Coil calculations

[Daves]

Yes, a detector that transmits 18kHz will also receive 18kHz. But if you resonate the RX coil, you should not resonate it at 18kHz as the phase stability will be poor. Most detectors resonate the RX coil somewhat above or below the TX frequency for good phase linearity. If you don't resonate the RX coil, then this is not a concern.

How can I perform RX and TX coil calculations?
(Number of turns, wire thickness, resonance capacity, etc.)

[Davor]

There are coil calculators, but their accuracy is not stellar. You may expect error range of over 20% because packing density greatly influences the final inductance.
Better option is to go with a "coil recipe" and measurement. You may decide to make a coil with precise inductance, or you may go with whatever you get and adjust at capacitors side. Manufactured coils usually have a few capacitors in them, so draw your own conclusions.
You'll find some elaborate coils described as having various magical properties, but when you see how un-special is a coil of Deus, your fuzzy sentiments about magical coils will anticlimactically drop off.
Seek coil data at geotech1.com (not forum)

[pito]

Don't waste time on calculations.
Tx- 150T , 0.5mm wire, Rx - 300T, 0.2 - 0.3 mm wire.
Good for most of the coil sizes and shapes.

[Daves]

Don't waste time on calculations.
Tx- 150T , 0.5mm wire, Rx - 300T, 0.2 - 0.3 mm wire.
Good for most of the coil sizes and shapes.

I've never heard of such a number of coil turns, it seems a little scary.

[Daves]

There are coil calculators, but their accuracy is not stellar. You may expect error range of over 20% because packing density greatly influences the final inductance.
Better option is to go with a "coil recipe" and measurement. You may decide to make a coil with precise inductance, or you may go with whatever you get and adjust at capacitors side. Manufactured coils usually have a few capacitors in them, so draw your own conclusions.
You'll find some elaborate coils described as having various magical properties, but when you see how un-special is a coil of Deus, your fuzzy sentiments about magical coils will anticlimactically drop off.
Seek coil data at geotech1.com (not forum)

What are we looking for in search coils?
What should be the l-c-r values in TX, that is, what are the optimum values? likewise in rx?

For example, low omage in TX, high omage in Rx etc. What are the examples of ideal coils and commercial projects?

[pito]

I've never heard of such a number of coil turns, it seems a little scary.

Because you stick with 50 years old design.





cola can 90 cm

[Davor]

Ideal coils would have very small resistance, but in real life such coils would be very heavy. Everything else is a compromise.
Say, archeologists would use carts to zig-zag the fields with their equipment, and therefore their coils may be heavy.

As for consequence of high resistance, you have more losses in Tx, and you have more thermal noise in Rx. The best opamps for front end have noise-equivalent resistance of about 40 ohms, so if your Rx coil has more than that, you may as well use a less expensive opamp. But because you may screw up noise in so many ways, you'll hardly be able to witness any difference even with a coil of 100 ohms.

[Carl-NC]

I've moved this to a new thread.

What are we looking for in search coils?
What should be the l-c-r values in TX, that is, what are the optimum values? likewise in rx?

For example, low omage in TX, high omage in Rx etc. What are the examples of ideal coils and commercial projects?

The coil and the detector are designed together, and coils vary widely depending on the detector design. The lowest TX-L I've seen is around 100uH, the highest above 10mH. I've seen an RX coils from 250uH - 30mH. Whether capacitance matters depends on the design. On the TX coil we usually shoot for 0 ohms, on the RX coil it usually (but not always) matters less.

In short: "It depends."