Anyone use the large butterfly coil with F75?

[tigerbeetle]

I haven't had a chance to use my 12x15 SEF "butterfly" coil with my new (month-old) F75. Anyone use this large loop yet, with F75? Any depth or ground coverage info? Any tips on best sensitivity or discrim numbers?

 

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[Dug]

I have used my big coil on about four outings so far. The first thing I noticed is that on soil where my fast grab Ground Balance would show an average of say 85 with a factory coil, with the big coil the same ground will only read as high as 54. In fact 54 is the highest number GB my F75 ltd will pull doing the fast grab anywhere with the 12X15. Average GB range seems to be 42-54. I have not experimented with a planted garden for depth, but I feel I'm getting about 2 inches extra depth by air test with it in BP mode over standard size coil. I don't have that same level of confidence in the default regarding big VS standard coil. One drawback with the big coil is trashy ground with multiple targets. I have found that I have to slow down and work twice as hard trying to pick a target out from many different angles with the larger coil than I would have using the standard coil. I feel my biggest advantage with the big coil is covering a lot of ground in flat open fields. For me it's back to the factory coil for woods and "busy" ground. But I will break out "godzilla" on a flat open field on a first trip through until I get a feel for where the multiple target site might be.

 

[tigerbeetle]

Great info. I've used my large loop twice (lengthy sessions) and couldn't figure if I got significantly greater depth but the increased ground coverage was remarkable -- no surprise with the size of the loop. It shined during what might be called exploratory hunts, i.e. walking through large woodsy expanses seeking any signs of life, so to speak. I downed the sensitivity during such reconnoitering runs. Then, when I hit iron, I upped the sensitivity and slightly reduced iron readings, but not all the way. Iron readings are like fingers pointing toward the good stuff. I can't believe how many folks totally tune iron out -- and lose massive amounts of sensitivity toward hard metal readings.

Using the large loop in high FE (iron) areas, like homesteads and farms, I was surprised to see the large loop's ability to ferret out good readings among FE. Technically, the large head should be more heavily impacted by the masking effect of FE. Instead, I nabbed hard metal items (mainly buttons) missed by the smaller factory loop, although they weren't overly deep. It sure seemed the big loop had an enhanced ability to see through soft metal to find the hard metal. Kinda weird. Also, I was surprised at the relative ease of centering a find, using the logo on the loop. I've developed this technique of backing the head (swinging it slowly) toward a reading to center on it. Still need a hand locator.

The arm strain with the larger loop is a considerable factor -- and I'm a fairly strong soul. Of course, I'm talking five or six hour hunts.

Outside of some always-appreciated one-piece Colonial and Federal period buttons, I haven't hit anything big with my larger loop but it seems a winner when it comes to hearing what's down there.

 

[Dug]

I agree with your observations. I too run my discrimination way down when scouting through woods since I want to pick up anything man made that will lead to pickets/camps/old house sites. Once on them I make adjustments. I forgot to mention that I noticed that the larger coil is not as likely to false on brush as the standard coil. Because I'm in such good soil in the SC Lowcountry I can get away with my sensitivity between 85-90 with the standard coil without any chatter/instability but wonder if that would cause occasional falsing on plant stems that I get? If so I'm wondering if the larger coil is handling more of the higher sensitivity without overload, which would explain less falsing and also explain the differing ground balance numbers?

I took the big coil back to some pounded spots but didn't dig anything depthwise that I would not have picked up with the standard coil. Until I get off my rear and plant a test garden I won't know what the depth gain is.