In this block diagram you can appreciate the innovative solution to isolate DC and ground loops from the USB port to the IQ+. With this isolation we avoid artifacts, spurs and any electric noise normally present on the USB port. The oscillator part is done via the Si570BBB operating in grade A (up to 945 MHz). The RF output from the Si570BBB is injected to a "mini circuits" Low Pass filter cutting the traditional forest of harmonics normally produced by this chip. Finally to keep same amplitude and phase the clean signal is divided in two outputs with the same amplitude and phase via a 2way Cero degrees splitter.
With and insertion loss of 3.4dB in each port the amplitude unbalance is only 0.01dB and the phase unbalance is only 0.07 deg. (all measurements @ 288MHz)
IQ+ Local Oscillator
IQ+ Local Oscillator Rev.B (final version) for 2m (LO=288MHz)
(photo as a reference, changes without notice)
IQ+ Local Oscillator Harmonics
The next two screen shots show the spectrum analyzer with the Harmonics plot, you can see how rich in harmonics is the Si570 if you don't take provision of a good Low Pass filter. The 3rd Harmonic (864 MHz) is only 13dB attenuated. You cannot use the Si570 without Low Pass filter.
Local Oscillator without band pass filter
After the Low pass filter (mini-circuits PSC-2-1+) the plot