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ADF4351 cross-modulation

Question asked by DavidRF on Aug 6, 2015
Latest reply on Aug 6, 2015 by DavidRF

I'm using the ADF4351 configured to generate two fixed frequencies simultaneously, 3000 MHz on the Aux output and 375 MHz (divided by 8) on the Main output.

 

When the divide-by-8 is enabled, the 3000 MHz signal has 375 MHz sidebands present.  Their amplitude is around -40 dBc.  Their relative amplitude will often jump, sometimes as much as 10 dB, when subsequent writes are made to R0.  Changing the output power settings in R4 does not affect their relative amplitude.

 

My register settings are:

 

R0 00960000

R1 08008009

R2 00004E42

R3 000004B3

R4 00B503FC

R5 00580005

 

This design uses a 10 MHz reference.

 

Any suggestions for reducing the level of these sidebands?

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