deep penatration

[okantex]

http://www.nexusdetectors.com/Science.html

in this link says

"
The next popular type of metal detectors, capable to compete for better depth, are the PI metal detectors.
Relative to the transmitted in the ground energy, the PI detectors are with lower efficiency than the IB. However the fact
that average PI metal detector can detect targets deeper under ground than average IB detector, is due to the very high level
of the transmitted signals (few hundred volts pulses). With that allowance in their basic principal the PI metal detectors can
win almost any competition for depth.

"
why can not we use IRF mosfet transistors in BFO and VLF?
can not we increase their dept by using this transistors instead of bc517 or else (npn).
what provents us from doing this.

EE brothers ,
I am wondering this.can you explain me.

[Qiaozhi]

http://www.nexusdetectors.com/Science.html

in this link says

"
The next popular type of metal detectors, capable to compete for better depth, are the PI metal detectors.
Relative to the transmitted in the ground energy, the PI detectors are with lower efficiency than the IB. However the fact
that average PI metal detector can detect targets deeper under ground than average IB detector, is due to the very high level
of the transmitted signals (few hundred volts pulses). With that allowance in their basic principal the PI metal detectors can
win almost any competition for depth.

"
why can not we use IRF mosfet transistors in BFO and VLF?
can not we increase their dept by using this transistors instead of bc517 or else (npn).
what provents us from doing this.

EE brothers ,
I am wondering this.can you explain me.

There are a number of problems related to increasing the TX power. The main ones are:
1. Too much output power will saturate the soil matrix and overload the receiver circuits with unwanted signals.
2. For an I.B. detector, doubling the output power does not double the depth. I believe the correct value is 2^6 (i.e. 64 times).
3. An I.B. detector transmits continuously, so increased TX power means decreased battery life, and more heat dissipated in the search head.

The P.I. detector does not suffer from these problems because it transmits pulses and not a continuous sine wave. Also, the transmitter is switched off when in receive mode, thus overloading of the receiver does not occur. In particular, the P.I. monitors the decay curve of the TX signal and is not affected by coil balance.

The bottom line is that you need to increase the TX power by a huge amount to get a small increase in sensitivity, and the bad points outway any benefits that may exist. In reality it's far better to concentrate on making better coils and receiver circuitry.