Round 10.5" DD 18.75 kHz (HF) coil?

[David]

I HAVE wanted a round 10.5" DD 7.5 kHz (MF) for a quite a while, BUT now a cheaper-good price on a used second-hand round 10.5" DD 18.75 kHz (HF) has come up that I am buying next month. I wonder if I will get about the same depth on silver coins as the round 10.5" DD 7.5 kHz (MF) ??

What else can anyone please tell me, being anything at all about the round 10.5" DD 18.75 kHz (HF) ?? It is not talked about very much here.

 

[Canewrap]

Hey, it really depends on the ground you're hunting in. If its good ground, the answer to your depth question would be yes. If its moderately bad ground the answer would be real close and in bad ground, no not the same.

 

[Donut]

I've had pretty good luck on small deep items with mine on the beach. I like mine on the beach because I can cover more area faster than with my 5 X 10 HF because of less overlapping.

Doug, Coloma,Mi.

 

[TURNMASTER]

David,
I would be willing to bet you will be within an inch most of the times. Might sound different though. My next will be the 10.5 MF. I seem to dig more iron with the HF coils I have. I think that may be because they are DDs, based on some of what I have read.

Let us know what you think of that coil.
Jeff

 

[Digger]

The higher frequency coils are more sensitive to lower conductive targets than the lower frequency coils. That is why those who successfully Prospect with an X-Terra do so with an 18.75 kHz coil. Gold has a lower conductivity than silver or copper, for example. Unfortunately, so does iron. I'd venture to guess that is the reason you are digging more iron with the 10.5 HF DD. Not because it is a DD coil. But because it is the higher frequency. As a side note, DD coils do not provide as accurate of TID as concentrics. Less sensitivity to iron and more accurate TID are two reasons I use the 3 kHz concentric at old farmsites. JMHO HH Randy

 

[Canewrap]

What does the higher frequency do to the ability to identify/seperate modern trash? I'm planning on hunting a site with so much old and new trash that I will have to use the HF 6" DD coil. I was hunting in there with the MF 10.5 and it was driving me nuts. Will I be able to pick out silver from other stuff at 4" - 6" with any reliability, using the 6" coil? I know there's silver there as a 20 minute hunt this past weekend produced a seated dime for a guy hunting with us and the site was occupied for something like 80 years. Granted, he was using an Explorer, but he wasn't using a small coil, just the stock DD coil.

 

[Steve(MS)]

Canewrap, for a little better understanding about why HF seems to work better in iron trash, we can step down memory lane for a moment.
Back in the early history of metal detectors, the first ones were mostly BFOs but then came the TRs.
The first TRs were high frequency, in fact they operated around 100 KHZ.
Now this was before true motion and ground balancing circuits.
These early TRs worked great in trash, in fact they can still outdo any modern detector today
provided the target is really close to the surface and mineralization isn't too bad.
The depth on these detectors were not very good, only a few inches at best.
Another thing that made these work so well was that they had just started making
DD coils along with the 100 KHZ.
So probably the reason why the 6" works well has to do with that it
is a higher frq and it is a DD coil.
Of course there is more in the equation besides Frq and DD, there is also the overall design
of a given detector/coils to take into consideration.
And yes, if you are in a very congested area, that coil can pull something out that a bigger coil
will miss but it has to be a very "busy" area, like a bed of nails.
If there are multiple targets under a stock sized coil, this coil should help pull out some goodies
but it does take practice to get the most out of it and one has to take more chances on the iffies.

 

[David]

Canewrap wrote: "Hey, it really depends on the ground you're hunting in. If its good ground, the answer to your depth question would be yes. If its moderately bad ground the answer would be real close and in bad ground, no not the same."

Thanks for that Canewrap! When you say, "in bad ground, no not the same." What do you mean ? Which coil with perform better in bad ground--high mineralized soil, the round 10.5" DD MF or HF ?

Look below, Minelab says HF coils perform better in high mineralized soils than LF coils. I always thought the opposite, that LF coils ignore iron mineralization better, but maybe Minelab is right below.


9 Concentric
3 kHz Coil
X-TERRA 70, 505 and 705 detectors
Water proof
Ideal for highly conductive targets such as silver, copper, large rings and relics. Performs well in all soils with the exception of highly mineralised soil.

9 Concentric
18.75 kHz Coil
X-TERRA 50, 70, 305, 505 and 705 detectors
Water proof
Has same properties as the 7.5kHz version, but more sensitive to low conductive targets. Also performs well when detecting for jewellery on ocean beaches.

10 x 5 Double-D
18.75 kHz Coil
X-TERRA 50, 70, 305, 505 and 705 detectors
Water resistant
This coil has great sensitivity, good ground coverage, and is easy to use in rough terrain. An ideal gold hunting coil, that also performs well for beach work.

10 Round Double-D
7.5 kHz Coil
All X-TERRA series detectors
Water resistant
For improved depth and ground coverage over the standard 9 Concentric, this is the coil to use. It also performs well in mineralised soils.

10 Round Double-D
18.75 kHz Coil
X-TERRA 50, 70, 305, 505 and 705 detectors
Water resistant
An ideal coil for beach work, and open areas, this coil offers good depth and sensitivity, and great stability in mineralised soils and beaches.

Information provided by:
Justin Adams
VP, North America and General Manager, Global Marketing
Minelab Electronics


Also thanks Doug(Donut), yes that coil is probably the best beach coil for finding gold jewellery deeper.

And thanks Jeff(TURNMASTER), yes the HF may be a little more sensitive to iron than the MF. I cannot let you know what I think of that coil until spring thaw because I live in the cold north, frozen ground, winter now.

Randy(Digger), very good input.

Steve(MS), that is an explaination I have never heard before, thanks. Makes me think. I first had a Bounty Hunter III BFO and then use to run a Compass Judge I Automatic TR back in about 1975-6. Even though the TR detectors has less depth, back then in those days we had 3 advantages, there was some but less littered with modern non-ferrous trash in the ground than now and combined with being the very first on many virgin areas to pick up coins and I had "long hair" that protected my neck(when detecting) and head better from the sun, now I have a bald spot so I have to keep covered up in the sun more. I loved the 1970's, what a riot and good times and still the best music ever, those WERE good days!

 

[Digger]

The differences in the three X-Terra coil frequencies have very little to do with target separation. Nor with TID, for that matter. Signal frequency does play a role in how well a specific target responds. But it doesn't sound like target response is the problem you are having. It sounds to me more like a target separation issue. And, the best X-Terra coil for target separation is the 6-inch DD at 18.75 kHz. The 6-inch DD coil is my choice due to the DD design and the small footprint. All DD coils will separate targets better than a comparible sized concentric coil simply due to the shape of the detection field. But something that many people overlook is the fact that adjacent targets are not always located to the right or left of the target you are after. It is just as likely that they will be toward the tip of the coil, or heel of the coil. Considering the smaller coil is analyzing less soil than a larger coil, at any one time, it has less of a chance to pass over multiple targets simultaneously. Add that to the "narrow" detection pattern of the DD coil and you have your winning combination.
I've hunted some very trashy sites with my eTrac and 705 "side by side". I've used the stock DD, the Joey, the 6-inch Excelerator and the 6 X 8 butterfly on that eTrac. A small DD is a small DD, so to speak. And when both detectors are used properly, the target separation is no better (or worse) with my eTrac than it is with the 6-inch DD on my X-Terra. The key to target separation with any detector is to slow down your search, slow down your sweep speed and cover the area from multiple directions. If there are dimes at 6 inches, I have no doubt you can find them with the 6-inch DD. Set your X-Terra up correctly and hunt the site methodically. Set the proper NC, Threshold, Sens, GB and hunt S L O W with zero discrimination and multiple tones. That's how I'd do it. JMHO HH Randy

[attachment 148679 17seateddimesfoundwiththeXterra.jpg]

 

[Digger]

in comparing how certain coils respond to mineralization, the chart you referenced is indicative of the coil design, not the frequency. DD coils, by design, are capable of neutralizing out the effects of high levels of mineralization more effectively than concentric coils.

Although the X-Terra is capable of operating in both magnetic and conductive soils, iron is not necessarily mineralization. In the case of hunting areas with hard buried pieces of iron, it is simply a low conductive target that has a propensity to mask adjacent targets. And, it's retentivity (causing phase delays that impact TID readings) proves to be challenging to many detectorists. JMHO HH Randy

 

[morelic55]

I agree with you Randy, MASKING is our worst enemy. All of the easy targets are gone in most "Worked Out" areas. I think that is why the FBS machines work so well because the sweep speed. The slower you work one the better, I've discovered that on my Safari. On the other hand, I have used the X-Terra 70 with the 10.5 DD med freq coil in iron laden spots, working slow and listening for the sweet high tone peep. I have dug Eagle Buttons at 12" and have pulled 3 to 4 square nails out of the same hole. Let's face it guys, the silver is not littering the ground like clad anymore, you have to work at it. There have been days that I have only recovered 2 or 3 good targets, but each time I go out, I learn more about my machine and how to combat target masking. Mark

 

[Frank-S]

Where can I find a DVD on how to use and set up a 705.
fjs5015@yahoo.com

 

[Canewrap]

My experience would indicate that the higher frequency doesn't handle mineralization as well. But, like Randy said the DD coils are an answer to the higher mineralization issue so both DD coils are gonna handle more mineralization well, but I think the MF coil handles it a little better than the HF. The Minelab wording you're citing is actually very carefully worded to almost make it seem as if each coil does better under most conditons, like the statement, "great stability in mineralized soils." Think about it, most ground has some mineralization, so that's not saying much. The wording that puzzles me is the one about the 3khz coil. The 3khz should handle bad ground better than any of the other concentrics. I guess they're also comparing it to the DD coils and perhaps there the configuration is more important.

 

[morelic55]

I wish I had the resources to produce a video on the 705 like a couple of guys did for the Fisher F-70 & 75. Bet they had alittle help from FT thou.........MO

Where can I find a DVD on how to use and set up a 705.
fjs5015@yahoo.com

 

[Jackpine Savage]

regardless of which coil you use proper technique is everything:

Set your X-Terra up correctly and hunt the site methodically. Set the proper NC, Threshold, Sens, GB and hunt S L O W with zero discrimination and multiple tones. That's how I'd do it. JMHO HH Randy

Happy New Year to one and all!

Tom

 

[SeniorSeeker]

When I owned my X-terra 70, I used the stock 7.5khz stock coil as well as the 5"x10" 18.75khz coil and most of the time I hunted with the DD coil. It was dead nuts on silver and the depth was better as well. Oh...and the DD coil had the added benefit of being much lighter and easier to swing all day.