Quote:
Originally Posted by WM6
Hi J_P
I am not suggesting to increase, but to decrease value of those C (from nF to pF).
OK, I can agree with your intention to follow original design. My word "stable" was someway inadequate, I mean stable sensitivity to usefull signal, not forced stability on TX signal (locked frequency).
No problem, I support original design you posted. What about PCB?
|
Hi WM6,
Yes, I see your idea.
But keep in mind, this capacitor does not carry the detected metal signal.
This capacitor transfers a small amount of the power from the TX coil to the RX coil for fine-tuning of the null.
We already have the 5K pot to adjust the strength of the null compensation which passes through this capacitor.
If we make the capacitor smaller, then we will lose our ability to make full adjustment of the null to arrive at a truly null RX coil.
A smaller value here will only allow a very small part of the nulling adjustment which we need for a good null.
The actual metal signal arrives as a VLF signal that the RX coil tunes from the air at the same locked frequency as the transmitter.
The small amount of TX power that passes through this capacitor is only used for trimming to a true null without needing to move the position of the RX coil.
But your concept is good for people who want to experiment with mods farther down in the signal path after the first 1K resistor.
Once the signal is properly nulled, then we could take a smaller signal which has all the tiny spikes, and use extra amplifier stages to examine the small signals closer.
This is for people who want to make mods.
For now I agree, we should present the original factory circuit which is capable of detecting some very strange signals without mods.
I think this will be the basic circuit that all modifications are derived from.
The PCB is copyright, so I cannot publish it.
But I can see where different components are located, so we can keep the components in a similar location as the original, and devise our own circuit boards.
I am thinking that any PCB we design can be very close to the original if we keep the components in the similar location.
We should be able to arrive at equal performance to the factory-new version of this metal detecting locator.
There are some components which are intentionally kept in certain locations to avoid interference from the VLF transmissions and reception.
I think that if you were to make a circuit layout that is much different, then maybe you will lose the great detection that is found in the original factory version.
We must have respect for the designer of this circuit, because he used some very innovative methods in his design.
I look at the meter circuit, and I see a transistor used for a meter protection to prevent it from burning up in case it finds a very strong signal that is too much for the meter movement.
And I see how he used diodes to form temperature compensation at the audio amplifier.
Very few treasure hobbyists will design these things into their circuits.
Yet these are the important things when we are treasure hunting and we find temperatures fluctuating from hot sun to freezing winter times.
And what circuit protection do hobbyists use when the "Phenomenon" becomes so strong that it will damage the electronics? None...
The engineer had these all these things in mind when he designed this circuit.
I will begin work on trying to devise circuit boards similar to the same layout for the components that the original factory model has.
This will take some time.
But it will be good to wait, because we will need to see if any more errors in the schematic can be found before we have a circuit board ready.
Assuming there are no errors in the schematic, it can be used for point-to-point wiring if some hobbyists want to begin for an early start.
I know kahyal will be anxious to begin construction, now that he has the schematic that he was asking for to show a pd that detectors metals.
Best wishes,
J_P