I'm evaluating the ADF4351 mounted on the respectively Eval Board.
I need to carry out a wide band synthesizer between 50MHz and 3GHz
So I replaced L2 and L3 (7.5nH) inductors with two 50 ohm resistors.
All ok over frequency above 200MHz.
Conversely in both pullup cases (with inductances and with 50ohm resitances)
I can't generate a single-harmonic signal under 150-200Mhz.
The synthetization at lower frequency generates a strong distorsion (also with even order harmonics) in the RFoutput.
It seems like a sort of an amplitude saturation, although the out level in terms of Vpp voltage remains the same.
I tried anyway to reduce the RFoutput level to the presetted -4dBm level however the distosion was still present.
Somebody have any idea, WHY?
SHOULD I CHANGE SOMETHING HARDWARE?