why

[Skippy]

Where to start....
* All this talk about Q factors is related to TX oscillators, not RX circuits, so don't concern yourself with Q of RX coils.
* Your Deus is not like other single-freq machines, so don't expect Q factors to be 'normal' at any of the operating frequencies. This Q concern is also irrelevant to Minelab BBS/FBS, Fisher CZ's, White's DFX/ VX3 / V3 and any other forced TX drive machines.
*That LCR calculator appears to be mathematically thorough. Yes, put capacitor resistance= Zero, I guess it's less than 0.5 Ohms in reality.
*Resonant frequency isn't just determined by L and C, if you have damping (Resistance) then the res freq drops. That calculator should show it, if you play around with some numbers. Try Q=100, then drop it to 15, then to 5 and you'll see.
*Have a look in an electronics textbook, or online for detailed explanations of the workings of damped harmonic circuits, forced resonance etc.

[Henrikras]

Thanks again.. That explains a lot.

[golfnut]

I dint know much about the ins and outs of this,,

Gut feel is,

if Rx coil is narrow band ( hi Q ) then it its phase centre is liable to shift about more.




if Rx coil is broadband ( lo Q ) then its phase response is less likely to hop about causing trouble.

The down side is a large R value will add noise to the preamp. S

[Henrikras]

Yeah like many things in life... One step forward and two step backward.

[golfnut]

with some aussie designs, the Tx freq jumps around to say, 3 different ones. The Coils on those are not resonant.

Anyone tried this approach for an experiment?

IE multiple Tx freqs, No resonance and I presume no Rx resonance either? Dont want to copy anything or infringe.

But broadband stuff is good at eradicating noise - in that you can extract signals from below the noise floor in other systems like CDMA for example.

S

[golfnut]

I beleive that we may miss a trick with the way our coil bundles are made.


In a radio or a power environment you would never bundle turns. I think the best performance is when turns sit side by side and in neat layered structure.

I dont have an explanation for why this is better,I can recall lecturer talking about it being better but no detail.


I want to make a Tx RX coil pair , bundled one Versus a Neat one and see if one 'Picks up" better than the other with a consistant Target pass on a Jig of some sort.

[Henrikras]

I made a picture. My guess is that Fig.1 will be the best, less turbulens ! But properly not much different.
A good Winding machine with torque will allso be a needed tool, to make a good coil.
Henrik.

[golfnut]

I would think fig 2

[Koala]

I made a picture. My guess is that Fig.1 will be the best, less turbulens ! But properly not much different.
A good Winding machine with torque will allso be a needed tool, to make a good coil.
Henrik.

Could not tell you which is best but

Seen some YouTube videos of coils being wound both Garrett and Tesoro use Fig2

Also seen a cross section of a SEF that was a Fig 2 also

[Skippy]

If you are machine-winding, and using self-bond wire, then you really HAVE to make the windings square or rectangular in cross-section, with hexagonal close-packed layering (like a bees honeycomb).
I think for home-built coils, rigidity is important. Coils need to be tightly bound, and preferably varnished / lacquered / resin-impregnated etc. I don't think for a DD coil the shape profile (round / square / rectangular) is important. But for a concentric, a square / rectangular RX coil with the TX bucking coil wound directly over it is a good thing, as it allows the touching windings to both be 'cold', minimising capacitive coupling between TX and RX.

[Henrikras]

Maybee some usefull in this... http://info.ee.surrey.ac.uk/Workshop...air_coils.html
My english is not good enough to understand everything.. Yes FIG 2 that must be the best.

[Qiaozhi]

Maximum inductance for a given length of wire requires a square cross-section. This is the construction assumed by Brook's equation, which is used in the coil calculator at the top of the Coils Forum.

[Koala]

some good information on coil building here

Things like " Painting a shield on an irregular surface can cause excessive noise in the detector " I have not seen before and polypropylene vs. polyester although it concludes there is no performance difference