Metal Detecting Q&A

[Steve-B]

Hi David

Thanks for the welcome. (who said anything about being human, I'm a detectorist)

I really do look forward to answering all the usual questions as best I can and hopefully dispelling some of the misconceptions some may have as well as some of the concerns, some of the explainations may also sit uncomfortably with you archaeological sensibilities, but they will be honst answers all the same, for example, detectorists use a facility on their machines called discrimination,which basically allows us to reject small ferrous signals such as nails. From a detecting point of view, small ferrous targets such as these can mask other more intesting signals, they also tend to be irregular,
totally unrecognisable 'lumps' of rust and in some areas are so numerous that it would just be physically impossible to extract them all (although some do).

However from an archaeological point of view (and I am guessing here as I am not one), I imagine that a scatter of nails may be indicative of some kind of archaeology...

Being a bit of an adventurous guy, I also look forward to exploring new areas for discussion and ideas for cooperation.

Ok, to kick off I will give a brief overview on the subject of coils as David has mentioned them.

You can actually tell a lot about a detectorist from the size of his coil (steady, its not true what they say about detectorists with big coils having.....), by this I mean that all metal detector are retailed with the stock coil fitted, this is the coil that the manufacturer feels is best suited for general purpose use.

However, there are various sized after sales coils that have been developedfor some machines that have specific purposes, which for the sake of general discussion fall into two main uses.

1/ Smaller Coils:

Normally a smaller coil would be fitted for use on a site where there is either restricted acess for a larger coil, for example in a stubble field or where there is a high level of iron infestation.

Obviously the smaller size of the coil willenable the use to detect in between the rows of stubble far more easily than having to 'wade' through it with the larger coil, which can be extremely tiring.

In respect of iron infested sites, if you can for a moment imagine three mettallic targets roughly in a triangular setting, two of the targets are ferrous and one is for example a small copper alloy buckle. OK, now if I was to search over this with a large coil the two ferrous targets would mask the non ferrous buckle. However if I went over the same area with the smaller coil I would have the chance of finding the buckle amongst the iron.... simple?...well not really, I would experience a loss of depth capabilites and I would also have to serach at a much slower rate in these conditions... this is due to the recovery speed of the detector in hand (which varies from machine to machine.

The recovery rate is basicaly the time it takes for the detector to 'recover'from 'seeing'one target to the next, this is part of the reason why it pays to detect slowly when sraching in ferrous infected sites...you may well have rejected the ferrous, but the machine is still 'seeing' it and ;recovering'from it. ( I will cover the topic of discrimination later).

There are other uses for a smaller search coilsuch as in beach detecting, rock pools, amongst undergrowth etc.. but the above covers the general use.

2/ Larger Coils

Larger coils are normally fitted when the user has the need for more ground coverage and increased depth.

Ground coverage is fairly self explanatory, some of the fields we detect on these days are extremely large, and search time limited. Another application is for use when beach detecting, again, time is of the essence when detecting at low tide, so a larger coil will cover more ground faster.

OK depth, there are times when in the field when the stock coil does not give adequate depth capabilities (or it is imagined that it doesnt) in reality, this may be due to depth of top soil inland and depth of sand on the beach (this is a whole other subject as the depth of sand can vary from one tide to the next..sometimes dramatically).The user may be part of a group searching (under licence) for WWII aircraft, or (contraversial, I know) the user may be searching on pasture where the tagets may well have settled deeper.

A larger coil will therefore give extra ground coverage and some extra depth, bearing in mind that even the largest coil will only realistically increase depth by a percentage, it doent follow that if it twice the size it willgo twice as deep.

There are draw backs to using a larger coil, the first is that it will be unusable in areas of high ferrous content, or where a larger number of non ferrous targets present themselves. Secondly in some cases there may be a loss of sensitivity to some smaller targets.

There are a lot of urban myths surrounding the actual depth performance of metal detectors, many of them spread by detectorists who also exaggerate the sizes of other things... (fish for example)

Well there you are, coil sizes in a nutshell... I can see that this may suggest some questions to you, please feel to ask away...