Sensitivity and the 10.5" coils?

[brissietex]

Hi all...

I have a couple of quick questions for everyone with the 10.5" coils....

Do you have to turn down the sensitivity when using any of the 10.5" coils as compared with the 6" and 9" coils?
How is the falsing on the 10.5" HF coil compared with the lower freqs?

I've been told by Minelab that multi-freqs have a tendency to handle the sensitivity better when using the larger coils than single freq machines like the X-Terra. I can believe this since the multi-freq machines can handle variable ground conditions better than single freq machines and as the coil gets bigger, more variable ground conditions can be experienced under the coil. This is likely the primary reason why there is no bigger coils than 10.5" for the X-Terra. You would need to drop the sensitivity to a level where it would negate the usefulness of the larger coil. If anyone in the know tell me if my line of thinking is correct or at least on course?

cheers...Keith

 

[B.T]

G,day Tex. I used to own the 10.5 medium freq coil and due to it being noisy in bad ground found that it had to be turned down so low on the sens to be workable that it was in effect taking a step backwards. I was able to run the 18.75kHz in the same ground on average 8 or so sens points higher (give or take). It also was open web and was a curse in thick scrub. I hated it very quickly on the goldfields. I have never liked open web coils full stop. I find them noisier than enclosed coils in bad ground(possibly because of less shielding) the whole base of an enclosed coil is shielded whereas an open web naturally is not and clumsy as a Roo with one leg in the bush.
I dont doubt that they are great for beaches , coin and relic hunting but you try to locate a small bit of gold on an open web coil and believe me you will soon be cursing the damn thing and ruing the day you bought it.

 

[rifleman]

I live in Arizona, and in coin hunting (not in the gold areas) I can run my 10.5 MF DD coil at 26 to 30 in most cases. I usually drop it to 26 or 27, but have not had trouble with falsing. I have not tried it in the gold bearing areas. The same holds true for my 6" HF DD coil. I suppose it depends on the ground mineralization in your part of the country.
I use the 10.5 MF coil for all of my coin and relic hunting unless I get into an area with a lot of junk. Then I'll switch to the 6" DD.

Good hunting, John K

 

[rwsnc]

I live in NC and, for the longest time, ran my sensitivity up around 20 - 25, but I kept getting all kinds of unstable readings.

FInally, I started running it around 15 - 18. That resulted in a MAJOR improvement in stability.


Regardless of what Minelab (or anybody else) tells you, experiment until you find what works for you.

 

[I a thr]

I agree, sensitivity is based on your ground mineralization. Living in Iowa my ground is great and have no problem with falsing when changing coils. I can run 28 - 30 most all of the time on any coil. However, It it not a major adjustment to change as a matter of hitting the mode button and the + or -. Very simple, takes about 2 secs. I do lower the sensitivity a couple notches if working corn stubble field as will get a bit of falsing if bumping old corn stalks with the big coil, but still 28 is about as low as I ever need to go.
Bill

 

[TomB]

Keith...I live and hunt in southwest Virginia where the mineralization is very high. I have noticed that when I auto ground balance I need to lower my sensitivity to 20 +or- a couple. However when I use the tracking feature I can raise the sensitivity to 28 or 30. Just recently I recovered a 1906 Barber dime, standing on its end at 8 1/2", in highly mineralized soil using the tracking feature and sensitivity at 30. I was using the 10.5 DD 7.5KHz coil on the X-70.

TomB

 

[brissietex]

Thanks to all who have replied...

Given that I mainly would be using the 10.5" on the beach (saltwater), would I be better off with a 7.5 or 18.75? I have the 5x10 18.75 and love it but would love a wee bit more coverage and depth on the beach. 12" would be nicer but I think the Minelab tech was correct in stating that single freq machines have more difficulty with larger coils in regards to sensitivity.

I am heading stateside in a few weeks so I may pick up a new coil for my XT-70 when I am over there. At AUD225 here, the coil is a wee bit too expensive for me to justify here while I can get one for around AUD170 in the shops in the States.

cheers...Keith