Lrl from Italy

[FrancoItaly]

Hi Napsterce,

I did it this way: instead of C10 I used a 22pF variable capacitor and then I soldered in parallel the 22pF capacitor and so I covered a range from a few pF to 44pF. It is to keep in mind that there is always the base/emitter capacitance of TR2 (about 10pF) in parallel to C10. Same procedure for L1, first I sold L1 with 4 turns and I vary the capacity of C10, then I sold L1 with 3 turns and so on. I use a soldering iron 12V powered.
What can disturb LRL are radio frequency transmitters located nearby and there is no way to eliminate them. Regarding the compass effect should decrease the sensitivity. It is possible that by varying L1 / C10 can be achieved a reduction of this effect without decreasing the sensitivity.

Best regards

[FrancoItaly]

You may use also a varactor diode instead of C10.

[Napsterce]

Thankyou Franco, i will test on a test field soon.

[dream_man]

Hello dear Franco;
what range of the output voltage is more comfortable for this circuit? .. 1 volt? or 2..3..4..5?
I've configured two 1pF capacitors in series and have 1 volt output.. Is it ok? .. or I need to remove one of them to increase the output voltage?

[FrancoItaly]

Hi dream man,

In the sensor stage the purpose is to obtain the maximum amplification but without there being self oscillation. If you used BC...C transistors I think that the gain is enough, then is necessary to act on the amplitude of 8MHz signal which goes to the base of TR2. The total value of C2, C3 and C4 is added to the parasitic capacitance of the PCB, in a case I did not use capacitors but only the capacitance of two neighboring tracks of the PCB and in another case, two twisted wires. So you should remove C3 and C4 and for C2 you should find the right value for an output of about 5 - 6V.


Best regards

[dream_man]

Thank you dear Franco for replying. So you mean that 1volt is low for output of sensor and must be between 5 to 6 volt?

[Napsterce]

I made two lrl's by Franco's schematics and they have output 5 to 6 volts and when i touch the antenna it decreases. If I am correct if treasure is found the voltage will drop even lower and maybe to 0 volts, is that correct Franco?

[FrancoItaly]

Hi dream man,

Yes but perhaps the lrl could work well with only 1V. 5V ensure that we have the maximum possible gain.

Best regards

[FrancoItaly]

Hi Napsterce,

No the presence of the target is marked by an increase of the signal.

Best Regards

[dream_man]

Hi dream man,

Yes but perhaps the lrl could work well with only 1V. 5V ensure that we have the maximum possible gain.

Best regards

Thanks Franco. Cheers

[mustefa ubram]

hi franco
Is there a difference between the output voltage in the face of a large and small target ?

For example, the maximum output voltage of the sensor for a coin is 6 volts and for a 20cm*20cm is 8 volts?Or is else?

Which parameters in this circuit is always fixed for various targets?
the minimum distance between the target and sensor For a coin dating back 500 years Subsoil and a large target 1 year old Subsoil output voltage is equal?
Or against the large target is always higher voltage And old creates only more sensitive?

best wish

[FrancoItaly]

Hi mustefa,

Unfortunately I have little experience with the LRL in the real research so I can not answer any of your questions. I decided to publish my LRL because other members of the forum could help develop this project not only to improve but also to better understand the behavior on real field.

Best Regards

[FrancoItaly]

some advice

As several new members of this forum have asked me privately tips for building my LRL, want to do a little summary about its construction and calibration.
The quartz and TR1 constitute the internal oscillator, TR2 is the mixer to which the 8Mhz signal arrives along with the "phenomenon" picked up by the antenna. TR2, TR3 and TR4 are the high gain amplifier, TR5 takes the signal (rectified by diodes) with high impedance and on the emitter there is the signal with low impedance. R15, R16, C17 and C18 are a low pass filter that cancels signal residues at 8 Mhz. I repost schematic and PCB. It's better to use a double face PCB, on one side we sold the components and the other side there is the shield
connected to ground, to avoid self oscillations. It's preferable to use transistors type BC...C because the high beta (gain), I use BC183C because I have a lot but work well also BC549C, BC109C, BC239C and others. All sensor stage is powered by 12V stabilized. For the first test do not connect quartz then look at out point, the DC voltage must be 0V. If not the stage is self oscillating then you must decrease the gain by changing C13 and C14 (from 560pF to 470pF or less) until there are no more oscillations.
Now connect quartz and measure out voltage, if the voltage is yet 0 you have to control the emitter of TR1, if the oscillator is ok it must be a 8Mhz signal of few volts peak to peak, otherwise change C1, for example from 330pf to 470pF or more. Signal out is better in the range 5-6V, if it is more then 6V you have to decrease C2,C3 and C4, sometimes it's sufficient the parasitic capacitance of PCB (removing C2, C3 and C4) or you can use instead of C2-C3-C4 two wires of about 6 cm twisted between them. If signal out is less than 5V you have to increase c2-C3-C4, for example if you use only C2 you have 1pF, if you use only c3-C4 connected in series you have 0.5 pF and so. To test if everything is ok touch the antenna and the out must decrease (100 - 200 mV or more). The target is signaled by an increase of the output voltage.

[FrancoItaly]

oops I forgot schematic and pcb

[FrancoItaly]

I want to add that the sensor stage is very sensitive and must maintain his calibration away from electromagnetic sources of interference. The same measuring instruments affect the function. I recommend using the oscilloscope only to control the operation of the oscillator, but not use it to measure the amplitude of the signal on the collector of TR3 and TR4, as this will radically change the output signal. The only useful measure without "side effects" it's the DC voltage at output of sensor stage. A useful indicator of good functioning is that the DC output is stable, but if there is superimposed an oscillation of a few hertz or more this means that there is a self-oscillation. I want to mention in passing that this LRL, in the first version, was a RF sniffer that self oscillated, but the output was stable and, quite by accident, I realized that functioned as LRL.