Coil size vs freq vs target size?

Im on a bit of a rambling here about target size vs coil size vs freq, im not mega tech minded but get the basics ok.
Most info suggests Low khz for deep large targets, high hkz for small less deep.

My 5 inch coil in 8hkz see's a 20mm hammered silver( small as a dime but half the thickness/weight) deeper in the ground than in 18khz, from this i read with coil size being small at 5" it reads the 20mm coin as a large target.
My 12x10 coil hits the same coin deeper in 18khz than 8khz, again i read from this the large coil obviously see's the coin as a small target.
So what would be the change over point in coil size vs khz for this known size target, what about an even bigger coil for deeper small stuff at 18khz? But then most coil manufacturers don't recommend big 15" coils for stuff as small? but i need a biggish coil to cover the big pastures aaaagggghhhhh heads getting pickled lol
On machines that are reported as 'deep' like nexus standard, aka, etc i haven't come across and vids of them pulling out such targets as above at any great depth, (there may be some in a foreign language i don't understand) and most of them seem to favour the lower freq and larger targets, is there really such a thing as a deep machine for 20mm or smaller coins?



Edited 3 time(s). Last edit at 09/14/2016 12:47PM by ghound.

For information, how does a hammered silver compare to a US dime conductivity (meter reading) wise?

____________________________________________________________________________________________________________
In a democracy, it is difficult to win fellow citizens over to your own side, or to build public support to remedy injustices that remain all too real when you fundamentally misunderstand how they see the world.

Small hammered coins in the ground come in around the foil on my machine with a really tight TID

ghound Wrote:
-------------------------------------------------------
> Small hammered coins in the ground come in around
> the foil on my machine with a really tight TID

I totally agree with you about silver hammered coins come in about the foil range,that is why its very important that we dont discriminate foil out as we would loose one of our most sought after targets,also suprisingly enough gold coins can come down very near the iron range,also this is why we its best advisable not too use a high amount of discrimination.

One thing also is that TID readings are OK of a fashion and reliable upto say about the 7'' depth region,then after that a TID can be very un-reliable,and as our coinage can be deeper due to the vast history that we have going back 1000s of years 'Audio' is king all day long and so much more reliable at depth,very important in my mind to have a decent set of headphones that block out external noise so that one can hear those very deep whispers in the audio threshold that could and can be a stunning find that could be missed if just relying on a TID reading.Just my personal opinion of course.

Regarding your original question about freq and coil sizes etc,its often been regarded as 12Khz as being a happy medium freq wise that will still hit targets like what 18khz does and also offer the depth advantage that a lower freq offers on a VLF machine,regarding coils sizes although not set in stone the 15'' coil size is about the most efficient maximum size and larger coils are just heavier and dont really offer any major advantage.Its all down too 'physics' or what ever the boffins call it.

PI machines are slightly different as they can operate a larger coil but of course they in them self have problems of discrimination,so its basically as clear as mud lol

If one of the smarter guys on here could workout a formula for the best coil size + khz for particular size targets in say 3 types of soils, low, med, high mineralisation it would really add to the forums knowledge base.

Hi there ghound
Here is a tip to clear out some mist...
We started out in -94 with a Fisher 1210 and a 8" coil with some sort of success. When gearing up via F 1266 and 1236 to the Quicksilver
we trimmed down the size of the coil to 5" and got a really versatile detector with good depth and superb separating abilities in our type of soil
and our type of man made thrash .
Here in Norway we have the same sort of hammereds you mention - they are thin,small,very lightweight and with variable silver content up through the centuries.....
We still have the big standard coils for our detectors ,but we seldom use them...
The Fisher Quicksilver used 5-and 15khz transmitted simultanously , and this combo have worked well for us for many years now.
Hope this was to some help

trond



Edited 2 time(s). Last edit at 09/15/2016 10:01AM by trond.

trond Wrote:
-------------------------------------------------------
> Hi there ghound
> Here is a tip to clear out some mist...
> We started out in -94 with a Fisher 1210 and a 8"
> coil with some sort of success. When gearing up
> via F 1266 and 1236 to the Quicksilver
> we trimmed down the size of the coil to 5" and
> got a really versatile detector with good depth
> and superb separating abilities in our type of
> soil
> and our type of man made thrash .
> Here in Norway we have the same sort of hammereds
> you mention - they are thin,small,very lightweight
> and with variable silver content up through the
> centuries.....
> We still have the big standard coils for our
> detectors ,but we seldom use them...
>
> Hope this was to some help
>
> trond

So basically what you are saying is that you have reduced your everyday use coil size down to much smaller than stock size and only use larger coils for specific site use,is that correct in how i interpret it ??

Opps what happened there /

John.



Edited 1 time(s). Last edit at 10/09/2016 06:29PM by auminesweeper.

Junk and Disorderly

You read me correctly, but for most of our detecting nowadays Eva and I will use the 14khz MXT with Jimmy Sierra`s Hotfoot coil -
small yet big enough - 2 1/4" x 9 1/4"
This combo works well,- it is ultralight, sharp cutting and with ok depth for our type of hunting and in our type of soil.

trond



Edited 1 time(s). Last edit at 09/16/2016 07:13AM by trond.

trond Wrote:
-------------------------------------------------------
> Junk and Disorderly
>
> You read me correctly, but for most of our
> detecting nowadays Eva and I will use the 14khz
> MXT with Jimmy Sierra`s Hotfoot coil -
> small yet big enough - 2 1/4" x 9 1/4"
> This combo works well,- it is ultralight, sharp
> cutting and with ok depth for our type of hunting
> and in our type of soil.
>
> trond

Trond,thanks for clarifying that,never used a Hotfoot coil but i do use a Jimmy Sierra Hotshot coil on my DFX which is a 12'' Concentric coil and is for its size as light as a feather and can swing that combination all day long,the 18'' version of the coil that you use is as rare as anything and command absolutely crazy high prices that is if you can find one that is.

Must admit recently i have started reducing my everyday use coil size down mainly due to the weight as i have a wrist problem as a result of a accident,but can still swing a big coil rig if i use a full GPX harness.

Thanks for the replys folks, i love soaking up the info!
I have been playing about with coils and freq so as im more informed of my setup to match ground conditions vs targets.

So on a hammered silver penny mentioned earlier this is where im at, only air tests but it's a guide.

5 inch coil best in 8khz
9 inch coil see's it about equal depth in 8 or 18khz
12x10 and bigger see's it best in 18khz and is deeper but not by much and good/bad soil conditions would dictate if a bigger coil would be of any advantage.

The 5" coil is the stand out coil in 8khz, it gets down to silly depths and is very impressive, just wish i had more hunting ground to suit it.

My detector isn't the high gain type John but it loses very little depth from it's air test in my med to high ground compared to the likes of the higher gain racer which it trumps for depth, it will however still see your hand in 18khz.

ghound Wrote:
-------------------------------------------------------
> Thanks for the replys folks, i love soaking up the
> info!
> I have been playing about with coils and freq so
> as im more informed of my setup to match ground
> conditions vs targets.
>
> So on a hammered silver penny mentioned earlier
> this is where im at, only air tests but it's a
> guide.
>
> 5 inch coil best in 8khz
> 9 inch coil see's it about equal depth in 8 or
> 18khz
> 12x10 and bigger see's it best in 18khz and is
> deeper but not by much and good/bad soil
> conditions would dictate if a bigger coil would be
> of any advantage.
>
> The 5" coil is the stand out coil in 8khz, it gets
> down to silly depths and is very impressive, just
> wish i had more hunting ground to suit it.
>
> My detector isn't the high gain type John but it
> loses very little depth from it's air test in my
> med to high ground compared to the likes of the
> higher gain racer which it trumps for depth, it
> will however still see your hand in 18khz.

If those 5" and 9" coils are Concentrics they will go a lot deeper and be more sensitive than their DD Counterparts, So if not then I would try and find out if your machine can run Concentric Coils and if it can I would be giving them a Go.

By using Concentric Coils you will dig a lot less Iron and be able to use much lower Disc settings by as much as 75% which means you will Dig a lot more good targets that you would normally walk over by using a DD,

Hope this helps.

John.,

It's all about target signal amplitude vs ground signal amplitude.

And then the frequency, coil shape, coil size, coil design, ground mineralisation makes things muddy.
Muddy because you can just about buy any configuration you imagine and suddenly you're on a winner.
A winner for your ground, your finds, your hunting style.

The only way to find the coil you "need" is go out and try,... the finds pouch is the best discriminator.
Because no matter how much you read, discuss, etc. etc. buy and try are the only foolproof method.

Therefor I can really relate to John's "Auminesweeper's" statement, that a detector that only runs concentric or DD is only half a detector.
My favourite VLF's are the X-terra 705, F75 Ltd because I can choose and pick the wright coil,... better said I can trial and error the wright coil.

Don't own the F75 Ltd any more, simply because my hunting style is All Metal and check in Disc. When I can get away with it. It has bagged me lots of finds
other people have simply walked over. Also the X-terra tracks the ground and in varying mineral,.. that's a real bonus feature.

John has a grounded tried and true love for the MXT.
You could say Johnb has the same feelings about his 705.

ghound Wrote:
-------------------------------------------------------
> Im on a bit of a rambling here about target size
> vs coil size vs freq, im not mega tech minded but
> get the basics ok.
> Most info suggests Low khz for deep large targets,
> high hkz for small less deep.
>
> My 5 inch coil in 8hkz see's a 20mm hammered
> silver( small as a dime but half the
> thickness/weight) deeper in the ground than in
> 18khz, from this i read with coil size being small
> at 5" it reads the 20mm coin as a large target.
> My 12x10 coil hits the same coin deeper in 18khz
> than 8khz, again i read from this the large coil
> obviously see's the coin as a small target.
> So what would be the change over point in coil
> size vs khz for this known size target, what about
> an even bigger coil for deeper small stuff at
> 18khz? But then most coil manufacturers don't
> recommend big 15" coils for stuff as small? but i
> need a biggish coil to cover the big pastures
> aaaagggghhhhh heads getting pickled lol
> On machines that are reported as 'deep' like nexus
> standard, aka, etc i haven't come across and vids
> of them pulling out such targets as above at any
> great depth, (there may be some in a foreign
> language i don't understand) and most of them seem
> to favour the lower freq and larger targets, is
> there really such a thing as a deep machine for
> 20mm or smaller coins?

HH
Johnb

scoopjohnb Wrote:
-------------------------------------------------------
> It's all about target signal amplitude vs ground
> signal amplitude.
>
> And then the frequency, coil shape, coil size,
> coil design, ground mineralisation makes things
> muddy.
> Muddy because you can just about buy any
> configuration you imagine and suddenly you're on a
> winner.
> A winner for your ground, your finds, your hunting
> style.
>
> The only way to find the coil you "need" is go out
> and try,... the finds pouch is the best
> discriminator.
> Because no matter how much you read, discuss, etc.
> etc. buy and try are the only foolproof method.
>
> Therefor I can really relate to John's
> "Auminesweeper's" statement, that a detector that
> only runs concentric or DD is only half a
> detector.
> My favourite VLF's are the X-terra 705, F75 Ltd
> because I can choose and pick the wright coil,...
> better said I can trial and error the wright
> coil.
>
> Don't own the F75 Ltd any more, simply because my
> hunting style is All Metal and check in Disc. When
> I can get away with it. It has bagged me lots of
> finds
> other people have simply walked over. Also the
> X-terra tracks the ground and in varying
> mineral,.. that's a real bonus feature.
>
> John has a grounded tried and true love for the
> MXT.
> You could say Johnb has the same feelings about
> his 705.

I have to agree,



Edited 3 time(s). Last edit at 10/09/2016 06:34PM by auminesweeper.