AV multiband VLF receiver

[fmnotes]

I do not understand you very well, but:

Nothing can happen without incoming signal.

You can get incoming signal from existing (military etc.) signal transmitter or from your own VLF signal transmitter (TX).

You need to know frequency of those VLF transmitter (TX) and select on your VLF receiver (RX) proper band by C selection switch.

Of course you can test your VLF receiver (RX) by usual signal generator. In this case you can one old relay and connect inner coil of relay to output of signal generator (or audio oscillator). Put coil near to your RX antenna and try to find signal by switching to different capacitor. If nothing happen then you need to check if one of semiconductors (in first line D7 and Q1, Q2, Q3) has gone. And check voltages if exist.

LOOK AT.

THE GREEN AND THE ORANGE LED TURNS ON, BUT LOCAL AUTHORITY LEANS VLF DETECTOR ON THE FERRITE, THAT IS TO SAY A LOT NEAR THE AERIAL OF RECEPTOR,
ALSO THE BUZZER IS NOT HEARD.

I CHECKED THE ALL TRANSISTOR, PASSAGES ALL GOOD,
I DO NOT KNOW THE PROBLEM.

ALSO I HAVE PLACED VARIABLE CAPACITOR, AND PLAY WITH THE FREQUENCY BUT THE RECEIVER IT DOES NOT HAVE BIG SENSITIVITY

[fmnotes]

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

I DO NOT FIND REASONS TO THANK YOU FOR YOUR VERY BIG HELP.

YOU THANK YOU VERY MUCH.

YOU KNOW YOU PROPOSE TO ME A VERY SENSITIVE RECEPTOR?

[WM6]

YOU KNOW YOU PROPOSE TO ME A VERY SENSITIVE RECEPTOR?

I can only repeat: it is not solution in very sensitive receiver, but in very directive antenna.

Very sensitive receiver without a huge filtration will give you the same mess of frequency but on higher and harder controllable level.

The only simple and effective solution is very directive and selective antenna.

But if you wish to receive only one exact frequency there are other simple solution too how to filter it out.

[fmnotes]

I can only repeat: it is not solution in very sensitive receiver, but in very directive antenna.

Very sensitive receiver without a huge filtration will give you the same mess of frequency but on higher and harder controllable level.

The only simple and effective solution is very directive and selective antenna.

But if you wish to receive only one exact frequency there are other simple solution too how to filter it out.

FRIEND MY I UNDERSTOOD,
BUT IN ORDER TO IT DETECTS THE SIGNALS FROM MY VLF, IT SHOULD THE INDUCTOR OF VLF THEY IS VERY NEAR THE FERRITI.
THE FERRITI I MANUFACTURED HIM FROM YOUR DIRECTIVES.
57mH. 2 FERRITE

[WM6]

FRIEND MY I UNDERSTOOD,
BUT IN ORDER TO IT DETECTS THE SIGNALS FROM MY VLF, IT SHOULD THE INDUCTOR OF VLF THEY IS VERY NEAR THE FERRITI.
THE FERRITI I MANUFACTURED HIM FROM YOUR DIRECTIVES.
57mH. 2 FERRITE

Yes, this is according project presented in schematic.

But if you wish to get even more directive antenna than proposed, you can glue in line (axial) more than two ferrite rod (say 3) and split coil wound on ferrite in 3 to 5 serial connected sections, then tune it on the best directivity.

Total inductance can remain the same of about 57mH, otherwise you need to change value of capacitors line.

[fmnotes]

Yes, this is according project presented in schematic.

But if you wish to get even more directive antenna than proposed, you can glue in line (axial) more than two ferrite rod (say 3) and split coil wound on ferrite in 3 to 5 serial connected sections, then tune it on the best directivity.

Total inductance can remain the same of about 57mH, otherwise you need to change value of capacitors line.

I THANK MY FRIEND I WILL MAKE TRIALS.

[Anwar2]

Hellow
WM6
thank u very much man ? for schematic iknow im late to say
but thank u for the nice diagram
Anwar2

[okantex]

Hi All ,

WM6 , I have a question for you .I have seen your drawings for tx -rx theory.

does not this vlf reciver ,receives g component of electromagnetic wave?
is not the g (magnetic wave) component of wave always in horizontal direction.
how can your ferrite see it .? since it is not vertical ( 90 degree to tx source).
is not the ferrite in null position when directed to underground target?

I do not understand as much as you , ı just try to learn, can you explain me more
thanks

btw , is any there anybody who tried this circuit?
is this circuit work in the same princible of emfad?

[okantex]

I inspected few vlf schematics of b field and E field circuits. yours is look like E field circuits.
you have low pass filter , you do not have high pass filters .does it mean if there is a working MSK ,it will effect reception below 24khz.
but since we are not looking for spherics ,or tweaks ..etc. powerfull signal is our choise.

[WM6]

Dear friend, better go back to MD. This theories will not solve your soul.

[okantex]

in anycase , you have replied , thanks.
I prefer learning how to fish, Indeed I do not like fish.

[okantex]

Dear WM6 ,,

I am sure you must have seen EMFAD shematics . in emfad there are more than 7 transistors till opto .
but at this scheme , just 3 , will it be enough for amplification.

regards
okantex

[WM6]

Dear WM6 ,,

I am sure you must have seen EMFAD shematics . in emfad there are more than 7 transistors till opto .
but at this scheme , just 3 , will it be enough for amplification.

regards
okantex

Why waste money for a little joy, dear okantex?

So better to stay with as low parts as possible.

Best wishes

[okantex]

Dear WM6
thanks for your replies , you know there are lots of crazy men like me who pays much more for for such hobbies and also for cigarettte or drinks...etc.
anyway , ıf you have not seen emfad schematic or picture ,I would like to find a link for you.
you think it is toy, you are right, but it is possible to sense metals with EMf reflections you know.
I just want to sense as emfad does , but with available frequencies.
may be we can add another capacitor for VHF as PDK does.

but I just want to be sure that this schematic is enough sensitive, I am asking you cause I am not electronic expert as you.
is this circuit a toy with these 3 transistors ,or does it need more like emfad does.

regards
okantex

[J_Player]

Dear WM6
thanks for your replies , you know there are lots of crazy men like me who pays much more for for such hobbies and also for cigarettte or drinks...etc.
anyway , ıf you have not seen emfad schematic or picture ,I would like to find a link for you.
you think it is toy, you are right, but it is possible to sense metals with EMf reflections you know.
I just want to sense as emfad does , but with available frequencies.
may be we can add another capacitor for VHF as PDK does.

but I just want to be sure that this schematic is enough sensitive, I am asking you cause I am not electronic expert as you.
is this circuit a toy with these 3 transistors ,or does it need more like emfad does.

regards
okantex

Hi okantex,
I am not an electronics expert any more than you are.
But I can tell you this circuit is only a toy circuit.
It is very simple because simplicity is the reason why WM6 designed it.
This circuit does not have any narrow-band tuners, or signal processing which can find very weak signals.
The S/N ratio is not good.
The purpose of this circuit is to experiment with the directional abilities of a ferrite, not to find difficult signals.
If you are interested in a sophisticated circuit that finds very difficult signals, then you will need a much more complicated circuit, with special filters and signal processing to isolate the exact signals that you are looking for.
This circuit cannot do this job.

But if you are looking for a fun toy, this circuit will give you hours of entertainment to learn how the ferrite is very directional.


Best wishes,
J_P