What is digital filtering?

[Mick in Dubbo]

Hi all.
I've been wondering if the Explorer has a ground balancing capability and found the the instruction manual (I own an XS) mentioned that it uses digital filtering. Wat is that as opposed to ground balancing?
thanks.
Mick Evans.

 

[Captain Kirk]

Mick,

Digital filtering is commonly used by computers instead of an actual physical filter made up of resistors and capacitors (and frequently inductors). The filtering is accomplished by taking successive samples of input data. Then the samples are weighted by various "scale factors" and then added together to produce a final result. There are several advantages to digital filtering which include cost and flexibility (making changes in the filter characteristics without having to change any hardware).

HH,
Glenn

 

[Mick in Dubbo]

Thanks Glenn.
Sounds like it is a separate thing to ground balancing.I know all detectors have filters, so I assume that this is what has been replaced by the use of digital filters.I 'm just trying to get a better understanding of the Explorer. I'm assuming that it is in fact a fixed ground balanced machine that compensates for mineralisation by sending down more than one signal at a time. Would this be correct?
Mick Evans.

 

[Captain Kirk]

I am reasonably sure of the following, but I do not qualify as an expert:

In frequency domain detectors the term "ground balancing" generally describes the following process:
* Find a place where the ground is free of targets.
* Move the search coil up and down over the ground.
* The detector measures the phase shift difference between the transmitted and received sinusoidal signals when the coil is over ground (when no target is present).
* The detector adds in a correction factor for that phase shift when the coil is over target free ground.

The term "ground balance" does not apply to the Explorers BBS detectors.. The BBS technology is a time domain and not a frequency domain detector. As such phase shift analysis is not used by the BBS detectors. These detectors use rectangular wave shape excitation and then analyze the wave shape of the pickup signal. The detectors remember the wave shape characteristics of the ambient conditions and then look for abrupt changes in the received wave shape as compared to the ambient. As the detector coil sweeps over the ground, the soil conditions usually change gradually compared to what happens when you sweep over a detectable target. In that sense, the effects of mineralization are rejected with no "ground balancing" per se. This is sometimes referred to as "automatic ground balancing".

HH,
Glenn

 

[Steve(MS)]

n/t

 

[Captain Kirk]

Steve,

You can study the Minelab patents. That is what I have done (but not exhaustively). But, this is not an easy read.

HH,
Glenn

 

[Steve(MS)]

Glenn, I wasn't meaning a slight on your knowledge or anything like that but would like to hear what ML would say on this. I think your explanation makes good sense too but I have read on other forums where some that may not know what is going on with the Explorer claim it has a "preset GB".
From my experience from using a good number of single freq detectors in my area, none of them whether they have manual GB or not have measured up to the overall performance of the Explorer even on low conductors like nickels where the Explorer is supposed to be less sensitive than some detectors with a higher freq transmit. Granted, I haven't tried the newest ones on the market but my guess is that they are similiar in performance as some of the better ones of the past. With the type detecting I do, I don't need a detector to be hot on tiny items where I would guess some of the high single freq detectors would do better.
So my take on all this is that from my experience, the Explorer nicely compensates for the ground challenges even when compared to the competition. The wildcard in all of this is whether someone elses ground makes more of a difference than mine.
This is only my opinion,
Regards.

 

[Mick in Dubbo]

Oh no! You just shot me with your 'Phase' cannon! Sorry Glenn. Due to my ignorance of electronics, I kinda feel like a Klingon at the moment. bottom line here by the look of it, is that Mine lab rewrote the book on how to deal with mineralisation issues.
Just to add a bit more confusion to the mix here,the Sovereigns have the same sort of technology, but have auto ground tracking. So I take it, that the FBS technology only goes part of the way to overcoming mineralisation. Otherwise, you could use the Explorer on the gold fields as well.
And just think. All I want to do, is use weapons of mass detection to seek out cloaked enemy vessels!
Thanks for taking the time and effort to explain it to me. Just wish that I was literate enough to comprehend it.
Mick Evans.

 

[Captain Kirk]

Mick,

It is very difficult to know the expertise level of your audience when posting.

First off, I think there is not much need to understand the detailed technical aspects of how metal detectors work. I, as an electronics engineer, am fascinated with technology. That is the reason why I read patents. For the average guy, that depth of understanding is not necessary to be a successful user of the detector.

Regarding the filter process:
There are basically two ways to filter. One is with hardware and the other is with software. Generally, but not always, software filter is preferred (especially if computing capability is available) because of cost, size and flexibility. The advantages of either is a really complex discussion.

Regarding the Sovereign technology:
I am not that familiar with the Sovereign. My understanding is that both the Sovereign and Explorer are the same basic BBS technology. Therefore, I would expect that ground balance behavior are about the same for both.

Regarding the the limitations of BBS technology, especially for gold:
Because of the lengthy computer processing for the BBS detectors, the recovery time is quite long.

Single frequency detectors will be generally more effective on gold and low conductive targets than BBS because of the concentration of the transmitted field in a single frequency as opposed to being spread over many frequencies.

Hope that I did not confuse you even more. HH
Glenn

 

[Steve(MS)]

Mick, I think your conclusion is incorrect that the Explorer have an lesser GB system than the Sov. Now that really wouldn't make sense to make a top of the line with something inferior to a lower priced unit. I think it could be used on the gold fields if you were only looking for lunkers, most who gold hunt opt for a GB PI or a high freq VLF, such as the gold bug or a lower high frq such as Xterra 70.

Another subject really needs to addressed here when mentioning ground mineralization is that even if a detector has manual or automatic ground balance is the fact that GB doesn't eliminate the effects on performance on detecting depth. Ground balance is only a small amount of disc applied to null the amount of mineralization present, in other words, for the most part, ground balance does not fix the problem of overcoming minerals. Where the Explorer and Sov are different that other VLF's is that it doesn't try to null out minerals, at least that is my take on it. Being more similiar to pulse detectors I think changes the approach to GBing when speaking about BBS or FBS.

 

[Mick in Dubbo]

While I won't pretend that the light has fully come on me me as yet, both of your posts has given me a new insight on what is going on. Thanks.I think that, for my part, as this has opened up a huge gap in my knowledge of what a detector is doing; it will be a good opportunity to read up some more about ground balancing. While one can detect quiet successfully without knowing this, I think that it can make you a better operator.
In regards to your comments about what the ground balancing is doing Steve; you may have explained why had had success with my Ace a couple of weeks back, when hunting in some noisy ground, I knocked out the first 3 notches of discrimination and reduced sensativity down to 5 bars. When I did this, the Ace performed fairy well (a lot quieter).
As far as my comments go in regards to the Explorer's not doing so well on the gold fields, it is based purely on what others have commented on, that seemed to have tried to operate the Explorer's in these conditions. At the week end, I will get a good opportunity to try all my detectors on gold field conditions. I'll be visiting a mate, who lives on a 40 acre block not very far from Hill End, which was the location of the first Gold rush here in Australia. On his property, there are quite a number of diggings from this period. While I'm not too concerned about looking for the yellow stuff, it will be interesting to experiment and see if I can get the detectors to operate in these conditions. There are a couple of quarts blows, and in some parts of his property (which is quite hilly) there is wall to wall iron stone.
Thanks for taking the time to post and if you are interested, I can post the results of what happened on the weekend, possibly on the Explorer forum.
Mick Evans.

 

[BlackX]

[quote Captain Kirk]Single frequency detectors will be generally more effective on gold and low conductive targets than BBS because of the concentration of the transmitted field in a single frequency as opposed to being spread over many frequencies.[/quote]

Do you think it's technologically feasible for Minelab to be able to swich to a chosen single-frequency or is that fixed by the hardware?

_R_