Getting ready to build the MPP

[KRinAZ]

Something for thought. A chart I posted in another thread awhile back. I kept the peak coil current constant for the test. Adding turns and increasing inductance might lower peak current and reduce the gain increase by the current ratio. With the same peak current the signal increased with the turns ratio squared. Signal strength should equal ampere turns. With a mono coil turns helps transmit and receive(squared). Gain in distance vs signal strength varies with coil size and shape. The chart shows what I got with my 8 inch round mono coil.

Many thx green, excellent test & results presentation, & food for thought

[KRinAZ]

I would not add windings but instead push the sampling delay toward 6 or 7us instead. There is little to be gained I believe in slowing down your coil further. You have plenty of inductance at 324uh. One question is, have you armored your coil yet? If not, it will probably have the effect of slowing down your coil anyway.Regards,Dan

Hmmm, thx Dan, I haven't put a shell around the coil yet - will do that & rig up a pole when I've mostly finished the electronics mods & tuning. I'm curious about how this coil would measure & perform with another basketweave turn, & I am experimenting with a mod to the coil template anyway, so I think I'll make an 8 turn version of the 8x10 & post it's test results...I'll also find the minimum stable & test with that delay & include in the results...may be a couple days...

[baum7154]

Hmmm, thx Dan, I haven't put a shell around the coil yet - will do that & rig up a pole when I've mostly finished the electronics mods & tuning. I'm curious about how this coil would measure & perform with another basketweave turn, & I am experimenting with a mod to the coil template anyway, so I think I'll make an 8 turn version of the 8x10 & post it's test results...I'll also find the minimum stable & test with that delay & include in the results...may be a couple days...

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By an '8 turn version' do you mean that you are going to have 8 wires in each of the slots or about 40 turns on the coil? That should put the coil well in excess of 450uh and I don't think it would decay in under 10us, just guessing. If you take a look at my post #31 in the CHANCE PI COIL thread the attached pictures show an 8" round coil with 39.4 turns of wire yielding a coil with 458uh of inductance. This coil will not allow my CHANCE PI to operate down at even 10us so a larger 8X10 elliptical coil would have even more inductance with the same number of turns.

By the way the increase in inductance after putting a shell or armor on the coil I believe comes from slightly crushing the open coil geometry with the wraps and is almost unavoidable. I have a couple of coils that were used in development of my 3:1 oval or RACETRACK style and after much handling un-armoured, they exhibited an increase of inductance I attribute to crushing. The change was from about 310uh to 325uh or about 5%. I am in the process of armoring with fiberglass a 4" X 12.5" 3:1 'Racetrack coil' and a picture of it ready for fiberglass is in post #232 of the CHANCE PI COIL thread. It now measures 328uh.

Best of luck,

Dan

[CAS]

Hmmm, thx Dan, I haven't put a shell around the coil yet - will do that & rig up a pole when I've mostly finished the electronics mods & tuning. I'm curious about how this coil would measure & perform with another basketweave turn, & I am experimenting with a mod to the coil template anyway, so I think I'll make an 8 turn version of the 8x10 & post it's test results...I'll also find the minimum stable & test with that delay & include in the results...may be a couple days...

I tried a coil with a higher inductance and it would not allow me to use a short delay and it didnt make it any better at longer delays (> 30us) although there was no appreciable decrease in performance.

[KRinAZ]

I tried a coil with a higher inductance and it would not allow me to use a short delay and it didnt make it any better at longer delays (> 30us) although there was no appreciable decrease in performance.

I got a similar result - the minimum delay the coil can be sampled at is now about 12uS, depth in air tests about the same - I'll elaborate a bit in another post...

[Qiaozhi]

I got a similar result - the minimum delay the coil can be sampled at is now about 12uS, depth in air tests about the same - I'll elaborate a bit in another post...

It depends on what type of target you were using for the depth tests. Sampling earlier allows you to detect targets with very short time constants, such as small gold nuggets or fine jewellry; and you will find a difference in depth for these objects. Unfortunately, sampling earlier also increases ground response.

[KRinAZ]

----------------------------------------------By an '8 turn version' do you mean that you are going to have 8 wires in each of the slots or about 40 turns on the coil? That should put the coil well in excess of 450uh and I don't think it would decay in under 10us, just guessing. If you take a look at my post #31 in the CHANCE PI COIL thread the attached pictures show an 8" round coil with 39.4 turns of wire yielding a coil with 458uh of inductance. This coil will not allow my CHANCE PI to operate down at even 10us so a larger 8X10 elliptical coil would have even more inductance with the same number of turns. By the way the increase in inductance after putting a shell or armor on the coil I believe comes from slightly crushing the open coil geometry with the wraps and is almost unavoidable. I have a couple of coils that were used in development of my 3:1 oval or RACETRACK style and after much handling un-armoured, they exhibited an increase of inductance I attribute to crushing. The change was from about 310uh to 325uh or about 5%. I am in the process of armoring with fiberglass a 4" X 12.5" 3:1 'Racetrack coil' and a picture of it ready for fiberglass is in post #232 of the CHANCE PI COIL thread. It now measures 328uh.Best of luck,Dan

Yes, by 8 turns I mean the number of windings needed to advance from position 7 to position 8 of the basketweave winding pattern. Since I also wanted to try changing the proportions of the various elipses that make up the template, I went ahead and made the 8 turn 8x10 with the coil spread out a bit & flatter. This modification did not work out well and confirms what is probably obvious (but it never hurts to experiment) - that it is best to keep the windings as tight & compact as possible & design the template accordingly. I will be making a new version of the template with this in mind. So - this 8 turn experiment with wide spacing made a coil with 338uH (quite low for 8 turns), 4.0 passive ohms, critical damping appx 1K(I need a better assortment of 2W resistors to get more accurate), minimum delay about 12uS. From my testing results so far it seems that the 7 basketweave turns for this size coil is the best balance between inductance (RX sensitivity) & speed (sub 10us sampling). I will next post the air test results of my MPP & the 7 turn BW (basketweave) mono coil...

[KRinAZ]

It depends on what type of target you were using for the depth tests. Sampling earlier allows you to detect targets with very short time constants, such as small gold nuggets or fine jewellry; and you will find a difference in depth for these objects. Unfortunately, sampling earlier also increases ground response.

Yes, I've found this to be very much true! I can perform air tests but without GEB it is unusable on the ground here in the heavily iron mineralized Arizona dirt. OK, one other change I made (don't think it made a difference after all the other mods I did though) is swap the NE5532 for a LM4562 - & since I'm mostly interest in seeking small gold nuggets I mostly test with small lead pieces that are all odd shapes like natural gold nuggets. Also the most prevalent metal trash in AZ is ammo shells so I test them also. For testing: SAT set for fastest recovery without affecting air depth tests, sensitivity at most sensitive, delay at 7uS (the minimum stable delay for my setup) - .44 & .61 gram lead at 2.75"/7cm, .96 gram lead at 5.75"/14.6cm, 1.97 & 2.51 gram lead at 6"/15.24cm, aluminum pull tab 11.5"/29.21cm, .22 caliber brass shell at 6.5"/16.52cm, aluminum .44 caliber shell at 12"/30.48cm, 7.62x39 steel & brass NATO shell at 11"/27.94cm, large iron objects (the edge of my utility trailer) unmeasured exactly but at least 40"/100cm. These all far exceed the Whites Classic ID VLF detector I compared with so I would consider depth & sensitivity a success, just need GEB to complete this project & start using in the field...

[KRinAZ]

MPP GEB

I read thru these posts recently but was unsure of the state of GEB for the MPP - I saw where Davor & others did a lot of great work on, & SilverDollar created nice schematics, do we have a plan & procedure to add GEB now?

[KRinAZ]

Threshold on MPP

Thought I'd see what popular opinion is on the Threshold sound for the MPP - personally I have spent many hundreds of hours swinging Whites Goldmasters & Classics & prefer their Threshold sound - never fatigues me & I can distinguish faint tiny targets with it. I have also put in enough time on Garrets, Tesoro's etc. (& they are similar but not the same) to know I like Whites Threshold best. What do others think? Would this be good for the MPP project? or perhaps make a mod to convert MPP to Whites style Threshold for those who want it? Almost all my experience is in the VLF world but I would think it could be the same/similar sound for PI...

[Davor]

I'm not sure what you mean by Whites threshold, so if you are up to it, you may try to demonstrate it in a video?

I read thru these posts recently but was unsure of the state of GEB for the MPP - I saw where Davor & others did a lot of great work on, & SilverDollar created nice schematics, do we have a plan & procedure to add GEB now?

My MPP stuck at all components on board, but zero conditions for me to breathe life in it. I intend to make it work with minimum changes, and when I'm happy with it proceed with a GEB circuit. I have it ready, and I have an absolute value circuit ready, but I'm not pushing it yet since I did not test it myself. A GB circuit should work for small gold even without the absolute value circuit though.

[Qiaozhi]

Thought I'd see what popular opinion is on the Threshold sound for the MPP - personally I have spent many hundreds of hours swinging Whites Goldmasters & Classics & prefer their Threshold sound - never fatigues me & I can distinguish faint tiny targets with it. I have also put in enough time on Garrets, Tesoro's etc. (& they are similar but not the same) to know I like Whites Threshold best. What do others think? Would this be good for the MPP project? or perhaps make a mod to convert MPP to Whites style Threshold for those who want it? Almost all my experience is in the VLF world but I would think it could be the same/similar sound for PI...

I assume you're referring to a silent-search mode? In other words, it only beeps when a target is found, otherwise there's silence (apart from the occasional chatter).

[KRinAZ]

I assume you're referring to a silent-search mode? In other words, it only beeps when a target is found, otherwise there's silence (apart from the occasional chatter).

Since I'm primarily a prospector searching for gold, I personally usually don't use disc modes if present on a detector - only all metal mode - so I'm actually referring to the Whites threshold sound in all metal mode (Classic series) or just the Goldmaster ("black box" & GMT/GMZ models) threshold (no disc mode so all metal all the time, where the threshold tone is always present (unless threshold control is turned down too low) as a faint hum & gets progressively louder with RX signal strength, but the freq is constant at around 1khz to 1.5khz (I believe, will try to verify) & sounds like a nice sine wave signal, hope that helps & let me know if you'd like more info on it.

[KRinAZ]

I'm not sure what you mean by Whites threshold, so if you are up to it, you may try to demonstrate it in a video?My MPP stuck at all components on board, but zero conditions for me to breathe life in it. I intend to make it work with minimum changes, and when I'm happy with it proceed with a GEB circuit. I have it ready, and I have an absolute value circuit ready, but I'm not pushing it yet since I did not test it myself. A GB circuit should work for small gold even without the absolute value circuit though.

Great idea on the video, I'm in between Whites detector's at the moment - I buy them when I come across a good deal & sell them bundled with some training, so there's a flow of Whites going thru my hands, next time I have one (hopefully soon) I will see if I can produce a short video on the threshold sound. & I don't recall reading any posts on your absolute value circuit, could you elaborate on that or refer to post #'s? Many thx for that & the update on the GEB circuit

[KRinAZ]

Since I'm primarily a prospector searching for gold, I personally usually don't use disc modes if present on a detector - only all metal mode - so I'm actually referring to the Whites threshold sound in all metal mode (Classic series) or just the Goldmaster ("black box" & GMT/GMZ models) threshold (no disc mode so all metal all the time, where the threshold tone is always present (unless threshold control is turned down too low) as a faint hum & gets progressively louder with RX signal strength, but the freq is constant at around 1khz to 1.5khz (I believe, will try to verify) & sounds like a nice sine wave signal, hope that helps & let me know if you'd like more info on it.

Update - the fixed freq may actually be appx 400Hz, & may vary some between models - as I get my hands on various models I will start measuring the threshold tone & if I remember correctly the Whites TDI [PI] series also have a very similar threshold sound & behavior.