Help. FISHER GOLDBUG g2

[Skippy]

Why have you quoted MY post, when ( nearly ) all your questions are for Pito.?
Question 5: Increasing the gain of the pre-amp is not easy. If you change the 'top part' of the feedback components, you will have to change all of R10, R11, C13, C14. Changing the R values to +30% is easy, reducing the C values to 77% is harder, especially when they are unknown values.
If you change the 'bottom' of the feedback network, you have the unusual L-C tuned circuit to deal with. I think you should leave that alone. Put a 75 Ohm resistor across R14, to make it 20 Ohms, then add 150 nF ( or 100nF plus 68nF ) across C16, to make it about 630 nF.
This should increase gain by 35%.
Question 7 : I wondered about this too. Pito likes two-box machines, maybe he thinks this is your solution to great depth.
He also said "To double the range you need to increase amplitude 10x times". The truth is you would need to increase amplitude by 50 to 60 times to achieve this pointless depth increase.
Magnetic fields decay according to an 'inverse third power' effect. This applies to the transmitted field of the detector, AND to the field of the targets. So the actual received target signal decays as 'inverse sixth power'. So in theory, for a very large target many metres from the coil, you would need 64 times TX to get double distance. For sensible 40cm distance targets, maybe 50 times TX is OK.

[Arcoman]

Why have you quoted MY post, when ( nearly ) all your questions are for Pito.?

you are more savvy. I don't trust pito))
There would be a lot of posts. and so I shortened it)) thanks for the answer

[pito]

4. why disable r70? = you don't want to put 100V to inputs of op amps, U1,U2
5. How to increase the gain? change what? your suggestion = Decrease R14 even up to 0 ohm
6. regarding air power. it was 25 for the average maneta. became 32-33. in discrimination mode. = video ?
7. How to place the tx coil 50 cm from the rx. cut the sensor? ) = I mean any spare coil which you have, not which belongs to detector = Rx testing coil.

[Arcoman]

Magnetic fields decay according to an 'inverse third power' effect. This applies to the transmitted field of the detector, AND to the field of the targets. So the actual received target signal decays as 'inverse sixth power'. So in theory, for a very large target many metres from the coil, you would need 64 times TX to get double distance. For sensible 40cm distance targets, maybe 50 times TX is OK.

My task is to get a stable, readable signal for an average 30-35 cm manet in discrimination mode. iron bunkers at a depth of 20 meters do not interest me. ))

[Skippy]

"My task is to get a stable, readable signal for an average 30-35 cm manet in discrimination mode"
Unfortunately, this is not an easy task. Your G2 / GoldbugPro operates at 19 kHz, which is not the best for copper / bronze / silver milled coins. And any single frequency machine struggles to eliminate ground signal properly, meaning deep targets have poor identification, unstable sounds, numbers.
Multi-frequency machines are able to give you something like your desire. They are deeper, and the identification is much better. If you are able to borrow or try a machine like Minelab Equinox, Vanquish; Nokta-Makro Legend, you would be surprised.
I have an Equinox, and I have dug a bronze half penny from 29cm, in very wet ground, with good target identification number / sounds.
https://www.allnumis.com/coins-catal...nny-1913-24365

[Arcoman]

6. regarding air power. it was 25 for the average maneta. became 32-33. in discrimination mode. = video ?

there is a lot of clutter at home. sense 100. discrimination.

[Carl-NC]

The Goldbug/G2 is designed for gold field hunting, where ground conditions are often severe. By increasing the TX strength and/or increasing the receiver gain you run the risk that the unit will overload in severe ground. You can always raise the coil a few inches and still hunt, and if your ground is not severe then you have a better detector.

[Arcoman]

The Goldbug/G2 is designed for gold field hunting, where ground conditions are often severe. By increasing the TX strength and/or increasing the receiver gain you run the risk that the unit will overload in severe ground. You can always raise the coil a few inches and still hunt, and if your ground is not severe then you have a better detector.

I think engineers are smart. and left a margin of safety. The current strength increased by only 15-20%. This is the range to stay in. The current in some devices is from 80-120 mA and they are stable. Ku will grow by 10-15. The device is stable in the apartment. somewhere far from civilization and it’s even quieter. lt6230 - 250khz there is a lot of reserve. I adjust the device for the best readings. it didn't work quite right.

[Op04]

With VLF the more current gave to coil it also mean the more vibration inside the coil that causing losing its origin resonance, other minus is more reacts to brick stone. Even we see detection in air look promising It's nothing better to ground respond perhaps trigger unwanted ground respond and eventually make the coil destroyed. It way differ from PI the more vibration on coil the better target respond

[Arcoman]

With VLF the more current gave to coil it also mean the more vibration inside the coil that causing losing its origin resonance, other minus is more reacts to brick stone. Even we see detection in air look promising It's nothing better to ground respond perhaps trigger unwanted ground respond and eventually make the coil destroyed. It way differ from PI the more vibration on coil the better target respond

the earth is cut off by the ground balance. bricks and hot stones with a resistor on the board. you just wave a piece of ferrite and twist it. Firit reactions do not , mean you hit the mark. there would be stability.how can the sensor be destroyed? you will miss what was and what is now. these are two big differences.

[Arcoman]

The current increased to 8 mA and the panic was absolutely terrible. Better suggest how to stabilize all this. Try your best for the common cause.
Question for the engineer. Why are capacitors c2 and c57 placed in parallel and in different places? Why in different places?

[Op04]

the earth is cut off by the ground balance. bricks and hot stones with a resistor on the board. you just wave a piece of ferrite and twist it. Firit reactions do not , mean you hit the mark. there would be stability.how can the sensor be destroyed? you will miss what was and what is now. these are two big differences.

Sorry I only play with tx850 not G2, after mods it only good in the air test, when I put the origin arrangement it mess the coil became useless, its a risk I don't want you to get through

[Arcoman]

Sorry I only play with tx850 not G2, after mods it only good in the air test, when I put the origin arrangement it mess the coil became useless, its a risk I don't want you to get through

in the tx850 you must first change all the wires, capacitors, rx wiring and input circuits. they are cheap there. It’s better to set the NPO to 1% -5%. then add a 10 kom trimming resistor. on r63 track cuts. if everything goes well. Then proceed to increase the current at tx. but you need to look at the inductance sensor. it's different for everyone. since the device is analogous to g2. should be like mine. it is stable, but up to 30 cm.

[Arcoman]

in the tx850 you must first change all the wires, capacitors, rx wiring and input circuits. they are cheap there. It’s better to set the NPO to 1% -5%. then add a 10 kom trimming resistor. on r63 track cuts. if everything goes well. Then proceed to increase the current at tx. but you need to look at the inductance sensor. it's different for everyone. since the device is analogous to g2. should be like mine. it is stable, but up to 30 cm.

removed resistor r71. There were fewer spontaneous triggers. reduced resistor r14 to 22.6 ohms - the signal became clearer at 30cm. but it’s a shame it’s smeared above.

[pito]

removed resistor r71. There were fewer spontaneous triggers.

This is required during Tx modification, when this is done after checking amplitude on C57, if is less than 5V resistor can be connected back if it is higher you need protection 4V zener diode.

C57 it main capacitor, C2 is fine tuning capacitor.