I have improved the performance of my lrl, I cannot say exactly how much, as I no longer have the original test field available, however in my current land there is a point where the original lrl signaled a weak signal right nearby, instead with the modification there is a fairly strong signal at about 2 m. The modification essentially consists of increasing the frequency of the quartz to 20 Mhz and of tuning L1 / C10 on a harmonic frequency of the quartz. In addition, I made R10 as trimmer to vary more easily the gain of the sensor stage. I have also improved the display stage by putting a fine adjustment and a coarse to make tuning easier. In this way it is possible to "lock" the output voltage of the sensor stage for a wide voltage excursion. The oscillator circuit has been modified to obtain a waveform as distorted as possible, furthermore the frequency of the quartz has been increased to 20Mhz. In this way, harmonics are also generated, one of which (I suppose the 4th or 5th) is tuned with the resonant circuit L1 / C10. For this reason C10 is now a variable capacitor. I also attach the diagram of the power stage. However, any circuit that provides stabilized 12 V is fine. In my diagram I have put a red led that flashes when the voltage drops below 15.5 V. I also enclose a new "help". It is almost essential to have an oscilloscope available, in fact the values of the oscillator components vary greatly depending on the type of quartz,there are types of quartz harder than others to make oscillation. The calibration of the sensor stage serves to obtain the maximum gain without having oscillations.
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