Re: Harmonic performance - SSB vs CW

Warren Allgyer

The signal at TP1, the output of the first mixer is a pure square wave as it is derived directly from the Si5351 in CW mode. The signal in SSB mode is much closer to a sine wave as it is a mix of the Si5351 square wave and the 45 MHz drive that has been filtered by the roofing filter of Y1 and associated components. 

The only filter that the CW signal encounters before the output filters is the 30 MHz LPF between TP1 and TP2. It has a 2 dB point of about 34 MHz in my case so any harmonics below that are unattenuated until after the final.

The obvious way to fix this is to do the CW generation prior to the roofing filter. What is not obvious to me is the best way to do that. As it stands it is pretty messy.


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