Is there really an advantage to a DD coil????

[robertj298]

I've read about the advantage of using a DD coil such as what came on my new E-TRAC but this makes me wonder. Here is a simple illustration showing the advantage in trashy areas but...why does my coil give a signal along the left or right edge of the coil without a target not even passing close to the middle?

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[Sever]

If you are able correctly to understand VERY LONG machine translation. I can quote one post on this subject from a Russian-speaking forum. This message seems to me very full.
Quote beginning

For beginners about Mono and DD coils

ice message" 09 Feb 2010, 15:37:41
Let's try to consider in general these two types of coils for acquaintance
In the theory a difference between mono and DD as you understand in construct and tactics technical characteristics. at mono coils the beam goes a cone from all plane, and at DD as though an edge through its center, from here...

Mono pluses in comparison with DD:
It is more than depth at cone peak, that is 10" mono coils on the center takes just as bigger 12" DD, but to edges of the coil depth at Mono sharply falls
Better purpose identification, that is any party to the purpose the will be identical. But we won't forget that if the purpose masking by ferrous metal, it is necessary to scan it from all directions, it isn't dependent on coil type
Better purpose centering at detection of exact location of a find

The DD pluses in comparison with Mono:
Stable depth on all length of the coil, that is it is more stable - the productive area of scanning, it is less than admissions
Stabler work and depth on the mineralized soil

General minus Mono and DD:
At increase in the size of the coil more than about 14 inches start worsening identification and sensitivity to the small purposes, coil unstable work raises

It everything in the theory, well and in practice we have full mess connected most likely with the concept "successful model" and "not successful model" of the coil of a line of firm of the producer. On this practician and responses of colleagues you shouldn't ignore, but also laws of physics who didn't cancel

I will try to bring the IMHO:

for search on the platforms littered by iron it is better to choose small 6" the Mono coil
for investigation and primary search on a platform it is necessary 10DD or 12 of DD
for a deep doborka (hunting behind that remained from those who was earlier) of the empire on rather pure place it is necessary big Mono or DD, the size from 12 inches to 15”
If you don't dig on war, be not fond of big "wheels"

As there is a distinction of coils in a form - round and an ellipse. Ellipse it is more convenient on a dense grass, in a bush, between trees. In certain cases smaller number of the purposes in coil capture

Well here in brief something like this, certainly there are many subtleties in certain conditions of search and personal preferences, for example in a postscoring, play not the last role, but I think that I described the general rules. If is what to add - that guys will add me

The detector X-Terra 705 can function
on various transmission frequencies with coils,
compatible to the VFLEX technology.

Concentric standard frequency (7.5 kHz)
This frequency is suitable for search more
main objectives on the main types of the soil. On
these the coil is available a sticker of M.

Concentric Low frequency (3kHz)
This frequency is suitable for search more
the large purposes at a bigger depth, and coins with
high conductivity (majority of coins
The USA), such coils reject signals better
from ferrous metals. On them there is a sticker
L.

Concentric High frequency (18.75 kHz)
This frequency is suitable for search more
the small purposes at a surface, gold
nuggets and the purposes with low conductivity
(stamping coins, small jewelry). On
these the coil is available H sticker

Double D (7.5 kHz and 18.75 KHZ)
By means of these coils the detector is better
adjusts balance of soil. They it is ideal
are suitable for search of gold nuggets in
to the the strongly mineralized soil or on
beaches with magnetitovy sand
Quote end
If something isn't clear - please ask

[Gold Maven]

So...your question is why you get a signal before your coil is directly over the target?

Is this really a problem? Turning your sensitivity down might help, but if you are hunting trashy areas, a small coil is what you need.

Good Luck.

[Coldshuz]

I think the OP is having the same issue I seem to be having with my Safari. I'll get a hit on say the right side of the coil, then as the center passes over it, it disappears. Swinging back towards the left side of the coil, the same thing however, further to the left of the original hit. Attempting to pinpoint with the coil, its as if the coil is between two targets. I've spent up to 30 mins on an area like this where nothing seems to change even after digging about a 3 foot circle and down up to 15". Usually fustrastion sets in and I fill in the hole and move on. Living close to KellyCo, I have considered taking it in for a check up to see if it's the machine.

[Sovereignelite]

I have always had some trouble pinpointing with DD coils. Hoping when it warms up I can finally get enough practice in to be proficient (eventually)

[robertj298]

So...your question is why you get a signal before your coil is directly over the target?

Is this really a problem? Turning your sensitivity down might help, but if you are hunting trashy areas, a small coil is what you need.

Good Luck.

No my problem is the DD coil is supposed to be better in trashy areas because of the narrow beam that shoots down the center of the coil from front to back. If you look at the illustration you see the nail on the edge of the coil not being in that beam. It doesn't really seem to work that way. My coil will pick up a nail on the very edge of the coil.

[Treasure_Hunter]

What detector are you using and what coil, what size?

I have been using DD coils for 5 years and love them. I use Minelabs so I don't have to be concerned about Iron and mine do give me signal on targets off the edge of the coil, I consider that a bonus.

You may want a smaller coil, hard to say since don't know size your using....

A good way to learn to pinpoint with DD is tape a coin or couple coins on a large piece of cardboard turn it over and flip it on ground where you have removed all signals and pinpoint the coins, try it with a nail and coin and see the difference, play with it with different targets, the larger the cardboard the better.

[robertj298]

What detector are you using and what coil, what size?

I have been using DD coils for 5 years and love them. I use Minelabs so I don't have to be concerned about Iron and mine do give me signal on targets off the edge of the coil, I consider that a bonus.

You may want a smaller coil, hard to say since don't know size your using....

A good way to learn to pinpoint with DD is tape a coin or couple coins on a large piece of cardboard turn it over and flip it on ground where you have removed all signals and pinpoint the coins, try it with a nail and coin and see the difference, play with it with different targets, the larger the cardboard the better.

I'm using the stock 11" pro coil that comes on the E-TRAC. I have no problem pinpointing with it, it is just the fact that it doesn't really have that narrow field of detection that it's advertised to have that kind of bothers me.

[Bart@Big Boys Hobbies]

I'm using the stock 11" pro coil that comes on the E-TRAC. I have no problem pinpointing with it, it is just the fact that it doesn't really have that narrow field of detection that it's advertised to have that kind of bothers me.

What your experiencing is true with all DD coils, not just Minelabs. If the target is shallow it will hit 3 times. Once for each side of the coil. Deeper targets will get one solid signal for the center of the coil. It is a GREAT way for a quick fast and dirty way to gauge depth.

[robertj298]

What your experiencing is true with all DD coils, not just Minelabs. If the target is shallow it will hit 3 times. Once for each side of the coil. Deeper targets will get one solid signal for the center of the coil. It is a GREAT way for a quick fast and dirty way to gauge depth.

My point is not that it isn't a great way to gauge depth or isn't a good coil, my point is it doesn't seem to have the narrow field of depth shown in the ad. I pictured, showing a nail not being detected at the same time as a coin is.

[Longhair]

Soil conditions, target content, and speciffic coil design all play roles in what you're describing. Wet ground will conduct better. Iron and zinc leach into the soil. And some coils are designed to be wider or narrower patterns.
There's likely nothing wrong with the coil. If there was, it would either false all over the place or simply not function at all.

And FWIW, that illustration is just theoretical and generic.

[bevo]

my eureka pinpoints like a sonofa.

[Jason in Enid]

No my problem is the DD coil is supposed to be better in trashy areas because of the narrow beam that shoots down the center of the coil from front to back. If you look at the illustration you see the nail on the edge of the coil not being in that beam. It doesn't really seem to work that way. My coil will pick up a nail on the very edge of the coil.

No, no, no! You are confusing the theoretical response zone with the reality. Very shallow targets will hit on the edges and the middle.

Here is the truth....

DD coils are made from two overlapping rings. Each ring puts out a donut shaped EM field. This give the strongest response down the center but doesn't mean it's the only spot you can recieve a target response.

DD and concentric coils both have advantages and disadvantages. They are tools. Pick the one that best fits your needs for that hunt.

[robertj298]

No, no, no! You are confusing the theoretical response zone with the reality. Very shallow targets will hit on the edges and the middle.

Here is the truth....

DD coils are made from two overlapping rings. Each ring puts out a donut shaped EM field. This give the strongest response down the center but doesn't mean it's the only spot you can recieve a target response.

DD and concentric coils both have advantages and disadvantages. They are tools. Pick the one that best fits your needs for that hunt.

Thats what I thought. The posted theoretical response zone is really false and misleading making one believe that a shallow nail will not be in the response zone while a coin in the middle will be.

[Jason in Enid]

That's because it would be far to confusing for most customers if the manufacturers tried to explain the realities of detector coil EM fields. Simple graphics which are MOSTLY true are "good enough".

[robertj298]

That's because it would be far to confusing for most customers if the manufacturers tried to explain the realities of detector coil EM fields. Simple graphics which are MOSTLY true are "good enough".

I would agree with you if they hadn't stuck the nail in the picture to make it look like it was out of the detection field.

[Jason in Enid]

At the relative depth the picture shows, it most likely would be.

[halfstep]

The dd coil can be confusing at times and takes a little learning. It will seperate targets better and won't mask targets very much. So you will hear multiple sounds from multiple targets and this can be hard to pinpoint one of the targets from the others. Since the coil has to be moving in order to read targets, it can make it difficult to locate targets in multiple hit zones. Try hunting some cleaner areas until you understand it better and then work your way into trashy areas slowly. I can swing through a lot of trash and not get confused and find the good targets. When it is trashy, I mainly rely on sound. I have a safari and it seems the sounds recover faster than the display does. This can be confusing if you are trying to get a ID on the target. Since the sounds recover fast from target to target, I learned to trust my ears. The dd coil is great for finding multiple targets and covers the ground better. I really like it once I got use to it.

[Jackalope]

The DD is an inductively balanced coil arrangement. There is a Tx coil on one side and a Rx coil on the other. Where they overlap is the most "sensitive" area and responds to the deepest and smallest targets. The Tx coil emits the EM field only. The Rx coil picks up the Tx field only if the balance is disturbed. Only two things can unbalance the coil: a metal that produces strong enough eddies or iron metal that produces a temporary magnetic alignment to the field.

Either an iron object (nail) or metal object (coin) near the surface (must be near due to the poorer sensitivity outside the center-line), can have a strong enough secondary field to unbalance the coil and drive a voltage in the Rx coil. However, the strongest return signal will be down the center-line of the coil.

This is why smaller DD coils are used in iron ridden sites - to narrow the response area. While the depth is somewhat less, it is likely that a larger coil's EM field is mostly being redirected by the iron anyway (any metal with permeability > 1 will bend field lines through the object). The concentric coil's EM field is also going to suffer, probably more, it will loose depth more rapidly than the DD.

Advertisers are not in the business of detailing the reality of detecting ... or explaining coil design limitations. How would that help drive sales? Drawings are often idealized and often intentionally misleading (like the 27 simultaneous arrows going into the ground - which are really innumerably weak harmonics of the primary. Only three freqs are actually used for anything despite that implied by the arrows). How about a pot of gold under the ground with the detector overhead - know anyone who ever uncovered a chest of gold or a pile of gold coins? Yeah, but you might be led to believe it was your destiny if you bought that brand detector based on the colorful advertisement.

If people knew how much time and effort is needed to learn and properly apply detecting techniques in the real-world, the detector market would take a huge dive.

[Longhair]

Drawings are often idealized and often intentionally misleading (like the 27 simultaneous arrows going into the ground - which are really innumerably weak harmonics of the primary. Only three freqs are actually used for anything despite that implied by the arrows).

Your accessment of how FBS (and FBS2) works are not quite correct. If you'd like to read the best explanation of how it really works, check out this post on findmall.
About that multi-frequency Thang.