Garrett THD hand held detector

[Topfmine]

I have got a Garrett THD hand held detector for body search but is also good for pin pointing when metal detecting. I noticed the other day i put in a fresh battery and its performance was really good, better than normal detecting further away. The inside is very similar to the Garrett prob pointer with a ferrite rod about 2 inches long. i was wondering how the detecting distance can be increased. If the battery of 9 volts was slightly increased by 1 volt would this make any difference. How much extra voltage would such a circuit board take.
Would turning the very small resistors with small slot on the circuit board increase performance. Could you change some of the components on the board to increase depth. Just curious how it could be achived.

[Carl-NC]

If it's the same design as the ProPointer, then it is an energy-theft type, which is akin to a BFO (proximity effect). That design tends to hit a brick wall in performance. If you have a variable power supply, then remove the battery & hookit up to the supply... vary the voltage from 7 to 8 to 9V and test detection distance at each. I expect that 10V would also be OK but I would not go beyond that.

[Topfmine]

Thanks.

[kt315]

ProPointer is on micro based, THD is analog.

[kt315]

THD

[Topfmine]

So could the THD be improved to detect a little further being analog.

[kt315]

you have to change a coil on bigger. i do not see problems. than bigger coil you set than bigger depth. that is main rule in detection.
good decision is to rego on bounty or tesoro miniversion. it will give perfecto depth you need.

[Carl-NC]

The THD schematic shows that it is an energy-theft design. KT is right, pinpointers are limited by coil size so a bigger coil will be the easiest way to get more depth. There is no simple circuit tweak that will magically give more depth. Also, the whole thing is regulated to 5V so my previous suggestion of testing different voltages is a waste of time. You could try swapping the 5V reg to a 6V or 7V reg but I would not expect anything but the barest measurable difference.

P.S. -- KT, the "VT" transistor should be NPN, not PNP.

[kt315]

thank you Carl. i take those pics from russians forums keeping, i do not check them. must correct.
btw i see ferrite rods in ali for low price. he could buy '200x10mm' rod and check the depth with it experimenting, at first.
https://www.aliexpress.com/wholesale...t=ferrite+rods

[Topfmine]

Thanks guys for your help. About ferrite rods, what part of the rod gives you deeper detection is it by the length or width or the windings. Would a rod of 250 mm x10 mm be better than a rod of 200mm x 10mm or the other way round say a 200mm x15mm over a 200mm x 10mm. Then theres the windings, more winding than less on the rod and does the thickness of wire affect. Does the the size of rod affect battery performance, drain it more. Sorry for asking these questions i am a bit of a novice learning about detectors.

[kt315]

start from 200X10, if THD is 50 mm length you get 2-3 times depth. you have to get equal same inductivity of new coil as in thd measured.

[Topfmine]

I will get a ferrite rod 200 x10 how many turns do i wind it and what size wire?

[kt315]

you must desolder THD rod and measure _____its____inductivity______. tell us the L.
then you do new coil with same wire and with same L.
or, measure frequency and wind a coil getting this one. something near 80-90kHz.