ideal RX opamp output level ?

[lonelyWOLF]

Hi..

how much should be ideal (VLF md.) rx opam output voltage then coils null?

regards..

[Carl-NC]

Ideally zero! But you'll never get there.

[lonelyWOLF]

thanks carl.
nice reply. I did not know

ok.. I'll ask diffrent
MD manufacturers how much mV set this point. ofcourse may be different
min or .max.?

regards

[simonbaker]

Hi..

how much should be ideal (VLF md.) rx opam output voltage then coils null?

regards..

With TGSL MD, if your coils are not shielded, you can sometimes get the voltage down to around 50 mV I think. If you have shielded coils, then it may be between .5V and 1.5 V.

I believe most people just find the minimum voltage, then very slightly push the coils together more until the voltage goes up maybe 25% -- just to the side of the null point.

-SB

[mikebg]

Hi..

how much should be ideal (VLF md.) rx opam output voltage then coils null?

regards..

IMNHO the ideal output voltage of RF amp for metal detecting is near to saturation. At this condition, it operates at maximal gain, ie metal detector has maximal sensitivity. If the opamp is ideal, voltage swing in output should be maintained allways near to rail-to-rail voltage. To achieve this, you need AGC (automatic gain control) for preamp and ABC (automatic balance control) for input.

[mikebg]

Ideally zero! But you'll never get there.

Carl, the attached image shows how should operate front end of a competent designed metal detector. The image was posted in your forum.
http://www.geotech1.com/forums/showp...71&postcount=7

[lonelyWOLF]

greetings...

I have tested a lot of these day.
if opamp output voltage is high (~500mV). switch after first opamp goes to overload. manual bias required. but not change distance the result is not good. if very low (10mV) it works poor.I'm get the best result own circuit opamp output level 75mV...
thanks for all reply's

Dagci,erol

[Carl-NC]

Mike, I was addressing loop null, which is what I thought Wolf was asking. Ideally, you want a perfect loop null, zero output voltage. Practically, a -60dB null is about all you can get.

This is for traditional VLF designs. There are ways to design a VLF with an un-nulled loop.

- Carl

[lonelyWOLF]

hello..

magic words "un-nulled loop"

if I understand correctly I tried this too.
rx opam used as a buffer no gain , no noise,no signal distortion..

shifted coil to other side until buffer output app.75mV ok..that's better. now, no effort for coils null..

regards.

Dagci,erol