X-Terra 30 Coil Advise

[59aardvarks]

Hello to all, I've just signed up the the forum this morning. There looks to be loads to useful information and discussions on the site, I'm sure that this be be a useful site to visit.


I'm quite new to this game and would appreciate some advice on coils.

I have a X-Terra 30 with the standard 9" concentric coil. I understand that this coil effectively produces a cone shaped search area into the soil. So the deeper it goes the smaller the area searched.

I believe I'm right in saying the 30 can use other coils as long as they are 7.5 kHz.

I also understand that a 10 by 5 DD coil is available. I've read that this coil produces a cone shaped search area (and goes deeper). Hence this produces a much larger search volume.

1. Are all my understandings above correct?
2. Are there any disadvantages to a DD search coil?


P.S. I'd be happy for any dealers to PM me prices on the DD coil. Please including shipping charges to the UK.

 

[OldeTymer]

Welcome 59aardvarks,

A DD coil produces more of a windshield wiper blade type of shape, as opposed to the cone shape of a concentric coil. The advantage of a DD is the ability to get better target separation as the "blade" can "see" though the target mix better, and is less affected by mineralization since it "sees" less of the ground surface.

The disadvantage is that a concentric coil will usually allow for better discrimination, but needs to be overlapped more for each sweep to minimize the loss of targets at depth. A concentric can, generally, search a little deeper than a DD of the same size, but the sweeps need to be overlapped more because of the cone shaped signal.

I suggest you do a search in this forum for post by "Digger". He has written extensively about his field work with the various X-Terra models, and knows of what he speaks.

Hope this is helpful.

Good hunting,
OldeTymer

 

[argyle]

your detecting with the Xterra 30, slightly, and with a bit better separation over the stock concentric coil aardvark, and all the future 7.5khz coils will suit.
It is a bit of theoretical nonsense however that the concentric produces a cone and the DD a blade that travels all the way into the ground, as the DD utilises a practical cone as well.
You have a straight centre hot spot on the 10.5"DD of around three inches, much similar to the stock coils rounded hotspot centre, and it is at this small amount of ground coverage that you hit on a deep target, and a deep target can be as shallow as just a few inches in some ground types.
The DD coil on an xterra will produce less falseing on ground where you get it, when compared to the stock coil and while noticable, the difference is only very slight as the TID units do not behave exactly like the conventional VLF's when comparing coils.
In regards to depth, I am buggered if I can see any real difference between the 9" and 10.5", only the 10.5" being slighty better in hotter ground and maybe a bees whisker deeper (probably just feels that way) and a better coil for me in all types of my hunting, and can say that I love it and will never put a concentric back on the xterra.

The 10x5 DD coil is at 18khz and will not fit the 30, only the 50 and 70. I doubt they will make one in 7.5khz. It's in what is called an elliptical shape and the depth difference between it and an 10" round in 7.5khz in depth is only very slight in these xterra units.

You have a really good detector in the set ground balanced Xterra 30. I have all three and prefer the 30. Once you work out how to cut down a bit on falseing they are much faster to set up and work the display's than the other two units. You will often read of ground balance being of the utmost importance to obtaining depth and to cut down on falseing in detecting aardvark, and while I have been a ground balance nut for twenty odd years I must say that the pre-set on the xterra 30 gives it no disadvantage over the 50 and 70. I detect from some of the heaviest mineralization in the world all the way through to dry sand and muddy creek banks and the 30 holds it's own with the 50 and 70. The 70 I use for a different type of detecting than the other two.
None of the xterra's get any real depth in real heavy ground, but that is just a part of the whole digital TID thingy and not a blame on the units themselves.

Hope this helps at all.

PS.....all metal all the time, solid tones and solid numbers and a mixture of the two, numbers not jumping more than one incretion, and ride your sensitivity button like you would a ground balance knob.

 

[59aardvarks]

Thanks to both argyle and Olde Tymer for your comments.

Obviously I can't actually change coils so I'll be sticking with the concentric

 

[argyle]

n/t

 

[Mick in Dubbo]

Great post Argyle. I found it quite informative.
Mick Evans.

 

[59aardvarks]

I get confused easily. So the 10.5 is available in 7.5khz.

I'm struggling to visualise the shapes of the search area's of the concentric and DD coils. Can any body try to describe the searched shapes in nice simply terms?
Does one of the coils have a greater searched volume, especially at the deeper part of the search area?



To summarise the other points made;

The 10.5 doesn't really give any extra depth (maybe just a touch),
The separation is better on the 10.5,

 

[Shenandoah Digger]

Two D's, back to back, search area on the straight part of the D's. I don't think the depth is better, but the coverage may be. I like the coil that comes with it. A smaller coil to search in trash would come in handy. John

 

[Welsh Neil]

Greetings Aardvark

At last someone else from the UK who uses an X-Terra 30! I have been using the machine for 4 months and I am really pleased with it. The only problems I have experienced involve the headphone socket going down and the machine turning itself off. Both of these are currently being resolved by Minelab for me. I imagine as mine was an early UK batch, you won't have the same difficulties.

Anyway - a word of advice dig the lowtones and down to an 8 signal and all the way up to 44. I have had a really low tone flashing between 4 & 8 that turned out to be a Roman follis coin of Maximinus and a low 8 that turned out to be 22ct gold and emerald ring. On both of these items the identity number changed to what you would expect when swept on the surface. Other finds include silver coins, Roman bronze key, Celtic bits, Medieval pot leg, lead toys, etc. As a turn on and go you can not fault the machine. If it says theres metal there then there is simple as that.

[attachment 42884 RomankeyandCoin.jpg]
Cheers
Neil

 

[Jackpine Savage]

These illustrations are from ML's website for the SD, GP series of nugget detectors. A concentric coils search field is nearly identical to the mono loop pattern pictured and as you can see is actually bowl shaped rather than cone shaped as is quite often mistakenly posted.

HH
Tom<p><center> Mono or Concentric map<br>[attachment 42900 Coil-Mapping-mono.jpg]<p>DD coil map<br>[attachment 42901 Coil-Mapping-DD.jpg]

 

[59aardvarks]

Many thanks, that is brilliant. A picture speak a thousand words and all that.

 

[Digger]

I'm surprised you heard the low tone audio response on targets reading 8, all the way up to 44. Low tones on the X-30 are programmed to be heard only when your target is identified as being in ferrous notch segment -4. All positive target ID's are conductive and are designed to produce either a medium tone or a high tone. Medium tone targets are from +4 through +28, with high tones representing +32 through +44. I'd be interested to hear if you were running in all metal mode or Pattern with all notches accepted. Thanks. HH Randy

 

[Tinfoil]

n/t

 

[Bavaria Mike]

I also got a DD with my 70. Thanks for the info and HH, Mike