Thanks MRChips. Revised circuit.View attachment 342864

No. The diodes go on the input of the gates.

 

If he connects directly to Q1, he is left with a signal inversion. But this is better met by just using another one of the inverters in the 4093, assuming one is available.

I don't think inversion matters since he is feeding into a frequency counter.
However, I had suggested using a FET for high input impedance and some gain. He ignored my suggestion.

 

I don't think inversion matters since he is feeding into a frequency counter.
However, I had suggested using a FET for high input impedance and some gain. He ignored my suggestion.

I tried the circuit per attachment and it works up to 3.5 MHz only.

No. He didn't ignore your suggestion, he doesn't know how to connect it up because no circuit
was suggested.

 

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