best coil for baracuda?

[waltr]

Really! over there in the USA ! That great! guess the boarders were not so hard to pass back then hahaha, I found this one over the summer with the TGSL, but its a One Penny not a half penny, it measures 33mm across and Wight 15grams, They are a great find as its a good indicator no one has detected where its found, as it rings up good! but don't get excited about its value lol I had it praised, it is considered very good condition, but because its a bank token and not actual money, its only worth 10$ CAD but for a bit of copper buried in the ground for a 168 years! Still a great find. Congrats I know I was really happy to find mine!

Yea, it is a great historical find but no monetary value just like the King George half penny and US large cent coins I've found.
Great yours is a full Penny (can't tell from pic) and much better condition than the half I found.
Picture here: https://metaldetectingforum.com/showthread.php?t=269101
The US was also having coin shortage issues particularly during and after the Civil War and many foreign coins were still legal tender.
Would love to know the story of how this coin made it down here near Philadelphia and then end in what was a farm field.

Ok, enough thread hijacking.

nonkapo,
How is the building going?

[nonkapo]

LoL my poor Baracuda put in shame the chinese knockoffs of Teknetics G2 and T2;-))). Focused on the dismantling manuals and desert safaris these days:-). Facing another issue with my spiral coils. Feel like when fixed in the housing and cross the second cable above i'm loosing sensitivity. In other words the coil detect the external end. Will update soon and probably open separate thread for this.

Tibuck19, KT mean basket coil, not ordinary as the air is better insulation than the epoxy. That's why you loose speed when you mold the basket. On the ordinary coil even if there is some effect cant be so bad. Correct me if I'm wrong.

[kt315]

[QUOTE=bbsailor Basket coil construction is designed to reduce the coil turn-to-turn wire capacitance that would be higher if the wires laid parallel to each other. Once advantage of reducing coil capacitance is the potential for that coil to sample faster due to less capacitance in the TX/RX circuit. When delays get below about 10 uS the type of wire needs to be considered so that the wire itself does not retain any eddy currents and then look like a target. That is why Litz wire makes a good coil wire when attempting to achieve low sampling time. The value of the damping resistor is a good indicator of how much coil and TX/RX circuit capacitance needs to be damped.

The ability to fully stimulate a target with a TX pulse requires that the coil discharge TC be five times faster than the target TC. Here is a thought experiment. A charged 2 uS target, fully stimulated, will fall to near noise in about 5 TCs or 10 uS for that target.That is why you would need to sample at less than 10 uS for a 2 uS TC target.

Now, to fully stimulate a 2 uS target requires a coil discharge TC of 2/5 or 0.4 uS. The coil discharge TC is determined by the coil inductance divided by the damping resistor value. A 300 uh coil would need a 750 ohm damping resistor to meet that requirement. Now you can see why making fast coils requires using many techniques to reduce capacitance and allow a higher value damping resistor to be used to fully stimulate small, low TC targets.

In mono coil PI metal detectors the op amp input resistor, typically 1K ohm, is ahead of two clamping diodes and while these diodes are conducting with a voltage above about 0.6V, the input resistor is effectively in parallel with the damping resistor thus effectively reducing the damping resistor value until the voltage falls below 0.6V. That is why DD coils that separate the RX and TX circuits are easier to operate at lower delays.

Optimizing coils should be done for a class of and small range of target TC ranges to have the best results. This includes the PPS rate, coil current, flyback clamping, damping resistor value, delay time, number of samples being integrated, coil size, coil sweep speed and coil's response to the soil and detecting environment.

The basket coil is just one way to attempt to reduce capacitance but there are many more things that need to be considered.

Joseph J. Rogowski[/QUOTE]

just transfer good post all-one-place.

[kt315]

Hi there, I've recently built Baracuda PI, and it works very well with a mono coil I've built, 23 cm diameter with 0.5 mm insulated copper wire, 22 turns, about 392 uH, but I know this awesome circuit can give more. ��

For now, I'm obtaining a sensitivity of about 10 ? 12 cm for a normal coin or ring, and some 20 ? 25 cm for some bigger object. I would like to know if someone out there did build or use this PI metal detector, and what particular coil is the best for it.

Thanks in advance. ��

just transfer good request in good thread.