NH-173 detector

[Thomas Weissbach]

If I understand right, the damping resistor shortens the coil (curcuit). higher damping resistor values lead to a longer delays, while lower values lead to short delays. For the overall resistance of the coil, the damping resistor does not have a lot of influence since it is in parallel to the coil, right? based on the different feedbacks here, people chose or would choose resistors between 390 and 680R für "small" coils like mine (22 and 40cm). How does the lower value damping resistor influence the initial pulse power (i assume lower values will slightly reduce pulse power).
When I measure my coils i get about 670uH at 1.85R
I have an oscilloscope, so actually i could measure the delay of the coils. I assume that i can be measured on the coil connection of the board while adjusting the resistance of the samping resistor

[Carl-NC]

That's backwards. A high damping resistor underdamps the coil and lead to ringing. A low damping resistor overdamps the coil and slows it down. What you want is critical damping, which depends on the inductance and its self-capacitance:

Rd(opt) = 0.5*sqrt(L/C)

Coil resistance has nothing to do with it. Self-capacitance is measured indirectly. Yes, looking at the coil decay while changing the damping resistor is a very useful exercise.

Add: the damping resistor value has little effect on pulse power or power consumption. It mainly affects decay speed and the minimum sample delay.

[ivconic]

[Thomas Weissbach]

That's backwards. A high damping resistor underdamps the coil and lead to ringing. A low damping resistor overdamps the coil and slows it down. What you want is critical damping, which depends on the inductance and its self-capacitance:

Rd(opt) = 0.5*sqrt(L/C)

Coil resistance has nothing to do with it. Self-capacitance is measured indirectly. Yes, looking at the coil decay while changing the damping resistor is a very useful exercise.

Add: the damping resistor value has little effect on pulse power or power consumption. It mainly affects decay speed and the minimum sample delay.

Thanks a lot for this clarification, this is very welcome Carl

[Thomas Weissbach]

thanks a lot for all your feedbacks, i will put the detector on the bench in the next days and check it with the oscilloscope, change the resistors discussed above, tune it accordingly and then redo the airtest.
Feedbacks to improve the layout are always welcome.

[kt315]

[Thomas Weissbach]

Hello Ivconic and Kt315
thanks a lot for clarifying how the oscillogram of the pulse should look like; changing damping resistance until no spike in the plane after the drop before the rise, the rise as far left as possible before a spike appears
Thanks a lot for your help

[Thomas Weissbach]

Hi all

i changed several parts in my NH173.

-LF356 to LF357
- R8, 680R 2W
- preliminary damping restistor value 680R (will be adapted after final asembly and evaluation)
- adjustable frenquency with a pot (207k - 1M) leading to a frequency range of 105-880Hz
- adjustable power pot 3.3k-14.3k leading to 26 - 400uA (espectively 48-175uA)

what gives a better deep searching result; low frequency with low uA and high frequency with high uA or just the other way around?

[kt315]

i changed several parts in my NH173.

good. why you can not read DELTA PULSE topic from start to end? you can find up all mods people did. you are like sir Amerigo Vespucci reopening USA. LOL!

thank you again for DP advertising. LOL!

[Carl-NC]

I don't know what this means:

- adjustable power pot 3.3k-14.3k leading to 26 - 400uA (espectively 48-175uA)

What current are you measuring?

[kt315]

I don't know what this means:

- adjustable power pot 3.3k-14.3k leading to 26 - 400uA (espectively 48-175uA)

What current are you measuring?

PULSE WIDTH pot. in sch it is 20k, but what he does i do not understand.

[Thomas Weissbach]

The trimmer for the "power" according to the NH-173 schematic is a 20k trimmer (R2), and for the frequency it is a 200k trimmer (R5) and a fixed 680k (R4) resistor (880k in total if both replaced by one poti).
I used a 1M Stereo-Poti to replace them both on one poti with resistors in parallel (to come close to the original resistance) and one in series to have a minimum resistance.

Therefore I asked (some posts ago) if higher frequency should come with lower current ("power according to schematic naming), or vice versa.
Carl informed that high current with high frequency could be hard on the components.

This was the reason to think about the following:
increase of frequency should come with a certain decrease in current ("power") to no overload the components. And since this is not assured when using a separate current (Power) and frequency pot, i thought about using a stereo-pot to ensure that frequency and current are controlled by one single potentiometer.

I will read the Delta Pulse thread (eventough i have not yet understood the direct link to the NH-173). If it is exactly the same schematic, why should one rename a product... well, I will see as soon as i read all of the tread. -> thanks for the hint.

[kt315]

frequency is fixed. 100 PPS for DP and 300 PPS for Sniffer XR-71. if you increase the freq in 3 times you get increase in current in 3 times.
you can read at sch why frequency fixed.

why should one rename a product

his right.... you can also rename NH into NIGHT GOLD HAWK, NIGHT GOLD STAR, GOLD DREAM, GOLD MASK, GOLD BUG, QUICK GOLD, etc. always use GOLD word in the name. people love that.

[pito]

GOLD word in the name. people love that. = and that is misleading and really good gold detectors are buried in a large number of not so good detectors. Nice slogan and Bragging without evidence are pushing away from these technologies.
100 PPS and 120 PPS in my opinion should be opposite way.

[Thomas Weissbach]

frequency is fixed. 100 PPS for DP and 300 PPS for Sniffer XR-71. if you increase the freq in 3 times you get increase in current in 3 times.
you can read at sch why frequency fixed.

why should one rename a product

his right.... you can also rename NH into NIGHT GOLD HAWK, NIGHT GOLD STAR, GOLD DREAM, GOLD MASK, GOLD BUG, QUICK GOLD, etc. always use GOLD word in the name. people love that.

So R2 on the NH-173 schematic correlates to pulse width (called power by the schematics creator). I agree, as long as a trimmer is used a s R2, pulse width is fixes, the same goes for frequency (R4+R5).
But when you use a Pot instead of the trimmers, you get variable pulse width and variable frequency in a certain range (linited/defined bay the resistance range - agree?

I also registered the increase in the uA as you write, you are right.


The story with the names... sure one can/is allowed to give your product any name, even if it is a more or less one to one copay of pulse star - sniffer or in this case NH-173. What was in my mind was not not "legal stuff" but traceability of the schematic. If you do not have the knowledge about the other names, it will be difficult to track optimizations done by others on differenty called equal schematics.