Conjecture welcome!

[rentasquid]

I noticed after the introduction of the last two detectors from Tesoro, that they have changed their direction of technology. The last three detectors have basically used their HOT technology, hunting around 15mHz. My impression, is that this frequency is better for hunting in the lower conductance range in targets, i.e. iron, gold, nickel and such. And, the lower frequencies (below 10) provide a better response at silver hunting. Is this correct in thought? So, I'm wondering why Tesoro is moving to those frequencies? Any ideas, thoughts and/or conjecturing?

J.

 

[JB(MS)]

"The target signal returned to the receive coil can be thought of as composed of two components, one we call x and one we call r. The polarity of the x signal (its direction) tells us if the target is ferrous or non-ferrous. The r signal has only one polarity. Also, the ratio of the x and r signal tells us the target’s phase. In addition, the signal magnitude (which relates to sensitivity) of both x and r are a function of operating frequency.

The x and r target signals are frequency dependent and obey very predictable characteristics when the operating frequency changes. We know that the x component decreases as the operating frequency decreases. Above a certain frequency the x component reaches a maximum. The r component acts differently. It is maximum at one particular frequency and decreases if you go up or down in frequency. We call the special frequency at which the r signal is maximum, the target’s “-3db” frequency. It also turns out that at the -3db frequency the x signal is one-half of its maximum value. This special frequency is unique to each target and is different for different targets.

The higher the conductivity of the target the higher will be the targets -3db frequency. Conversely, the lower the conductivity the lower the -3db frequency. The -3db frequency of the high conductivity target will also make the r signal peak at a high frequency, normally well above the operating frequency of the VLF detector. This will make the high conductivity target have lower sensitivity on the VLF detector because the r signal amplitude drops if we are significantly below the -3db frequency. Simply put, maximum sensitivity on a VLF detector would be if we position the operating frequency directly at the target's -3db frequency. For example, a dime and penny have a -3db frequency of about 2.7KHz. This is where their r signal peaks and would be the best frequency for picking them up using a VLF detector. However, a silver dollar has a -3db frequency of 800Hz. Nickels, on the other hand, have a -3db frequency where its r peaks at about 17KHz. Targets like thin rings and fine gold are higher still. Clearly there is no one frequency that is best for all these targets. The best you can do is have an operating frequency that is a compromise.

As you can see the ideal frequency for each target is different. In addition, for best performance the operating frequency to read x should be different from the frequency to read r. The best we can do is reach a compromise frequency but generally we can say high frequencies are best for low conductivity targets and low frequencies are best for high conductivity targets."

 

[rentasquid]

and I could understand most of it. I was thinking on the right lines, but I still am curious as to why Tesoro is moving their operating frequency higher, out of the "coin range"? Or, does it not really matter that much?!?

 

[JB(MS)]

When the Minelab Sovereign was released I thought it would be the ideal detector, 17 frequencies from 1.5 to 25.5 kHz would cover the optimum frequency span for the type targets I hunted, plus reports said it was a killer in trash. I drove to the nearest dealer, almost 300 miles round trip, and bought one. Big disappointment. In our low mineralization it didn't get good depth, it's sensitivity to small rings and other small, low conductive targets ranged from pathetic at best to nonexistent and in some of the iron laden trashy places I hunted it stayed in a deep null and was useless. I sold it but a couple of years later let some guys from the Northeast convince me it had problems and bought another one. Same results so I gave up on having one detector that was ideal for all types of hunting.

Here's another qoute from George to further confuse the issue, followed by one from Gary Finch about the optimum frequency for a single frequency detector.

"To obtain discrimination we need to read both the x and the r signal components. As I said the best response to the x signal is not the same as the r signal. We need to be at an entirely different frequency for x. Generally for best discrimination we need to have an operating frequency well above the targets -3db frequency."--George Payne.

From an article by Gary Finch on one of Andy Sabisch's old OnlineTh'er detecting forums:
"I've done a lot of research and field tests on this over the years, and the results have consistently indicated that a detector with an operating frequency between 10 and 15 KHZ does the best job on a wide variety of targets, from relics to gold nuggets. This is one reason Tesoro detectors are so popular as all around units: most of them operate between 10 and 12.5 KHZ, where they are extremely efficient.

My conclusions about operating frequency have come from years of tests, both the usual in-ground tests on buried targets, (which of course are always a little subjective, even in the most unbiased), and many scientific tests on buried targets to determine the amount of voltage response generated, using an oscilloscope and recorder, etc. (No big deal about this, I just wanted to learn the truth about it for myself, and had the necessary equipment).

I've talked with George Payne about this, and this was one reason why he designed the Treasure Baron as a 12.5 KHZ single frequency unit: after a lot of tests he came to the same conclusion. This was the optimum frequency for detecting all metals."

 

[rentasquid]

that makes sense! Thanks for the response JB!!!

J.

 

[Wirechief]

Hi everyone and I am curious if reactance is considered a big part of the formula? Is X referring to reactance? Thank you all and nice to meet everyone. de John the Wirechief out Blackwell way.

 

[MaineDigger]

That was a very informative post. But, do those "rules" still apply with digital technology, or is it that the new technology is being developed "around" those rules?

For the example, the MXT. You turn it on and it says MXT 1.0. I believe the treasure baron has a "chip" as do many other machines. Regardless of frequency, have they just been programmed to "interpret" the response of that frequency on certain metals?

If not, then why do the shadows operate at 19.2?