Frequency question.

[bk]

Can anyone explain what the advantage of multiple frequency detectors have on depth and I.D.?
I always thought having a frequency adjustment on a detector would allow you to change frequencies in order to minimize interference from power sources and or other detectors in close proximity.
From what I understand, detecting with a multiple frequency detector, you are able to get better discrimination at greater depths. I know that the high end Minelabs use this and I also believe Fisher has a patent on a Fourier system that they first incorporated on the CZ models.
I am looking to try a Minelab X-Tera 70 detector. This detector requires additional coils that operate at different frequencies rather than having them operate in one detector using the same coil.
What is the advantage to that?

 

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[Willy]

I've done a lot of side-by-side testing of single and multifrequency detectors and haven't seen any depth advantage when using a multifrequency detector where I hunt. The mineralisation is pretty extreme here and even a copper penny is apt. to read as iron at more than 6", often less. I have an Xterra70 with stock and HF DD coils and it goes as deep as any MF detectors I've used. One area it has them beat, however, is sensitivity to tiny low conductive targets. I'd say that it's comparable in sensitivity to the Minlab XT18000 (running at 20 KHz) that I had a few years ago. This rocks since I also nugget hunt. ...Willy.

 

[bk]

Willy,
Thanks for your input!
I was reading your discussions in the Minlab post after I had already posted this question.
Good information!

 

[U.K. Brian]

The X-Terra advantage is to Minelab in parting you from more money. Apart from the cost of a range of coils there is also the time factor in swapping them over.
A better solution would have been one coil and switching between frequencies at the control box. You could then compare how a target responds to a different frequency instantly.
Compass did it years ago on some of their Challenger series.
Re multifrequency I agree with Willy. I have multifrequency machines but they don't get used in land, only for really contaminated beach sites and preferably I would use a P.I. if possible.

 

[bk]

Thanks to all of you for the advice.
Brian, That is kind of what I thought too. It would seem to me that having the frequency adjustments on the control box makes more sense than having to change coils all the time. Our soil conditions here are pretty neutral.

 

[Willy]

I kinda wish that the X70 had a switch-selectable frequency control, but wishes and fishes and whatnot. One thing I noticed when I had my XT18000 was that it didn't seem to be as good on tiny gold as one would expect, given the 60KHz freq option. This kinda jives with what I've read on the AMDS site. Maybe there's a (slight?) tradeoff involved in having a coil handling multiple frequencies. This could become a major factor when prospecting since even the slightest reduction in sensitivity can influence results in a negative manner. Even though it's expensive to buy different coils to switch frequencies on the XTerra70, it seems to be effective. So far, with the HF DD coil, it is showing perfomance/sensitivity that rivals (and in some cases exceeds) dedicated gold detectors. One question I have for those carping about the expense of buying coils to switch frequencies: How many other (current) detectors on the market offer the ability to change freqs.? If the detector only had a single operating freq. people would generally still buy it and be happy with its' performance. I will admit that the units are a bit pricey.. but they ARE made in Australia. Detectors made in the USA are said to be rather expensive in Australia; shipping and duties will get ya every time. ..Willy.