Wide band Amlifier?

[Tinkerer]

Wide band amplifier?

Traditionally we have been using wide band amplifiers at the front end of the PI detectors.
However, when I look at the readout (pic1) of the FFT, below, I see the 450uH, 11” diameter RX coil (pic2) spectrum, it looks more like a high Q filter than a wide band receiver, with the frequency very much concentrated at 1Mhz.

In comparison, (pic 3), Is a wide band receiver antenna, where one sees a spectrum spread over a wide range of frequencies.


Both readings have been made in the same environment.


Would anybody be so kind as to explain to me the reason we use a wideband pre-amplifier for the PI?

Tinkerer

[Carl-NC]

Would anybody be so kind as to explain to me the reason we use a wideband pre-amplifier for the PI?

Transient speed and overvoltage recovery.

[Tinkerer]

Transient speed

Thanks Carl,

I understand the need for transient speed, in fact I believe this is the important part and not the recsponse to a sine wave that is often used to characterize the coils.
As for overvoltage, I have included a clamp that reduces the gain of the preamp above 3 volts, because I felt that I do not need that part of the curve.
The problem that I have, is the lack of information to be able to compare the output of my coil / preamp setup with others so that I could judge if I am doing good or if my results are mediocre.

Tinkerer

[Tinkerer]

Rest of the post

Thanks Carl,

I understand the need for transient speed, in fact I believe this is the important part and not the response to a sine wave that is often used to characterize the coils.
As for overvoltage, I have included a clamp that reduces the gain of the preamp above 3 volts, because I felt that I do not need that part of the curve.

Now, when I push the gain to 3,3000, and it works, although noisy, I can see no negative effects, except that the normally very short eddy current from a 0.6 gram gold nugget, now extends to 100 uS. I can sample my 310 uH coil at 8 uS with this gain and relative high power TX.
Now, this being a NE5534 opamp, with this amount of gain the bandwith gets quite narrow, so why does it work?

The problem that I have, is the lack of information to be able to compare the output of my coil / preamp setup with others so that I could judge if I am doing good or if my results are mediocre.

Tinkerer