Smaller coils were the better choice way back when a smaller-size coil was standard on many detectors. By 'smaller-size' I include coils that are round, or close to round shaped, and 5" to 6½" in diameter. A 'mid-sized' coil,
to me, would be a round-shaped coil of about 7" in diameter, or an elliptically-shaped coil of about 5X9½. In a given year I might mount and use a larger-size coil, that could be a 'standard' size offered in recent years like 9", 10" or 11" or so in diameter, perhaps 2 to 4 times ....
in a year! The exception to that would be if I was searching a wide-open, sparse-target beach where, a lighter-weight coil of about 11" works okay for me.
I've preferred smaller-size search coils since late '71, and as the years have progressed the desired coins have been getting fewer and tougher to find, and that makes most sites a higher percentage of trash to deal with. Smaller coils work in and around debris much better to help find the partially-masked keepers. Brush, rocks, building rubble and other obstacles also need to be maneuvered around for best success.
Foildigger said:
Monte, would you consider 2-3 targets under a 7” coil a “densely littered” environment?
A site can either be relatively 'clean' and not have any type of interfering metal trash near desired targets, or a site can be 'littered.' ANY unwanted target, better known as 'trash', that is in close proximity to a desired target is some form of 'litter' than can interfere with a desired target's response. The more litter present, the more good-target masking we have to deal with. So Yes, having 2-3 targets
"under a 7" coil" could be considered a "densely littered" environment. But we have to give the situation even more consideration that simply a numbers count.
A.. Consider the unwanted, masking trash targets:
• How large are those 2 to 3 trash-target pieces?
• What is their shape?
• How thick are the unwanted targets?
• What type of metal are the trash targets made of?
• How close are the trash pieces to the desired target?
• Are the 2 or 3 trash targets closer to the search coil, on the same plane, or deeper than the desired targets you're searching for?
• Is the trash all on the same plane, or is some shallower and some deeper compared with the good-target's depth?
B.. Also consider the desired-targets description:
• Is the good target you encounter smaller-size, comparable-size, or larger-sized than the nearby trash?
• What is the thickness and shape of the good target you encountered?
• Considering the shape, what is the good target's orientation to the search coil?
• Is the good target a lower-conductivity object, a high-conductivity object, or is it somewhere mid-range in conductivity?
C.. Describe the search coil in use:
• Specific diameter and physical shape?
• Search coil type, such as Concentric or Double-D?
• Remember, search coil 'dynamics' or 'behavior' is influenced by the above, as well as the size and placement of the internal Transmit and Receive windings. Equally important is the metal detector's design, transmit power, and overall circuitry design and performance with specific search coils.
D.. The specific metal detector circuitry design, and its strengths and weaknesses in performance:
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(This is a combination of how one or more engineers designed the detector to perform, and equally important the ability or skill of the detector operator to: Learn and understand what each function can and can't do; How to select the best settings for a particular task; Know the different search modes and how to select the best one for the site; Use the best search techniques.)[/size]
• Know that 'separation' or 'quick-response' are frequently used terms that do not always prove out in actual applications. Some detectors can be very quick-response designs and hit desired targets in a very close orientation, however, if you add a nail or some other unwanted object to the target mix, those very same detectors do not handle Discrimination well to also recover-and-respond to nearby accepted targets.
• Some makes and models require a more 'controlled' search coil sweep speed. They might call for a hesitation before reversing the sweep direction. They might not handle a faster sweep well, especially in a highly mineralized ground environment, or by-design they require a little brisker coil sweep speed to achieve improved performance. Some circuitry designs are very forgiving and will allow a good range of sweep speed and provide very good performance.
• Some makes and models have a terrible time trying to reject unwanted ferrous trash, and especially rusty tin.
• Some models provide a tighter visual Target ID that can lock-on reasonably well to mid-depth or deeper targets, while other units from the same manufacturer tend to have a jumpier or more inconsistent numeric VDI response even where there are no trash targets nearby.
Above all, know and remember this: There is no such thing as a 'perfect' metal detector or coil and a savvy, Avid detectorist will have an outfit of at least two metal detectors to complement each other and provide a selection to best handle a variety of hunt site challenges. I've owned at least two detectors since late '71, and for the bulk of the time since about '73 or so, I have maintained a Detector Outfit of at least 4 detectors and other times anywhere from 6 to a dozen. No, I didn't need them all, and some have been duplicate models, like I have a few of now, so I can just keep a different search coil on all models to have them handy to grab-and-go. In my current Regular-Use Detector Team are 6 models I use. Of them, 3 are dedicated more for Relic Hunting the more remote and very iron contaminated old sites, and 3 are assigned duty for more urban Coin Hunting applications. I have duplicates / back-ups of at least three of these models, and I also have some detectors that are in my den and are my Specialty-Use models.
Foildigger said:
More back ground:
I’m mostly hunting for coins or jewelry and am excited at the prospect of finding coins from the 1800’s or earlier on the yard of an old farm house that my property borders. I’ve only spent a couple hours there so far and my finds are limited to what I believe is an old winter horse shoe, a 1913 penny, various clad coins, nails and other trash.
I wish you the best of success. Sine the early '80s I have concentrated the bulk of my detecting efforts on older locations that had their main activity from about 1850 through the Depression Era. I have found an impressive amount of old coins, trade tokens, and small artifacts.. That said, I can also say I found the most from about '83 through '98, and while I still "get my share" I have to put in more time and effort because it's getting tougher the more the places have been hunted.
Foildigger said:
With multiple items under a 7” coil, it’s difficult for me to pinpoint the good one from all the iron around it. To me, it’s like trying to pinpoint a needle point.
Yes indeed. Hunting in any very trashy site can be difficult and it takes patience combined with us doing all we can on our part. One thing we have to do is realize that if a site isn't clean and free of near-target masking, then each of us faces the same difficulty. We have to work the location slowly and methodically in order to get the coil over all the targets, then do our best to master the skills of listening to the audio responses and trying to isolate the good ones from the bad. For the most part, TID is just about useless when there are a lot of targets crowding the electromagnetic field. It will not be accurate, nor will it lock on very well. We have to live with it and get the best information we can, both visually and audibly, then recover all that we suspect might be good. in tiume we can learn to handle things better.
Foildigger said:
Settings with the 7” coil have been 14 and 20 frequencies, 3, 4 and 5 tone, 80-89 gain.
With the Anfibio Multi I use 14 kHz about 90% of the time, and 20 kHz in some very dense iron littered sites at other times. I use the 7" Concentric coil for at least 80% or more of my general purpose hunting, and the 5" DD coil gets mounted for most of the rest of my work in trashier locations. The only search modes I use are: 3-Tone for most day-to-day hunting in trashier conditions; 2-Tone for places where the primary junk encountered is nails or other wire-iron debris; and Deep for more open areas with very little good-target masking; Iron Audio Volume is on '1', or '2' if it is a noisier environment; and my saved, start-up Sensitivity is '99' in 3-Tone and '95' in 2-Tone and Deep modes. I adjust from there as desired
Foildigger said:
For me, so far, the 7” concentric doesn’t hit as hard as the 11” DD does over a good target. I don’t know if it just doesn’t like the soil/rock combination here or if it’s me and lack of expertise.
It might just be needing more time afield with the 7" Concentric coil. I had one for the Racer 2, the Impact, the Multi-Kruzer, and as my preferred daily-use coil on the Anfibio Multi. I never had an issue with any of the 7" coils I had, and it hits very solid and performs quite well for me.
Foildigger said:
I have developed enough skill to pinpoint and retrieve a coin with a blunted screw driver, as long as it’s within 4” of the surface and not under a rock, but if it’s surrounded by iron, and/or rocks, my percentages decline abruptly!
In urban, Coin Hunting settings I usually recover 95% of my targets to about 4" or even 5" using a rounded-off screwdriver. It sure makes it quick and keeps things clean.
Foildigger said:
My magnetic meter is often half or more up the scale (when I think to check it) but at other times no reading at all. When I ground balance, the readings are usually in the 70-80’s and the soil is very rocky. Does either a concentric or DD coil design have any benefit over the other in this soil?
I maybe glance at the MMI two or three times a year and that's it. GB'ing in rocky conditions can sometimes take a little more effort, if bad ground. Yes, the coil 'type' might have some goods or bads, but honestly I haven't had any issues with coil selection. Today, I have four models with a Concentric mounted and two with a Double-D, and I'll be hunting mostly very mineralized locations, mostly around old gold mining camps and ghost towns.
Foildigger said:
I haven’t taken the time to make a test garden (assuming I can find a clean area!) for testing the 7” concentric, as I only have clad coins to use and I know there has got to be older coins on the neighboring property.
Thank you
The way I look at it, the world is full of a "Test Garden" that's been naturally lost and is waiting for us to find it. Besides, no sense trying to find a clean area to plant a garden if most the places you are going to search are trashy, and it would take a year or two for everything to settle and get compacted and be 'natural' for the Test Garden to work well. And not all the targets we are looking or are going to be found in the same orientation that we would selectively bury them, anyway. Nor in the same mineralization.
Nope, I just go hunt and learn each detector as I go and that seems to work just fine.
Monte
