Phase Measurement and Magnetic Susceptibility

[Jim Hemmingway]

Here's a link if anyone is interested in a prospecting related read...

http://forum.treasurenet.com/index.p...,384948.0.html

Jim.

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[scott565]

Thanks Jim for another very informative article.
One question:
Across detectors, how important is the output power of the transmit coil?
It would seem to play a role, especially in conditions where the trash or ground effects are not similar in conductivity to the available targets. In lots of conditions, it may not matter as the ground effects would just get amplified by a stronger impulse.
I have never seen any discussion of this, but I kind of liken it to shining a flashlight at objects - the less intense the light, the fewer items will be made visible by it.
-Scott

[Jim Hemmingway]

Hi Scott…I don’t know how important the transmit power is beyond what is available with our current crop of VLF detectors. It seems to me that if further increasing the transmit power would produce significant or practically useful depth improvements, then the manufacturers would have done it already. But that’s guesswork on my part.

Then too, some modern VLF units offer TX adjustments or a 'transmit boost' function to improve depth. I have no firsthand experience to know how much these features improve depth .

As to how much extra power would needed to generate a meaningful depth increase. Here’s a response from a White’s engineer I found on a different forum …

“TX Boost: This feature boosts the TX voltage from 10V to 30V. The age-old claim that the FCC limits detector TX power IS A MYTH. What happens when you turn on TX Boost? Well, you get only a very slight increase in depth, with a major drain on batteries. This is the REAL reason that detector TX power is limited, and why the deepest detectors require a motorcycle battery. I rarely use TX Boost... but in one heavily hunted field, I found a very silent area, turned it on, and started getting faint deep signals. So it can be useful in certain situations." You may have to adjust the gain if you boost the TX but it all just depends on the situation.”

Perhaps someone with expertise on the subject will enlighten us further. I’ve asked your question elsewhere and may have more information to post in a few days…depending on what I learn…but no promises...

Jim.

[scott565]

Thanks, Jim.
I really appreciate your insights and knowledge - even your guess work

Do you think it would be meaningful to compare power outputs across manufacturers of machines similar in coil size and frequency?
I know a lot goes into the receiving technology, but if the power is not there, is it game over?

HH!
-Scott

Hi Scott…I don’t know how important the transmit power is beyond what is available with our current crop of VLF detectors. It seems to me that if further increasing the transmit power would produce significant or practically useful depth improvements, then the manufacturers would have done it already. But that’s guesswork on my part.

Then too, some modern VLF units offer TX adjustments or a 'transmit boost' function to improve depth. I have no firsthand experience to know how much these features improve depth .

As to how much extra power would needed to generate a meaningful depth increase. Here’s a response from a White’s engineer I found on a different forum …

“TX Boost: This feature boosts the TX voltage from 10V to 30V. The age-old claim that the FCC limits detector TX power IS A MYTH. What happens when you turn on TX Boost? Well, you get only a very slight increase in depth, with a major drain on batteries. This is the REAL reason that detector TX power is limited, and why the deepest detectors require a motorcycle battery. I rarely use TX Boost... but in one heavily hunted field, I found a very silent area, turned it on, and started getting faint deep signals. So it can be useful in certain situations." You may have to adjust the gain if you boost the TX but it all just depends on the situation.”

Perhaps someone with expertise on the subject will enlighten us further. I’ve asked your question elsewhere and may have more information to post in a few days…depending on what I learn…but no promises...

Jim.

[Jim Hemmingway]

Hi Scott…

By all means have a look at various detector transmit outputs if it will satisfy your curiosity. At the end of the day IMO it would be more meaningful to compare the overall performance between the units of interest to you on known targets in the area you search. I’d suggest a side-by-side comparison over some buried targets to see what suits your preferences and works best for your intended use. If that is not possible, you can chat with others in your area…for example drop into the local shop and see what they suggest and / or join a club and see what others are doing.

Any decision-making should consider the nugget size that generally exists in an area, will you be searching known mining areas loaded with iron trash, and the levels of magnetic iron minerals you may encounter…not to mention hotrocks. Select a detector that offers the features best suited to deal with those parameters and that you feel comfortable using. Hope that helps…

Jim.

[Jim Hemmingway]

Scott...

Here’s a link I’ve come across that helps to address your question about transmit power. There is an interesting reference to the MXT in the last paragraph providing a comparison between MXT with an increased voltage across the coil relative to the DFX when operating at 15 kHz only.

I suggest you read the replies within this thread as the writer does a correction further down…

Jim.

http://jb-ms.com/Carlsforum/Oct31-2007/1190584476.html

[Jim Hemmingway]

Scott...here's another link you'll find interesting...Carl really spells it out clearly...

http://forum.treasurenet.com/index.p...,349475.0.html

Jim.

[Matt (CA)]

Hey JIM, this is a terrific article about VLF operation and ground minerals. Really liked the part about testing rocks. This sort of information is not easy to find so thanks for putting it together. Good luck up north, looks like we'll see you there again this year.

[Jim Hemmingway]

Thanks Matt, looking forward to seeing you again. I'll be camped nearby at Loon Lake.

Jim.

[Lanny in AB]

Jim--you're the king of Tech--you really know your stuff, and it's very obvious you've invested a ton of time to get to know it. Thanks for being so unselfish in sharing it.

All the best,

Lanny

[Jim Hemmingway]

Hi Lanny, geez thanks a million for commenting on this article. It was a lot of fun to do the write-up and its a subject that I have a profound interest in learning more about. Such information has enhanced my prospecting skills resulting in more finds in recent years.

Years ago, there was no internet when I started out. Reliable information was difficult to find. So, I figured I'd make a point of writing a few articles to provide information to newcomers. This may well be the last of such posts for some time but it has fulfilled a nagging desire to do it for a very long time...and hey...I'm not getting any younger these days...

All the best Lanny, its good to hear from you again

Jim.