NH-173 detector

[kt315]

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?

Eric did variable SECOND STROBE DELAY vs FIRST DELAY. you can find this post in the Archive.
how you think to fight with electromagnetic field influence EMFI from electric nets? i reminder in US it is huge problem even at ocean beaches.

[Thomas Weissbach]

I will see how it works in the field... where I plan do work with the detector is several km away from power lines, (electric) railways and hundreds of meters away from houses and mobile phone antennas...
If the cangeable range and pulse width does not do any good, i can still set it to 12k for the R2 "power" pot and 120 or 300Hz for the frequency pot (means to its original settings).

I made an air test to compare it with what i did in the beginning of this thread. on 120Hz and 300Hz with R2 at 12k it behaves equally, so this setting can be achieved again if required.

I also tried to set the damping resistor; according to the original drawing it is 2.2k. I checked it with my tektronic 2215 and found out that the thing starts "clipping" at approx. 1.6k, the damping resistor is now set to 1.8k.
The scope is set somewhere betweem 20 and 50uSec.

the lower base before the rise is not traceable with my scope - as far as i can say; i can not strech it further. But when using smaller resistors than 1.8k, there was a peak after the slope.

Measurement on pin 10 of U2 CD4538BE is between 20 and 50uSec

[kt315]

your Research is wonderful. ordered new pcb batch 20 pcs. a color is RED, like Ivconic prefers.

according to the original drawing it is 2.2k.

you make DEEPER***. it's mean no huge necessity to tune overdamping resistor. if you do PI detector for gold nuggets then yes, be cause FIRST DELAY will be very short (kinda 5...10us). but do not try that in the NH. you just will waste a time.

*** Глубинник. Рамочник. Только самые крупные объекты, отрезая мелочёвку.

[Emersonpaz]

I will see how it works in the field... where I plan do work with the detector is several km away from power lines, (electric) railways and hundreds of meters away from houses and mobile phone antennas...
If the cangeable range and pulse width does not do any good, i can still set it to 12k for the R2 "power" pot and 120 or 300Hz for the frequency pot (means to its original settings).

I made an air test to compare it with what i did in the beginning of this thread. on 120Hz and 300Hz with R2 at 12k it behaves equally, so this setting can be achieved again if required.

I also tried to set the damping resistor; according to the original drawing it is 2.2k. I checked it with my tektronic 2215 and found out that the thing starts "clipping" at approx. 1.6k, the damping resistor is now set to 1.8k.
The scope is set somewhere betweem 20 and 50uSec.

the lower base before the rise is not traceable with my scope - as far as i can say; i can not strech it further. But when using smaller resistors than 1.8k, there was a peak after the slope.

Measurement on pin 10 of U2 CD4538BE is between 20 and 50uSec

I think you are sampling 20uS for the first and second sample. Do a test, replace C6 with 4n7 polyester, it will increase the sample to around 42uS. For me it works much better.

[Thomas Weissbach]

I will have to check if i find 4.7nF (i think this is what you are suggesting) in my tube amplifier component collection; most probably not polyester but maybe PTFE, PP ore something else (of course no standard capacitor).

Can you please identify C6 on the pcb for me; by drawing is not goof enough to read it and on the pcb it is no possible ti identify the cap is not (there are several 1.5nF)

What will the improvement and effect be like when I replace C6 (according to schematic 1.5nF) with 4.7nF?

[Emersonpaz]

between U2 and U3 next to R14 is C6

[kt315]

I think you are sampling 20uS for the first and second sample. Do a test, replace C6 with 4n7 polyester, it will increase the sample to around 42uS. For me it works much better.

your reopen of sniff sniff is wonderful. i give you graphics.

[Thomas Weissbach]

between U2 and U3 next to R14 is C6

thanks a lot Emerson, i really appreciate your help

[Thomas Weissbach]

I replaced C6 1.5nF with 4.7nF as proposed by Emerson.
The 2 caps are fixed on a toggle switch, so that it is possible to choose between the 2 first sample delays.
it is remarcable; the longer delay also leads to some better detection distance in the air tests.

Sorry for the flimsy detector cover; i had to use material that was available in my office and laminated some printer paper. For the FSD switch I havent found the time to adapt the cover.

[kt315]

ok. you just move SECOND STROBE at right side on axis X. representing axis X and axis Y on flatness, also here is DELTA PULSE pattern curved line inflicted.
delta is a symbol of Greek alfabet, so present it yourself. THE FORM like the symbol. we say DELTA impulse pulse signal.
we say also reverse pulse.
you move SECOND STROBE in a range with low amplitude of the DELTA.
Carl will say more be cause english is not my native. anyway, you may read all info in ITMD.