Lrl from Italy

[brs]

http://store1.up-00.com/2016-05/1462916372161.jpg

[FrancoItaly]

I don't understand, the scheme is correct, the presence of a target is signaled by an increase in voltage to the signal input (from sensor), then at out of IC3A the signal decreases (the signal is applied to inverting input). When signal at not inverting input of IC3B is more low then 6V (Determined by the R12 / R13 voltage divider) the out of IC3B goes low (zero volt) and then the LED lights up and the buzzer sounds.

Best Regards

[brs]

Thank you Franco
accept greetings

[abdou2014]

I want to make this change. is there anyone who is interested ?

[FrancoItaly]

Before making any changes you have tested the LRL on the field ? In my opinion my LRL works only in the 100Mhz range. The low pass filter is no critic as the output is a DC voltage
with some residual RF (8Mhz).

Best regards

[Mohlrl]

hi Franco. In your opinion, transistor with hfe 450 is good?

[FrancoItaly]

Yes I think it's ok, look " http://alltransistors.com/transistor...ansistor=22466 ", 450 is the minimun value for " hFE " ( transistor gain ). Anyway for more gain you can increase C13 and/or C14. Any transistor BC...C series with 150Mhz frequency or more is ok.

[abdou2014]

location of the filter corrected .what is the resonance of LC circuit ? and why we not add a resistor for get a wideband .

[FrancoItaly]

LC resonance is about 100 Mhz, I have not measured accurately, It must be taken into account the capacitor formed by the BE junction of TR2 (about 10pF). C15 is a simple coupling capacitor with a very low impedance at the frequency of 8MHz, should at most is a simple high pass filter. The set of C15, D1, D2 and C16 constitute a full-wave rectifier, while TR5 operates in emitter follower with high input impedance and low output impedance. R15, R16, C17 and C18 constitute a lowpass filter to eliminate the residual signal at 8 MHz.
I repeat that the sensor stage is very critic for the high gain, in my opinion it should be built on a separate PCB, preferably double-sided, with components soldered directly on the copper of a part, while the other part is connected to ground and serves as a screen to prevent auto-oscillations. I will post again my original PCB.

[abdou2014]

So your device is Capacitive detector , and if we add an antenna in base of TR2 we have a Static and Capacitive Detector . I'm right ?

[goldfinder]

capacitive sensor

Sounds like he is using the capacitor as a scalar sensor to detect the gravity eminations of the minerals ( gold).
Goldfinder

[FrancoItaly]

I do not know if it is a Capacitive detector. Static presupposes very high impedance receiver, but it's not the case.

[abdou2014]

PLEASE Mr FRANCO WERE WE PUT THE VARIABLE CAPACITOR FOR TUNING. IN C9 OR C10 (8 MHz Stage). AND WHAT IS ITS VALUE?

[FrancoItaly]

In place of C 10 and the value is 22pF. Usually the variable capacitor has the range from 4 to 22pF. To test lower frequencies you must add in parallel a 10pF capacitor.

[abdou2014]

THANK YOU