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Single Frequency Vs Multi


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Here’s a topic for all you “Rocket Scientists” out there (and anyone else who’d like to chime in).

I was having a discussion with another dealer.  He felt that single frequency worked better because there’s a certain amount of performance loss with Multi.  I was always of the opinion that Multi-Frequency was the best for most types of Metal Detecting.  It allows you to hit ALL the targets that react better to certain kHz.

Here’s an example from another hobby of mine (most of us have more than one).  I shoot muzzle loading guns.  The “Round Ball” type projectile that was used for hundreds of years performs best when shot out of a rifled barrel with a slow twist.  Twist refers to the how many inches of flight it (the projectile) takes to make one revolution.  The conical bullet came out during the Civil War and requires a faster twist.  For modern muzzle loading rifles a slow twist would be 1 turn in 56, 60, 66, 70, etc. inches. For conicals, 32, 28, 24, etc. inches.  In the 70s, one company came up with the idea of a “Compromise” twist; 1 tun in 48”.  That way you only have to buy one gun.  You can use Round Balls for Target shooting and Conicals for hunting.  It shoots both “well”.

Having said all that, does the Single Frequency work better than the Multi?  Is there any kind of lack of performance or trade off having them (kHz) work simultaneously?

Thanks!

Walt

 

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That would be a great question for Carl Moreland at GeoTech.

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My thoughts is it would alter the impedance of the coil for each frequency. If that was the case one coil might be better than another with different frequency. 

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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.

 

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27 minutes ago, 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.

 

Do you think they could make the Nox better by  using specific coils like say a coil made more for  saltwater use  in the beach modes?

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10 hours ago, 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.

 

What evidence is there that a MF loses depth in MF mode?

What do you mean by a MF machine will be 'noisier'?

I'm looking at getting a MF detector, currently have the Nokta Simplex but don't like it as there is too much chatter even with low sensitivity and ground balance.

The MF machines I'm looking at are the Minelab Vanquish 540, Minelab Equinox 600 or 800, or the new Garrett Ace Apex. There is unclear information about what frequencies they use then in multi-frequency mode, and what difference it makes. The Apex doesn't have 40khz for example. 

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Chatter on the Simplex might be the mineralization, did you try to nudge up the discrimination? I have the Multi Kruzer and can trim that out and get the machine to run nice and quiet even in some of the most horrid conditions. Had it in the river which is tidal yesterday, found a paper thin Indian Head penny about 8-10" down in hard pack gravel with tons of iron. My buddy had difficulties ground balancing his Nox 800 in the same area, not because it is MF vs SF but because those large round coils can be difficult in some areas. I found the MK to be a very high gain machine in general, running it at 3/4 the sensitivity tames it down but nice to have power under the hood. I think most people run them just too high making them sparky with irradic id #'s as they are very sensitive machines.

You may want to check out the eliptical coil for the Simplex, Sven did some testing on them.

The Apex looks to be a very tame smooth running MF machine. Being splash proof puts it ahead of the Vanquish but probably not a Nox 800 killer. The eliptical dd looks like it will be pretty universal, be nice to see what other coils come out for it.

I have found the Garrett machines to be very tame except the AT Max which is chattery. From the little bits I have seen on the Apex it appears to be as stable as the AT Pro but with MF so id #'s are probably much more accurate. Note there is only 1 coil for the Apex right now. Apex only runs at 5, 10, 15, 20khz. Nox 800 going upto 40khz can be used for tiny gold ie gold prospecting.

Apex should work very well with those key frequencies for the majority of detecting. Salt water hunting, lower frequencies do better.

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12 hours ago, Dances With Doves said:

Do you think they could make the Nox better by  using specific coils like say a coil made more for  saltwater use  in the beach modes?

Any time you run multiple frequencies (as a beach mode would) the coil is, by necessity, a compromise. A coil optimized for high freq nugget hunting isn't optimized for low freq deep silver, so there could be optimized SF specialty coils. The nice thing about a wideband machine is it is less finicky about coil parametrics and easily corrected for in software, assuming you know what coil is being run. And ML has a coil ID chip in each coil that does that.

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2 hours ago, crow said:

What evidence is there that a MF loses depth in MF mode?

See the example in my post. In general, any MF design will be slightly hotter on particular targets in SF mode than in MF mode, unless it has been software-corrected to slightly dumb down the SF mode(s) to match the MF mode.

Quote

What do you mean by a MF machine will be 'noisier'?

I was speaking specifically to EMI, which is better coupled in a wideband (MF) design than a dedicated SF design. But an MF design may (or may not) do better with ground noise.

Both issues are relative to a particular design and may not compare well to other designs. Ferinstance, the V3 is slightly better on deep silver in 2.5k-only mode than in MF mode. Yet a different MF detector in MF mode may beat the V3 in 2.5k-only mode on deep silver. Same thing with noise... it's possible that a particular wideband (MF) detector will handle EMI better than a particular dedicated SF detector just because the guy who designed the wideband detector did a better job paying attention to the details. But if you took that same wideband design and converted it to narrowband it should come out even quieter.

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