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Single Frequency Vs Multi


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5 hours ago, King-Of-Bling said:

Very interesting topic and I don't know if I'm off base here but will compare a MF against a PI on a beach. Granted , a PI is a completely different animal. What I do know is a MF can have great discrimination but in heavy black sand it can overload. Basically rendering it useless ! It won't work. Depth is also an issue. Under these same conditions , my PI can struggle as well. I may have to raise the coil 6" off the sand and go very slow. But it works ! Of course discrimination is an issue compared to a MF. A MF machine does not "reign supreme" on all beaches. In fact , it may not operate at all. What many don't realize is that we have different styles of hunting , which can change based on conditions. And that should be in direct correlation to what detector you choose for the job.

I used to like in Southern California.  A couple times we went down Beach Detecting after a storm.  You could see thick concentrations of Black Sand laying on the surface.  A SF VLF machine just wouldn’t work.  It would overload as soon as the coil got close to the ground. 

At that time, Minelab’s FBS and BBS technology (Explorer & Excalibur) was the only game in town.  That type of MF worked very well as did the PI’s like White’s Surfmaster, Garrett's Infinium LS and Sea Hunter.  If you didn’t have one of those, you didn’t hunt!  I’ve never tried anything like a Spectra or Equinox Series detector under those conditions.

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On 8/4/2020 at 4:07 PM, GB_Amateur said:

This thread has me wondering about the performace difference between the Nokta/Makro MultiKruzer and the standard (14 kHz fixed frequency) Kruzer.  (I realize most of this discussion has been comparing simultaneous multifrequency, not selectable multifrequency as the MultiKruzer is -- {5 kHz, 14 Hz, 19 kHz}.  From an experiemental standpoint, both have 14 kHz.  Are the coils interchangeable between those two?  That could be good or bad for the fixed 14 kHz unit, I guess -- making a coil optimized for a single frequency as opposed to making a coil which can operate for multiple frequencies.  I think this is one of the things Carl was getting at.

I would think that for as long as the Kruzer family has been out, someone, somewhere has done such a comparision....  Whether it's been done under enough varying conditions (e.g. different ground conditions) is another story.

Kruzer and Amphibio family machines use the same coils, external battery option, and headphones. Only difference between the Kruzer and Multi Kruzer should be the MK has selectable frequencies. If there are differences then it might be due to a software update difference.

In trouble areas I find it easier to access the frequency rather than the frequency shift. I tend to get lazy and if it means I may lose less than an inch in depth I can deal with that. So far even in air tests I can barely tell the difference in depth with the different frequencies. I do suspect the 5khz on the beach in beach mode would make much more of a difference than land or fresh water hunting.

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On 8/4/2020 at 12:07 AM, Geotech said:

Steve's reply is very accurate. MF trades off raw depth for other benefits. For any given MF detector, it will go slightly deeper in a SF mode depending on the target. Ferinstance, in MF mode the White's V3 will detect a nickel & quarter very equally. In 2.5k-only mode it gets the quarter deeper than MF but the nickel less; in 22.5k-only mode it gets the nickel deeper but the quarter less.

Also, an MF machine is a wide-band design and will tend to be noisier than a dedicated SF machine which is narrowband. An MF machine run in SF mode is very likely still wideband and not as potentially quiet as a dedicated narrowband SF machine.

 

hi carl!
 so in your view, is (s.m.f.) a better performer in heavily trashed parks, as opposed to single frequency?

(h.h.!)

j.t.

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Properly comparing the two should involve understanding the fundamental principal used for each detector's version of MF signal processing. Some do it well, and others don't. I'll focus on multi frequency, since it might generally be considered less sensitive.

It's an engineering challenge to effectively get the most out of MF, so the advantage depends a lot on the specific implementation. The Rx signal must be properly handled in an MF detector. It's very complex. Because of the wideband nature, there's a wider spectrum to filter and process. If MF has a loss in signal strength, that can be compensated by boosting the Tx signal at the cost of battery life.

Low quality MF detectors would be expected to underperform, if such detectors don't properly transmit or process the signal. It takes a good deal of R&D to get MF working at it's best. The White's V3i is an example of a good attempt at 3 simultaneous frequencies. It's not modern anymore though

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On 8/9/2020 at 10:17 AM, jmaryt said:

hi carl!
 so in your view, is (s.m.f.) a better performer in heavily trashed parks, as opposed to single frequency?

(h.h.!)

j.t.

That has more to do with recovery speed than number of frequencies.

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On 8/4/2020 at 2:54 PM, Bohemia Miner said:

My home was built in 1900.  My backyard is polluted with rusty iron in different sizes and stages of deterioration.  When iron becomes rusty, the metal detector no longer sees it as such.  So, Iron Mask and Discrimination can’t do their job.  It reads anywhere from foil to gold to silver. 

My thought and the reason for the thread in the first place is that I’m guessing that because it’s all over the VDI Spectrum, each frequency that excels on the numbers that they react to best, are seeing it (rusty iron) as targets.  As a result, all I’m getting is a lot of noise. 

I ran the single frequency Simplex and that noise was GREALTY reduced.  Having said that, I set my Equinox at 10 kHz only with far better results than Multi.

The whole point of Multi-Frequency is so that targets aren’t missed.  The biggest complaint I received from customers who purchased the 14kHz Whites MXT was that they weren’t finding any deep copper or silver coins.  However, I had a friend who declared that his MXT would spank his Minelab Explorer on gold rings every time.

 

So that brings me back to my original question, is there a “trade off” in performance between single frequency and multi?

It will come down to what your coil goes over and sounds off on. Not if one vlf freq vs multi vlf freq is better than the other. I found using multi freq on an equinox would false quite a bit in iron contaminated trashy areas swinging the coil near the iron trash before canceling it out while swinging over the iron trash. 

 

In single freq mode the equinox I had would do better in iron infested sites. 

 

So with this being said....maybe try using just single frequency mode for a bit and see what happens. I would go ahead and dig all of those iron targets out anyway to see what is beneath them. 

 

If you missed a target while swinging over a spot in multi freq mode then switched to single frequency mode and actually swung over the target while going back over the same area.....how would you know what mode would be better??? 

There is no way to know for sure unless one was to grid off an area and dig every thing in that spot until you heard no more targets at all then change frequencies or put it in multi frequency and do the exact same thing to see if anything was left. 

 

 

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In general Single frequency is better and bestest than MF.

My friends that followed me, I wrote review when the metal detector was in parachute. The following years they emailed me and said you are right Hamid. My friends are dealers. 

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On 8/14/2020 at 7:22 PM, bigtim1973 said:

It will come down to what your coil goes over and sounds off on. Not if one vlf freq vs multi vlf freq is better than the other. I found using multi freq on an equinox would false quite a bit in iron contaminated trashy areas swinging the coil near the iron trash before canceling it out while swinging over the iron trash. 

In single freq mode the equinox I had would do better in iron infested sites. 

So with this being said....maybe try using just single frequency mode for a bit and see what happens. I would go ahead and dig all of those iron targets out anyway to see what is beneath them. 

If you missed a target while swinging over a spot in multi freq mode then switched to single frequency mode and actually swung over the target while going back over the same area.....how would you know what mode would be better??? 

There is no way to know for sure unless one was to grid off an area and dig every thing in that spot until you heard no more targets at all then change frequencies or put it in multi frequency and do the exact same thing to see if anything was left. 

I had similar problems in parks with the 6" coil.  Not so much with the 11".  I did run it in 10 kHz to see if I could duplicate the results I had with a borrowed Simplex.  They were similar.

I'm thinking of doing just that but was waiting for the grass to die.  Anybody else not water their grass in the summer to avoid a bigger water bill?  lol

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On 8/3/2020 at 10:59 AM, Steve Herschbach said:

A highly tuned single frequency detector can do the better job on some tasks, and multifrequency on others. In many situations it will make no difference which you use. They are just tools in the tool belt, each to be used when one provides an advantage over the other.

Multifrequency provides a clear and undisputed advantage on mineralized saltwater beaches. Multifrequency also gives the engineer more information to work with as regards discrimination, providing generally better discrimination results. A single frequency detector tuned to a specific high frequency may derive some benefits for gold prospecting, for example. Or better EMI resistance. It is like manual versus automatic transmission. One is not better than the other per se, it is just two ways of doing things. I prefer a machine that offers both options.

Selectable Frequency & Multiple Frequency

 

Great explanation and solid response Steve, thanks!

All the best,

Lanny

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