NH-173 detector

[Thomas Weissbach]

I have bought a used NH-173 PI-Detector in Switzerland, equipped with a 20cm and a 40cm coil.
Pretty well made, 12V power supply, carbon stem, light weight housing and coils.

When I tested it, it works pretty good and deep for Iron, but I could not detect a 5.7g Gold nugget at all (neither with the 20cm coil, not - of course - the 40cm coil).
At no distance was the nugget detectable in air, neither was my marriage ring with white/yellow gold 7g...

My Vallon detects the Nugget in 25cm.

Is this normal for the NH-173 detector? It is said that it can detect gold, or is 5 resp. 7g not big enough for this detector?

Thom

[Emersonpaz]

Test with the DELAY close to minimum. and the potentiometer RANGE at the minimum. And sensitivity maximum.
With 20cm coil

[Thomas Weissbach]

yes, actually it can detect the 5.7g nugget with the 20cm coil in 7cm and the 7g gold ring in 12cm. with the 40cm coil it can only detect the ring at 10cm, a hand axe is detected at 40cm with the large coil.
Settings: manual GB at minimum, Delay minimum, range minimum, senstivity is fixed on the PCB with a jumper, so at max.

Would it help to increase the power of the impulse on R2 (according to manual, should not be set to max, whatever that means), can anyone suggest the direction and how to measure the pulse power?

Comparison to the Vallon VHM3CS with standard coil, not UXO: gold nugget: 25cm, ring 30cm, hand axe >50cm
speaks for the Vallon mine detector...

[Nightryder]

Have you tried different types of metals? I mean other than gold and iron? This should give you a better understanding of the issue. I assume you don't have an oscilloscope or even LCR meter, and unfortunately many of those who assemble these detectors to sell out, do not either. They are only after the money not the reputation. If there is an issue with the device, it could range from usage abuse by the first hand user to bad quality components or inaccurate values of them like faulty damping resistor or miscalculated coil inductance or..or..or... I mean you can not really tell without a proper test of the circuit board.


I read somewhere that the NH-173 detector was a copy of the sniffer xr-71. If this is true, maybe you want to search the forum for threads regarding the xr-71. Let this be your last option, but first you should contact who sold it to you or even who made it.


Good luck!!

[Thomas Weissbach]

I already contacted him. after some fiddling around with the pots, it was able to detect the nugget at faible depht.
I have an osci i bought for building tube amplifiers, tektronix 2215 but never tested any of my metal detectors (since up to now, the used to work properly).
This was my first PI, and besides that short air test on the nugget I did not use it up to now, since we need a detecting permission which I will only get in November. So there is actually no possibility to test this one on ground (not even allowed in your own garden here in Switzerland). And all the other detectors are waiting for that same permission in the garage too. I just wanted to make sure that this one works before using it in November.

[Nightryder]

I already contacted him. after some fiddling around with the pots, it was able to detect the nugget at faible depht.
I have an osci i bought for building tube amplifiers, tektronix 2215 but never tested any of my metal detectors (since up to now, the used to work properly).
This was my first PI, and besides that short air test on the nugget I did not use it up to now, since we need a detecting permission which I will only get in November. So there is actually no possibility to test this one on ground (not even allowed in your own garden here in Switzerland). And all the other detectors are waiting for that same permission in the garage too. I just wanted to make sure that this one works before using it in November.

Glad to hear that. Happy hunting!

[Thomas Weissbach]

Dear all,
have made a comparison between my old Fisher CZ6 Quicksilver (5+15kHz), the Vallon VMH3CS and the NH-173 (120Hz) based detector I bought used in Switzerland.
The air test has been done as follows:
all metal mode (fisher)
sensitivity max
ground balance manual off (except vallon)
outside the house, underside of coil horizontal 1m over ground
moving objects from above towards the coil underside
first detection / tone has been used to measure the distance between object and coil

The objects used are:
N9 horse shoe
3dl Cola Can
5 Swiss Francs
2 Swiss Francs
1 Swiss Franc
5 Rp
2 Euro
1 Euro
20 Ct
gold ring 7g
nugget 5.7g

interestingly, the NH173 in standard setting (60% power on R2, 120Hz) did not overall perform better than the Fisher and the Vallon.
For the horse shoe the NH 173 gives some more distance with the 40cm coil (approx. 15-25%), for the Cola tin the fisher is best, followed by the NH-173 and the Vallon. For all the other objects, the Fisher and the Vallon are much more sensitive than the NH-173 (slightly depending on the material to be detected).

I have tried several power settings for the NH-173 (R2 Pot), the max setting of R2 seems to lead to higher detection distances for the detection of the horse shoe only with the large coil, whereas for all other metals (coins, Cola can, gold ring and nugget) the detector looses detection distance. The Frequency was not changed (120Hz).

Does anyone have a compareable test on the NH-173? I am actually a bit unsatisfied with the detection distances of the NH-173 in my air tests. They are not better than the Vallon (PI) and the Fisher (VLF).
Unfortunately, my Relic Hawk does not work anymore (although it shows 5kHz on the coil). I will test this one as soon as I have it running again.

[Emersonpaz]

NH 173 (DELTA PULSE 2) even schematic, its use is recommended for large targets. Although it can be adapted to small targets, mine is operating at 300Hz, the response to small targets is much faster.

[pito]

I see on your tests cola can, here is test of my design for it.
https://www.geotech1.com/forums/foru...-coca-cola-can

[Thomas Weissbach]

based on optimization feedbacks from Emersonpaz i have changed some minor things in my NH-173;
- Replaced R4 (680k with 270k) to be able to get a frequency of 300Hz with the R5 trimmer
- should replace R8 (680R) to 2W due to higher temperature

gain in detection distance is very good, see table compared to original setting;
- for the large coil it is mainly large iron objects and the Cola can
- for the small coil it is all over the objects

Question for the specialists; would it be possible to change the oscillator to a stronger model, to be able to make the NF-173 more flexible concerning
- frequency setting (instead of R4 and R5 a 1M poti could be placed, allowing a large range of frequencies)
- pulse power (instead of R2 a 20k poti could be placed, allowing easy access to pulse power

What would be needed if the oscillator could be changed to a stronger version?

It looks interesting what improvements can be made with some simple adaptions of the NH-173...

i am not a detector electronics specialist, came to this due to unhappiness with mi PI and interest in the vallon. Nontheless, i used to build tube amplifiers and are able to do basic electronics.

thanks Thomas

[Emersonpaz]

Thomas, I'm glad you were able to improve the performance of your detector. I'm also not an expert in electronics, this is just a hobby for me. I believe that this configuration I gave you is the most rewarding. increase the frequency further and the pulse will only drain the battery faster and will not result in a large gain in distance.

[Carl-NC]

The short answer is, yes, you can make the oscillator more variable. But be careful of creating ranges that can overheat the circuit, like high frequency coupled with high pulse width. The best solution is to use a micro that can place limits on timing, so that if you set TXf=1000Hz you cannot set TXw=200us as well.

[Thomas Weissbach]

Hi Emersonpaz, I agree that more power will drain the battery faster, but my detector has a 13.8V tooling accu, so this would not be so critical. I worry more about what youmentioned in your PM; creating heat, destroying the oscillator.

Hello Carl, this sounds interesting; it means that at a certain frequency a certain maximum of power is available only (what i can understand to not overload the components). This again would require a modification of the whole cirquit since frequency and power would need to be linked in a certain way to not damage the electronics.
But this goes way beyond what I can understand of it...

PS: I got my Minelab Relic Hawk running again and added it to my above mentioned table of air detection distances. It was the typical Relic Hawk issue; broken cable in the coil connection cable (inside / right after the mil spec plug).
The Relic Hawk is less senisitive than all the other detectors i tested.

[ivconic]

Sorry for this question, but are you sure you understand what the "S M L" switch does and what it is for on the Relic Hawk?
As for the PI detector, the fastest thing you can do is replace the TX FET transistor with a better one.
I'm not the least bit surprised by the CZ6 from your chart... it's my favorite series of detectors.

[Thomas Weissbach]

Hi Ivconic, i used the S mode for the test since the M (various size and dephts objects) and L mode are for large and deep objects and this would have avoided the gold ring. Nonetheless you are right, this most probably has reduced the detection depth for the horse shoe and the Cola can. I can repeat the tests tomorrow with the M and L Mode for comparison and for unjudged results.

I agree with the fisher CZ6, this is a real good machine despite its age, pretty easy and very deep. I receive a 1266x soon from England too.

Thanks for the feedback on the TX FET, what would be recommended,if i remember right, it is an IRF840 on the print