VLF Eldorado

For advanced designers:
IMNHO the TX section and RF amp (RX preamp) section in Eldorado are not designed properly:
1. TX section is inefficient because of low equivalent capacitance of TX tank. To increase ampere-turns of TX coil, need larger capacitances in the Colpitts oscillator and an additional capacitor in parallel to TX coil. The TX coil should be low ohmig.
2. Suppression of parasitic TX modulation. A proportional controller is used to suppress parasitic amplitude modulation caused by change of distance coil - ground and change of ground properties. However for best AM suppresion, a P.-I. (proportional - integrating) controller should be used.
These drawbacks are avoided in  Garrett's TX designed by Bob Podhrasky (see the attached circuit diagram).
3. RF amplifier amplifies frequency of power mains and its harmonics!
4. Thermal noise in input are increased by two 5k resistors!
To be continued later (when I draw the correct preamp circuit).

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 and people tell me that chemistry is hard to learn, i didnt understand much of that at all LMAO

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Beaks, please note how starts my posting
"For advanced designers:"
Now we know that you are not designer, but  if you ask something, we will try to answer.

Eugene, the TX section and RF amp of Royal Sabre are the same as in Eldorado. They have the same drawbacks. Oscillator phase noise is not important for metal detector because it uses TX voltage as reference for synchronous demodulation. Important is the parasitic amplitude modulation of TX caused by conductivity of soil. The amplitude of oscillation diminishes when TX coil approaches to conductive soil. This is important drawback because it modulates the AIR signal. Since the GND signal is also modulated by the same frequency when TX coil moves, the synchronous demodulator senses as if there are two different ground signals. It can not eliminate both simultaneously.
Thermal noises in input of RF amplifier are not so important for metal detecting because the AIR and GND signals are relative much more large. However, the designer should strive to reduce them reducing resistance of input resistors. He should  especially reduce amplification of the AC signal induced in RX coil by power line, because it can choke the RF amp (preamp).

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Good Stuff to find by every one!   

Trust me, You can build a good machine if you know what your doing!

This is not for the Faint of heart!

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		Quote:			Posted by Eugene52
	There are only a few "Advanced Designers" that frequently visit our forum . So a good idea might be to start a new Tech-Talk area topic " For Advanced Designers Only "  . I myself will not post in that area . But since I have a good background in electronics beginning back in 1974 I will still Read , Study and Learn all the new Design Ideas posted on this forum . In my experience Engineers need the Bench Technicians and the Techs need the Engineers. That's the way it is in the Industry and always will be . Designing and Engineering is full time , Repair and Troubleshooting is full time . That's the way I saw things for so many years . The only time you would see an Engineer working on the production line is if the Union Technicians went on strike !!!! I am not a designer , just love to Build Circuits and or repair broken Metal Detectors I buy . A lot of Project builders on this forum , and they will also read the Design posts  . HH...............Eugene

If you want to learn, you have to dive in and do the thing!

Hang around people that know a boat load more then you do and it Rubs off on you!

You 2 will learn!

Yep!  I Started that way!

 

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