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OK, here is that full but probably incomplete list:

 

Selectable Frequency

1989 Minelab Eureka Ace Dual            8    19.5 kHz

1993 Minelab XT 17000                6.4    32 kHz

1994 Compass X-200                6    14 khz

1997 Minelab XT 18000            6.4    20    60 kHz

1999 Minelab Golden Hawk        6.4    20    60 kHz

2002 Minelab Eureka Gold        6.4    20    60 kHz

2005 Minelab X-TERRA 50                7.5    18.75 kHz

2006 Minelab X-TERRA 70            3    7.5    18.75 kHz

2009 Minelab X-TERRA 305            7.5    18.75 kHz

2009 Minelab X-TERRA 505        3    7.5    18.75 kHz

2009 Minelab X-TERRA 705        3    7.5    18.75 kHz

2009 XP DEUS            4    8    12    18 kHz

2016 Rutus Alter 71        Variable 4 - 18 kHz

2017 Nokta Impact            5    14    20 kHz

 

Multi Frequency

1991 Fisher CZ-6            5 & 15 kHz

1991 Minelab Sovereign            BBS

1992 Fisher CZ-5            5 & 15 kHz

1993 Minelab Excalibur            BBS

1994 Minelab Sovereign XS        BBS

1995 Fisher CZ-20            5 & 15 kHz

1996 Fisher CZ-7            5 & 15 kHz

1998 Minelab Sovereign XS2/XS2 Pro    BBS

1998 Minelab Excalibur 800/1000        BBS

1998 Fisher CZ-7a/7a Pro        5 & 15 kHz

1999 Minelab Explorer S/XS        FBS

2000 Minelab Sovereign XS2a Pro        BBS

2001 White's Beach Hunter ID        3 & 15 kHz

2001 Fisher CZ-70 Pro            5 & 15 kHz

2001 White's DFX            3 kHz & 15 kHz (Simulates single frequency by ignoring half the dual frequency signal)

2002 Minelab Sovereign Elite        BBS

2003 Minelab Explorer II        FBS

2004 Minelab Quattro MP            FBS

2004 Fisher CZ-3D            5 & 15 kHz

2005 Minelab Sovereign GT        BBS

2006 Minelab Explorer SE        FBS

2008 Minelab Explorer SE Pro        FBS

2009 Fisher CZ-21            5 & 15 kHz

2012 Minelab CTX 3030            FBS2


Selectable Frequency or Multi Frequency

2009 White's Spectra Vision        2.5 Khz or 7.5 kHz or 22.5 kHz or all three at once

2017 Minelab Equinox                  5 kHz or 10 kHz or 15 kHz or 20 kHz or 40 kHz plus multi frequency options

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Why is it AKA machines never get a mention at all? With their single frequency coils, frequency can be changed the same way as the X-Terra range. With their selectable frequency coils, they don't utilise harmonics to select frequency, in contrast they utilise a simple mechanical switch to increase or decrease the amount of windings used inside the coil.

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Because for all intents and purposes AKA machines do not exist in the United States. I wrote the article, and I only mention what pops into my head. I know next to nothing about AKA and they are far enough off my personal radar that I simply did not think of them. Nothing nefarious, just the way it is. I will attempt to get more familiar with them and even add them to the list when I know more, but the bottom line is if they want attention in the U.S. they need to do more to get it. A few dealers and a service center is the first step. I may be just a local yokel but if I have to mail it out of the U.S. to get service than I am not interested.

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Good article Steve, but wrong on the harmonic info. Switchable frequency machines switch to different fundamental frequencies, not harmonics of the base frequency. Most of them run sinusoidal transmitters so there are no harmonics, and they switch in different capacitors to do so.

Also, the DFX doesn't really run in single frequency mode. It always transmits/receives 2 frequencies, just ignores one of them in "single" mode.

 

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And by the way Ringmoney, feel free to start a thread on AKA and bring us up to speed. Like you asked, why does nobody mention AKA? That does include you also. I post stuff all the time just to be informative. There is no forum rule against others doing the same. I would welcome it!

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5 minutes ago, Geotech said:

Good article Steve, but wrong on the harmonic info. Switchable frequency machines switch to different fundamental frequencies, not harmonics of the base frequency. Most of them run sinusoidal transmitters so there are no harmonics, and they switch in different capacitors to do so.

Also, the DFX doesn't really run in single frequency mode. It always transmits/receives 2 frequencies, just ignores one of them in "single" mode.

 

OK, I need to edit that. Now that you point it out and I think about it, kind of obvious. If you are running at a single frequency there can be no harmonic in use.

Thanks Carl - I love learning stuff!

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Just now, Steve Herschbach said:

OK, I need to edit that. Now that you point it out and I think about it, kind of obvious. If you are running at a single frequency there can be no harmonic in use!

Well, it's more complicated than that. Instead of a sinusoid, you could run a square wave drive which generates a triangle wave current, which does have a fundamental and harmonics. This is exactly what a Fisher CZ does. A SF detector could demodulate only the fundamental (ignore the harmonics), and vary the square wave frequency to whatever it wants, the advantage of which no coil capacitor needs to be selected. The V3 does it this way (in SF mode), and I'd guess (but don't know) that the Alter 71 does it this way, too. But I expect most of the switchable frequency detectors on your list run sinusoidal transmitters.

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I try but there is a reason Carl why you design detectors and I just use them. I try to learn just enough to understand why the things I observe in the field happen the way they do, but my brain taps out after that. :smile: Luckily I stayed out of the whole harmonics thing in the magazine article.

I think my latest edit got it cleaned up - Thanks again.

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