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Multi Iq Spectrum Test


Wayfarer

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Since it snowed today here in Boise, I was stuck inside with nothing to do but fiddle and experiment with the new Equinox.  I was able to do a basic spectral analysis of my Equinox 800 to try to see what frequencies it uses.  I got some very interesting results.  Bear in mind that this only measures all frequency outputs and does not measure if they are being "fired" in rapid sequence.  An oscilloscope (something I don't have anymore) would be required to make that measurement.  

Here is a shot of the Equinox in Park1 mode with "0" ground balance setting:

It looks like the two fundamental frequencies are 7.7 kHz and 38.8 kHz (with a possible third frequency at 18 kHz, but that would break with the past precendent of two basic frequencies in BBS/FBS).  The short spikes around 30 kHz is external noise.  Clicking through the different modes made NO difference, so all the difference between the modes is all being done in DSP, not by varying frequency.  All the different modes looked identical to this screen shot I posted below for multi park1.

5a84e87440a21_multipark1.thumb.JPG.7d949960471ac0036c82fa7b65f0b66c.JPG

Here is the background noise with the machine off, so you can see what is external interference:

5a84ea2f6b6f2_backgroundnoise.thumb.JPG.de9f91dc3455f4638bc8c521dbcce82a.JPG

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One of the interesting findings is that the single frequencies clearly show up exactly where they are supposed to be, but Multi frequency does not actually use any of the signal frequencies.  It seems single frequency is being generated just in software, and that the single frequencies have no relation to the Multi IQ frequencies.  It's almost what would happen if you "forced" a CTX to operate on single frequencies.  The single frequencies really do appear to be just an add-on that the engineers left in as an interesting oddity but nothing more.   Contrast this to the White's V3i which actually does generate its multi-frequencies by operating each of the three fundamental frequencies simultaneously.  

So here are each of the single frequency modes (in Park1 mode), from 5 kHz on up.  You can clearly see the dominant spike is right where you would expect it to be:

5 kHz:

5a84ebc82a1e2_5kHzpark1.thumb.JPG.a93b58e19b854fc6e5b92de86281cefd.JPG

10 kHz:

5a84ec1b6f472_10kHzpark1.thumb.JPG.0891d10bc94303d29d0f88d8a853c595.JPG

15 kHz:

5a84ec2dda68d_15kHzpark1.thumb.JPG.6c7d3ca7e4aeed49a88c7846cbc9f75c.JPG

20 kHz:

5a84ec3d05039_20kHzpark1.thumb.JPG.889f56860d031b828c6bb12d02aa3591.JPG

And finally 40 kHz:

5a84ec52ba6db_40kHzpark1.thumb.JPG.534bf30073e8fbe28140c160e007518d.JPG

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39 minutes ago, Chase Goldman said:

Interesting.  How are you capturing the frequencies (i.e., conducted or transmitted using an antenna and rf receiver)?  And in the Multi IQ spectra, what about the prominence a few clicks under 20 Khz?

I just edited my post to include the possibility of a third fundamental frequency at 18 kHz as you noted.  The two biggest spikes (the two most powerful frequencies) are still at around 7.7 and 38.8 however and in keeping with Minelab engineering tradition, it's likely that those two are the main frequencies.  There's probably some engineering reason that there are two fundanental frequencies, but I don't know enough theory to understand it much further. However you can see there are also several other frequencies being emmitted, just less power.  Whether the Equinox uses those extra frequencies in its DSP algorithms is anybody's guess.

I'm using a software defined radio receiver that feeds into my PC.  Capturing the rf is actually really simple.  I just have a short wire antenna coming out of the back of the SDR receiver draped across the front of the coil.  A metal detector is really just a radio transceiver that is always transmitting when its turned on.  

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Thanks.  Thought it might be something like that (rf receivier). Glad you posted the info.   ML implied they were using a pulse-width-modulated scheme.  If all those frequencies are being transmitted simultaneously into the coil, the resulting radiated frequencies will be a function of the duration of each of the fundamental frequency pulses which, as you noted, we can't predict without knowing the modulation scheme but can observe the resultant output (which doesn't refute that the fundamental transmitted frequencies are not indeed 5-40 khz).  The really interesting finding from your spectral analysis, is that the output spectrum IS THE SAME REGARDLESS OF MODE.  I agree then, the secret sauce that defines the search mode behavior/target optimizations is in the way they PROCESS the return signal from the spectrum generated since the output spectra does not appear to vary as a function of mode.  Theoretically, however, there may be a number of different ways the fundamental frequencies can be modulated to result in the given spectrum.  I doubt, however, that they are doing that.  One advantage of not varying the output spectrum, is that it makes it easier to normalize target ID for a given target type regardless of the mode you are using (except if you switch to single frequency mode).  I can't recall if there has been verification of target ID consistency between Multi IQ operation and single frequency operation across the board.

 

Great stuff.  Thanks again Wayfarer.

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Very cool.....

Also nice to see the V3i is indeed what they said it is.... 3 true frequencies simultaneously.

Yup the V is still ahead of it's time in many ways.

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 equinox transmits in 5-80khz and accepts 5-40khz, and over 40khz all filters .. under the patent ... Tx motor -3wave. but the basic sensitivity of the multifrequency to the objects will be much more like the Spectra ..- there is quite similar to 1f -7.5 khz ....beach program is a question ... does not it work in bost?

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There is a lot more going on with the Equinox than just a transmit frequency.  Internal program processing is as important as about anything else.  Signal manipulations through their proven Algorithms (program instructions).  I don't mean to jump to soon, but the 800 is proving to me, personally, it is superior to other machines I've had over the past 20 years. 

 

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28 minutes ago, Mark Gillespie said:

 I don't mean to jump to soon, but the 800 is proving to me, personally, it is superior to other machines I've had over the past 20 years. 

 

Thats it! I cant take it any longer.....I'm ordering one TODAY!!!  :blink:

strick

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I think I will wait a couple more years before I order anything new.....:biggrin:

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