Long and inconclusive first F75 / Mars 7" DD Lion coil report

As you may or may not know I am quite enamored with my F75LTD DST model. There is nothing quite like hunting with a stone cold stable F75, which I was hardly ever able to do prior to DST. I have a broad selection of coils for it and the majority of the time I carry a couple with me into the field and switch them out as I have need. For DD coils I have the 5”, 5x10”, the stock 7x11” and a Russian RIF Ranger 10x14” coil. The Russian RIF coil was a big disappointment, but I still use it for shallow clad hunting looking for hotspots. For concentric coils I have the little 3x6” elliptical and the 10” elliptical concentric. I also regularly use the 7.8 kHz 11” Triangulated concentric coil from the F44 on my F75. The 11” Triangulated coil isn’t tuned for the F75 but it bangs hard on anything up to about 7”, which meets my needs.

When I owned the Rutus Alter 71 I was looking for coils and started paying attention to MARS MD, a company that makes aftermarket metal detector coils. They recently started making a round 7” DD they call the Lion that caught my eye and when they become available stateside I bought one for my F75.

The 7” Lion DD came with a coil cover, mounting hardware and connection cover and it’s a very good looking coil. You can view it on their website.

It air tests about an inch to an inch and a quarter deeper than the 5x10” coil in Disc mode. In CL mode the 5x10 will hit a nickel out to about 15” and the Lion will hit it good out to 16” - 16 -1/2” It is also a very sensitive coil. I probably should redo that test with the nickel taped to ruler instead of my hand because I discovered when bench testing my micro jewelry test target that the Lion picks up my hand and even my fingers. It’s a very sensitivity coil. When I figured out what was going on I put my tiny 10k White Gold 3mm stud earring in a book for testing and it was hitting it almost as good as the little 3x6 concentric does, which is 100% better than the 5x10 DD.

Just a note for those that are not aware….Dave Johnson makes gold prospecting detectors and that is the basic DNA of the F75 and I have come to the conclusion that for pure hots in the 13 to 20 kHz range there is nothing hotter than the F75 LTD, my tiny little micro jewelry test target proves that conclusively in my opinion.

Back to the Lion. It is very sensitive yet stable.

My first use of the coil was in a very difficult location. This site is a soccer field built in an arroyo flood control area. It is a high EMI, high mineralization site. With the Lion mounted on the F75, in JE mode and 3 tone, it ground balanced neutral with the F75’s ground grab in the high 70s giving numbers of 79 and 78. The FE304 graph was mostly on 1 and .3 the majority of the time. As I moved infield it would drop to .3, as I moved back to the sidelines it would return to 1. The difference is the amount of dirt. More dirt in the infield, less dirt on the sidelines. Along with the mineralization there is lots of little iron and hot gravel under the sod. To make it even worse the city had recently aerated the field leaving little ground plugs that look like brown goose poop all over the place.

I once drove through a thunderstorm at night where the lighting was so intense that there was more light than dark for a good thirty minutes. It was like that detecting this field. The dark was the iron tone, the lighting was the high tone. The high tone falsing from the iron and gravel and little ground plugs was so great that any high conductive hunting was out of the question even though I persisted and was able to recover some clad, it was readily apparent I couldn’t keep that up. So I raised the disc to max, notched in high foil, nickel and square tab, put it in delta pitch audio and started listening for the lower tones amid all the high tone noise.

The coil didn’t false in the wet grass and didn’t suffer from any EMI with DST invoked, but the basic high sensitivity of the coil added to the ground noise of the high tone falsing. I didn’t like the way the coil profiled targets but that was more likely a setting issue as I had my all metal mode all jacked up on high gain for bench testing and I didn’t go back and reset. Just plain laziness on my part. I mean it pinpointed fine but the high sensitivity picked up a lot of ground noise along with the pre and post target response and you can’t profile a target at that high a setting. Id numbers are pretty close to stock, some seem to vary a number or two but for the most part were pretty in tune.

The high ground minerals really constricted the coil footprint at depth. Lots of surface coverage but at depth it was a pretty narrow window which required some extra attention on coil overlap.

I dug some fairly deep targets for that site but nothing to brag about. To tell the truth I was just happy to bear with it for a couple hours. I didn’t find anything to write home about. Targets were the normal low conductive what nots, nickels, some zincs that were reading low, along with a bunch of can slaw and foil. Over all a very hard first hunt test for the coil. I brought the 5x10 DD along but after the barrage I went through I didn’t have the mental stamina to put it on and compare on that visit.

When I left the site I wasn’t thinking about how to setup the F75 to better handle the site conditions, I left there thinking that I need to come back with the V3 in correlate mode and see if there is anything good there. That is the trouble with owning multiple units; instead of taking the time to figure out how to best overcome the site’s challenges with one unit you just toss it in the back and grab another. Once again, pure laziness on my part.

I plan on returning there later in the month and do it all over again with both the 7” and the 5x10 and give it another go with more focus on overcoming the site conditions and proper setups.

I know not everyone has my ground conditions to deal with and this write up isn’t valid for anyone but myself. So next report will include some more neutral soil conditions that more people can relate to,

HH
Mike



Edited 1 time(s). Last edit at 11/07/2018 07:12PM by Mike Hillis.

Very comprehensive report Mike.
It sounds like the F75 while shielded from EMI still picks up audibly on every little tick and pop in the soil matrix, is that correct?
Cheers,
Drew.

Great report Mike.

A stable F75 is an awesome unit.

As far as going back over a site with another unit as opposed to trying to figure out settings to overcome the site's challenges, that to me is smart, not laziness.

There are times when a different unit will perform better over the same site no matter how much you try to tweak a unit or try to figure out the previous unit you were using.

Going back over the site with a V3 in correlate mode, in either signal or multi frequency and trying different filters to see what else you can sniff out, is good thinking in my opinion. You can learn much about the site when using different units.

Only issue with switching units is, after swinging an F75 for a few hours, when switching to a different unit, a lot of units feel like a cinder block !

The F75 is a sweet unit to swing.

I just love mine i havent all the package you have but i wont need them .The only which i find tempting is the Cannon coil from Cors/Nel and the ultimate 13" has a good reputation on a lot of machines.



Thanka for your amazing report that s maybe what Lost treasures was lacking....

RR