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Vanquish 440: Correlation Between ID Values, Notch Segments, And Audio Tones


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On 12/1/2021 at 12:52 AM, PimentoUK said:

"Segments and tones just lump the ID ranges together? "

Broadly speaking, yes, that's what happens.
However .... the audio and the visual ID's do not HAVE to correlate. Audio performance needs to be fairly 'immediate' , whereas a visual identifier can be slower. Advantage can be taken of this difference to produce visual data that is more 'averaged', to produce more repeatable/consistent/less jumpy information.

I've no idea what ML do on their Eqx/Vanquish models, but as an example from First Texas Products:
The Teknetics T2 machine used exactly the same processing for audio ID and visual ID. It's design was later developed into the improved 'park-hunting variant', the Fisher F75. This used different processing for the two outputs, and their publicity material drew attention to this improved target ID ability. As a user of the F75, I have seen the odd 'discrepancy' that this produces. We have a lot of coke ( part-burnt coal ) in our UK farmland, and it often reads in the very-low non-ferrous range, but can be in the 'large iron' zone, or up as high as some coins. Sometimes a lump will consistently give 'Iron' audio, but low non-ferrous ID's on the screen.

“Sometimes a lump will consistently give 'Iron' audio, but low non-ferrous ID's on the screen.“

Just curious how notching on F75 would work in this situation: e.g. if you notched out the low non-ferrous IDs would that block the iron audio that those lumps produced even though the ferrous ID range corresponding to this audio was not notched out?

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"Just curious how notching on F75 would work ...?"

Not wanting to take this off-topic, but:
Disc and notching do apply to ONE of audio or visual display, I honestly can't remember which.. 'display' is the likely one. I recall NASA-Tom Dankowski coming up with some 'optimum' disc setting that he found eliminated small iron ( nails ) but let the maximum amount of other stuff through, and it always seemed to me that it was playing on this audio/visual difference. A disc setting of '6' seemed to give audio more like '12' .. ?
Anyhow, it was never something that troubled me. I found the machine worked best if you ran it fully open with no disc settings, ( ie. tone ID; all metals accepted). The moment you start introducing any kind of discrimination, you start getting into the wierd zone. The machine has many quirks and design flaws, the User Manual is no help, using 'Notch' is asking for trouble, it has notch-related functions the manual doesn't even mention, it's easy to invoke some notch setting and not realise it, and because you can't set discrimination higher than 65 ( why? ) , you can't properly make use of the 'notching in' feature....

And then there's the odd relationship between disc setting and sensitivity, unexplained, that makes the glaring 'sensitivity hole'.

And the ridiculous step change in EMI pickup when you change 'disc' from 5 to 4.


NASA-Tom's mega-thread on the F75:



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