# How can I attenuate noise from synchronous divider and OCXO?

I am experimenting with a square OCXO, dividing its output frequency to 1kHz using a 4017 synchronous counter and feeding the output to a sound card using Spectrum Lab software. I can then record it and pass it to another software to visualize the output.

I don't have a spectrum analyzer but my question is what can cause that noise around the 1kHz output frequency from the IC?

Here is the schematic of the circuit:

Here is the result of my recording of the signal:

Ideally it should be much less noise. I should not neither see the harmonic at 2 kHz, and on the spectrogram scale I would expect to see the 1kHz signal like this (red is the ideal output, blue is the real one.

Any idea on how this overall noise can be attenuated somehow? Can this be related to the noise of the OCXO itself?

edit - the OCXO is a square wave one, all ICs are with 100nF caps, and there is also a larger one for 5v DC. the output measured in Volts from the divider to the soundcard is 0.6 V and yes I am using a 10k trimmer before the sound card to fine tuning it. /edit

• You are not showing the waveform of the signal. But obviously there is a 2 kHz component if the FFT says so. Based on the very zoomed-out waveform view, it looks darker in the bottom than on top so there must be some sort of asymmetry or clipping happening. Zoom in and show the data sheet of the OCXO. It may have sine wave output which is bad for divider, and if there's no bypass caps, it may worsen the jitter, spreading the peaks. I hope you are not directly feeding in a 5V square wave to a sound card input? Commented Nov 16, 2023 at 7:53
• the OCXO is a square wave one, all ICs are with 100nF caps, and there is also a larger one for 5v DC. the output measured in Volts from the divider to the soundcard is 0.6 V and yes I am using a 10k trimmer before the sound card to fine tuning it... Commented Nov 16, 2023 at 8:36