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I am new here so there may be a better forum to ask this question so redirect me if needed.  I have a Teknetics Delta 4000.  I need to probe  a fiberglass tube 2 inches in diameter to see if I can detect a copper beryllium strip which should be inside.  Unfortunate I cannot get closer than 16 ft to the tube.  I have found a 25 foot 5 pin DIN cable that would extend the cable that is on the 4000.  I could then detach the pickup coil and mount that on a 16 ft PVC rod leaving the electronics and readout with me.  I only need to know if there is something there or not there.  The rod is 100 ft off the ground and 16 ft out from my closest reach.  Anyone ever tried to extend the cable?.  I know it is not a perfect situation but I would save me a lot of money if I can detect the metal strip.  Regards   Mike

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1 hour ago, K4PI Mike said:

I have found a 25 foot 5 pin DIN cable that would extend the cable that is on the 4000.

I assume you mean you've found one you can buy but don't want to invest in this extension cable if there's no chance it will work.  (Otherwise I'd say "try it and tell us!").  The good news is that some gold detectors that allow the control unit to be detached from the shaft and mounted on a person have coils with longer cables (e.g. ~8 ft compared to ~3 ft).  The fact that they go this route (require you to buy a separate coil with long cable as opposed to an extension), though, makes me wonder.  And you're going to add another 17 feet....  Another issue is impedance matching the two cables, which is probably critical.  (This means the two cables need to have similar inductance, capacitance, resistive properties in combination.)  But now I'm getting out of my comfort zone.

This is a really good question for Carl Moreland and his Geotech forum members.  Unfortunately it's not as easy to join that forum as this one.  He might answer a PM from here, though.

The other thing that might make this difficult is how conductive the Be-Cu strip is.  If it's large enough (thickness and extent) then probably possible.  If it's super thin or tiny you may still have problems.  Also, I assume this 2 inch diameter fiberglass tube is reasonably far from other conductors, otherwise that could nix your plan, too.

 

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Thanks for the input.  I don't mind buying the cable but thought maybe someone had already tried this.    I found and extension cable for about $20 so might be worth a try.  The Be-Cu strip is about an inch or more wide but fairly thin, Thicker than a standard  tape measure.  Probably just have to go for it and see.  Will keep you posted.

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I’ve seen extensions up to three feet on VLF detectors, but 25 feet? I have to think it would change the target id numbers at least, but if all you want to do is get a signal it may work. For $20 if it was me I’d JW go for it and see what happens.

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Obviously, you could have the control head near the search head, using the current cable, then extend the audio cable.

Low impedance audio line can run 24' easy and then you would not have to worry about RLC of the long search coil cable interfering with operation. Plus you could use any old cheap 2 conductor wire.

Joe W3TKO

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2 hours ago, K4PI Mike said:

The Be-Cu strip is about an inch or more wide but fairly thin, Thicker than a standard  tape measure.

That should be plenty big enough for a detector like the Tek Delta to pick up within a few inches of the bottom of the coil.  (Again, assuming there's not some other larger nearby target interfering.)

 

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Hi Joe, well weight is a big consideration ie trying to maneuver the control head along with the pick up coil on a 16+ ft stick of pvc.  The Pickup coil is very light in weight so moving it around alone  would not be to much of a problem.  Being a ham you probably know where I am going.  I am using a SteppIR antenna and I want to see if the tape is actually moving in the fiberglass tube.  The motor is drawing current but by varying the length there should be an SWR change and there is not.  It is director # 1 on a 4 element 32 ft boom SteppIR.  The motor can be running but the tape not moving due to a stripped sprocket.  It is 100 ft off the ground so a big jog to take down or expensive to rent a bucket truck to check it out.  If I find the tape is not moving I will rent a bucket truck and repair it but not before I am completely satisfied it is bad.  73 Mike K4PI

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Yeah, Mike, a 16' piece of PVC would be like a noodle even without weight on the end! I'm just offering a solution in theory....but you know what Yogi Berra said about theory.

Now if the tape is moving, you should be able to pick a more convenient spot to measure, say 1' or 2' out the innermost point of travel of the tape. If it is moving, you should be able to detect movement at that point.

Sounds to me like it is not moving though, sadly, if you are not seeing any change in resonance.

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K4PI Mike

Three alternate ideas; attach a hand wound loop/inductor to the end of long pole. With two wires connected to an Inductance meter, a Grid Leak meter or a Beat Frequency Oscillator (BFO). Slide the loop around and along the length of your antenna element looking for a change in reading.

I hope one of these will work for you,
Chet
 

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A handheld pinpoint probe would likely detect the copper sheet, and would be easy to attach to a glass-fibre rod etc. The audio beeper will be hard to hear from 15/20 feet away, you will need to use it at a quiet time.
Pinpointers unfortunately tend to drift with time, this depends on the make/model , some may be better in this respect. This would mean having to turn it off, then on again to 'recalibrate' it.

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