Ground Filtering, Sweep Speed, Recovery Speed (DFX Emphasis)

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Trying to understand how each of these settings interact can be a monumental task to a new user of the Whites DFX. After a fair amount of reading and studying I am really starting to get a grasp on the topics and I have reached a new level as a DFX user. Many thanks to Jeff Foster and his book - "Digging Deeper with the DFX", the Whites Instruction Manual and many forum contributors which I have learned from over the years.

I have owned the Whites DFX for just over 2 years now and it has taught me the real nuts and bolts of the hobby and how a metal detector works in general and how to get the most out of your detector (a task I am constantly learning). Prior to that, I used a Garrett Ace 250.

It really helped me to understand these topics by writing it down in my own words once I felt all of the pieces coming together. In particular, Sweep Speed is a setting that throws many people off; the name alone is tricky - and the manual does a poor job of explaining it, however, once you understand Ground Filtering, the Sweep Speed setting begins to make sense.

Ground Filtering - “High-Pass Filters”: Filter out slower changing signals (ground minerals) and pass faster changing signals (targets). Think about the ground as one big target, upon which desirable targets are located. You have to block the majority of the target (ground) to know when you are over a desired target (silver). If the ground was made of silver and the desired target was ground, you would use the same logic since Ground Filters are simply measuring the change when a different target passes through your coil’s search pattern. Ground Filtering allows the detector to report to you when a significant change in the data under the coil has occurred - signaling you to dig. In other words, Ground Filters block the noise of the ground and only [mostly] pass the noise of a target. As the ground gets noisier, more filters are required.

A faster coil sweep causes signals to pass more quickly under the coil resulting in more “passed” signals from a given Ground Filter setting. A slower coil sweep causes signals to pass more slowly under the coil resulting in less “passed” signals - and more contaminated signals - from the Ground Filter. Increased Ground Filtering is also increasingly reliant upon a consistent physical sweep speed of the coil over the ground. I would also argue that as you increase Ground Filters, a faster coil sweep is required to maintain performance on a given target at a given depth (with ground characteristics being equal).

As a target gets smaller and/or deeper it will begin to appear smaller and “less significant” to the detector - creating a signal which changes less. As this happens, the Ground Filters will begin to filter-out the target signal. Too much ground filtering will erode or block a target signal - do not use more Ground Filtering than necessary. On the other hand, a similar thing happens when not using enough Ground Filtering - the target signal may be so contaminated with mineralization that it is blocked by your discrimination settings OR you see a “smear” and don’t dig the target.

Sweep Speed: Since Ground Filtering works by blocking slower changing signals, the speed at which the coil moves over the ground is vital to the effective performance of the ground filters. A given target can be made to appear to change slower or faster by simply slowing down or speeding up your coil sweep on each pass.

The Sweep Speed setting on the DFX allows you to fine tune the rate at which a given Ground Filter performs. As you move the coil over the ground at a faster rate, the DFX sees ALL target signals (including the ground) changing at a faster rate which may cause additional ground noise to contaminate a target signal. Increasing your Sweep Speed setting can help curb an increase in signal contamination due to the physical coil movement.

Stated another way, when you increase the Sweep Speed setting, you are telling your machine this: “I am swinging the coil faster now so the ground mineralization is changing faster so please increase the Ground Filtering slightly.” Even if you don’t swing the coil faster, you are still telling your machine to slightly increase the Ground Filtering.

I would recommend adjusting your Sweep Speed setting anytime you change your Ground Filter setting as you may be unnecessarily filtering target signals otherwise.

Recovery Speed: This setting is more directly related to the coil movement than Sweep Speed, despite the name. A faster Recovery Speed helps the user hear targets in close proximity to one another by allowing the machine to sound on both targets. A slower Recovery Speed will send more target information to the user by sounding a stronger (and longer) target response.

Having a slower Recovery Speed can allow deeper “accepted” targets to overcome adjacent junk targets without suffering from increased signal contamination (choppiness) from the junk target. The reverse is also true, however, in that a junk target can more easily mask a good target for the same reason. This highlights the importance of approaching a site from multiple angles.

Trashy sites demand a faster Recovery Speed in order to differentiate more targets which are closer together.

The more that I experiment with this setting, the more I think that I swing my coil too fast.

Coil Size/Shape: Smaller coils (shooters) and narrower coils (DD Style) see less of the ground due to their size and shape. As a result, they see less overall ground mineralization and these smaller coils also pass over targets more quickly, causing a faster change in target signal. However, the magic of a small coil lies in the fact that the ground mineralization does not change but the proportion of a target within the detection range does - it increases - which results in a better defined target ID and an exponential increase in the effectiveness of the Ground Filtering system when using a smaller coil.

Smaller coils make the Ground Filters more efficient by seeing less ground noise, making targets appear larger relative to the ground mineralization and passing over targets more quickly than their larger counterparts - all properties which are fundamental to Ground Filter operation. Smaller coils can benefit a user by making a given GF/SS setting much more efficient. Smaller coils can also benefit by the use of LESS GF/SS which may result in better depth and performance.
 
This is some really good info. The info varies with detector brand and experimenting can give best results. As an example, the Ace 250 has a tendency to overreact at higher sensitivities. Lowering the sensitivity BUT increasing the sweep speed causes better target response with less ground response-and vice versa. So if I'm in a testy situation, I do this. I also would use this info in a competition hunt-fast speed but slightly lower sensitivity- the detector wouldn't overreact to the ground OR fairly close competitors.:cool:
 
Nicely rewritten Local! DDwtDFX was worth it's weight in gold!

One thing I would add, if you are in an area with very little mineralization using a Filter of 3 and a sweep speed of 1 will get you the most depth. I have experimented with sweep speed as is explained in the book but seem to always end up at 1 in my location.

Also when cherry picking in trashy school yards and other places that you have no expectation of digging deep holes, use a filter of 2. It reduces overall depth and cuts down on the ground noise. In this same type of environment using a lower AC sensitivity will also help with the trash separation, as you are not searching for deep targets, just good ones!
 
Thank you so much for explanation. I have a DFX 300 and am very new with this unit. I have read the manual and Jimmy “Sierra” Normandie’s book ‘Understanding White’s DFX.’ The explanations in Mr Normandie’s book were much easier to understand than the manual, but I feel that if I keep reading these sources over and over and practice with this unit, I will make some great finds.
Again, thank you for your explanation.
 
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