Interesting Experience

Tom:

Was out back playing in my test garden and stumbled across something unusual. I have a clad dime buried recently at 4" deep in close proximety (3") to a large, bent, rusty square nail buried recently at 4" deep. Normally get mostly iron grunts all around with occasional iron false squawk from this target. Decided to try something different.

When swinging the F-75, the shaft of the detector is at about a 45 degree angle, so I decided to tilt it back more (like to a 25 to 30 degree angle). Started twisting my wrist left and right with the tip of the large coil making an arc back and forth over the target. Interestingly, I started receiving high tones and as I circled the target most of what I heard was high tones.

Probably just an anomaly but could be significant.

Ron

I had a embarassing experience about a month ago...... where I was demo'ing a CZ and a F-75 to a coworker in my test garden. Ironically, BOTH units had lost approx 2" of total depth capabilities. I was making every EMI/Geophysics excuse in the books.
DISCOVERY/RESULTANT!!! = I only THOUGHT I was wearing my digging/detecting boots. In actuality...... I was wearing a pair of steel-toe'd safety boots! It took 2 days to discover this..... as when I was ready to head out (on a different day) to go on a real hunt,,,, I grabbed the wrong pair of shoes again.... and THEN realized my error. Soooooooooo...... before proceeding on my detecting trip... I just HAD to put on the wrong boots and head to the test-garden. SURE ENOUGH; DITTO! Same resultant. My deepest targets were undetectable. ----- Then I switched to the "no metal" shoes/boots.... and suddenly I had full performance restored!
Funny thing.......... The steel toe'd boots would NOT give any audio 'interference' signals,,,,,, BUT..... would definately induce "silent masking"! I preach this, teach this (((and I think I even talk about this in the video))); YET, I got nabbed by it again!
-----Sooooooooo...... I wonder if you are setting the angle of the coil on your detector....so as to be FURTHER away from your body,,,, giving you different results.

Tom

Ron is this using the stock DD coil or the small coil..I have Been Hunting a 1916 homesite 6 acres..It use to be an old Dairy farm and over the last 40 years its been a lawmower repair shop shed..Metal everywhere from all over the yard and around the house..getting signals from 6 to 12 all over the place at one spot the F75 sounds like a M16..with Iron targets I counted over 8 targets at a fast sweep
Iron is a Nightmare..i did pull a 1977 clad dime at 4" near the steps But thats it mostly can slaw and Iron when dug..I haven't give up yet But it has Been Discouraging...
Tom great story on the work Boots..I can see where it would be easy to make such a mistake..I have been Detecting with my 3 year old and her get close to the coil and pick up her sho lace eyelets..Drove the machine nuts ..took me a second to figure out what was happening..lol..james

I often wondered about the steel toe shoe thing even though you can't hear there interference, interesting.
I've also had my doubts about the proper wrapping of the coil cable and what results a sloppy wrapping job may have?
Ken

Tom:

Yep, the large DD coil is quite a bit farther away from my body but I wear rubber moccasins and didn't have any digging equip. with me. Are you suggesting that our bodies affect the coil field, even though no metal is present? I know that objects near my ham antennas distort the field and cause a certain amount of power to be reflected back toward the transmitter (VSWR).

I thought that maybe the way the coil was sweeping in an arc; the physical distortion it caused in the field may have created a situation where part of the trans. signal and part of the received signal were 180 degrees out of phase. In other words; canceled each other out. If it canceled out the iron phase but didn't affect the dime phase, maybe that's what's going on. Best I can figure.

Ron



Edited 1 time(s). Last edit at 05/09/2008 09:19PM by jackalope.

No, no....... No Voltage Standing Wave Ratio to mention ...in reference to coils; however, inductive balance is critical,,,, in concert to imped. matching (similarities; ....but not quite the same). And your body should hardly interfere with performance of coil/unit..... only minutely'. -----Now..... the arc..... the 'angle-of-attack'...... the coils approach angle INTO the composite multi-target config has major performance-outcome characteristics/resultants...... so much so..... that the final resultant can be "go" or "no go" as far as detection of the non-Fe target in co-locate w/Fe target. Hunting for non-ferrous targets amongst iron is a electromagnetic nightmare for the detector. Ferromagnetic materials produce a 'electro' and a 'magnetic' ('E' & 'H') response and have a large hysteresis (magnetic memory) element with a very slow electromagnetic decay rate; due to the high magnetic permeability factor of the material (the iron). In other words........ the return signal of a Fe/iron object "hangs in there..... for a long while" from the iron object..... due to it's slow decay rate; where as ..... the return signal from the non-ferrous object is a very 'short' blip in time duration (compared to iron); subsequently "overriding" --- washing out --- masking... the short-blip return signal from the non-ferrous (diamagnetic) target. Non-ferrous targets produce (for the most part)... ONLY the 'E'...the 'electro' response. This is HIGHLY audibly demonstratable/evident whilst using a Pulse Induction (P.I.) detector. A PI detector will produce a very short audio response over a non-ferrous penny. Now...... over a 1943 steel penny,,,,, the audio response starts to eminate BEFORE the coil is passed over the target.... as the coil "APPROACHES" INTO the target; subsequently giving a much longer audio report over the exact-same-size target ((( apples-to-apples ))). This is the definition of 'magnetic permeability' (( Degree/Magnitude of "magnetizable susceptability"..... or 'willingness' to accept magnetization )).

Off my rocker..... AGAIN!

Tom

Ken,

I STILL wrap the bulk of the coil wire tightly..... up high on the stem...... just beneath the control box,,,,,,,, with nearly a straight shot of minimal coil-wrap on the entire lower stem. I've performed test-garden (fixed condition environment...... controlled variables) testing with coil wire near the coil...... and ... conversely; near the control box....and found no difference. HOWEVER..... a floppy, losely wrapped coil wire that is 'in motion' and near the coil .... can do strange things.
The Fisher coil wire quality .... and (finally) Minelab coil wire is (now) superior stuff. EM shielded.

Tom