What is this anomaly??

[JCR TX]

I tried & have not been able to duplicate NASA Tom's observation in my mild-medium mineral test bed. I am curious to see if the next update might have some effect on what he is seeing. It all works toward improvements.

 

[Picketwire]

If its silent how do you know its there?

Tom takes a dime and checks how far the detector will air test it with the coil on the ground in each individual frequency and frequency offset before he even starts to detect. He said the noisiest are usually the worst as far as depth is concerned but even when two or more are relatively the same, as far as being quiet, one will air test farther than the rest. He also says that the best offset is not site specific and changes even from one minute to the next at times. If two frequencies are equally quiet but one is an inch or two deeper, what else would be the cause?

Getting back on track with the OP , has anyone tried to replicate the anomaly and been successful?

I have seen reports that in certain individual's test gardens, that SMF was just as deep as 4khz frequency. I haven't seen any updates on that forum on the subject. To view the thread see "Legend what are we looking for Tom???" by calabash digger on that forum.

 

[vlad]

The multi is a mystery as the information on the exact frequencies they use and how is proprietary. Would love to see that.

Since multi has been out since 89 (and Fisher invented it) I think its not proprietary and is understood. Besides ML and Fisher, Whites, NM and Garret use it,
Ask NASA Tom, or Ty Brooks who wrote the Tek Talk column for WET for many years.

Tom takes a dime and checks how far the detector will air test it with the coil on the ground in each individual frequency and frequency offset before he even starts to detect. He said the noisiest are usually the worst as far as depth is concerned but even when two or more are relatively the same, as far as being quiet, one will air test farther than the rest. He also says that the best offset is not site specific and changes even from one minute to the next at times. If two frequencies are equally quiet but one is an inch or two deeper, what else would be the cause?


I have seen reports that in certain individual's test gardens, that SMF was just as deep as 4khz frequency. I haven't seen any updates on that forum on the subject. To view the thread see "Legend what are we looking for Tom???" by calabash digger on that forum.

The first question is does one set of wires handle all the frequencies, or is there multiple sets"and how many oscillators? What frequency of operation for the Transmit and Receive windings was the loop designed for, and what is its inductance? (main) Changing frequencies away from that changes the Q of the loop for a different frequency, and can cause a phase shift that can become excessive. (getting into efficiency involves the First Law of Thermodynamics, energy conservation and that I cannot explain well) The Transmit and Receive windings inductance, resistance and effective Q is always different for each frequency: the perfect number of turns for one frequency to get best sensitivity might work at other frequencies except with a loss in efficiency which gets worse the further diverging from the alpha frequency. Absolute sensitivity is not the concern here but rather having a loop that is more versatile in use of many frequencies. Would a loop made for one frequency be more efficient, I would say so: but how many people will be willing to spend the money for 5 or 6 loops?
Comparing two frequencies will depend on the difference between them in kHz, and how much battery power is used. The question is not that they are equally quiet but at what sensitivity does each get noisy. Having worked with stereos a lot I know that any circuit has inherent noise, and trying to remove it can be very expensive. Many times the fix is to put it into a part of the spectrum where it is least noticed. One thing Troy told me he tried to do was have a receive section that was as "clean" as possible because it increased depth more cheaply that spending an equal amount in transmit.
Did Tom bother to rebalance the detector each time he did the test? (I recall tests using some VHF detectors that would hit a coin in the air at 16 inches, but not hit the coin laid flat on the ground.)
Temperature has a big effect as Jerry Tyndall proved with his Nautilus detectors and constantly rebalancing the loop windings, and rebalancing the ground.
People report many things and may not recognize they may be biasing results too. While the stories are interesting they are anecdotal, personal observations non-systematic or scientific and may or may not be true. But they are a lot of fun to read.

 

[Picketwire]

Did Tom bother to rebalance the detector each time he did the test?

Tom does the test every time he detects. I would guess that he is smart enough to ground balance every time also. You might post there and ask him. Also note Carl's response to the thread. He is a pretty well known metal detector engineer responsible for the Whites TRX, Fpulse and Tekpoint, and the XP pinpointer among others, founder of the Geotech Metal Detector website and currently working for Fisher.

 

[DigDog]

Since multi has been out since 89 (and Fisher invented it) I think its not proprietary and is understood. Besides ML and Fisher, Whites, NM and Garret use it,
Ask NASA Tom, or Ty Brooks who wrote the Tek Talk column for WET for many years.

The first question is does one set of wires handle all the frequencies, or is there multiple sets"and how many oscillators? What frequency of operation for the Transmit and Receive windings was the loop designed for, and what is its inductance? (main) Changing frequencies away from that changes the Q of the loop for a different frequency, and can cause a phase shift that can become excessive. (getting into efficiency involves the First Law of Thermodynamics, energy conservation and that I cannot explain well) The Transmit and Receive windings inductance, resistance and effective Q is always different for each frequency: the perfect number of turns for one frequency to get best sensitivity might work at other frequencies except with a loss in efficiency which gets worse the further diverging from the alpha frequency. Absolute sensitivity is not the concern here but rather having a loop that is more versatile in use of many frequencies. Would a loop made for one frequency be more efficient, I would say so: but how many people will be willing to spend the money for 5 or 6 loops?
Comparing two frequencies will depend on the difference between them in kHz, and how much battery power is used. The question is not that they are equally quiet but at what sensitivity does each get noisy. Having worked with stereos a lot I know that any circuit has inherent noise, and trying to remove it can be very expensive. Many times the fix is to put it into a part of the spectrum where it is least noticed. One thing Troy told me he tried to do was have a receive section that was as "clean" as possible because it increased depth more cheaply that spending an equal amount in transmit.
Did Tom bother to rebalance the detector each time he did the test? (I recall tests using some VHF detectors that would hit a coin in the air at 16 inches, but not hit the coin laid flat on the ground.)
Temperature has a big effect as Jerry Tyndall proved with his Nautilus detectors and constantly rebalancing the loop windings, and rebalancing the ground.
People report many things and may not recognize they may be biasing results too. While the stories are interesting they are anecdotal, personal observations non-systematic or scientific and may or may not be true. But they are a lot of fun to read.

Alot of truth to unpack there lol. Perhaps ML had it right with the Xterra and swapping out coils. I suppose the trade off is lose of depth.
What would be interesting to know and they say its proprietary is the exact frequencies that are used, how many at a time etc. using multi modes. im sure with the right equipment you can see it.

 

[sprchng]

I think the real "truth" to unpack here is if an anomaly even exists. Was it a fluke or is it repeatable? Curious minds want to know!

 

[DigDog]

Sorry. Since its been unpacking for over two months i thought maybe you gone through the box by now. My bad.
Sometimes when your sitting around the fire house waiting for a fire conversations develop lol