combination with coil calculator (and LC resonance online calculator) you should to measure your capacitor used in TX LC tank circuit too. Sometimes parts tolerances are to high to rely on nominal value marked on its only.