Whites Surf PI schematic

[scs]

Bulgaria,Sofia,1943-44

[homefire]

LOL The Final Stage of Demodulation always ends between the ears.

[waltr]

Why would be matter when that final signal only goes to head phones?

[ionut_mtb]

You need to LOOK at the Whole schematic.
U7D is switched at the SAME Rate as the 4093 (switched Once per Pulse/sample cycle).
The LEVEL of the signal through D3 ALSO goes to the base of Q6.

I've edited my post above:

edit: the audio signal that come through D3, from sample1 is cutted by U7D switch, result frequency of audio and voltage variation of sample1 give the amplitude. right?

now, as SCS said, why is like this and no opposite? Does it matter?

[waltr]

I see U7D switch only put the base of transistor to ground, on and off. the signal from cd4093 is not going to transistor base.

You need to LOOK at the Whole schematic.
U7D is switched at the SAME Rate as the 4093 (switched Once per Pulse/sample cycle).
The LEVEL of the signal through D3 ALSO goes to the base of Q6.

[ionut_mtb]

U7D switching is what creates the Audio Tone (frequency of audio is Same as Coil pulse frequency).
Then the LEVEL of the signal through D3 Modulates the Amplitude (loudness) of the Audio tone.

So when all is properly adjusted and metal come under the coil the Audio tone increases in volume.

I see U7D switch only put the base of transistor to ground, on and off. the signal from cd4093 is not going to transistor base.

edit: the audio signal that come through D3, from sample1 is cutted by U7D switch, result frequency of audio and voltage variation of sample1 give the amplitude. right?

[waltr]

Little hard to understand for me the audio. In the way i can explain, sample from ic4D 4093 closes the switch ic7d 4066, result audio transistor Q6 off. Aprox 100us off Q6, rest of signal (1450us-100us=1350us) on. Why? What we hear in the audio, not sample1 voltage change? What is cutting ic7d switch?

[ATTACH]41326[/ATTACH]
[ATTACH]41327[/ATTACH]

U7D switching is what creates the Audio Tone (frequency of audio is Same as Coil pulse frequency).
Then the LEVEL of the signal through D3 Modulates the Amplitude (loudness) of the Audio tone.

So when all is properly adjusted and metal come under the coil the Audio tone increases in volume.

[ionut_mtb]

The output transistor is closed for a long time and loose for a short time. It should be flip.

Control output sound transistor???[ATTACH]41325[/ATTACH]

Little hard to understand for me the audio. In the way i can explain, sample from ic4D 4093 closes the switch ic7d 4066, result audio transistor Q6 off. Aprox 100us off Q6, rest of signal (1450us-100us=1350us) on. Why? What we hear in the audio, not sample1 voltage change? What is cutting ic7d switch?

[tifred]

Good airplan SCS

[scs]

Control output sound transistor???

[scs]

The output transistor is closed for a long time and loose for a short time. It should be flip.

[ionut_mtb]

In circuit there is a problem with creating the sound. Everybody make" Surf" and no one notices ...

as long as is working... no one thought about it. is the 4066 D switch cutting over audio signal?

[scs]

In circuit there is a problem with creating the sound. Everybody make" Surf" and no one notices ...

[peppe30679]

Thanks for the reply.
Yes, i live in mineralised zone (volcanic area), but also vlf detector work well: i'm sure it's a calibration problem...... i'll try, but unfortunately i haven't an oscilloscope.

[ionut_mtb]

Hello guys
I have a little problem with my SurfPi (Silverdog Kit): the detector in the air work well, but if i bring the coil to the ground, receive sound even if it does not detect metals (false signal).
Do i need to adjust the trimmers better?
Thanks for your help

If detector beep's every time you sweep it might be earth field elimination problem. If have oscilloscope check sample1 and sample2 to have same width. if not check values of the to be exactly the same as in schematic.