DDS AD9910 Arduino Shield RF Signal Generator

[MaxGaspa]

Recently I've got an RF generator based on AD9910 with Arduino. The linnk to the manufacture is

https://gra-afch.com/catalog/rf-units/dds-ad9910-arduino-shield/

It has a 40 Mhz TXCO and is working at 1GHz sampling.

Observing the spectrum of a 200 MHz signal (-30 dBm nominal power) with my Ultra SA I observed a "strange" spectrum near the carrier (SA with 4 Mhz span , RBW 30 Khz)

Hereatfer the link to the spectrum image

https://drive.google.com/file/d/130d0kFAi0Ng9DkvypV0Np_d61f4_brEa/view?usp=sharing

there are several sidelobe,  -25dBc, aroun the main carrier.

My guessing is that the generator is not working properly. It seems there is jitter in the carrier  (no modulation is activated).

I'd like to get some opinion on the spectrum. Should I accept this kind of spectrum from this generator? It it normal?

Far from the carrier the phase noise seems OK but near the carrier the signal doesn't seems "pure enough" for the the AD9910

I sent several e-mail to the owner of the site / designer of the board but no reply from them.


Any opinion, idea, advice,suggestion?

Thx

Max

[Bud]

I think it is not the oscillator but the PLL multiplier inside the chip not locking properly. There should be a few external components that form a PLL loop, selection of these component values is critical. It could be that the design was incorrect (copied from another product, etc). Yes this manifestates as  jitter.

[erikka]

The side lobes appear on my device if the supply voltage is too low or not stable.
The supply of the whole setup is extremely critical. It works best with a 7.5V external supply.