Nexus and transmit power.

[dfbowers]

My methods may be way off base, but I did an experiment a few years back to measure the relative field strength of a few different models. I posted the results here but can no longer find all the references. Just for fun, I made few field strength measurements of the Nexus Credo and Nexus Standard MkII. Wow... even if it's wrong, I applied all the same mistakes to all my measurements. You can get the picture!
Don.

[kt315]

http://www.geotech1.com/forums/showt...riments/page17

#422

[Skippy]

They should be good in high-EMI environments, in theory, anyway. If your RX gain is reduced 5-fold, that's got to quieten a machine down. I don't recall reading any forum comments anywhere about how pickup-resistant they were, I might have a look later. It makes the front-end circuitry easier and cheaper to design, I'm sure. No expensive opamps, no need to carefully optimise the balance of all the different noise sources.

It would be interesting to hear peoples thoughts on the negative effects of higher TX strength (apart from the obvious battery drain). Do certain soils cause trouble, maybe magnetically saturating?

High TX power is clearly not an essential feature, though. I'm sure the XP Deus will have a pretty low output, it's a single-ended coil, powered from a single LiPo cell, but the machine seems to have adequate performance.

[ivconic]

They should be good in high-EMI environments, in theory, anyway. If your RX gain is reduced 5-fold, that's got to quieten a machine down. I don't recall reading any forum comments anywhere about how pickup-resistant they were, I might have a look later. It makes the front-end circuitry easier and cheaper to design, I'm sure. No expensive opamps, no need to carefully optimise the balance of all the different noise sources.

It would be interesting to hear peoples thoughts on the negative effects of higher TX strength (apart from the obvious battery drain). Do certain soils cause trouble, maybe magnetically saturating?

High TX power is clearly not an essential feature, though. I'm sure the XP Deus will have a pretty low output, it's a single-ended coil, powered from a single LiPo cell, but the machine seems to have adequate performance.

I can talk only on pretty specific and narrow use of metal detector; the coin shooting.
In coin shooting you don't need high TX power. You need low noise RX instead.
My best coinshooting experiences are gained with detectors which are usually providing 11-16Vpp TX.
I can't be sure but assume that high power TX will most likely produce contra-effects in such use, especially on highly mineralized soils.
More the power coming from TX; more the hotrock&minerals will be "energized" too. Alternative em fields from such "obstacles" will completely mask the target bellow.
And this i seen on the filed so many times.
That's for coin shooting under the common conditions that i've seen so far.
But if you're aimed on deep and larger targets; than high power TX can be beneficial.

[dfbowers]

Yes. The Nexus Std MK11 is an excellent performer near EMI sources. I walked right under some high tension lines last week and did not even notice. The wife had to turn off her Whites Spectrum.
Battery drain can be problematic with standard alkaline batteries but NMHI rechargables give me 10 hours or so.. quite acceptable and outlast me every time I go out.
Depth is awesome if that is what is needed. I have no regrets at all.
Don..

[Skippy]

It's unfortunately pretty difficult to modify most machines to see what the effect of increasing / decreasing TX 'power' has on detection ability. Typical TX circuitry means you would have to vary the power supply to that part of the circuit, which has knock-on effects on how the TX drive interfaces to oscillators/logic/micro's. Then there's adjusting the gain of the RX stage without messing up phase shifts. If you start off with a low-power machine, then lower the power further, you're likely to get noise / EMI trouble. If you took a high-power machine and dropped the TX power, then you'll have problems jacking up the gain, and circuit noise may be an issue there. And I suspect it's not a 'linear' thing, anyway, and doubling or halving the TX voltage would make minimal difference, maybe if you have half/normal/double at the flick of a switch you might get somewhere.

The only machine I can say has this feature as standard is the XP Deus, with its 3 TX 'power' levels, the software takes care of the RX 'gain' change. I doubt there's more than a 2:1 voltage difference between low and high settings, though. This is enough to make a decent battery drain change, allowing for TX power being proportional to (TX voltage)^2, which is important when you cannot change the battery. And I've not seen any user reports saying there's any noticeable difference between the 3 power settings (obviously some/many users somehow expect depth to magically double....)

[ivconic]

It's unfortunately pretty difficult to modify most machines to see what the effect of increasing / decreasing TX 'power' has on detection ability. Typical TX circuitry means you would have to vary the power supply to that part of the circuit, which has knock-on effects on how the TX drive interfaces to oscillators/logic/micro's. Then there's adjusting the gain of the RX stage without messing up phase shifts. If you start off with a low-power machine, then lower the power further, you're likely to get noise / EMI trouble. If you took a high-power machine and dropped the TX power, then you'll have problems jacking up the gain, and circuit noise may be an issue there. And I suspect it's not a 'linear' thing, anyway, and doubling or halving the TX voltage would make minimal difference, maybe if you have half/normal/double at the flick of a switch you might get somewhere.
The only machine I can say has this feature as standard is the XP Deus, with its 3 TX 'power' levels, the software takes care of the RX 'gain' change. I doubt there's more than a 2:1 voltage difference between low and high settings, though. This is enough to make a decent battery drain change, allowing for TX power being proportional to (TX voltage)^2, which is important when you cannot change the battery. And I've not seen any user reports saying there's any noticeable difference between the 3 power settings (obviously some/many users somehow expect depth to magically double....)

Yes it is difficult to notice the difference. I haven't noticed significant difference.
I guess that's because i am using only 22.5cm coil for quite some time.
Would be good to line up all the existing coils for Deus and perform more serious testing.
Also the targets... it would be very complicated to make detailed testing bed with several groups of targets on different depths and with different sizes.
I guess more significant would be to check for the behavior (while changing TX power) on highly mineralized soil.
Most of the time in numerous video demonstrations and comparable testings i see similar situation; soil was "easy" with pretty uniform content.
Testing beds are picked that way so that there is no random targets in soil, only one specific target is showed all the time in such demonstrations.
It's easy to show extreme depths of some model against others.
That's relevant only if you plan later to visit such soils where you have only one target at the time on each let's say 2 square meters area.
Which usually is not the case in real world.
Roman and Byzantine sites are nothing like that, not even close.
There are areas on such sites with 100 and more "targets" on 1 sq. meter! 99 of such "targets" are junk, trash, iron oxide, hotrocks, blacksand, minerals and mineral particles.
Only 1 from those 100 "targets" could be the coin.
High TX power in such situations will not do. It will produce lot of side effects and none benefit.
What's use than from "deep" detector in such situations? None.
...
I might be wrong but if i remember correctly; you can adjust TX power and RX gain at White's Eagle series too.
On second thought; i am sure for Eagle Spectrum, XLT and DFX.

[Nexus]

Difference on power settings will be noticeable only if the TX power increases many times not only percentage wise.
With the MkII the main reason for more power output is to achieve high sensitivity with very low noise, therefore as smooth as possible threshold. Since the electronic gain has its limits the other way to go would be a high TX output.

Now about the smooth threshold. The reason for me to seek the best threshold possible is simple. It is the only way to reliably search for the deepest targets, which are most often a faint and very faint signals. A chattery detector can not get this kind of job done.

Increasing the TX power does not affect the soil and metal targets equally. Metals always get more saturated with Eddy currents than soil, other wise metal detecting as a whole would be impossible.

It makes every sense to use as high as possible TX output and as low as possible electronic gain, because there is no other way to go really deep.

[WM6]

Difference on power settings will be noticeable only if the TX power increases many times not only percentage wise.
With the MkII the main reason for more power output is to achieve high sensitivity with very low noise, therefore as smooth as possible threshold. Since the electronic gain has its limits the other way to go would be a high TX output.

Now about the smooth threshold. The reason for me to seek the best threshold possible is simple. It is the only way to reliably search for the deepest targets, which are most often a faint and very faint signals. A chattery detector can not get this kind of job done.

Increasing the TX power does not affect the soil and metal targets equally. Metals always get more saturated with Eddy currents than soil, other wise metal detecting as a whole would be impossible.

It makes every sense to use as high as possible TX output and as low as possible electronic gain, because there is no other way to go really deep.

WHERE and HOW to put coil tank resonance in your here explained principles?

[Nexus]

Yes it is difficult to notice the difference. I haven't noticed significant difference.
I guess that's because i am using only 22.5cm coil for quite some time.
Would be good to line up all the existing coils for Deus and perform more serious testing.
Also the targets... it would be very complicated to make detailed testing bed with several groups of targets on different depths and with different sizes.
I guess more significant would be to check for the behavior (while changing TX power) on highly mineralized soil.
Most of the time in numerous video demonstrations and comparable testings i see similar situation; soil was "easy" with pretty uniform content.
Testing beds are picked that way so that there is no random targets in soil, only one specific target is showed all the time in such demonstrations.
It's easy to show extreme depths of some model against others.
That's relevant only if you plan later to visit such soils where you have only one target at the time on each let's say 2 square meters area.
Which usually is not the case in real world.
Roman and Byzantine sites are nothing like that, not even close.
There are areas on such sites with 100 and more "targets" on 1 sq. meter! 99 of such "targets" are junk, trash, iron oxide, hotrocks, blacksand, minerals and mineral particles.
Only 1 from those 100 "targets" could be the coin.
High TX power in such situations will not do. It will produce lot of side effects and none benefit.
What's use than from "deep" detector in such situations? None.
...
I might be wrong but if i remember correctly; you can adjust TX power and RX gain at White's Eagle series too.
On second thought; i am sure for Eagle Spectrum, XLT and DFX.

You are actually very correct. High power output is of no use on trashy sites just like there is no use in there of any detector that can perform air test miracles.
On the other hand low power detector is of no use on not so contaminated sites where hoards and coins can be very deep.
But then we can find every reason for anything to be useful or useless.

The Deus may be one of the best general purpose detectors out there, very good for trashy sites, but the sacrifice is real depth and very low sensitivity to long time constant signals, like hoards, bronze statues and large non-ferrous objects, like pots, helmets ect. It is simply a detector oriented after the small targets above all.

So it all comes down to personal preference.

[Nupi]

I agree largely with the explanation from Nexus .
To give a practical example, the prototype MD-works 35 volts - pp.
The modified Smart 27 volt - pp. and they are both better in mineralized soil than the Deus and multiple brands.

[Carl-NC]

The only machine I can say has this feature as standard is the XP Deus, with its 3 TX 'power' levels, the software takes care of the RX 'gain' change. I doubt there's more than a 2:1 voltage difference between low and high settings, though. This is enough to make a decent battery drain change, allowing for TX power being proportional to (TX voltage)^2, which is important when you cannot change the battery. And I've not seen any user reports saying there's any noticeable difference between the 3 power settings (obviously some/many users somehow expect depth to magically double....)

The White's V3 has a "transmit boost" setting which triples the TX voltage, from 10V to 30V, but the RX gain is not compensated. Typically it adds about an inch of depth on a coin. In a resonated system the battery drain should not change much vs TX "power" level, but that's highly dependent on the actual design.

[Nexus]

WHERE and HOW to put coil tank resonance in your here explained principles?

That will depend on the particular circuit that you are working with. In general if you can double the voltage supply to your TX that will result in most cases to 4 times power output if there are no other changes.
You will find that increase of TX and lesser use of electronic gain makes a better detector.
High TX is no danger for mineralized soils, because the bulk ground interference is a result of both TX and electronic gain. So if you reduce one or the other or both the end result will be always the same.

The Nexus Standard MP works with constant 60.3 Ampere/turns and it is astonishingly stable in all conditions if one does not over do the over all detection range.

I actually intended to publish one of the MP prototypes TX and RX ends, which are much different than the production MP now, but still outperformed every other IB on mineral conditions. That is if anyone would be interested to see how it was done. I am talking about the MP prototype on the video link bellow.

[Skippy]

Quote:"The Nexus Standard MP works with constant 60.3 Ampere-turns"

That is rather large, for sure. My calculations for the Fisher F75 indicate 3.4 Ampere-turns (based on 34 turns, and 0.1 A RMS current). And the stock 11" x 7" 'bi-axial' coil has a very elliptical transmit coil, more than 2:1 diameter ratio, so I don't think it would read very high on DonBowers test setup.

[WM6]

I actually intended to publish one of the MP prototypes TX and RX ends, which are much different than the production MP now, but still outperformed every other IB on mineral conditions. That is if anyone would be interested to see how it was done. I am talking about the MP prototype on the video link bellow.

Thanks. Your contribution are very welcome.

Which Nexus model could cope with high mineralization best?