I want to generate a clock for a z80 CPU using a crystal oscillator but somewhere between 8 and 13.5mhz the voltage drops and with 20mhz it's about 1 volt peak to peak. I have tried numerous circuits including the one below using a 74hc14 and a 74hcu04 with the same results , what could I be doing wrong? one of the circuits I tried

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    \$\begingroup\$ What are you using to measure the voltage? If scope, what is the bandwidth of the scope and probe? \$\endgroup\$ – AlmostDone Apr 5 '18 at 14:18
  • \$\begingroup\$ I'm using an analog scope that can go up to 35mhz and I have some cheap eBay probes at 10x and they write 100mhz 600v on them \$\endgroup\$ – C32 Apr 5 '18 at 14:20
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    \$\begingroup\$ I suspect what you're seeing is the 35MHz bandwidth coming into play. \$\endgroup\$ – AlmostDone Apr 5 '18 at 14:21
  • \$\begingroup\$ Would they advertise it as a 35 MHz scope if it altered the results on just 14 MHz? Or could it need calibration? \$\endgroup\$ – C32 Apr 5 '18 at 14:24
  • \$\begingroup\$ Look at the graph of a single pole, low pass rolloff characteristic. If your scope and your probe combined are 35MHz BW, that means your displayed amplitude will be 70% of the actual amplitude for a 35MHz signal. Perhaps someone reading this on more than their phone can answer properly with some graphics or a circuit sim. \$\endgroup\$ – AlmostDone Apr 5 '18 at 14:31

what could I be doing wrong?

Your schematic show a schmitt trigger as the oscillator's inverter - this is incorrect - it should be a fast unbuffered inverting device for this circuit to work correctly and accurately.

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  • \$\begingroup\$ Isn't the 74hcu04 unbuffered? I believe I read somewhere that it is. Anyway, the problem was my probes . Apparently higher frequencies can result in lower voltage reading \$\endgroup\$ – C32 Apr 5 '18 at 17:59

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