Quote:
Originally Posted by fmnotes
HELLO.
MANUFACTURED HAS SOMEBODY THIS MANUFACTURE?
I I FINISHED HIM YESTERDAY AND HAVE PROBLEM.
IT DOES NOT HAVE BY NO MEANS SENSITIVITY.
IN ORDER TO IT TURNS ON THE LED IT SHOULD YOU LEAN THE GENERATOR OF FREQUENCIES IN THE KERAIA.GIATI?
WHEN WE OPEN THE RECEPTOR THE GREEN LED IT SHOULD IT TURNS ON?
WHO KNOWS YOU HELP ME
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The purpose of the green LED is to show when there is a signal detected from the receiver.
If you turn on the power and a signal is received from the antenna, then the green LED will turn on.
Stronger signal will cause brighter green LED.
The other LEDs also show strength of signal when power is turned on, or meter can also show signal strength.
These LEDs do not show what frequencies are received.
They only show the strength of the signal.
The frequency received can be selected by using the switch to select capacitor C1 to C5.
These capacitors will adjust the resonant frequency of the ferrite antenna to make resonance for only one frequency.
But if you connect an oscilloscope, you will see there are other frequencies present in smaller strengths than the resonant frequency.
The circuit is a very simple radio receiver for detecting VLF signals at the location of the ferrite coil.
It is a wideband receiver which has the bands divided into 5 different bands.
It can receive various frequencies within the range that is selcted by the capacitor switch.
This is designed to be a simple and cheap way to build a receiver that can be used to experiment with radio waves passing through the ground to locate buried things.
It is not designed to be a sophisticated narrow band receiver with special signal processing.
I did not build this receiver circuit.
The instructions I make are only from looking at the circuit to see what is the intended function.
If you make an error in the wiring, then this circuit will not work correctly.
Also, you may need to adjust the values of the resistors or capacitors for best performance.
Some of the components will not have the exact values you see marked on them.
This is not a problem, but it can cause slight difference in the expected frequency.
You will see that the 10k value I show for R4 modification will give maybe only half of the meter movement.
You can reduce the value of R4 modification to maybe 8k or 5k to send a stronger current to the meter.
Or if you use a meter that moves full scale at a different current than 1 ma, then you will need to change the resistor R4 to make a good reading when you are detecting a strong VLF signal.
You can test to see if your receiver is detecting a signal by using a signal generator connected to a loop of wire 10 or 20 cm diameter with 10 turns of wire.
Any wire thickness will work ok.
Then turn on the signal generator and make a sweep of frequency that your receiver is tuned to receive.
The receiver should be placed a short distance away from the coil of the signal generator, maybe 1-3 meters distance.
When the receiver is set to C4, you can sweep the signal generator from 3KHz to 30KHz.
You should see the green LED and the other LEDs become bright.
When you move the receiver away from the signal generator, then the LEDs should become less bright.
If you use the meter modification, you should see the meter is stronger when the receiver is moved close to the signal generator.
You can also test other frequencies by sweeping the signal generator at these frequencies when the receiver is connected to different capacitors.
C1 -- sweep signal generator from 3Hz-30Hz
C2 -- sweep signal generator from 30Hz-300Hz
C3 -- sweep signal generator from 300Hz-3KHz
C4 -- sweep signal generator from 3KHz-30KHz
C5 -- sweep signal generator from 30KHz-300KHz
If the receiver is wired correctly, then you should see some signal when the signal generator is turned on.
I do not recommend connecting the aerial antenna.
This kind of antenna does not work well for receiving signals in the range from 3 Hz to 300 KHz which the receiver can receive.
The ferrite antenna should work very well.
Best wishes,
J_P