Oscillator power!!!!

[WM6]

Although you may have noticed that several metal detector manufacturers erroneously still refer to the coil as an antenna in their literature.

.

Agree, there is some confusion in terms. But we know different detector and different coils. RX coil in BFO detector work exclusively as an antenna.

[Qiaozhi]

Agree, there is some confusion in terms. But we know different detector and different coils. RX coil in BFO detector work exclusively as an antenna.

Although a BFO generally operates at a higher frequency than an IB detector, the search coil cannot be considered as an antenna. Antennas have dimensions comparable to the wavelength of the signal of interest. In the case of the BFO, the coil still operates in the near field where metallic targets can affect the inductance of the coil.

[Aziz]

LRL's have antennas! Some have more than one!

So it's better to avoid any antenna term in the serious metal detecting terminology.

It is what it is: A coil

And I like the near field term for |z| < R and far field term for |z| > R (related to the coil center of a mono-loop coil).

[WM6]

Although a BFO generally operates at a higher frequency than an IB detector, the search coil cannot be considered as an antenna. Antennas have dimensions comparable to the wavelength of the signal of interest. In the case of the BFO, the coil still operates in the near field where metallic targets can affect the inductance of the coil.

Qiaozhi, this affect only to BFO TX coil (and Tx circuit). BFO RX coil work still as pure (RX) antenna (RX antenna can be positioned and working far away from near field effect). Maybe term antenna lead from BFO in which case it is true.

[Aziz]

A ground penetrating radar (GPR) has an antenna. But this has nothing to do with LRL's.

So who is going to increase the TX power now?

But consider, it has also negative side effects:
- heat
- instability
- increased ground effects
- higher battery drain
- heavy coils and leads (you need high Q coils)

[WM6]

- heavy coils and leads (you need high Q coils)

Yes, very important (higher Q - lower TX power needed). But this do not mean that heavy coils is required.

[mikebg]

But consider, it has also negative side effects:
- heat
- instability
- increased ground effects
- higher battery drain
- heavy coils and leads (you need high Q coils)

There are more negative effects at increased TX power:
- Increased AIR signal,
- Saturation (overload) of preamp,
- Interference of working nearby detectors.

[Aziz]

Hi Mike,

There are more negative effects at increased TX power:
- Increased AIR signal,

This is, what I like very very much. It's a big plus.

- Interference of working nearby detectors.

Getting rid of the competion in the field: It's also a big plus.

Sarcastic Aziz (for once)

[Qiaozhi]

Qiaozhi, this affect only to BFO TX coil (and Tx circuit). BFO RX coil work still as pure (RX) antenna (RX antenna can be positioned and working far away from near field effect). Maybe term antenna lead from BFO in which case it is true.

In a BFO there is only one search coil, which is used to create an electromagnetic field. When a metallic target enters the field it alters the inductance of the coil. It is the change in inductance that is detected. So there is no "receive coil" as such.

[maikl]

Qiaozhi is right. BFO has only one TX. CCO (double BFO) has two TX coil. No transmitter TX and receiver RX.

[WM6]

. So there is no "receive coil" as such.

Sure not, there is an RX antenna (in form of coil). What we are speaking about?

[WM6]

Qiaozhi is right. BFO has only one TX. CCO (double BFO) has two TX coil. No transmitter TX and receiver RX.

Some basics for you (who is speaking about two TX coil?):

BFO (Beat Frequency Oscillation) - Metal Detectors using BFO technology have two coils of wire, one large coil is located in the search coil of the detector, the other small coil (act as RX antenna) of wire is located within the System Control Pack. Each coil of wire is connected to an oscillator that produces pulses of current. These pulses of current pass through the coils generating radio waves. A receiver housed within the System Control Pack receives the radio waves and makes a series of tones based upon the frequencies of the radio waves. When the detector search coil passes over a coin or other metal item a magnetic field is created around the coin or metal item, this magnetic field causes interference with the frequency of the radio waves generated by the search coil. And changes the tone produced by the reciever (of radio waves, and radio waves can be received only by antenna, not by finger, and antenna is coil - always - in this case RX coil).

PS: Telescope antenna act electrically as coil (inductor) too.

[pebe]

I don't know who dreamed up that definition of a BFO detector, but he was way off the beam.

[WM6]

Or graphically (in mikebg style):

[WM6]

I don't know who dreamed up that definition of a BFO detector, but he was way off the beam.

Or you are way off the beam. If we speaking of pure BFO there is in question only word "coils" (line 4) have to be (TX) coil.