Understanding of how HH circuit works

[DOOLEY]

i constantly think , i'm missing something here , think brain think , right start again.

someone please invent a time machine , then we can go 20-30 years ahead , look back and laugh , it would be like looking at the lottery numbers the day after , where they look so obvious.

i think were missing something obvious , and when we find it , we will all laugh,roll on that day.

[DOOLEY]

the fellow called "moodz" now he's onto something , ballanced coils.
one giving + response, one giving - responce = twice the differance which has to = twice the sensitivity.
on the face of it , right direction to go,but is twice as far as we can go ?

what can get us deeper , smaller , possitive , deffinate responses.

[Tinkerer]

i constantly think , i'm missing something here , think brain think , right start again.

someone please invent a time machine , then we can go 20-30 years ahead , look back and laugh , it would be like looking at the lottery numbers the day after , where they look so obvious.

i think were missing something obvious , and when we find it , we will all laugh,roll on that day.

As the great advocate of "out of the box" thinking, I say you are on the right path.
Yes, there are other ways and many times they have been thought of a long time ago. But, with all due respect, in the time of tubes and 20% resistors, without MCU's, many an excellent idea could just not be effectively executed. Or at least not as well as it is possible today.

Links and numbers of hundreds of metal detector patents have been posted on this forum. To study them all, how long would it take?
But, there are hundreds of ideas floating in this patent pool. A fishing trip may produce the fish with the golden coil in it's mouth.

Tinkerer

[WM6]

As the great advocate of "out of the box" thinking, I say you are on the right path.

Tinkerer

After years of "out of the box" thinking, we, at the end, need to put something "in box".

Seems box is still full of speculative circuitry only.

[EEE]

Thank you Carl and Doodly for the explanations.

[uvgunkhuu]

which is correctly value

i do not understanding decaying signal 0.7v to 0 v as preamp gain out
700v or
- rail

[DOOLEY]

hello uvgunkhuu,

i understand what you are thinking,0.7v to 0v input at 1000 gain =700v,i was once confused by that.

but....the diodes are simply to protect to op-amp from the flyback,we could use shottky diodes (0.2v) also,but the op-amp would still "rail out" for some time before it shows to decay curve we want to look at.

at 1000 gain and a 10v op-amp supply we are only looking at the last 10mv of the decay curve.

so,diodes safely limit op-amp input to 0.7v,and at this input voltage the op-amp is "railed out" until the input voltage drops to 10mv,at which point we start to see the curve we want to look at from the output of the op-amp all the way down to 0v.

think i'm roughly right there,but don't mind being corrected.

[Dr Vel]

Carl what is the inductance of the coil in the HH? I was thinking about using a 12 inch Jetco coil form for my coil. Looking at it I realized it is a nice rugged design which would be a shame to open up just to use the form if as is it could be used. Studying it I found 70 uH and 1/2 ohm for the coil. Inside is a trimmer capacitor which can be adjusted with a screwdriver through a hole. Using a scope and grid dip meter I find at max C = 705 KHZ and at min C = 915 KHZ, or just under 1 MHZ. This equates to a variable capacitor of 432 pF to 728 pF in parallel with the 70 uH coil. Do you think this coil could be used in the HH as is or do I really need more turns? Just hate tearing apart this nice looking coil if it would work in a PI MD as is.

[6666]

DrVel

Carl what is the inductance of the coil in the HH?

The doco said 500uH