Quote:
Originally Posted by Esteban
No mystery here, no ovnis, no vampires, there is people wich wish extend this theme to legend field! 
You catch this small difference in the audio out of the IC, but you can't ear normally. So the simple beeper do the job.
Any simple audio amp. can do the job, but in this case you can't achieve much distance.
Semiconductors base is ready for to accept electrons, these semiconductor has noise causes by termal movement of atoms. The field of the good conductive metal buried for long time affect the vecinity of the electrons in the semiconductor, and produces a small microvolts, very easy to undrstood this.
So a antenna system connected to this input and adjust the system at the best point of sensibility, out of false beeping, is OK for to do the job.
In other words, also you don't need RF part, yes audio, but RF is more sensitive, and as I use here receiver part, I call this passive device, this is in my terminology regarding electronic LRL. Other thing is a system based in transmitter/receiver, so I can name this as active device. Also radio transmitter/receiver or metal detector (IB, BFO, resonance-off, etc.) is active for me.
All depend of your imagination in electronic LRL systems, never ends ideas in this field.
But for to know all this you must go to inland in relic sites, no dictate from a chair and a computer.
Regards
Esteban |
Hi,
can I make some guesses and questions ?
You add a turn to the tuned circuit , right ?
That way you lower the frequency of tuned circuit from the standard 88-108 MHz FM band of receiver to something less... say 60-80MHz... ok.
But then you wire a cap from omnidirectional antenna to the volume pot... of radio and parallel it with another used for external sensitivity settings.
OK... if so... I suppose then your beep generator is something threshold detector that drives a 555 timer and give pulses to the buzzer... maybe a selfoscillating one like the sonalarme we talked about.
Ok: if there's a reduction of signal strenght at antenna at the tuned frequency , and if there's no agc control on the radio active, you'll get lower volume ... so can trigger the audio generator.
The second option is a tuned circuit after antenna and before the circuit... passband filter for the radio input...maybe tuned to a particular frequency.
All seems have a meaning till now but then...
the questions are:
1. what causes the signal strenght reduction ?
2. what's the frequency of tuned circuit and why if any particular frequency instead of others ?
3. is there some broadcast or other kind emission at that frequency that superimpose with the supposed "useful" signal ?
Kind regards,
Max