Ground Balance Methods

[Danno]

Question regarding ground balance please,

Reading the DEUS manual, it appears to ground balance in two different ways depending on what mode you are in,

1. Goldfield (or all metal) says it is an exact ground balance point that matches the ground phase.
2. In the discrimination modes it says that all the ground numbers are rejected below the setting.

It almost sounds like the ground balance in the motion modes are like the discrimination setting but for the ground region of the scale.
Am I right thinking this? and how many different methods are there to achieving ground balance? Thanks.

[Carl-NC]

Some detectors have true GB in all-metal mode but not in disc mode. In those cases, all-metal will have a threshold audio you can hear and when you are GB'd and you can pump the coil over the ground and the threshold will stay consistent. Disc mode is silent search (no threshold audio) and GB will be some preset value that may or may not be accurate. Because there is no audible threshold you cannot hear the imbalance and the disc processing will prevent the ground from creating a target signal. If the ground is very consistent and you maintain a very level sweep then this method works OK. If ground is variable, uneven, or your sweep isn't level then ground signals can mask targets.

I think what the Deus is doing is real GB in both AM and disc modes. However, it appears they also apply a silencer to anything below the current GB point so as to silence cold rocks. The silencer is turned off in Goldfield mode.

[Danno]

Thanks Carl,
Can you elaborate a bit more on what true GB is please? and what is not true GB method?

[Carl-NC]

True GB is where the phase of the R-channel demod is adjusted so that ground signals are nulled. This can be done by manual adjustment or by automatic means (ground tracking). Other detectors use a fixed phase for the R-channel, usually set with ferrite, which works fine for weaker soils. But even manual & auto GB are only able to null out a particular soil phase; hot rocks & cold rocks can still come through.

The Deus has auto ground tracking so I'm pretty sure it has true GB in disc mode. I think they apply disc on top of that to silence hot/cold rocks.

[Danno]

Out of interest and using the Deus GB scale, lets assume the actual ground reading is 78 but you have it set on 90, what would be the effect on the detectors operation if a) the ground is not strongly mineralised or 1-2 bars, b) the ground is strongly mineralised or 6-8 bars.

Mineralisation strength in this case as per the bar on the Deus.
Is there a trade off in setting the GB high (90) if the mineralisation strength is low?

[Carl-NC]

If strength is low enough then having a misadjusted GB is not much harm. That's why fixed-GB detectors work OK in milder soils. If strength is high the a misadjusted GB will create very noisy operation as you sweep the coil over the ground unless the ground is perfectly flat, perfectly consistent, and the sweep is perfectly level.

If ground=78 and GB=90* then lowering the coil to the ground will create a positive ground signal. Some people intentionally offset the GB very slightly below the ground point (maybe by 1 point) on the theory that they never want to get a negative ground response because that can mask a weaker positive target signal. However, 12 points of offset will probably create a very strong ground signal and that will also mask weak targets. Also, it is common that people slightly lift the coil at the ends of the sweep which will create a negative ground signal even with a "positive" offset, and this could mask a weaker positive target signal. Again, weak ground is not so much a problem, but generally there are no advantages in a misadjusted GB, except for the "1 point positive offset" which I am not convinced really helps.


*GB is actually set lower than the actual ground loss angle, but this is commonly called a positive offset.

[Melbeta]

When setting ground balance, I prefer to hear the audio hum. I search only for faint deep targets. I have lost interest in near the surface targets myself. I also use a special audio amplifier, with a bypass switch. I search with the amplifier wide open. When I hit a target, I switch into bypass, and see the target is faint and deep. If it is I dig it. If not, I go on detecting. My amplier uses no batteries for power. It has zero noise and it is crystal clear... I do not release the schematic of the circuit. Why? I want no competitors near me when I detect. My amplifier was built for me by an excellent engineer to not achieve noise in the circuitry. He knew what he was doing. He used to wind all size of coils for his vintage detectors. He would wind them, with one end connected, as he was winding, when the audio came in, he said you cannot wind them any better then that. He left a some for the connection and stopped winding. Now all I said is what he said, so I cannot explain it any further. He was the chief engineer for Tranex which build industrial transformers for sale.
Melbeta

[getsa]

The way of winding coils sounded VERY interesting!... It is understandable that you cannot share the issue, concerning audio amplifier, but if you are willing to share some more details about the technique of winding it will be extremely useful for all who make their own detectors. For example - where or what one end is connected to (to the detector`s PCB or to some other device, waiting for the sound to appear), with connected second coil and in some achieved state of balance or this is done only with the wounded coil and so on...
Regards,

[andon80]

I'm curious about the coil winding method too, I'm following

[Carl-NC]

What Melbeta describes is for winding a BFO coil, not an IB coil. BFO is sensitive to getting just the right inductance for operation. However, you can easily fix a wrong inductance by using padding capacitors.

[dbanner]

You know, the fundamentals don't change, but technology does. Negotiating ground has been a 75 year journey, at least. The math is there, the science is there.
And now, the technology exists.
I've been taught to think of things in terms of "phase".
But I I think of ground in terms of wave.

[Danno]

I think what the Deus is doing is real GB in both AM and disc modes. However, it appears they also apply a silencer to anything below the current GB point so as to silence cold rocks. The silencer is turned off in Goldfield mode.

Now that does make some sense, there is a silencer setting and I always thought it strange it had a -1 setting, maybe this is to turn it off.