pd based on bfo

[mustefa ubram]

hi to all
Please comment on the overall plan
pd detector with feritte antenaa.Based on bfo detector
If sending signal by Ferrite antenna At the point where the metal is rapidly changing due to the sensitive nature of the ferrite core frequency This change in frequency can be based on the type of bfo metal detector was processed.
Please give your opinion on this issue

[detectoman]

mustefa: these project semms very interstant, thanks

[WM6]

mustefa: these project semms very interstant, thanks

Yes, for pinpointer in best case.

[mustefa ubram]

Yes, for pinpointer in best case.

hi wm6
Do you have a schematic for this area.(For the transmitter antenna ferrite).please give.
Such a system can be remotely discriminate between ferrous and non ferrous metals.Ferrous metals are low frequency ferrite core and And non-ferrous ferrite antenna frequencies high.
Please comment
G.L

[mustefa ubram]

hi
Oscillator with a ferrite antenna for transmitter
please comment

[WM6]

hi
Oscillator with a ferrite antenna for transmitter
please comment

BFO distinguish between metals as on your scope pics is possible only in near EM field (direct target impact on the TX coil/tank) and not in remote RF field too.

[mustefa ubram]

BFO distinguish between metals as on your scope pics is possible only in near EM field (direct target impact on the TX coil/tank) and not in remote RF field too.

wm6
Is whether this method can be used for remote sensing(BFO WITH FRITTE ANENNA TRANSMITTER)
What are your suggestions for remote sensing wiyh bfo tape pd?
Please get some help
G.L

[WM6]

You can not change frequency of search oscillator (TX oscillator) on remote (say couple of meters) except by very very big targets like battle tank.

If you cannot change frequency of search oscillator, you cannot get nothing out of BFO mixer (except by coincidentally oscillators drift).

BFO is not good platform to construct remote detecting PD.

[WM6]

But, there are always some "but".

You are asking for filtering on another thread.

Here your BFO is coming to use.

BFO principle can be used as simple way to filter out (or "in") desired frequency as per example 73kHz by mixing it with proper constant frequency and then filter out wanted results (your mixing frequency) in one of such way:

1. very simple: you can use piezzo summer and calculate your mixing frequency to resonant frequency of piezzo summer.

2. simple upgraded: by adding VLF filter in line with above summer.

3. Hi tech: by using cheap (about 80 euro) pocket scope with FFT function and observe frequency spectrum at output of your mixer (if your mixing frequency appear you will clear see it and distinguish from noise):

http://www.jyetech.com/Products/LcdScope/e096.php

[mustefa ubram]

tank you wm6
I believe that many of the systems used for remote sensing of metal from BFO
For example, the zahori
A reference frequency is generated with 555 and a frequency that is received from the environment.Frequency of the incoming frequency is disrupting the balance.and......
what is your comment?

[WM6]

tank you wm6
I believe that many of the systems used for remote sensing of metal from BFO
For example, the zahori
A reference frequency is generated with 555 and a frequency that is received from the environment.Frequency of the incoming frequency is disrupting the balance.and......
what is your comment?

There are always wideband spectrum of frequencies (noises, hums) in air from different natural and artificial sources.

You can use those frequencies to mix it with your reference (BFO) oscillator frequency to get selected and frequency dependent mixing results from your device.

But basically static charge sensing devices like Zahori, do not need mixer to sense static (or alternating) charges in environment.

[J_Player]

tank you wm6
I believe that many of the systems used for remote sensing of metal from BFO
For example, the zahori
A reference frequency is generated with 555 and a frequency that is received from the environment.Frequency of the incoming frequency is disrupting the balance.and......
what is your comment?

Hi mustefa ubram,
The Zahori is an electric charge detector. It does not use a BFO circuit.
It detects electric charges from the air in the location of the antenna.
The purpose of the 7555 and 4066 ICs is not to act as a BFO.

The reason the 7555 and 4066 were added to the circuit are for two reasons:
1. The antenna can collect a large charge after awhile, and this charge can become too much voltage for the circuit to make good detection.
The 4066 is used to discharge any charge which comes to the amplifier periodically so it will always be near zero volts.
Then for a very short period of time it will allow the antenna to capture charges from the air until it will cause the amplifier input to discharged again.
Any The 4066 will also save any charge that the antenna collects so we can still read it while the antenna is being discharged before it will collect a new sample of the air charge.
This process of capturing a small charge for a short period of time, and then discharging the antenna is repeated very fast, so you will have a continuous stream of separate charge samples taken from the antenna.
It happens fast enough so the changes you see appear to be continuous when you move the antenna to places that collect a different amount of charge from the air.

2. The 7555 is set to 50 Hz if you live in Europe, or 60 Hz if you live in the Americas.
The reason for the 7555 to use these frequencies is not to create a BFO detector.
The reason is to create a digital filter which will remove the interference from power lines.
The electric field caused by power lines will interfere with your collecting charges in the air.
But if you collect a sample at the exact same time during each cycle of the mains power interference, then you can effectively cancel some of the AC noise from power lines.
The 7555 sends the signal to the 4066 to discharge the signal 50 or 60 times each second.
The 4066 will also save the sample which the antenna collects after the antenna is turned off between samples at a rate of 50 or 60 times a second.
This is the purpose of the sample and hold section which is located between the two amplifier stages, so you will not see an interruption in the signal while the antenna is being discharged.
At the time when the antenna is being discharged, the meter continues to read the saved sample so you will not see the effects of the signal dropping to zero volts 60 times a second.
Then, when the new sample begins, you will see the new updated charge reading from the new sample.
This process will repeat 60 times a second (or 50 times a second in Europe), which is fast enough that you cannot see it happening.
You will only see smooth changes as you move the antenna to different locations.

In the end, we see the Zahori is not a BFO detector, but an electric charge detector.
The 7555 and 4066 ICs are added only to improve the performance of collecting a charge, so we will not see any interference from power lines or from overloading the antenna.


Best Wishes,
J_P