LMX2571: Clock reference isolation limitation to 90 dBc @ 24 harmonic: Improvement possible by config?

Dear Ladies and Gentlemen

The question is regarding the RF performance of the LMX2571 in the synthesizer mode.

We are currently having a reference clock of 19.2 MHz. By generating the 350 to 470 MHz signals, we have seen the 18 to 24 harmonic of the reference clock with around -90 to -100 dBm on the output signal, while the output signal is at +3 dBm output power.

We have seen, that when we decrease the PFD frequency (increase the N-counter value), the power level of these harmonics decreases as well. Now we are curious to know following points:

• Do you have a specification of the max harmonic power of the reference clock at the output?
• Do you have a “optimization” procedure where the reference harmonics are reduced to the max?
• Do you have any power supplies blocking information that leads into better clock signal isolation regarding the RF output signal?
• Do you have any reference documents that deal with this topic?
• Or do you have any software that helps to optimize the reference clock isolation performance?

I'm looking forward to your reply - many thanks in advance.

Thanks and best regards,

Hanspeter Oppliger