Inductance and resistance tolerance

[m23585]

From your experience guys, how do you think what are acceptable tolerances for inductance and resistance when building a coil, compared to factory ones? Example: could we assume that when designing a coil, inductance could be +- 20% of factory one and similar for resistance? Thanks

Regards

Greg

[Silver Dollar]

When buying parts like caps and inductors they are sold with a wide variance (unless you pay
extra for tighter tolerance). I've seen +50% -100% listed for some electrolitic caps, others
are 20% or less.

I have experianced a marked difference between detectors of the same model (lower end ones) so
would assume it is tough (or expensive) to hold tolerances on these things...

The coils are a big variable. It doesn't take much to change the recieved signal. I can see temperature
variations in the coils I build. They generally work better with some warm up time!

[m23585]

Ok, I wounded my first two coils. I followed calculations from coil calculator and online wire resistance calculator, which gave me such results: Tx- 1.07mH, 4.8ohm; Rx- 6.53mH, 36.8ohm. These results are very close, to results taken from factory coil, so I was happy with that. Coils are shielded with aluminum tape and wrapped with electrical tape. Results I have are as follows: Tx- 0.98mH, 5.4ohm; Rx- 6.04mH, 41.8ohm. Hopefully these differences are not an issue. But my question is, if the copper wire I used is not so good quality maybe? I mean resistance difference is not I would expect (based on calculations given from calculator). So, what do you think, does it have anything with wire quality?

[Silver Dollar]

You should be fine! The transmitter likes to have lower resistance and you have 5 ohms.
The receiver will match the input opamp better with higher resistance so is not that critical.
Which detector are you building?

[m23585]

Well, trying to build DD coil for Troy Shadow X3 Cheers

[Silver Dollar]

Ahh nice rig! A DD should work great on it! Just take your time with the nulling.

[m23585]

I was able to buy original 5x10" Troy coil. Tx: 1.1mH, 3.9ohm; Rx: 6.55mH, 47ohm. So, actually I'm not so far away with those parameters in my home made DD coil.