Fisher F Series Vs The Minelab Xterra 705

[scoopjohnb]

I'm going to jump in here regarding the Iron-silver wrap around of the X-terra vs the Fisher F75/F19.

On the X-terra a large iron signal will indeed give you more false hi-tones. This indicates either your ground balance is off or indeed a very large piece of iron.

The Fishers don't exhibit this wrap around as much because they've chopped off a little of that very high conductive ID for you. So rather than iron starting to high-tone false when your ground balance is off, it grunts more and more. Leaving you with the question. Is my GB Off or am I coming into more iron?

Want to hunt with the X-terra like the Fisher, just notch out that highest number.

I prefer not to myself, but sometimes on rough mineralised ground I will notch out that number, making it huntable.

Why I don't like to do it,... fixed ground balance that is spot on has given me some deep and accuratly ID-ed targets. And the X-terra running in all notches open gives me the most chance of it happening. 

[HardPack]

GB,

I'll check out the iron/silver wrap around- page 78.  I was retired on the 4th of July.  Retirement is like being a kid again, it is worth the wait.  I just wanted to let you know we have a winter freeze warning until Wednesday but no snow until Thursday. Texas only thinks they have the most cows and Alaska still believes it has the most snow. Google: Tamarack, California 1911, I got place up there with an old log mill, lumber camp & several cow camps nearby just waiting for to be detected in the Spring.  If you're interested in trading one your MD's for a pair snowshoes let me know. Thanks for the follow up, I'll give it a read tonight by the fire. Oh, forgot to mention the toll roads & immigrant trails...

Later short timer.

[GB_Amateur]

13 hours ago, scoopjohnb said:

Want to hunt with the X-terra like the Fisher, just notch out that highest number.

I prefer not to myself, but sometimes on rough mineralised ground I will notch out that number, making it huntable.

Why I don't like to do it,... fixed ground balance that is spot on has given me some deep and accuratly ID-ed targets. And the X-terra running in all notches open gives me the most chance of it happening.

In fact I have notched off the highest (most conductive) bin, 48, which I think is where pure silver (>99%) would hit,  But that hasn't been enough.  I've had to notch off the next bin (46 = US silver dollar?) as well.  Also, you mention "large iron" as being the culprit.  The word "large" is, of course, relative.  But I get wrap around on 1 inch (2.5 cm) long nails.

Randy Horton also prefers the coin/jewelry all-metal mode as opposed to coin/jewelry with notching.  (And for those not familiar with the X-Terra 705, these are both independent of the unfiltered(?) prospecting mode.)  He also prefers full tones, which shows up on the display as 99 values but in reality Horton says it's more like 30 (I think that's what he says).  I've tried these and it takes a lot of practice because the sounds are all over the place when you're swinging over trashy ground.  I've tended to compromise and use max tones but with all the iron range (negative TIDs) and the top two most conductive bins notched off.  I can easily switch to filtered all-metal to check iffy signals.

What I really wonder about is whether I have a lemon.  I've heard so many good things about the X-Terra 705.  And yet it hasn't been an easy detector for me to use.  I'm notching off the 46 bin.  Do others have to do that to squelch the wraparound signals?  I have a friend who owns a 705 and I'd like him to try mine out and tell me if it matches his.  But unfortunately we don't live all that close and he and I are both busy with our "real" jobs which makes it difficult to find a common time and place for such a test.  In the meantime I'm sitting tight and awaiting next spring's warm weather to get back to operating it.

[scoopjohnb]

You are experiencing wraparound on that size of iron because the sens is too high or you are using the high frequency coils.

Don't dismiss the medium frequency coils, they have a lot to offer.

If the sounds become too mixed and muddled, drop down on the number of tones.

99 tones is great on isolated targets,... but a real pain when the trash starts.

[Steve Herschbach]

I have not found a detector yet that will not "wrap high" on certain ferrous targets. Large hard steel nuts and bolts, axe heads, large washers, flat "tin" steel, broken square nails, etc. DD coils in particular can be problematic.

It is mainly a problem for coin hunters, as the signals fall into the high coin range. The problem is made worse when people disc out the low ferrous range. The targets that produce these signals usually deliver mixed VDI numbers, both very low and very high. Discriminating out the low signals leaves only the high signal, which sounds like a coin. This is the main reason I usually do not block out target ranges but hunt via tones only. That way I hear the mixed responses that reveal these items for what they really are.

Lower frequencies, lower sensitivity, and concentric coils can all help, as can full spectrum visual displays like on the White's XLT/DFX/V3i and Minelab Explorer/CTX models.

[Steve Herschbach]

To further illustrate. Most detectors are set up to deliver a single Visual Display Indicator (VDI) number or Target ID number by averaging everything under the coil. Single clean targets like a coin tend to deliver a tight VDI range, whereas ferrous targets can deliver mixed VDI numbers. Unfortunately most machines average the mix into a single predominate response.

Minelab and Whites full spectrum displays can shows multiple VDI responses simultaneously. The diagram below shows the Whites SignaGraph display of a coin and a ferrous item. The visual response difference is obvious.

If the operator discriminates out the low ferrous range, all that the machine delivers is that high end audio response. If everything is set to accept with ferrous low tone and non-ferrous high tone, now you get a high tone response on the coin but mixed low and high tones on the ferrous.

The CTX 3030 Target Trace function serves a similar purpose.

[Steve Herschbach]

 Finally, some detectors have a gated audio or binary audio design which is intended to make the machine sound clean and sure of itself. All targets resolve into a single VDI number and a single audio tone.

This is problematic in dense trash and on these troublesome ferrous targets. Newer fast response designs have more of a real time audio that paints a fuller picture of what is under the coil but can also be hard for novices to deal with. Still, this is the basis for the XP DEUS and the Nokta/Makro designs. Garrett refers to it as "tone roll audio" and provide this explanation in the AT Pro manual:

[HardPack]

Steve, GB, Scoop,

Attempted to post this earlier but was sign-out twice (failure to launch or pink slipped ?)

If I understand correctly several posts explain this issue as a “transient high tone blip”.  I have experienced the same TID jump from -8 to +48 with the XT705 when over larger pieces of sheet metal buried deep enough not to over-load the MD.  From what I have read the coil transmit signal creates a magnetic field around the metal objects that pass through the transmit field (in my case an 18.75 kHz 5.5x10 DD).  The return signal to is analysis-ed by the MD based on size, shape, thickness, orientation, texture, conductivity, etc yielding a TID and tonal response.  If the metal target is larger than the coil transmit field the metal target is not fully enclosed by the coil transmit field creating a tonal “blip” as the signal pulses over the target surface ( perhaps a failure to wrap?).  When over these flat thin larger iron targets my ears pick up a slight sparky background noise while the TID is shifting from -8 to +48 often settling on +48.  Often when detecting in heavy iron trash, after a few confirming digs, I notch out -8 through -4 and +48.  I hear a cleaner tonal response on the smaller thicker silver coins that lock between TID +44 and +46. Others have recommended using a lower frequency concentric coil. I don’t have enough experience to agree or disagree with Horton’s wrap around compass theory but I have my misgivings.

Perhaps someone with more experience, such as Steve, can help clarify.  (never mind)

HP

[Steve Herschbach]

Randy was not the first to envision the VDI scale as circular instead of linear. Regardless, I think the posts I made while you were working on yours cover it pretty well.