Friday, December 28, 2012

Marker generator

 I've built a similar circuit to this one for a 500Khz pll circuit some time ago but this one will be used as a dial marker calibrator.

 I works diving a fixed frequency for a fixed value, the square wave output will be rich in harmonics on multiples of the resulting frequency (good, the world isn't perfect).

10Khz spot on from 5.120Mhz:

The oscillator part of the circuit:

The IC was the "HEF" version but basically the same stuff (more or less)...
Resistor between pin 10 and 11 is a 100K Ohm one, the other a 2K. Fixed capacitor was by trial and error, to get crystal on the exact frequency, somewhere near 39pF and the variable one a little more: 39+20var, see 4060 datasheet.
 I didn't had a 10.240 (immediate choice) crystal (only 10.245) but a 5.120 was in the junk box so that was the one used.
Reset pin (12) is grounded.

If you need 1Khz marker then a standard 8192 crystal can be used, just divide by 8192....
Other frequencies... just do some math, "divide ratio" is on the image.

The output part:

The output circuit on the above image wasn't tested (just normal cap coupling was) but I'm sure it will give nice peaks because diode will conduct very shortly on the down flank of the square wave, generating lot's of 10Khz harmonics and more than the simple square wave. I need a scope to verify that....maybe next year...

And the assembly:

 Have a nice weekend...

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