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Thread: Selecting Ground Filters

  1. #1
    Super Moderator deolslyfox's Avatar
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    Selecting Ground Filters

    Folks have been askin' for some information on selecting Ground Filters. Most are askin' about Sweep Speed.

    The below chart will help you select the best Ground Filter for your sweep speed. If you want to take into consideration Ground Mineralization and EMI, then the chart will help point you in the right direction using those factors as well.

    How to read the chart ..... Let just take a couple of examples.

    Using ONLY Sweep Speed:

    .5 to 1.25 fps = 5Hz
    1.5 to 1.75 fps = 7.5Hz
    2.0 to 2.25 fps = 10Hz
    2.5 fps and up = 12.5Hz

    A "rule of thumb" to remember is:

    Ground Filter = Sweep Speed X 5.

    Using ONLY Mineralization:

    Very Low Mineralization = 5Hz
    Low Mineralization = 7.5Hz
    Moderate Mineralization = 10Hz
    High Mineralization = 12.5Hz

    Using ONLY EMI:

    Low = High Pass
    Higher EMI = Bandpass

    If your sweep speed is 1.65 fps then you would want to use the 7.5Hz filter. (1.65 X 5) = 8.25, which is closer to 7.5 then it is to 10.

    Like my previous Recovery Delay chart, this information is meant ONLY to "get you close". YOU decide what factors you want to drive the filter selection. Then, optimize your settings in the field.

    I will offer one suggestion .... You CAN change your physical sweep speed ....

    You CAN'T do anything about Ground Mineralization or EMI. If you find yourself in a HIGH Mineralization and HIGH EMI environment, then you want the 12.5Hz High Pass filter.

    In other words, in priority order, select the best filter considering;

    o Mineralization first
    o EMI next
    o Sweep Speed last

    Adjust your physical sweep speed a bit for the best target response after selecting the best filter for the environmental conditions.

    Hint: At any level of mineralization, the slowest sweep speed that you are comfortable with will generally produce the best results. A "good average" sweep speed is 1.50 to 2.25 fps.

    Hope this is helpful. Da FoX


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    Last edited by deolslyfox; 06-21-2010 at 08:08 PM.
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  2. #2
    Forum Pope Nitro 54's Avatar
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    Good info Fox Your sure fill up my bookmarks
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    Super Moderator deolslyfox's Avatar
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    You sound like a John Denver song ..... "You fill up my book marks ...."
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  4. #4
    Junior Member mighty_mace's Avatar
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  5. #5
    Gold Member plarson's Avatar
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    Thanks Fox!

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    Gold Member incomenet's Avatar
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    Thank you, always good info.

  7. #7
    Exalted One Robert's Avatar
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    I still bounce between the 10.0 Band & 12.5 Band....can't really decide which one I like better...even though my ground is low in mineralization...I do have a faster swing rate... ....and the Band Filters really do filter out more EMI...that's a no brainer for sure .....good info Fox

  8. #8
    Super Moderator deolslyfox's Avatar
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    I have only had to move up to the 12.5Hz filter a couple of times, and that was on the beach when I was workin' with Normal / Normal instead of Salt / Salt, just to see if I could find the limits of the algorithms.

    As an aside, I found that Normal / Salt / 12.5Hz was a "usable" setting on the beach. A little noisy in spots, but usable. That's just info. Salt / Salt is the way to go on the beach .... 10Hz is all the filter I need at Daytona / New Smyrna ....
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  9. #9
    Guru Evan/tn's Avatar
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    Good info fox
    I have kept my ground filter at 10 band,it seems to give me the best response to targets in my area.
    **********Swinging Whites since 1978**********

  10. #10
    Super Moderator deolslyfox's Avatar
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    That's what counts Evan .... Find what works best and stick with it ....
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  11. #11
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    Da FoX,
    I was thinking about your chart this morning while MD and wondered if the following statement is true: Since there are three factors that determine filter setting (Ground Mineralization (GM), EMI and swing speed) and two are uncontrollable, would it be best to set the filter based upon the GM and EMI and then adjust one's swing speed to match the chosen filter?

  12. #12
    Super Moderator deolslyfox's Avatar
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    [QUOTE=bobamis;634379]Da FoX,
    I was thinking about your chart this morning while MD and wondered if the following statement is true: Since there are three factors that determine filter setting (Ground Mineralization (GM), EMI and swing speed) and two are uncontrollable, would it be best to set the filter based upon the GM and EMI and then adjust one's swing speed to match the chosen filter?[/QUOTE]

    Heres 's what I said in my post ....

    I will offer one suggestion .... You CAN change your physical sweep speed ....

    That's EXACTLY what you should do .... Especially since its the only way you have to accommodate the swing speed that the filter likes best ...

    If there's anything I hate worse than diggin' pulltabs, its missin' a gold ring.

  13. #13
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    Thanks, Da FoX. I went back and reread the text attached to the chart and saw you had addressed exactly what I had asked, that one should adjust their swing speed to match the filter setting. Sorry for bothering you with my redundant question!

  14. #14
    Guru jadesun's Avatar
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    awesome info fox
    Does apply somehow to the m6?
    "Learning is the eye of the mind."
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  15. #15
    Super Moderator deolslyfox's Avatar
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    The recovery speed of the M6 is so fast that any "reasonable" sweep speed is OK. MXT is pretty much in the same boat. Since you can't change filters, etc, there's really not much application.
    If there's anything I hate worse than diggin' pulltabs, its missin' a gold ring.

  16. #16
    Exalted One Dave's Avatar
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    Quote Originally Posted by deolslyfox View Post
    You sound like a John Denver song ..... "You fill up my book marks ...."
    Like a night in the Forest ...like the Mountains in spring time... like a walk in the Rain...like a storm in the desert..like a sleepy Blue Ocean..
    You fill up My Book marks...Fox's make Us a new Chart ...LOL..Thanks Fox...

    Great Post Fox !!
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  17. #17
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    Just can't get this sussed .....................

    OK - I have been trying to work out what filters I should use having been advised to go with 5KHz Band Pass as "it goes deeper" (I was told). Now, I have fairly mild minerals (I'm in the UK) - ground VDI from -85 to -92 that only changes slowly and I have no EMI whatsoever. Using a modified C&J program (accepting -95 to +95 and using Tone ID to sort out the targets) in 3-Freq Salt mode, Rx @ 11 and Sens 90/65 - all set to be stable but sharp and with a good ground balance. But, I am not a slow swinger ......... probably 2 seconds right to left and the same back again for a 5' arc. So having read the above and studying the chart I began to think I had got it all very wrong. This afternoon I decided to test it out on the field with a hammered silver penny. I dug a hole 6" deep and dropped the coin in and covered it. With RD set at 70 I got a decent repeatable signal with 5KHz but nothing with any other filter setting despite the chart suggesting 10 or 12.5KHz filters. Changing the RD didn't make any discernible difference. Does anyone have an idea why Fox's (always reliable) advice and my experience should be so different?
    TIA.
    Colin.
    2010 hammie count - 24: 2011 = 1
    Keen to hear from V3/V3i users in the UK

  18. #18
    Super Moderator deolslyfox's Avatar
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    Ramases:

    I kept looking at the chart and it finally dawned on me what was going on with your testing.

    I have cleaned up the description to (hopefully) make it less confusing. The chart is really in 3 sections. How to select the ground filter using;

    o Sweep Speed only
    o Mineralization only
    o EMI only

    When you start combining EMI, mineralization, sweep speed and other settings such as what is accepted / rejected, sensitivity, etc, the only "safe" method is trial and error.

    The purpose of the chart isn't to try to match up every combination of sweep speed / mineralization / EMI condition, and from your post, it looks like that is what you interpreted the chart to mean. Sorry. My bad. I should have been more clear.

    Mineralization should be the #1 consideration in filter selection. That's why I had this "tip" embedded in the post.

    Adjust your physical sweep speed a bit for the best target response after selecting the best filter for the environmental conditions.

    Please take another look at the chart and see if it makes more sense to you, and if it supports your field testing.

    Thanks for the input .... This is the kind of stuff that helps everyone !!!
    Last edited by deolslyfox; 06-20-2010 at 11:57 AM.
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  19. #19
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    Cool Ah - I think I AM getting there ..............

    Quote Originally Posted by deolslyfox View Post
    Ramases:

    I kept looking at the chart and it finally dawned on me what was going on with your testing.

    I have cleaned up the description to (hopefully) make it less confusing. The chart is really in 3 sections. How to select the ground filter using;

    o Sweep Speed only
    o Mineralization only
    o EMI only

    When you start combining EMI, mineralization, sweep speed and other settings such as what is accepted / rejected, sensitivity, etc, the only "safe" method is trial and error.

    The purpose of the chart isn't to try to match up every combination of sweep speed / mineralization / EMI condition, and from your post, it looks like that is what you interpreted the chart to mean. Sorry. My bad. I should have been more clear.

    Mineralization should be the #1 consideration in filter selection. That's why I had this "tip" embedded in the post.

    Adjust your physical sweep speed a bit for the best target response after selecting the best filter for the environmental conditions.

    Please take another look at the chart and see if it makes more sense to you, and if it supports your field testing.

    Thanks for the input .... This is the kind of stuff that helps everyone !!!
    Thanks Fox .............. that all makes sense. I had always thought that mineralisation was the key factor. I've been at this game for almost 30 years and it has been a key tenet of detector setup that the level of mineralisation dictates a lot of the settings we have to use. I had just began to think that the software driven approach of the V3(i) meant that this was not the case now. I'm actually quite pleased that it is as it is 'cos I understand the old rules quite wel!! Now, if you can produce a chart that tells us exactly what is low, medium and high mineralisation and the filters/sweep speeds that go with it - that'd be GREAT!!
    Cheers.
    Colin.
    2010 hammie count - 24: 2011 = 1
    Keen to hear from V3/V3i users in the UK

  20. #20
    Super Moderator deolslyfox's Avatar
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    Colin .... That is the stuff that long discussions are made of .... Chapters in books have been dedicated to mineralization and what it is (ferrous, non-ferrous, magnetic, conductive, iron, salt, etc).

    And "low, medium, high" mineralization is kinda relative too ....

    I have charted and graphed "mineralization" over the years, and all I can tell you is that the more I learn, the less I understand ....

    The BEST way to deal with mineralization is to adjust the unit in the field for optimized operation.
    If there's anything I hate worse than diggin' pulltabs, its missin' a gold ring.

  21. #21
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    Quote Originally Posted by deolslyfox View Post
    Colin .... That is the stuff that long discussions are made of .... Chapters in books have been dedicated to mineralization and what it is (ferrous, non-ferrous, magnetic, conductive, iron, salt, etc).

    And "low, medium, high" mineralization is kinda relative too ....

    I have charted and graphed "mineralization" over the years, and all I can tell you is that the more I learn, the less I understand ....

    The BEST way to deal with mineralization is to adjust the unit in the field for optimized operation.
    It is SO refreshing to hear that! I have been doing exactly the same thing for years and as you say, it just seems to get more confusing. TBH I've adopted the approach of probing to check ground VDI and unless it is way off from where I expect I just plough on with my "standard settings" and make minor tweaks as I go. I'm SO glad it's not just me who's having to "wing it"! Cheers, Fox.
    2010 hammie count - 24: 2011 = 1
    Keen to hear from V3/V3i users in the UK

  22. #22
    Super Moderator deolslyfox's Avatar
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    You have to take a "practical approach" to mineralization and overall environmental conditions. There are just too many variables that interact with mineralization, and as you know, it can change drastically in a matter of yards, depending on where you are.

    Some innocuous things will make a large change in a particular spot. Like that quiet park that you can hunt when its dry, but drives you crazy after a rain or after the sprinklers run. The salts in the fertilizer are driving the conductivity up. So - the filter you selected earlier for the non-conductive soil isn't what you need when its wet. Swing speed has to change and your RXG will probably need to drop a bit .... You leave that spot and go to another and you need to return to your "original" settings.

    Happily, we have the "tools" available with Spectra to deal with mineralization. About the only thing White's couldn't build in was "experience". Maybe the little charts along with discussions here on the forum will help other folks gain some knowledge and experience that will help.

    Good luck and good hunting. Da FoX
    If there's anything I hate worse than diggin' pulltabs, its missin' a gold ring.

  23. #23
    Senior Member pablo61's Avatar
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    Good teaching Fox. I've learned from experience that your physical sweep speed has a big influence on what filter to use. If you sweep to slow using the 10 or 12.5 filter you are going to miss targets.
    PVV

  24. #24
    Senior Member pablo61's Avatar
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    Fox, why are you using high pass for high emi. Thought the manual said to use band pass? Sorry if i missed something.
    PVV

  25. #25
    Super Moderator deolslyfox's Avatar
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    Quote Originally Posted by pablo61 View Post
    Fox, why are you using high pass for high emi. Thought the manual said to use band pass? Sorry if i missed something.
    Nope you are correct .... I updated the post AND the chart .... Let me know if this one is more clear.

    Thanks .... Da FoX
    If there's anything I hate worse than diggin' pulltabs, its missin' a gold ring.

  26. #26
    Senior Member pablo61's Avatar
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    Looks good. Thanks for the hard work
    PVV

  27. #27
    Bronze Member CyberSage's Avatar
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    The 5Hz Band Pass filter setting is somewhat of an anomaly in the filter settings. There is a radical change in stability as far as EMI is concerned. You can achieve noticeably higher RX and DS settings under this filter setting. As mineralization strength increases you have to swing slower and slower to achieve good tonal quality and frequency alignment on a coin target. Bob Canaday a long time Whites engineer tipped me off to this shortly after I received my Vision detector. This one single thing increased my depth more than anything else. I am in moderate strength soils and this filter designed for sweet ground still works the best for me. Once again slow swing speed is key.

    Jack

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