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Hello Dear All.

Please see the attached pic. As you see i have used a germanium Diode and am going to drive to a logic gate (74hc14N). But the forward voltage of diode is 0.3v, whereas the 74hc14N can't active with it! So i have to amplify the signal, please guide me. Thanks.

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  • \$\begingroup\$ The rectified signal after the diode is dependent on the amplitude of the signal received by the antenna and possibly L1. Without knowing what the antenna signal is it's difficult to make a recommendation. \$\endgroup\$ – Andy aka Jul 19 '18 at 14:18
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    \$\begingroup\$ The forward voltage of the diode isn't the problem. The amplitude of the radio signal is the problem \$\endgroup\$ – JRE Jul 19 '18 at 14:31
  • \$\begingroup\$ What are you really trying to do? \$\endgroup\$ – JRE Jul 19 '18 at 14:32
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You are misunderstanding what the Ge diode does. If your signal is 2V then the Ge diode passes the rectified voltage minus 0.3V.

However, it won't really work because there is nothing to discharge the coupling capacitor C6. A resistor from D1/C6 junction to ground would help.

If you want to make a frequency counter front end I would suggest reviewing publicly available designs. Depending on the frequency, a JFET and/or an ECL gate may be useful. Here is one that is useful up to tens of MHz. There are many copies of this, originally from Weeder Technologies.

The HC132 is a Schmitt trigger input NAND gate which behaves similarly to your 74HC14, so you can ignore it and the PIC.

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