Bigger Coil, More Energy?

[kac]

From what I understand the coil is matched to the detector and needs to have a certain amount of impedance so if the coil is bigger it would have the same amount of copper just spread out over a bigger area. If there is more copper then there is a chance the frequency will drop and not perform as well. Some if not most companies will have small boards in the coil with capacitors to adjust the coil to the detector.

You planning on making coils? I thought about making a better concentric for my Garrett but they have a proprietary connector that isn't available to the public.

[Chase Goldman]

19 minutes ago, kac said:

From what I understand the coil is matched to the detector and needs to have a certain amount of impedance so if the coil is bigger it would have the same amount of copper just spread out over a bigger area. If there is more copper then there is a chance the frequency will drop and not perform as well. Some if not most companies will have small boards in the coil with capacitors to adjust the coil to the detector.

You planning on making coils? I thought about making a better concentric for my Garrett but they have a proprietary connector that isn't available to the public.

Not necessarily, impedance is not just resistance (which is determined by copper wire diameter and length) but also the diameter of the coil introduces inductive reactance which also "impedes" electrical current so these are balanced to enable the coil to match the output circuitry of the detector.  VLF detectors are simply inductive balance machines where the two loops (a transmit loop and a receive loop) in the coil be they coaxial (typically concentric but can also be coaxial elliptical loops) or double-D overlapping Tx and Receive loops are perfectly balanced to produce a null signal until a metallic target is introduced into the balanced field area causing a phase imbalance that is then detected.  As Steve and others have suggested, there is perhaps some difference in the power put into the larger diameter transmit coils to produce a larger/deeper detection field but the field strength/density is lower primarily because of the larger area of the coil, not the power put into it.

 

 

[kac]

So when companies put in small circuits with caps on them is that to adjust or boost the power on the coil so it better balances with the detector?

[Chase Goldman]

Yes those are typically just passive impedance matching circuits.  But sometimes they are also more sophisticated active "smart" circuits with programmable chips that may tell the detector how to reconfigure to accommodate the specific coil characteristics.  Detector manufacturers don't typically like to give much public insight or tech details into these special smart coil designs.