Minipulse Plus Rev My time has come!

[waltr]

Waltr
"I said "smaller" gold nuggets. My HH2 will detect natural gold nuggets down to about 5 grams but none smaller."
Is that grains not grams? 5 grams that would be totally unaccpetable to me . stock Mpp revd 1 gram 4 to six inches 6x9 figure 8 coil.

My mistake, smallest gold nugget was 0.5 gram that I ran tests with.
This fits close to your 1 gram @ 4-6 inches.

[green]

Will do all first thing in the morning and report back measurements and scope readings...Aside fast coil,I want to make a coil at 300uH that damps with 300-400 resistor..then have it as standard I can go to next step I didn't yet,the coil shielding..I read that some people use kitchen aluminum foil as shield,it's cheap and I'm gonna try it because my order on scotch24 hasn't come in yet..The critical point as I understood is to have space between coil wire and shield right?Also I read that some people make the shield compact and leave a gap 3cm at the end of coil wire exit ,others say that they shield leaving 2cm gaps between each wrap of shield..I will try all of these methods..at the end the coil is the most significant part of a detector...As for the srf measurement green your way suits me fine,I saw a circuitwith two 9v batteries and some parts to get in circuit measurement on oscope..There is also Gary's circuit at the end of the great fast coil paper of bbsailor but I don't have a working function generator at the moment to test it..I wonder if I can simulate the generator pulses with a 555 ..

Connect a 500pf capacitor across one of your coils to make it damp with a 300-400 ohm resistor. Don't think a 555 would oscillate at 3MHz. The kitchen foil acts like a target and connecting a ground wire to it can be a problem. The foil can be cut so it wouldn't act like a target.

[mushaba]

1. Picture of two coils I posted awhile back. SRF measured the way I suggested with scope connected to amplifier out of operating PI. Lead wires used between coil and circuit that I have measured have a capacitance of a least 1pf/inch. A 3/4m lead would have 3times the capacitance of the coil. Don't know how fast a 20cm diameter 300uH coil could be made. I think anything around 3MHz SRF without the lead is fast enough. Interested in the specs of coils others have made. Repeated the tests today using procedure reply#110 with scope lead clipped to ground lead making a pickup loop. I've been shorting the not wanted coil when measuring SRF of IB coils(separate Tx and Rx). Tried again today wit the flat radial and flat basked overlapped. Reads close to single coil reading. Maybe there is a better way?

Wow!Great coils green,excellent srf...

[mushaba]

I would be interested in the final SRF reading of the completed coil with leads attached. Rin is R1. I would try a 4148 across R8 and maybe a 4148 in series with a 500 or 1k resistor across R8 with diode cathode to amp out end of R8. Need to adjusting for best signal at TP3.

Will do all first thing in the morning and report back measurements and scope readings...Aside fast coil,I want to make a coil at 300uH that damps with 300-400 resistor..then have it as standard I can go to next step I didn't yet,the coil shielding..I read that some people use kitchen aluminum foil as shield,it's cheap and I'm gonna try it because my order on scotch24 hasn't come in yet..The critical point as I understood is to have space between coil wire and shield right?Also I read that some people make the shield compact and leave a gap 3cm at the end of coil wire exit ,others say that they shield leaving 2cm gaps between each wrap of shield..I will try all of these methods..at the end the coil is the most significant part of a detector...As for the srf measurement green your way suits me fine,I saw a circuitwith two 9v batteries and some parts to get in circuit measurement on oscope..There is also Gary's circuit at the end of the great fast coil paper of bbsailor but I don't have a working function generator at the moment to test it..I wonder if I can simulate the generator pulses with a 555 ..

[green]

Tommorow I will paint and make the final mount the coil to the detector chassis...Still haven't figure out the battery compartment...
Anyway,I will take the outer wire insulation from an rg cable to insulate the "leads"coming out of the coil case.I will solder them to an rg62 cable,is it possible soldering affect the coil reading?Also i believe all parameters will change(coil leads+rgcable+rg connectors to MD)is there a way to measure capacitance from inside the detector?For sure I will connect a pot to check for critical damping..and at last is there any ideas how to make TP3 output waveform more stable ?

I would be interested in the final SRF reading of the completed coil with leads attached. Rin is R1. I would try a 4148 across R8 and maybe a 4148 in series with a 500 or 1k resistor across R8 with diode cathode to amp out end of R8. Need to adjusting for best signal at TP3.

[green]

1. Picture of two coils I posted awhile back. SRF measured the way I suggested with scope connected to amplifier out of operating PI. Lead wires used between coil and circuit that I have measured have a capacitance of a least 1pf/inch. A 3/4m lead would have 3times the capacitance of the coil. Don't know how fast a 20cm diameter 300uH coil could be made. I think anything around 3MHz SRF without the lead is fast enough. Interested in the specs of coils others have made. Repeated the tests today using procedure reply#110 with scope lead clipped to ground lead making a pickup loop. I've been shorting the not wanted coil when measuring SRF of IB coils(separate Tx and Rx). Tried again today wit the flat radial and flat basked overlapped. Reads close to single coil reading. Maybe there is a better way?

[mushaba]

Tommorow I will paint and make the final mount the coil to the detector chassis...Still haven't figure out the battery compartment...
Anyway,I will take the outer wire insulation from an rg cable to insulate the "leads"coming out of the coil case.I will solder them to an rg62 cable,is it possible soldering affect the coil reading?Also i believe all parameters will change(coil leads+rgcable+rg connectors to MD)is there a way to measure capacitance from inside the detector?For sure I will connect a pot to check for critical damping..and at last is there any ideas how to make TP3 output waveform more stable ?

[waltr]

I think it was grams but going from memory. I'll check my notes at home tonight and post back.
It could have been grains or grams but the idea is that the smaller the target the earlier sampling needs to be to detect it.

Also, most gold targets are not pure gold so the conductivity is quite low giving a small TC.

[godigit1]

Waltr
"I said "smaller" gold nuggets. My HH2 will detect natural gold nuggets down to about 5 grams but none smaller."
Is that grains not grams? 5 grams that would be totally unaccpetable to me . stock Mpp revd 1 gram 4 to six inches 6x9 figure 8 coil.

[waltr]

Also i want to make a coil that damps near 300 - 400 Ohms just to have it as reference..

A simple bunch wound enamel wire coil around 400uH should get you there.
These are what I use. C ~ 120pF and SRF ~700kHz needing ~500 Ohm Rdamp.

[mushaba]

I would consider that fast.A coil with an SRF greater than 1MHz is fast.

I try to understand why a 320uH coil made from magnet wire has better SRF than a 3DSS made from PTFE...

Also i want to make a coil that damps near 300 - 400 Ohms just to have it as reference..

[waltr]

So capacitance is 14pF...How low must it be to consider a coil "fast"

I would consider that fast.
A coil with an SRF greater than 1MHz is fast.
The coils I use with my HH2 have SRF of 300-600kHz and not fast so first delay is greater than 12-15usec.

[mushaba]

No, the capacitance goes lower if the SRF is higher. The equation of resonance for an LC is: fc = 1 /[2PI*SQRT(L*C)].
So if L is constant and Fc increases then C must have decreased.

So capacitance is 14pF...How low must it be to consider a coil "fast"

[waltr]

You say its not fast enough to detect gold nuggets?Then i have to make a faster coil since the MPP has the ability to detect them with a fast coil..

I know that coils discussions and posts are a lot but with short guidance from all of you i will try to make a faster one

I said "smaller" gold nuggets. My HH2 will detect natural gold nuggets down to about 5 grams but none smaller.
The returned signal of these are dependent on their size and these are what a Fast coil and very short first delay is about
.

To excercise yesterdays lesson about coils and Rdump calculations i wrapped a new coil

[ATTACH]46209[/ATTACH]
[ATTACH]46210[/ATTACH]

Measured SRF with oscope and probe loop precedure,counts 2.38MHz

Rd=pi*L*SRF --> Rd=3.14 * 0.00032 * 2380000 --> Rd=2391.4 Ohms

Rd*Rd= L / 4*C --> C= L / Rd*Rd*4 --> C= 0.00032 / 2391.4 * 2391.4 *4 --> C = 0.00032/5718794 --> C = 5.59 e-11 --> 55pF

Conclusion:As SRF goes higher the Rd goes higher therefor capacitance goes higher.So we supose to lower the SRF but how???

And my embarassing moment of the day,what do you mean by "lead" ??

No, the capacitance goes lower if the SRF is higher. The equation of resonance for an LC is: fc = 1 /[2PI*SQRT(L*C)].
So if L is constant and Fc increases then C must have decreased.

"lead" is the wires or cable from the coil to the circuit. This 'lead' has capacitance and becomes part of the coil (RLC) when measured or installed.

[mushaba]

If you are unsure of genuine LF357AN (I even got fake chips from genuine local dealer, seems they were also fooled), You can use NTE937M.(NTE Electronics) This is genuine direct equivalent replacement for LF357. I use this in my delta pulse. It has slew rate of 50V/uS.
You know it is genuine because it comes in official sealed plastic bag direct from NTE Electronics. You can check out their website for an address of closest dealer to your location.
They have a huge catalog of parts and an on line cross reference database. They specialize in manufacture of direct replacement parts and they are always 100% genuine.

Thanks a lot dbanner i looked at tme store i buy parts from and sadly its out of stock...I will enquiry them about the stock...Ultra thanks!!