F-75 Manual

Tom:

In the F-75 manual, under Search Techniques, Estimating Target I.D. on page 29, in the third paragraph " For instance, if discrimination is set at 12, and most sweeps result in no visual target ID, the target is most likely iron even though the majority of the ID numbers will be greater than 12". If it said most sweeps result in no AUDIO target ID, it might make some sense. Is this just a typo or am I just missing the boat?

Ron

What this is trying to say is the f75 has 2 ways to see the target ( tone and ID) , but if the disc is on 12 everything below is iron and whet the No. comes up you can dig it if you think it is a coin. all so on the DE mode from 5 to 15 is a low gain, so if you us 16 you have more gain and depth, from 15 down is the iron. I use sen. 70 or up, disc. 16, notch 35 (36 if looking for war time nickels), DE mode most of the time, tone 3H. I use the small coil and can get a dime at 8" this way. All so they say if you put the frequency on 7 it will go deeper??? Hope this helps.

John:

I'm understanding the independence of the Visual ID system from the Audio ID system. What I'm not understanding is the sentence that says if most sweeps result in no visual ID ... even though the majority of the ID numbers will be greater than 12. It looks like it's saying that even if you get no visual ID that you will still be getting visual ID numbers. How can you get no visual ID and still have the majority of visual ID numbers above 12? Like I said in the original post if it read; For instance, if discrimination is set at 12, and most sweeps result in no AUDIO target ID, the target is most likely iron even though the majority of the ID numbers will be greater than 12. This might make some sense.

Thanks for sharing your settings and the heads up on Discrimination in DE, 5 thru 15, being a low gain area. Not sure about notching (out) either high nickel (30 - 35) or low tab (36 - 45). My understanding is that if your Discrimination setting is i.e. #16, then notching #35 will notch (out) the high nickel area (31 - 35) and notching #36 will notch (out) the low tab area (36 - 45). That seems like too much area to notch (out) but I'm willing to learn.

When I purchased my F-75, I also got the small coil. My Sunray probe will be here tomorrow. Looking forward to using the whole system.

Thanks for the heads up on freq. F-7, which I think would be 13.158 kz. My understanding is that F-1 is 12.821 kz, so that's the range of the freqs. available. Based on what I've read, I'm thinking there's some benefit to switching freqs. Reading Tom's article makes me realize that just a little deeper can take you a lot farther back in time (target wise).

Ron

I believe that what the manual means is. If with those settings, iron, with a VDI more than 12, say 13,14,or 15. Will not display a ID number, even though the ID is above 12. So if your disc is set to 12, numbers 13,14,15 will not be displayed either if the target is iron, but you will get an audio response. I do not own a F75,this is what I am getting from reading the posts.

Try going to www.fisherf75.com my help, all so I made a error on the 5 to 15 it is 5 to 19, so use 21 or 4 for more gain.

Ron,

I agree it should read no audio response. Also when they say it is [most likely] iron that is where careful resweeping of the target to see if you can get a fairly consistent tone or ID may result in some good finds.

Tom

Interesting thread. On the F-75 (and T-2), yes...... the VDI, audio tone-ID, and Disc are completely independent of each other. If anything, the audio ID vs. the Disc setting more closely parallel each other. This electronic design architect is deliberate..... and is a attribute.
Example: If you set Disc at '29'....and you pass a 'V' nickel that normally ID's as a '28' under the coil; the VDI will remain blank and there will be no audio response. Now.... this is NOT to say that you could detect higher conductive targets underneath the nickel. . . . a very common misconception.

__Another case-in-point --- recent experience/example; I had been detecting a parcel of land in Sanford, FL for nearly 2 years with the F-75. For very specific testing reasons, I have always kept the Disc on a setting of '10'. This parcel of property was moderately heavy with iron. I removed ALL non-ferrous targets out of this area with F-75..... to the best of my (and F-75's) ability. -----Now...... my testing would ensue. I now (finally) dropped Disc to a setting of '6' ((( been waiting to do this for a LONG time ))). MANY more non-ferrous targets came to light. The most noteworthy educational target was a fairly worn 1963 silver Roosevelt dime at a measured 6" depth. Out of the ground...... It ID'd as a continous '70'. In the ground, it ID'd as a 'bouncer'........ VDI jumping from 46 to 97 AND DEPTH WAS READING 11". In 'monotone', the audio was fairly clean and solid. Invoking 4H tones.... and the target audibly ID'd as a moderately solid/somewhat repeatable 3rd highest 'zinc' tone (what would be catagorized as CZ-70 'relic' tone). If I put the F-75 into 3H tone option..... the dime would ID as a mid-tone/aluminum soda-tab trash tone. This is nearly unimportant....and not nearly as important as the following info.... prior to recovery:
When I first detected this target (1963 silver dime)..... First, I was surprised that I had missed this specific target (and many others). Second, BEFORE I even thought of digging this target...... I flipped the Discrim back to '10' and found my primary answer. The dime completely disappeared. NO audio response.....and no VDI. Dropping the Disc down to '6' again...... and the silver dime NOW was bouncing again on the VDI between 46 to 97. How and Why would this VDI 46-to-97 non-ferrous target be Disc'd out at a Disc setting of '10'???? When I first attempted recovery of this target, I dug a 8" x 8" x 8" cube of soil/plug. I pulled the plug out of the ground and flipped it over. Because the target was reading 11" deep.... I had some certainty that the 8" plug did not contain the target; subsequently resulting in my 'dunking' the coil down to the bottom of the hole....... only to find no target. Then I swept the up-side-down plug I just pulled from the ground...... and found the target only 2" deep from the bottom side of the plug. I scraped away the dirt until I found a silver dime..... and could see the impression of the dime in the dirt at the 6" depth strata. The F-75 was completely wrong on the ID and also completely wrong on the 11" depth reading. Hmmmmmmm. Not happy and needing definitive resolution acquisition....."WHY" this happened. I proceeded to rapidly 'shave' the dirt plug from the bottom side... at approx 1/16" increments .... utilizing 20 lbs test monofilament fishing line until I Found the answer; a blood spot in the soil (from a COMPLETELY decomposed small nail) at the 4" depth strata..... partially masking the dime. ........This validates the independence of VDI vs. audio ID vs. Disc setting. It also validates EM signal attenuation via the iron oxide blood spot..... and why the 6" deep dime registered as 11" deep. Good thing the dime was not an inch deeper (7" deep)...... or the blood spot was not 1" shallower!
The F-75 was incorrect about ID and depth. That's okay..... as the Explorer completely 'nulled' over this target..... the Coin$trike was silently masked with no audio at all..... and the CZ was iron-falsing with high-tone/low-tone bounces.... very indicative of what 90-Deg. bent nails do to a CZ.
Conclusively; Try this with your F-75:

Place Disc on a setting of '0' (zero). Find/detect a few different nails. You will see them ID as say: '10' & '13' & '11'. Now..... place Disc on '7' and watch them completely disappear!!!..... both audibly and VDI.

Tom

So Tom, I'm getting that the idea is to use the lower Disc. setting #6 so even ferrous items above #6 will be detected and possibly close proximity non-ferrous items also.

Disc. of #10, you lose the ferrous targets and the non-ferrous targets also. Is it typical that the EM from the ferrous target is so strong that in Discriminating it out you lose your chance to hear the non-ferrous target?

Only thing I can compare it to is Ham Radio. Sometimes the background noise is so loud, it covers up the the good signals. Occasionally, someone will put a strong (loud) carrier (hetrodyne) on the freq either intentional or unintentional. You would think the loud carrier tone would block out everything and sometimes it does. Other times it just knocks down the noise enough so that the good signal, once covered up by the ambient noise, can be heard. It's weird but it does happen.

Ron

In theory,,,,,,, in an ideal world; Targets are spaced far enough apart so as to be single, solo targets....... not tilted, not near hot rocks, not near iron, no dirt mineralization etc....... This would allow the detector to ID targets with greatest accuracy. HOWEVER; This is not reality ..... not the real world. Fact of the matter is; Nearly all targets are somewhat/somehow handicapped. First, to answer your question; As a good target (say a coin) is moved closer to any other metallic object, a multiplicity of problems are introduced to the detector. Now add dirt mineralization, tilt the coin, add a hot rock or two, etc..... WELCOME TO THE REAL WORLD! This is genuinely what we contend with as detectorists and detector engineers. How do you correct and compensate for infinite unpredictable variables?! .. Secondly; What may be categorized and classified as "these two targets are too close to each other" to Brand 'A' detector & coil Assy may present different results to Brand 'B' detector and coil Assy. The extremely enhanced adjacent target separation characteristics afforded by a elliptical Double D coil presents just exactly such. A coin and a pull-tab... both at a 6" depth....... and adjacently separated by 6", poses a severe problem to a 10.5" concentric coil,,,,, but does not even approach "problem" status to a 11" elliptical DD coil.

More food for thought!

Tom

Tom:

Is it just a coincidence, or is it something significant, that the VDI jumping between 46 and 97 midway point is approx.71? (ID number of the Rosy dime.) When faced with situations like this (repeatable VDI jumping) would it be reasonable to use the midway point as a possible ID? I'll dig a few just to see.

Ron

Ron,

Mostly coincidence. In situations like this..... COMPLETELY ignore the VDI. Rotate your body around the target until you have the best/most clear audio report. ((( This is usually best performed in monotone ))). NOW...... and only NOW,,,,, you may look at the VDI,,,, but for a distant secondary data input. You should already know (at this point) that you will/will not recover this target.

..... At this point, you may want to play with a interesting geophysics iron magnetism phenomena; At the point of 'Max Q' audio resolution...... start rotating your body AWAY from this Max Q point whilst sweeping coil. You will notice that when you start rotating into the iron masking culprit .... you will witness the VDI numbers climb very high,,,,, until you rotate your body far enough out of detectability of the non-ferrous target. Audibly, the signal will sound very ratty....,,,,, just prior to complete loss of the non-ferrous 'good' target. Iron masking does weird things!

Tom

Tom:

Seems like there are so many variables that can fool a person, that a single tone allows you to focus a little better. 1F and 2F are a little too whiny for me. At Disc.#6, with a solid /clear signal, do you dig everything? VDI certainly takes a back seat but how about the confidence indicator and the FE3O4 indication? Does "beep and dig" result in lots of junk this way?

Wish it would warm up!

Ron

In most cases, digging everything is not feasable or practical. If you are relic hunting at a old site.... then the 'dig everything' policy applies strongly, with potential discretion (if modern trash exists at old site). In iron infested sites, completely ignore the Conf. scale and the Fe3O4 scale. Yes, monotone 'simplifies' things like reducing human fatigue factor. ......,,,,,,,, No matter what, you will always recover trash items; a inevitable part of the hobby. What counts is the RATIO of trash-to-good targets.

Tom

Tom:

If using Disc. #6 in JE, monotone with no notching and getting a good/solid tone, do you have any guidelines as to dig/no dig? You mentioned that you would normally make your dig/no dig decision before you looked at the VDI. Digging all non-ferrous targets works for me but many of the good hits will be iron. Practiced somewhat on different objects, both ferrous and non-ferrous, to see if I could distinguish good from bad tones as per the DVD. If all targets were at the same depth, it might work for me but what sounds sharp at 8" will sound whiny/broad at 2". I'm wondering if maybe I should stick with 2F or 4F until I get more experience.

Ron

Ron,

First, I would nearly never recommend using 'JE' mode for normal inland hunting. Too many variables that can cause the unit to be unstable in JE mode. In large open farmer fields where hardly any (tiny) iron flecks abound, may be one-in-few places the JE mode will function well. You are better off using DE or PF mode inland .... and at a higher Sens setting (vs. JE mode at lower Sens setting) as this will allow greater depth on 'coin-sized' objects. The JE mode boosts detection on very tiny objects....... and if you are around an old homestead, the JE mode is 'mental overload'. The other part of JE mode is; you must learn WHERE to set your Disc level to specifically accomodate WHAT types of iron/oxides/flecks/flakes so as to mitigate mental fatigue. Different types of iron respond dramatically different in JE mode; consequently requiring different Disc settings.
Secondly; It's not the 2F or 4F mode that makes a difference. It's monotone mode.... and NOT being in the JE mode. And monotone is for hunting relic sites that are littered with iron.....with your intent to dig EVERYTHING that is non-ferrous anyway.

If you are coin hunting in a modern park...... then I recommend 4-tone.

Tom

Thanks Tom, that sorted things out for me. Last time out, and although the ground was frozen, I used JE with Disc #6, monotone and started picking up small/weak targets at 12" to 13". Probably iron flecks/flakes at 4" or 5" but fooling the machine into thinking they're deeper. I'm going to put in a couple of hours today at the nearest ballfield. Having this F-75 and not being able to get out because of the weather is tough.

Ron