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Frequency Question


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I have a Tarsacci on the way, should be here by mid week.  Reading some of the posts 18 KHz hasn’t been as productive hitting silver in some of the posts I have read.  


I will be hunting pasture, old camp sites and old house sites.  There will be iron and sometimes lots of it.  Hunting for Buttons, bullets and other relics would you use 6 kHz 9 kHz 12 kHz or back to the 18 kHz.  Silver of course would be a high conductor, I would think brass and lead might fall into the mid range conductors.  


if anyone would share their experience with me I would appreciate it. .  

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It was a video testing different coins in different frequencies and it may been made by Aaron . I first said another but that’s not correct.

 Chuck 

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The Tarsacci is not unique amongst detectors with multiple selectable frequencies regarding the tradeoffs associated with using the different frequencies for different target types.   Except for simultaneous multifrequency detectors that simultaneously transmit and process target signals in different frequency bins, you usually have to balance out the competing effects and pick some sort of middle ground that is biased to the likely targets at a particular site.  In other words, you are going to have to choose the frequency that is best suited to MOST of your targets of interest.  If you are going mostly for relics, then I would default to the higher frequencies - doesn't mean you won't hit silver, but some of the deepest silver may escape your ear simply due to the fact that the higher frequency does not penetrate as deep (more on that if you want to read on).  If you want to go for deep silver, then lower the frequency.  You will still hit the mid-conductors but some tiny targets might more easily slip between the cracks (e.g., p-caps).  I found however that if you are hunting mineralized dirt, then you tend to want go with the lower frequencies to simply lower the ground noise and to let the salt balance filter do its magic in the hot dirt.

Based on previous posts of your finds and knowing your experience this following info probably nothing you don't already know but may be a useful primer on the the effect of different operating frequencies for others:

Lower Frequencies penetrate further into the ground and are therefore good at locating large deep targets and more optimally resonate with high conductive targets - therefore - if you are specifically after deep silver you will want to use a lower operating frequency.  Lower frequencies are also less susceptible to ground noise especially that generated in highly mineralized dirt.  On the down side, lower frequencies are less able to resolve smaller targets like micro jewelry and gold bits and lower conductive targets.  Furthermore, lower operating frequencies are often more susceptible to power line generated EMI.

Logically, the higher frequencies resonate better with smaller, low conductive targets like aluminum, brass, lead, and gold alloys but can't penetrate as deep as the lower frequencies.  They are less susceptible to power line EMI but perhaps more susceptible to other higher frequency EMI sources such as RF interference from cell phones, radios, wi-fi etc.  Higher frequencies can help better separate non-ferrous targets in thick iron, too.

Now the thing is, we are not talking about huge deltas here.  The difference in target detectability between 6 and 18 khz is probably on the order of an inch or two max.  The smaller targets are also naturally harder to detect at significant depths regardless of frequency simply due to the fact that the smaller footprint results in a lower induced magnetic field strength.

The key is to not to overthink it and simply realize that if you want to maximize target recovery you need to ensure, first and foremost, that you get sufficient coil coverage across the site and it is best to grid the site if possible by detecting in two different directions and use different operating frequencies on each pass.  This enables you to utilize the advantage of both the low and high frequencies on the site.  If your time is limited, then choose a middle-of-the-road frequency and attempt maximum coverage.

HTH 

 

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11 hours ago, Chase Goldman said:

On the down side, lower frequencies are less able to resolve smaller targets like micro jewelry and gold bits and lower conductive targets.  Furthermore, lower operating frequencies are often more susceptible to power line generated EMI.

When I was operating the Minelab X-Terra 705 which gives the choice of 3 kHz, 7.5 kHz, and 18.75 kHz operating frequency (requiring a coil change, though), the lower the frequency the more trouble I had with iron wrapping around to high conductor.  Is that a characteristic of low frequencies (where the iron range is compressed and the high conductor range expanded, relatively speaking) or do you think it's more likely due to something specific to the detector + detectorist combination?

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15 minutes ago, GB_Amateur said:

When I was operating the Minelab X-Terra 705 which gives the choice of 3 kHz, 7.5 kHz, and 18.75 kHz operating frequency (requiring a coil change, though), the lower the frequency the more trouble I had with iron wrapping around to high conductor.  Is that a characteristic of low frequencies (where the iron range is compressed and the high conductor range expanded, relatively speaking) or do you think it's more likely due to something specific to the detector + detectorist combination?

I do think that is probably driven primarily by frequency as well.  Good point.

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On the Deus, the fact that the machine can be set up such that target ID floats with frequency (higher frequencies result in higher TIDs on a given non-ferrous target) is used to advantage as an iron check feature.  A falsing high ferrous or mixed ferrous target such as a bottlecap TID at 18 or 25 kHz will stay the same or INCREASE if operating frequency is lowered, which is a dead giveaway that the target is ferrous or mixed ferrous.  Whether iron flashes or not is probably more a function of the nature of the target (e.g., mass, shape, and degree of corrosion) than perhaps frequency.  I guess the best that can be said of the frequency effect is that “it depends” but at least you have the option to switch frequency on the fly to interrogate the target and to determine if it’s response to different frequencies is consistent with a non-ferrous target or if the response is erratic, indicating probable ferrous.

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I have a 7" dime and 6.4khz hits it best, but i did scroll thru all the others, up to 18khz. I got some loss of depth at18khz but still got the signal well.so if you are in iron prone spot and probly could not get deep anyway 18khz could serve you well.  and around EMI having the BLACK SAND ON  helps simmer it down

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