NH-173 detector

[ivconic]

Ah, then it's ok. I had the IRF840 in mind. But other colleagues will surely have better ideas. I have the handicap of not being able to easily acquire better and newer fets, so I have been "condemned" to the IRF740 and IRF840 for years.
...
The "S M L" switch is actually a switch that determines "recovery speed" or "reactivity" and has a direct effect on the depth of the detector in relation to the type and size of the target.
I expect much better results from Relic Hawk. Although it is a very old model ... it is still the reference for a deep detector when we talk about VLF I/B.
1266X! Another one of my favorite models! I envy you! 1266 will not delight with enormous depths, but it is very good in many other aspects.

[Thomas Weissbach]

Thanks ivconic, i did not know about the technical deteail of the S-M-L switch, just on the use of it. I will make an air test today with all the settings as in S-Mode and test M and L for the same objects.
I know that the Relic Hawk is actally a very deep VLF, this is why I bought it used in 2009 from an Englishman. I like it a lot, it is despite its total weight easy to handle when you put the box and battery on the belt.

On the other hand for the NH-173 i will check if i can make something with a stereo pot to manage increase of frequency while at the same time decreasing of the power in a certain amount (to not have to go to deep into electronics).
But therefore i need to check the effect of the power trimmer (original 20k) at say 1k/20k and the frequency trimmer (200k + 680k resistor of say 50k/1M. this might give me the ranges, on which i can test the sensitivity.

[Thomas Weissbach]

here are the values for the Relic Hawk including M and L Mode, as well as for all detectors an additional 25cm diameter stainless steel salad bowl.
The Relic Hawk performs in L Mode better on the stainless steel bowl than the also VLF Fisher CZ6.
The Vallon with standard (non UXO) coil out performs the VLFs by a couple of cm.
The NH-173 at 300Hz out performs the Vallon by 5cm with the 40cm coil,

[ivconic]

[Emersonpaz]

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

Does your board have the LF357 or is it the LF356? and what value of the damping resistor are you using?

[Thomas Weissbach]

It has the LF356, i think it is a 120k (R19)?

[Emersonpaz]

Damping resistor is in parallel with the coil in NH173 is R7. I use the LF357 the gain is higher. Take a look at the datasheet..

[Thomas Weissbach]

In my schematic R7 is 2.2k and goes across the search coil, right.
Is it possible to change the LF356 to LF357 without additional changes in the circuit?

[Emersonpaz]

yes lf357 same pinout just replace. I was curious if your board uses 2.2kohms as damping.

[Thomas Weissbach]

yes it uses 2.2k, yours too? I will check if i can get a lf357 to exchange the lf356

[Emersonpaz]

No, I use 390ohms damped for my 26cm 330mH 1.5 ohm coil.he used 2.2k for how many watts?

[Thomas Weissbach]

interesting. is this resistor correlating to the coil resistance or to any other component in the cirquit, or is it variable not not really necessary to keep the 2.2k according to the original schematic?

[kt315]

yes lf357 same pinout just replace. I was curious if your board uses 2.2kohms as damping.

yup, in original sch of DELTA PULSE 2.2K is damping. i do not see a problem. i just changed it to 680 in sch without a reason LOL.

[kt315]

interesting. is this resistor correlating to the coil resistance or to any other component in the cirquit, or is it variable not not really necessary to keep the 2.2k according to the original schematic?

DELTA PULSE is working with big FIRST DELAY. if you need to short it less then you must retune the resistor to less value because FIRST STROBE will move at left of absciss X.
normal minimal FIRST DELAY for DP is 40+us while with 1x1m coil it is set to 100-120us in a field job.

[Nightryder]

In regards to the damping resistor, it depends on your particular coil's specifications. In other words, you could be using two similar detectors and a different coil for each. Their damping resistors should be different values. Some hobbyists do not solder the resistor to the board, but instead they attach it to the board with the coil's two ends through a 2 pins terminal block for future coil change. In some more modern schematics, damping resistor is referred to as Rd, and no specific resistance value is assigned to it. I think the original coil designed for your detector was 1000 uH or so and that's where the 2k2 came from.


I highly recommend you to watch these two YouTube videos from the member Surf Detector's channel:

https://www.youtube.com/watch?v=CrJ5tFFmWyo

https://www.youtube.com/watch?v=Gr__N4_k2Mc