I have tried to program the ADF4350EB2Z rev B according to what it is displayed in fig1 but the results is different as showed in sa-out figure. It seems that below 1GHz the spurs are increasing quite a lot. Could you tell me why, please?
The 'spikes' you are seeing in sa-out.jpg are not spurs. They are harmonics caused by using the frequency divider.
The VCO frequency and harmonics of the VCO frequency are mixing with the divided frequency and harmonics of the divided frequency. All the mixing results in the spikes you see in your spectrum analyzer.
I don't know what your application is, but I recommend you put a filter on the RF output to remove these signals. Perhaps a band-pass filter around your frequency range.
Hi thanks for your answer...I haven't got it yet 100%...so I understand that
the harmonics generated by the VCO at 2400MHz are mixing with the harmonics generated by the output divider to produce the sa-out.jpg?
Is this what you mean?
Also, the harmanics from the VCO frequency are mixing with the main signal generated by the output divider,
And, the harmonics from the output divider are mixing with the main signal generated by the VCO.
ah! ok! I understand....I was hoping to use this chip to transmit a frequency from 150MHz to 4GHz.....in steps of 10MHz or near (is a special Radar application).
Could you suggest a way around? (if there are any?) , please?
Best is to try changing the pull-up element to 100 nH.
The divider is used to achieve frequencies lower than 2.2 GHz, and does generate quite a lot square wave characteristics. But levels of <-10 dBc are typical for frequencies below 2 GHz.