DFX :Balance salt&ferrous in dual frequency mode?

[Zadok2]

If one frequency of the DFX is balanced to salt and the other to ferrous black sand, can you consider this as having "ground balanced out" both noise sources at the same time? Wouldn't the frequency balanced to salt suffer a lot of interference in hot ground?

Someone said a book by Jeff Foster had something on this.

 

[Larry (IL)]

I didn't know you could do that......

 

[UK Brian]

Jimmy "Sierra" Normandi first wrote about this. He has a section on it in his book "Understanding Whites DFX" published by Whites in 2002.

 

[Zadok2]

Thank you!

 

[SteveP(NH)]

If one frequency of the DFX is balanced to salt and the other to ferrous black sand, can you consider this as having "ground balanced out" both noise sources at the same time? Wouldn't the frequency balanced to salt suffer a lot of interference in hot ground?

Someone said a book by Jeff Foster had something on this.

I am the one who posted this on another board on this forum. It is on page 45 of Foster's excellent book.

Hey glad you made it over here. I believe the way it works (and I am at work now and don't have Digging deeper with the DFX with me but I believe it has to do with the way that the DFX uses the 2 frequencies. There are two different modes for operating in dual frequency one is called best data and the other is called correlate. So the cpu is looking at both frequencies at the same time and rarely do both suffer from noise at the same time. It can give priority to the one that has the "best data" or least interference. In very bad ground correlate mode is better to use, this way a target has to appear good on both frequencies simultaneously before it is considered a real target and passed along to the end user. Most of the time is is better to run in best data mode, in fact I was at a black sand salt water beach last Sunday and was running by DFX with the Gain set at 3 and the AC sensitivity at 75 and it was as quiet as a church mouse.

Keep in mind too that the DFX has a user settable amount of ground filtering and in very mineralized soils you can increase the ground filtering more than would be good in milder soils as well.

 

[Carl-NC]

No, both frequencies are simultaneously balanced to ferrite, then salt is removed by subtracting the salt responses of the 2 frequencies.

- Carl

 

[Larry (IL)]

Thanks Carl.

 

[Zadok2]

Good stuff! Thanks, everybody.

 

[SteveP(NH)]

No, both frequencies are simultaneously balanced to ferrite, then salt is removed by subtracting the salt responses of the 2 frequencies.

- Carl

Hey Guys I know both of you guys know tons more about the DFX than I do so I am not trying to be a smarta$$ but trying to better understand my DFX which I have just owned for about 10 months now.

Here is the bit that confuses me - on page 45 of Jeff Foster's book he has a section called "Dual Frequency Ground Balance that says,

"The way that the G.E.B. system works in the Dual Frequency modes is very similar to the single frequency modes except that in Dual Frequency there are two regions on the VDI scale where the DFX will ignore targets. One of these regions is fixed and the other is adjustable.

The fixed ground balance region is set to ignore the effects of conductive moisture (i.e. saltwater) around a VDI of +2. The adjustable ground balance is set by the ground balance procedure to ignore ferrous mineralization that produces VDI numbers nearer the -95 end of the VDI scale.

This "two region" ground balance provides excellent performance at saltwater beaches where the ground's VDI number makes wide swings between the salt area (near +2) on wet sand and the iron area (near -95) on dry dark sand. It can also be beneficial at inland sites where soluble compounds like de-icing salts and commercial fertilizers can cause the ground's VDI readings to fluctuate widely." [end quote]


This sounds like two different explanations of how the GEB system handles ground balancing when in a two frequency mode.

The reason I am trying to clear this up is not just for curiosity's sake but it seems to me that it would make a difference about where you should perform the air balance and ground balance procedure. If Jeff is right then you shouldn't need to go down to the wet sand to GB as the fixed region will automatically be set to wet salt regardless if the sand is wet under the coil when you GB the machine, while if Carl is correct it seems like you would be better off going down to the wet sand and do the GB there. I know the autotracking system (if enabled) will modify the GB to a correct value but it still seems like you would be better off using the wet sand unless the fixed region is always the same.

Thanks guys.

 

[Larry (IL)]

Both are right Steve, Carl just makes it simpler to understand. BTW, Carl is the Manager of Engineering for White's.

 

[SteveP(NH)]

I think my confusion came from jumping to the conclusion that Jeff was talking about what each frequency was doing when he wasn't saying that at all. He was saying that the salt gb value is fixed and the adjustable region is determined by the gb procedure and then the results of the fixed and adjustable regions are used by both frequencies.

Is that right? and if so then it would be best to find an area that had black sand (on the beaches I hunt on it is really very dark purple) so that the adjustable gb region gets set to the ferrous mineralization as the salt doesn't matter since it is a fixed value. Though I guess as long as you have tracking enable it shouldn't matter as much. Last Sunday the beach looked like it had zebra stripes of dark and light sand. There was some coastal flooding at the high tide and so the beach was all under water and the waves left that zebra pattern once the tide receded.

I had a good day anyway though - just goes to show you how well the DFX can handle tough black sand ocean beaches - here is a shot of my two best finds ....

[attachment 178966 detecting-finds-11-9-2010-0.jpg]

 

[DELTA196]

No, both frequencies are simultaneously balanced to ferrite, then salt is removed by subtracting the salt responses of the 2 frequencies.

- Carl

Carl,
I think you have that backwards?? Mark Rowan in the DFX video says both frequencies are balanced to salt and the ferrite is removed by the scalling and subracting.