Increasing Depths

[hisoka147]

Upon building this unit, my actual air testing result is that my loop coil Antenna measuring 12 inch can detect a pop can at least 15 inch in height.

I want to increase more depth and I need any opinion from anybody. Thanks

[BobCat]

I built two of these, one unmodified with an 8 inch flat wound flat coil to compare with the other one that I made different coils for and modifications to the board. The coil I ended up using, I made two 6 inch 30 turn each coils connected in series. It looks like a double D coil but connected to the board like a mono coil. No real increase in depth but greater sensitivity to smaller targets. IC 9 and 10 were replaced with AD711 opamps (they are a pin for pin replacement for the TL081 or TL072). The AD711’s gave an increase in depth sensitivity to smaller targets and made the detector a little more stable. R23 was replaced with a 1K OHM multi turn trim pot. I got the greatest increase in depth at 10 OHM’s. Another modification that will help with operating the detector is to install a 5K trim pot in series between R26 and VR2, this makes for a fine and course adjustment on the main control of the detector. Air tests between the two detectors on coins does not show much more than 1 inch. Out in the field detector 2 sound out loud on targets that are weak or not at all with detector 1.
Detector 1 unmodified
Pop can in air 22 inches
Copper penny 8 inches in the ground 1/4-reading on the meter.
40 grain lead bullet has to be touching the coil.
Detector 2 modified
Pop can in air 26 inches
Copper penny 8 inches in the ground 3/4 reading on the meter.
40 grain lead bullet 1 1/2 inches
Good luck
Bob

[hisoka147]

Thank you very much for sharing your modification. I'll try to do some adjustment on those parts that you've mentioned and I will provide later the results.

I made some readings about the coil and they say that increasing current on the coil also increases the magnetic field around the coil thus giving deeper penetration. I just wonder how to induce more current flow with Gary's PI coil.

[hisoka147]

I made some adjustment on R23 as you stated Bob, I replaced R23 with a 50K potentiometer and with proper adjustment I can now detect a pop can at exactly 3ft in air.

Another test I made was to create a larger coil but I was disappointed because there are no increase in depth but a decrease. I don't know what went wrong but I'll try to make another one.

[hisoka147]

Okay, I made a mistake about the assumption in making a larger coil for deeper penetration. I made another one and I am amazed I could detect the pop can at exactly 1.5 meters in Air! but of course with some modification on the circuit board.

Now I'm contented about the sensitivity of my detector and it's time to create a design for it's appearance.

[silverdog]

could you please share some of your modifications ?

[6666]

here is some info on the chip

http://pdf1.alldatasheet.com/datashe.../AD/AD711.html

[fastgold]

Which version of the ad711 did you use and did you also try 8in coil instead of dd2 on modded version.How much overlap did you have on "dd2" version and if continuous, does ext wire of coil 1 cont to internal of coil2 with flow in same dir in both

[BobCat]

Which version of the ad711 did you use
AD711J

and did you also try 8in coil instead of dd2 on modded version
I tried an 8 inch flat wound bifilar coil. The mono double D coil is a little better on small objects. There was no difference between the two coils on the larger objects.
How much overlap did you have on "dd2" version and if continuous, does ext wire of coil 1 cont to internal of coil2 with flow in same dir in both
About 50% overlap
And yes the exit wire on one coil connects to the input wire on the other and both are wound in the direction.

[fastgold]

<P>bobcat,thanks for the info as I'm a newbie when it comes to this type of stuff.What do you use as a faraday shield as i was thinking of using foam core with coils laid over recesses&nbsp;in foam and glued,&nbsp;painted&nbsp; outer cardboard shroud&nbsp;(Shielding paint) laid in old whites coil&nbsp; cover. D o you use a plain piece of card board or something between coil overlap&nbsp;to stop shorting out etc,mark</P>