9-inch coil vs the 6-inch coil (concentric)

[X-Terra70_TreasureHunter]

How much more dirt does a 9" concentric coil process
compaired to a 6" concentric coil.

Formula for volume of a cone shaped object:
(1/3) * π<pie symbol> * r² * h = Volume
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6" coil
.3333 * 3.1416 * 9 * 6 = 56.54314152 Cu. Inches
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9" coil
.3333 * 3.1416 * 20.25 * 9 = 190.83311478 Cu. Inches
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Total Volumes:

9" coil 6" coil
190.83311478 / 56.54314152 = 3.75 times as much "dirt"
to be processed at any one time.

So by useing a smaller coil you chances of having trash in
a plug w/ a good target decrease, because of amount of
dirt being processed at a time.

This results in the odds of a 9-inch concentric coil having both
trash and treasure under the coil simultaneously to be 3.375
times greater than when using the 6-inch.

According to George Payne, the father of today's metal
detector technology, a silver dime responds best to a
frequency of 2.7 kHz. Nickels and gold jewelry respond
best around 16.5 kHz. All other US coins are most
responsive to frequencies under 10 kHz. Gold nuggets are
better served with a frequency of 20 kHz or faster. But
again, I've found silver, copper and gold with each of the
eight X-Terra coils.


A 3 kHz coil sends an electromagnetic field into the ground 3,000 times per second
A 7.5 kHz coil sends an electromagnetic field into the ground 7,500 times per second
A 18.75 kHz coil sends an electromagnetic field into the ground 18,750 times per second

Pattens Mode:
Yes, using discrimination can and will result in target blanking.
Trash + treasure at the same time = Blanking. If you are using
the factory notch rejection on Pattern 2, you are rejecting over
half (15 out of 28) of the possible notch segments (phase shift)
that any target might provide. Since you indicate you are hunting
in a high trash area, you are "blanking out" the tone more than
half of the time, when in Pattern 2. Slowing your sweep speed
will help reduce the effects of target blanking. But using a smaller
coil, preferably DD, will greatly improve your success.

Thanks to Digger USA and others who have posted about the X-terra
Series everyone will learn about this machine.

Dave

 

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[goldeagle]

thanks for the info DAVE i have been learning the xterra 505 with 7.5hz and i have been getting alot of pennies,while the 7.5 gives me good hits i get mixed signals on say the 1700;s penny or british farthing hit i got yesterday was not a solid hit jumping between 33-42 on my id,i almost asumed trash so the wife started to dig 4-6inches down there she was old georegvous cant make out the date yet,anyhow like you said even if it sounds like junk i have to check them out.same goes for a silver pence found last week 6 inches down but mixed tones,i will get back to you when i try out the dd in 7.5hz.from what i am learning is to fine tune each individual coils it will take some time but it sure beets work.lol

 

[X-Terra70_TreasureHunter]

Goldeagle to decide which coil to use, you need to concider
the following things.
______________________________________________________
#1 is the area you are going to be hunting littered full of trash.
#2 which mode are you going to hunt in.
#2a Prospecting mode
#2b All Metal
#2c Discremenation mode 1, 2 or 3 for the x-terra70
If i am coin shooting i set up both the Prospecting & AM modes
so i can listen to the creshendo of the target in prospecting
mode then flip over to AM to check the VDI of the target and
also see if there is any trash next to the target.
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Some times you will get a good hit just a (2") few inches
down in pin pointing mode then barely move the coil and
get a trash hit like (7") down after coming out of pin point
mode thats the reason i like the 10.5" DD 7.5kHz &
6" DD 18.75kHz coils better than the stock coils because
you can separate the good and bad targets a lot easier
than you can w/ a concentric coil.
_______________________________________________________
If you are working a place that you know for shure has very
little trash use the 9" 3kHz concentric coil....it is a Go getter
for deep silver and copper targets.
________________________________________________________
If your going to hunt a farely new Tot Lot that you do not think
will have old coins in it and are only after Clad and Jewelery
try useing the 10'' x 5'' DD 18.75kHz Elliptical coil, yes you will be
processing more dirt at a time than you will w/ the 6" DD
18.75 kHz coil.
_________________________________________________________
Now this is my prefferance for the over lapping of a coil

Concentric coils overlap by: 1/2 the Diameter
DD coils overlap by: 1/3 the Diameter
_________________________________________________________
And yes always wear head phones w/ a metal detector to
drown out the background noises so you can hear those faint
tones from a deep target like the Grey Ghost Originals, Rat Phones,
Black Widows, Sunray Pro Golds...your better headphones will
have a limiter switch on them so the you can hear faint target's
and shallow targets do not blow out your ear drums.
_________________________________________________________




DAVE

 

[goldeagle]

thanks for all the help,i am trying to keep up here!anyhow this is a learning curve,i have found copper down to 7 inches with stock 9in 7.5hz,but in the parks i am using the d.d. 7.5hz and haveing hard time pinpointing i have a crappie i think v-4 pinpointer from kellyco, might have to upgrade.but i got the d.d. 7.5 to hunt near a revolutionary battlefield to help get some depth i have found a silver pence and a british copper with the stock was trying to see if i can get silver and maybe relics from that time,i start in all metal then if i get mixed signals i goto the dicr. mode say 1 or 2 to see if i can tell if its trash?am i doing this right?

 

[X-Terra70_TreasureHunter]

Hi goldeagle here are instuctions for pin pointing
w/ that 7.5kHz DD coil.

It's a new ball game when it comes to pin pointing
w/ a DD coil you have to find the sweet spot on the
coil where the signal pegs out the meter in pin pointing
mode, side to side and front to back, on my coil the
minelab logo sticker is right on target.



Video:


Dave

 

[Trackerman]

Hmm wonder i have the stock 7.5klhz 9inch concentric coil and think its a great coil. So far i have found 3 rings and plenty of coins with it in a short time owning my xterra 305 wich by the way is a great detector. I also own the 9inch 18.75klhz concentric coil and like the 7.5klhz stock coil better. It seems as though the 7.5 hits coins a bit better and as far as jewlry ive found more rings with the 7.5klhz and nicer finds. So the question is i wonder does it really matter if the coil is 15klhz or higher to be a good jewlry and coin coil doubt it. Any ideas